JP4255077B2 - Optical amplifier and light source - Google Patents

Description

The present invention relates to an optical amplifier having a broadband and low noise characteristic , including a broadband optical amplification medium that can operate even in a wavelength range of 1.5 μm to 1.7 μm , using a tellurite glass for optical amplification . In addition, the present invention provides a reliable, low-loss, low-reflection, non-quartz glass optical fiber and silica-based glass optical fiber constituting an optical amplification medium , or non-quartz glass optical fibers having different core refractive indexes. In addition, the present invention relates to an optical fiber connection structure to be connected with, and a light source.

  In order to expand the transmission capacity and improve the functions of an optical communication system, optical signals of a plurality of wavelengths are combined and transmitted in one optical fiber, or conversely, a plurality of optical signals propagated through one optical fiber. Research and development of wavelength division multiplexing (WDM) technology that demultiplexes an optical signal of a wavelength for each wavelength is currently underway. In this transmission method, it is necessary to transmit a plurality of optical signals having different wavelengths through a single optical fiber, and to relay and amplify the optical signal in the same manner as in the past according to the transmission distance. Therefore, in order to increase the optical signal wavelength and increase the transmission capacity, an optical amplifier having a wide amplification wavelength band is required.

  Further, the wavelength of a system for maintaining and monitoring an optical communication system is considered to be a wavelength between 1.61 μm and 1.66 μm, and development of a light source and an optical amplifier for the maintenance and monitoring system is desired. ing.

  In recent years, for the purpose of application to the optical communication field, research and development of an optical fiber amplifier using an optical fiber having a rare earth element added to the core as an optical amplification medium, for example, an Er (erbium) doped optical fiber amplifier (EDFA), has been promoted. Applications to optical communication systems are being actively promoted. This EDFA operates in the 1.5 μm band where the loss of silica-based optical fiber is minimized, and has excellent features such as high gain of 30 dB or more, low noise, wide gain band, gain independent of polarization, and high saturation output. It is known to have

  One of the performances required when the EDFA is applied to WDM transmission is that the amplification band is wide as described above. So far, a fluoride EDFA using fluoride glass as a host of an Er-doped optical fiber amplifier has been developed as an EDFA having a wide amplification band.

  By the way, when tellurite EDFA is used, 1.53 μm to 1.3 μm wider than 1.53 μm to 1.56 μm wider than the wavelength amplification band from 1.53 μm to 1.56 μm wider than the conventional quartz EDFA and fluoride EDFA amplification bands. Collective amplification in a wavelength band up to 61 μm is possible. Therefore, it attracts attention as an EDFA for future ultra-high capacity WDM systems.

  By the way, the performance required for an EDFA for a WDM system is (1) wide bandwidth of amplification and (2) flatness of amplification. First, the broadband property of amplification will be described.

When this Er-doped tellurite optical fiber is used as an amplifying medium, the amplification band is widened because the tellurite glass has a ⁴ I _13/3 level and ⁴ I _15/2 level of Er that cause optical amplification in the 1.5 μm band. This is because the stimulated emission cross section of the level becomes larger than in other glasses, and in particular, in the long wavelength region of 1.6 μm band, it takes about twice as much value as in other glasses. Therefore, in the tellurite EDFA, it is easy to obtain a large gain in a long wavelength region as compared with other EDFAs.

Incidentally, the amplification degree in a short wavelength range is determined by the difference between the occupancy of ⁴ I _15/2 level position of Er ground levels and ⁴ I _13/3 level position of occupancy. That is, if the ⁴ I _15/2 level is not occupied at all, the gain can be obtained up to a short wavelength such as 1.50 μm.

However, if the fiber length is increased in order to obtain a high gain in the long wavelength region (for example, around 1.60 μm), the occupation ratio of the entire fiber of the ⁴ I _15/2 level increases, and the gain in the short wavelength region increases. Cannot be obtained, and the noise figure (NF: Noise Figuve) near 1.54 μm is also increased. Therefore, even if it is a tellurite optical fiber, the amplification band which can be covered with one optical fiber will be limited. Actually, the operating wavelength range of low NF and high gain obtained by using one tellurite optical fiber is about 60 nm from 1.55 μm to 1.61 μm.

  Next, the flatness of amplification, which is the second property required as an EDFA for a WDM system, will be described.

By the way, the performance required for an EDFA for a WDM system is (1) wide bandwidth of amplification and (2) flatness of amplification. While tellurite EDFA is excellent in amplification broadband, amplification flatness is inferior. For example, the gain deviation at a gain peak wavelength of 1.56 μm and 1.60 μm is 15 dB or more (A. Mori et al., Supra). Therefore, in order to flatten the gain, it is necessary to apply a gain equalizer such as a fiber Bragg grating to the EDFA. However, if the gain deviation is too large, it is difficult to design a gain equalizer for flattening, or gain equalization cannot be achieved without using a plurality of gain equalizers. is there. In fact, in the case of the tellurite EDFA, since the gain deviation is 15 dB or more, the gain deviation applied to the WDM system is not realized even if the gain equalizer is used.

  In order to change the shape of the original amplified spectrum of the EDFA, it is necessary to change the shape of the stimulated emission cross section spectrum.

  In the case of tellurite EDFA, a fiber host having a large stimulated emission cross section in the vicinity of the 1.6 μm band may be used to flatten the gain spectrum and facilitate gain equalization. This is because in that case, the gain deviation between the wavelength band from 1.53 μm to 1.56 μm and the 1.6 μm band can be reduced.

As a fiber host of conventional tellurite EDFA, TeO ₂ —ZnO—Na ₂ O—Bi ₂ O ₃ glass (Japanese Patent Application No. 9-30430) is TeO ₂ —ZnO—Li ₂ O—Bi ₂ O ₃ (Japanese Patent Application). Glass such as No. 9-226890) is used. In these glass systems, the gain deviation is 15 dB or more.

  Here, the development status up to now will be briefly explained.

  In US Pat. Nos. 3,836,868 to 3,836,871 and 3,883,357, Cooley et al. Show that laser oscillation is possible with tellurite glass doped with rare earth elements. However, Cooley et al. Have not yet made fiber, and do not mention adjustment of the refractive index necessary for fiberization and thermal stability of glass.

On the other hand, Snitzer et al. In US Pat. No. 5,251,062 expands the amplification band of EDFAs when tellurite glass is used, and further, optical fiber is essential for optical amplification. The composition range of tellurite glass that can be included and made into a fiber is specifically disclosed. The glass is a ternary system composed of TeO ₂ , R ₂ O and QO (R is a monovalent metal other than Li and Q is a divalent metal). That is, Li is excluded as a monovalent metal due to a decrease in thermal stability.

  In US Pat. No. 5,251,062, Snitzer et al. Compare the fluorescence spectra of erbium ions in the tellurite glass and quartz glass, and the tellurite glass has a wider spectrum width. If glass is used, EDFA broadband amplification is possible, and addition of praseodymium, neodymium, etc. is possible. By adding these optically active substances, an optical fiber using the ternary tellurite glass can be used. It is said that optical amplification is possible. However, U.S. Pat. No. 5,251,062 has no specific description such as gain, pumping wavelength and signal wavelength indicating that optical amplification has actually been performed. That is, US Pat. No. 5,251,062 merely shows the composition range of ternary tellurite glass that can be made into a fiber, and only shows that it is possible to add optically active rare earth elements. .

  Snitzer et al. Is described in US Pat. No. 5,251,062 in JS Wang et. Al, Optical Materials, 3 (1994), pp. 187-203 (hereinafter referred to as “Optical Materials”). Figure 2 shows the thermal and optical properties of various tellurite glasses containing other compositions. However, there is no specific description about optical amplification and laser oscillation here.

  Snitzer et al. Added neodymium for the first time in JS Wang et. Al, Optics Letters, 19 (1994), pp. 1448-1449 (hereinafter referred to as Optics Letters), which was published immediately after the above-mentioned document. This is the first report on laser oscillation using tellurite glass single-mode fiber.

The single mode fiber has a core of 76.9% TeO ₂ -6.0% Na ₂ O-15.5% ZnO-1.5% Bi ₂ O ₃ -0.1% Nd ₂ O ₃ and a cladding of 75. It consists of a composition represented by% TeO ₂ -5.0% Na ₂ O-20.0% ZnO, and performs laser oscillation of 1061 nm with 818 nm excitation. Although the fiber loss is not described in this document, the core composition Nd ₂ O ₃ -77% TeO ₂ -6.0% Na ₂ O-15.5% ZnO-1.5 is included in the optical materials. % Bi ₂ O ₃ , cladding composition 75% TeO ₂ -5.0% Na ₂ O-20.0% ZnO fiber (estimated to be the same as described in Optics Letters) at 1.55 μm It is described that it is 1500 dB / km and 3000 dB / km at an excitation light wavelength (0.98 μm) (see FIG. 1. This figure shows Er ^{3+ 4} I _13/2 → ⁴ in tellurite glass described later. I _15/2 emission and Er ^{3+ in} fluoride glass compared with ⁴ I _13/2 → ⁴ I _15/2 emission).

The core composition of the fiber is _Bi 2 _{O 3} wherein differs from the U.S. Patent ternary No. 5,251,062 in that is applied, the glass having a composition applied is _Bi 2 _{O 3} in the ternary There is no mention of thermal stability in this Optics Letters nor in the Optical Materials, US Pat. No. 5,251,062.

  However, the above-mentioned fluoride EDFA has an amplification band of about 30 nm, and this alone is still insufficient for expanding the bandwidth of the fiber amplifier for expanding the bandwidth of WDM.

On the other hand, as described above, tellurite glass has a wide fluorescence spectrum, and therefore, it has been shown that the amplification band may be expanded if it is a host of EDFA. It is also shown that a ternary system composed of TeO ₂ , R ₂ O and QO (R is a monovalent metal other than Li and Q is a divalent metal) can be made into a fiber, and neodymium based on the above composition. A laser oscillation of 1061 nm was realized with the doped single mode fiber.

  However, EDFA using tellurite glass has not been realized yet. The following are issues for realizing the Tellurite EDFA.

  For that purpose, first, it is necessary to show the difference between the target EDFA and the neodymium-doped fiber laser realized so far, that is, the difference between the erbium emission in the glass in the 1.5 μm band and the neodymium emission in the 1.06 μm band. There is.

  The former optical transition is schematically shown in FIG. That is, in order to obtain the intended stimulated emission from level 2 to level 1, it is excited from level 1 to level 3 (a level higher in energy than level 2), and from level 3 to level 2 An inversion distribution between levels 1 and 2 is formed by the relaxation to. This is called a three-level system. On the other hand, as shown in FIG. 3, when the final level of stimulated emission is not the ground level but level 1, which is the upper level of the ground level, this is called a 4-level system. Compared with the four-level system, the three-level system is less likely to form an inverted distribution because the final level of stimulated emission is in the ground state. Therefore, in the three-level EDFA, it is necessary to increase the excitation light intensity and to reduce the loss and increase Δn of the fiber itself. The increase in Δn is for efficient excitation.

  Here, it is simply shown that even if optical fiber amplification can be performed if the fiber loss is large, the amplification band cannot be expanded.

  FIG. 4 shows a schematic diagram of the wavelength dependence of the gain of quartz-based EDFA and tellurite EDFA. As shown in this figure, the tellurite EDFA can be expected to have a wider optical amplification than the quartz EDFA. However, the glass other than the quartz glass has a larger loss in the communication wavelength band than the quartz glass. Therefore, this loss substantially reduces the gain in the optical fiber amplifier.

  As schematically shown in FIG. 5, when the loss is small, the amplification band of the tellurite glass is close to the above, but when the loss increases, the amplification band decreases.

  By the way, in recent WDM transmission, in order to increase the transmission capacity, the transmission speed per channel is increased. For this purpose, it is necessary to optimize the chromatic dispersion characteristics of the Er-doped optical fiber itself constituting a part of the transmission line. However, attention has been paid to the chromatic dispersion of the Er-doped optical fiber itself. Was not paid.

  In the case of tellurite glass, the wavelength at which the material dispersion value becomes zero is located in a wavelength band longer than 2 μm, and the wavelength dispersion value of a high NA (Numerical Aperture) fiber used for EDFA is usually 1.55 μm band. , And takes a value of −100 ps / km / nm or less. For this reason, even when the fiber is used as short as about 10 m, the chromatic dispersion value of the fiber is a large value of −1 ps / nm or less.

  Therefore, in order to use the tellurite EDFA for long-distance high-speed WDM transmission, it is necessary to make the chromatic dispersion value as close to zero as possible. However, as described above, since the material dispersion value of tellurite glass becomes zero in the wavelength region of 2 μm or more, in the tellurite glass fiber, the structural parameters of the fiber as in the case of quartz fiber should be optimized. As a result, it is impossible to take the method of bringing the chromatic dispersion value in the 1.55 μm band close to zero.

  The tellurite optical fiber can also be used as a Pr (praseodymium) host for 1.3 μm band amplification. However, as described above, the tellurite optical fiber has a large chromatic dispersion value as an absolute value in the 1.3 μm band. Therefore, when a high-speed optical signal is amplified using a tellurite optical fiber, distortion of the pulse wavelength is induced, so that it is difficult to use the optical communication system without correcting the chromatic dispersion value.

  Next, connection between the non-silica optical fiber and the silica optical fiber will be described.

  When a non-quartz optical fiber as described above is actually used for amplification or nonlinear optics, it needs to be connected to the quartz optical fiber with low loss and low reflection. However, the non-quartz optical fiber and the silica optical fiber have different core refractive indexes, and when they are connected as shown in FIGS. 6 and 7, there is residual reflection, which can be applied to practical use. Connection cannot be realized. In these drawings, reference numeral 1 is a non-quartz optical fiber, 2 is a silica optical fiber, 5 is an optical adhesive, and 6 is an adhesive. In FIG. 6, no optical adhesive is present on the fiber connection surface. For this reason, as shown in FIG. 8, a ghost (acts as noise) generated by reflection of both connection portions in the output signal due to residual reflection existing between the silica-based optical fibers 2a and 2b and the non-silica-based optical fiber 1. Occurs and the signal quality is significantly degraded. For this reason, the residual reflectance of the connection is required to be −60 dB or more (in the case of an optical fiber amplifier) (references “Takei et al.,“ Optical Amplifier Module ”, Oki Electric Development, vol. 64, No. 1, pp. 63-66, 1997 ”). For example, the core refractive indexes of Zr-based fluoride fiber, In-based fluoride fiber, chalcogenide-based glass fiber (glass composition As-S), and tellurite glass fiber are each 1.48 to 1.55 (varies depending on the glass composition) ), 1.45 to 1.65 (varies depending on the glass composition), 2.4, and 2.1, and the return loss R (unit: when connected to a quartz fiber (core refractive index to 1.50)) As for the relationship between dB and residual reflectance, the residual reflectance shows a negative value, whereas the reflection attenuation amount shows the absolute value of the residual reflectance and has a positive value. Desired.

However, n _NS and n _S are the core refractive indexes of the silica-based fiber and the non-quartz-based fiber, respectively. Return loss between Zr-based fluoride fiber, In-based fluoride fiber, chalcogenide-based glass fiber (glass composition As-S), and tellurite glass fiber and quartz-based fiber is ∞ to 35 dB, ∞ to 26 dB, respectively. 13 dB and 16 dB. For Zr-based fluoride fibers and In-based fluoride fibers, the return loss can be increased (residual reflectivity is reduced) by adjusting the glass composition and bringing it closer to the core refractive index of the silica-based fiber. However, this is subject to significant restrictions in producing practical fibers (for example, considering precise control of glass composition during fiber production and consistency with glass compositions suitable for producing low-loss fibers). . The connection between silica-based optical fiber and non-silica-based optical fiber is
1) The conventional fusion splicing cannot be applied due to the difference in softening temperature between the two fibers (softening temperature of silica-based optical fiber is 1400 degrees, softening temperature of non-silica-based optical fiber is 500 degrees);
2) Since there is no optical connector manufacturing technology suitable for non-quartz optical fibers, there is a major problem in connecting the two due to the inability to apply the optical connector connection technology. For this reason, the Zr-based fluoride optical fiber and the In-based fluoride optical fiber do not depend on the glass composition, and the chalcogenide-based glass optical fiber, the tellurite glass optical fiber and the silica-based optical fiber are reliably and low-loss, A general-purpose connection technology for connecting with low reflection has been demanded.

FIG. 9 and FIG. 10 show one of conventional connection technologies developed in order to solve this problem (Japanese Patent Laid-Open No. Hei 6-27343). In this technique, first, the non-quartz optical fiber 1 and the silica optical fiber 2 are held by optical fiber holding housings 7a and 7b, respectively. Here, the optical fibers 1 and 2 are respectively positioned by the V-groove substrates 8a and 8b, and are fixed to the optical fiber holding housings 7a and 7b by the adhesives 10a and 10b and the optical fiber fixing plates 9a and 9b. . Also, the purpose of suppressing the reflection that occurs when each fiber is connected to the connection end face of one optical fiber holding case holding the optical fiber (in FIG. 9, the optical fiber holding case 7b holding the optical fiber 2). A dielectric film 18 is provided in advance. As shown in FIG. 10, the connection between the silica-based optical fiber 2 and the non-silica-based optical fiber 1 is performed after adjusting the optical fiber holding housings 7a and 7b so that the optical axes of the optical fibers 1 and 2 coincide. The connection is made using an ultraviolet curable resin-based optical adhesive 5. At this time, the connection end faces of the optical fiber holding housings 7a and 7b are perpendicular to the optical axes of the non-quartz fiber and the silica fiber 2, respectively. Deteriorate the return loss. Therefore, this prior art attempts to reduce reflection at the connection point by the dielectric film 18. However, in this conventional connection, it is necessary to precisely adjust the refractive index of the optical adhesive 5 and the refractive index and film thickness of the dielectric film 18. That is, if the core refractive index of the non-quartz optical fiber 1 is n ₁ and the core refractive index of the silica fiber 2 is n ₂ , the refractive index of the optical adhesive 5 is adjusted to n ₁ , and the dielectric film 18 The refractive index n _f and the film thickness t _f must satisfy the conditions of the following expressions (3) and (4).

Where λ is a signal wavelength (a wavelength to be used).

  As described above, in this conventional connection technique, a dielectric film is used to form a low-reflection / low-loss connection, so that the refractive index of the optical adhesive 5 and the refractive index and film thickness of the dielectric film 18 are determined. It was necessary to adjust precisely, and there was a big problem in realizing a connection portion with excellent characteristics with good reproducibility and yield.

  As a second conventional technique, as shown in FIG. 11, the connection end faces of the optical fiber holding housings 7a and 7b holding the optical fibers 19a and 19b are arranged in a direction perpendicular to the optical axis of the optical fiber. The optical fiber holding housings 7a and 7b are aligned with each other so that the optical axes of the optical fibers 19a and 19b coincide with each other, and are connected using the optical adhesive 5 to reduce reflection. There is an oblique connection method that realizes a low-loss connection part. This connection is a method that can be applied when the core refractive index of the optical fiber 19a and the core refractive index of the optical fiber 19b substantially coincide with each other. It could not be applied when the core refractive indexes are different from each other, such as a fiber and a silica-based optical fiber.

Accordingly, an object of the present invention, the stimulated emission cross-sectional area of 1.5μm band Er was used Teruraitogara scan for optical amplification as fiber host to become flatter, it can operate in particular wavelength range of 1.7μm from 1.5μm It is an object of the present invention to provide an optical amplifier and a light source having a broadband and low noise characteristic including a wide-band optical amplification medium. Furthermore, reliable and low-loss different non silica-based glass optical fibers to each other to each other and a non-silica-based glass optical fibers constituting the optical amplifying medium and the silica-based optical glass fiber, or core refractive index in the optical amplifier or the like, low The purpose is to provide a general-purpose and practical connection technology for connection by reflection.

In order to solve the above problems, an optical amplifier and a light source of the present invention include an optical amplification medium using tellurite glass having the following configuration.

(1) Tellurite glass is a material glass for optical fibers or optical waveguides,
0 <Bi ₂ O ₃ ≦ 20 (mol%),
0 ≦ Na ₂ O ≦ 35 (mol%),
0 ≦ ZnO ≦ 35 (mol%), and 55 ≦ TeO ₂ ≦ 90 (mol%)
It has the composition which consists of.

(2) In the tellurite glass according to (1), preferably, the added amount of Bi ₂ O ₃ in the tellurite glass is
1.5 <Bi ₂ O ₃ ≦ 15 (mol%)
It is in the range.

(3) Tellurite glass is a material for optical fiber or optical waveguide,
0 <Bi ₂ O ₃ ≦ 20 (mol%),
0 ≦ Li ₂ O ≦ 25 (mol%),
0 ≦ ZnO ≦ 25 (mol%), and 55 ≦ TeO ₂ ≦ 90 (mol%)
It has the composition which consists of.

(4) Tellurite glass is a material glass for optical fiber or optical waveguide,
0 <Bi ₂ O ₃ ≦ 20 (mol%),
0 ≦ M ₂ O ≦ 35 (mol%),
0 ≦ ZnO ≦ 35 (mol%), and 55 ≦ TeO ₂ ≦ 90 (mol%)
And M is at least two monovalent metals selected from the group consisting of Na, Li, K, Rb, and Cs.

(5) The tellurite glass according to (4) preferably has an addition amount of Bi ₂ O ₃ in the tellurite glass.
1.5 <Bi ₂ O ₃ ≦ 15 (mol%)
It is.

(6) Tellurite glass is a material glass for optical fiber or optical waveguide,
0 <Bi ₂ O ₃ ≦ 20 (mol%),
0 <Li ₂ O ≦ 25 (mol%),
0 <Na ₂ O ≦ 15 (mol%),
0 ≦ ZnO ≦ 25 (mol%), and 60 ≦ TeO ₂ ≦ 90 (mol%)
It has the composition which consists of.

(7) The tellurite glass is a material glass for an optical fiber or an optical waveguide in which erbium is added to at least a core, and has a composition in which Al ₂ O ₃ is added to the material glass.

(8) Tellurite glass is a material glass for an optical fiber or an optical waveguide, and the material glass composition is composed of TeO ₂ —ZnO—M ₂ O—Bi ₂ O ₃ —Al ₂ O ₃ , M is one or more alkali elements.

(9) Tellurite glass is a material glass for optical fibers or optical waveguides,
The material glass composition is:
0 <Bi ₂ O ₃ ≦ 10 (mol%),
0 <Li ₂ O ≦ 30 (mol%),
0 ≦ ZnO ≦ 4 (mol%), and 70 ≦ TeO ₂ ≦ 90 (mol%)
0 <Al ₂ O ₃ ≦ 3 (mol%)
It is characterized by being.

(10) Tellurite glass is a material glass for optical fiber or optical waveguide,
The material glass composition is:
0 <Bi ₂ O ₃ ≦ 15 (mol%),
0 <Na ₂ O ≦ 30 (mol%),
0 ≦ ZnO ≦ 35 (mol%), and 60 ≦ TeO ₂ ≦ 90 (mol%)
0 <Al ₂ O ₃ ≦ 4 (mol%)
It is characterized by being.

(11) (1) to the tellurite glass of any one of (10), preferably, the addition amount of _Bi 2 _{O 3} in the tellurite glass,
4 <Bi ₂ O ₃ <7
It is.

  (12) The optical amplifying medium is an optical amplifying medium comprising an optical fiber or an optical waveguide having a core glass and a clad glass, and any one of (1) to (6) or (8) to (11) It consists of the tellurite glass of description.

(13) The optical amplification medium is an optical amplification medium comprising an optical fiber or an optical waveguide having a core glass and a cladding glass,
The core glass is
0 <Bi ₂ O ₃ ≦ 20 (mol%),
Preferably 1.5 <Bi ₂ O ₃ ≦ 15 (mol%),
0 <Na ₂ O <15 (mol%),
5 ≦ ZnO ≦ 35 (mol%), and 60 ≦ TeO ₂ ≦ 90 (mol%)
Is a tellurite glass having a composition consisting of:
First composition: 5 <Na ₂ O <35 (mol%), 0 ≦ ZnO <10 (mol%), and 55 <TeO ₂ <85 (mol%),
Second composition: 5 <Na ₂ O <35 (mol%), 10 <ZnO ≦ 20 (mol%), and 55 <TeO ₂ <85 (mol%),
Third composition: One composition selected from the group consisting of 0 ≦ Na ₂ O <25 (mol%), 20 <ZnO ≦ 30 (mol%), and 55 <TeO ₂ <75 (mol%). It consists of tellurite glass.

  (14) In the optical amplification medium according to (12) or (13), preferably, at least one of the tellurite glass of the core glass or the tellurite glass of the clad glass is added with erbium or erbium and ytterbium. ing.

  (15) In the optical amplification medium according to any one of (12) to (14), preferably, at least one of the tellurite glass of the core glass or the tellurite glass of the clad glass is boron, phosphorus And at least one selected from the group consisting of hydroxyl groups.

  (16) In the optical amplifying medium according to any one of (12) to (15), preferably, at least one of the tellurite glass of the core glass or the tellurite glass of the clad glass is Ce, Pr. , Nd, Sm, Tb, Gd, Eu, Dy, Ho, Tm, and an element selected from the group consisting of Yb are added.

(17) The optical amplifying medium is an optical amplifying medium made of an optical fiber or an optical waveguide made of at least a material glass in which erbium is added to a core, and the composition of the material glass is tellurite glass to which Al ₂ O ₃ is added. It is characterized by being.

(18) The optical amplifying medium is an optical amplifying medium having an optical fiber or an optical waveguide having a core and a clad made of material glass and erbium added to the core, and the composition of the material glass is TeO ₂ It is a composition comprising —ZnO—M ₂ O—Bi ₂ O ₃ —Al ₂ O ₃ , wherein M is one or more kinds of alkali elements.

  (19) In the optical amplification medium according to any one of (12) to (18), the cutoff wavelength is preferably 0.4 μm to 2.5 μm.

In this specification, the laser device has the following configuration .
(20) The laser device is a laser device having an optical resonator and a pumping light source, and at least one of the optical amplification media provided in the optical resonator is any one of (12) to (19). It consists of the optical amplification medium as described in above.

  (21) The laser device is a laser device in which a plurality of optical amplifying media made of optical fibers with at least a core added with erbilum are arranged in series, wherein at least one of the optical amplifying media includes (12) to (19) It consists of the optical amplification medium as described in any one of these.

  (22) The laser device is a laser device having an optical amplification medium and an excitation light source, and the optical amplification medium is composed of the optical amplification medium according to any one of (12) to (19). Features.

In this specification, the optical amplifier may have the following configuration.
(23) The optical amplifier is an optical amplifier including an optical amplification medium, and input means for inputting excitation light and signal light for exciting the optical amplification medium to the amplification medium. 12) It consists of the optical amplification medium as described in any one of (19).

  (24) The optical amplifier is an optical amplifier in which a plurality of optical amplifying media made of an optical fiber having at least a core added with erbium is arranged in series, and at least one of the optical amplifying media includes (12) to (19) It consists of the optical amplification medium as described in any one of these.

  (25) The optical amplifier is an optical amplifier using tellurite glass as an amplifying medium, and the dispersion medium compensates for dispersion by a wavelength dispersion value having a sign different from that of the optical amplifying medium in at least one position before and after the optical amplifying medium. Is provided.

  (26) In the optical amplifier according to (25), preferably, the optical amplification medium is an optical waveguide made of tellurite glass to which a rare earth element or a transition metal element is added.

(27) In the optical amplifier according to (25) or (26), preferably, the tellurite glass is TeO ₂ —ZnO—M ₂ O—Bi ₂ O ₃ or TeO ₂ —ZnO—M ₂ O—. Bi ₂ O ₃ —Al ₂ O ₂ (M is one or more alkali elements) or TeO ₂ —WO ₃ —La ₂ O ₃ —Bi ₂ O ₃ —Al ₂ O ₃ .

  (28) In the optical amplifier according to any one of (25) to (27), preferably, the dispersion medium is an optical fiber or a fiber Bragg grating.

The optical amplifier of the present invention has the following configuration.
(29) The optical amplifier is an optical amplifier in which a plurality of optical amplifying units including an optical fiber doped with erbium as an amplifying medium are arranged in series, and at least the second and subsequent stages of the plurality of optical amplifying units For example, a tellurite glass optical fiber is used as an optical fiber material, and an erbium-added concentration and an optical fiber length product are in the tellurite before the optical amplifying unit made of the tellurite glass optical fiber. An erbium-doped optical fiber smaller than a glass optical fiber is used.

(30) In the optical amplifier according to (29), preferably, the tellurite glass is TeO ₂ —ZnO—M ₂ O—Bi ₂ O ₃ or TeO ₂ —ZnO—M ₂ O—Bi ₂ O ₃ —. It has a composition consisting of Al ₂ O ₃ (M is one or more alkali elements) or TeO ₂ —WO ₃ —La ₂ O ₃ —Bi ₂ O ₃ —Al ₂ O ₃ .

(31) In the optical amplifier according to (29) or (30), preferably, as a material of the amplification medium, together with the tellurite glass optical fiber, a fluoride glass optical fiber, a quartz glass optical fiber, a fluorophosphate glass An optical fiber, a phosphate glass optical fiber, or a chalcogenide glass optical fiber is used.

The optical amplifier according to any one of (32) (29) to (31), preferably, at least one optical amplification portion of the front side of the optical amplifying portion consisting of the tellurite glass optical fiber, tellurite glass optical fiber Other optical fiber materials are used.

(33) In the optical amplifier according to any one of (29) to (32), preferably, the Er addition concentration of at least one optical fiber disposed in the front stage of the optical amplifying unit made of the tellurite glass optical fiber. And the optical fiber length product is smaller than the Er addition concentration and the optical fiber length product of the tellurite glass optical fiber.

(34) The optical amplifier is an optical amplifier using an optical fiber to which erbium is added as an amplification medium, and at least two or more tellurite glass optical fibers having different erbium addition concentrations and optical fiber length products are arranged in series. The arrangement includes at least one arrangement structure in which an optical fiber having a small optical fiber length product is disposed in front of an optical fiber having a large optical fiber length product.

(35) In the optical amplifier according to (34), preferably, the tellurite glass is TeO ₂ —ZnO—M ₂ O—Bi ₂ O ₃ or TeO ₂ —ZnO—M ₂ O—Bi ₂ O ₃ —. It has a composition composed of Al ₂ O ₃ (M is one or more alkali elements).

(36) A first optical amplifier in which a plurality of optical amplifying media according to any one of (29) to (35) are arranged in series, wherein the optical amplifying medium is a non-quartz glass optical fiber . The first optical fiber and the first optical fiber hold the end portions of the second optical fiber made of glass having different core refractive indexes in the first and second housings, respectively. In the state where the second casing is aligned so that the optical axes of the first optical fiber and the second optical fiber coincide with each other, the connection end surfaces of the first casing and the second casing are connected. The optical axes of the first optical fiber and the second optical fiber are inclined at different angles with respect to the vertical axis of the connection end face, and the optical axes of the first optical fiber Of the connecting end surface of the second optical fiber and the inclination angle θ ₁ of the connecting end surface with respect to the vertical axis When the inclination angle θ ₂ with respect to the vertical axis is such that the core refractive index of the first optical fiber is n ₁ and the core refractive index of the second optical fiber is n ₂ ,

It is connected in a state satisfying the Snell's formula.

  (37) In the optical amplifier according to (36), preferably, the connection end surfaces of the first casing and the second casing are connected via an optical adhesive.

  (38) In the optical amplifier described in (37), it is preferable that the connection surfaces of the first casing and the second casing are connected in close contact.

(39) In the optical amplifier according to any one of (36) to (38), preferably, each of the first and second optical fibers is a non-quartz glass optical fiber.

(40) In the optical amplifier according to any one of (36) to (39), preferably, the non-quartz glass optical fiber is a tellurite glass fiber , a Zr-based or In-based fluoride glass fiber, or a chalcogenide. It is one type of glass fiber.

(41) In the optical amplifier according to any one of (36) to (39), preferably, the non-quartz glass optical fiber is a tellurite glass fiber , a Zr system, or an In system to which a rare earth element is added. One of fluoride glass fiber and chalcogenide glass fiber.

(42) In the optical amplifier according to any one of (36) to (38), preferably, the second optical fiber is a silica-based glass optical fiber, and the angle θ ₁ is 8 degrees or more. .

(43) The optical amplifier is an optical amplifier in which a plurality of optical amplifying units including an optical fiber doped with erbium as an optical amplifying medium is arranged in series, and the non-quartz glass light constituting the optical amplifying medium The first optical fiber, which is a fiber, and the first optical fiber are respectively held by the first and second casings at the ends of the second optical fiber made of glass having different core refractive indexes, The first casing and the second casing in a state where the first casing and the second casing are aligned so that the optical axes of the first optical fiber and the second optical fiber coincide with each other. When connecting the connection end faces, the optical axes of the first optical fiber and the second optical fiber are inclined at different angles with respect to the vertical axis of the connection end face, respectively, and an optical fiber connecting end faces of the optical axis inclination angle theta ₁ and the second with respect to the vertical axis When the relationship of the tilt angle theta ₂ is, with n ₁ the refractive index of the core of the first optical _fiber, the refractive index of the core of the second optical fiber and n ₂ with respect to the vertical axis of the connection end face of the optical axis of the fiber,



The first optical fiber is a tellurite glass optical fiber used as an optical fiber material, and the optical amplifying unit before the optical amplifying unit made of the tellurite glass optical fiber is connected. Erbium-doped optical fiber is used whose erbium-doped concentration and optical fiber length product are smaller than the Er-doped concentration and optical fiber length product of the tellurite glass optical fiber,
The second optical fiber is a silica glass optical fiber, and the angle θ ₁ is 8 degrees or more.

(44) The optical amplifier according to (43), wherein the tellurite glass is TeO ₂ —ZnO—M ₂ O—Bi ₂ O ₃ or TeO ₂ —ZnO—M ₂ O—Bi ₂ O ₃ —Al _2. O ₃ and having a (wherein, M is one or more of an alkali metal element) or a composition consisting of _{TeO 2 -WO 3 -La 2 O 3} -Bi 2 O 3 -Al 2 O 3.

(45) In the optical amplifier described in (43) or (44), the connection end surfaces of the first casing and the second casing are connected via an optical adhesive.

(46) In the optical amplifier according to any one of (43) to (45), the connection surfaces of the first casing and the second casing are connected in close contact with each other. .

According to the present invention, the stimulated emission cross-sectional area of 1.5μm band Er was used for optical amplification tellurite glass as fiber host to become more flat, operable in particular wavelength range of 1.7μm from 1.5μm It is possible to provide an optical amplifier and a light source having a broadband and low noise characteristic including a broadband optical amplification medium. Furthermore, non-quartz glass optical fiber and silica-based glass optical fiber constituting the optical amplifying medium , or non-silica-based optical fibers having different core refractive indexes can be reliably connected with low loss and low reflection. And practical connection technology can be provided. Accordingly, the optical amplifying medium, the characteristics of the optical amplification device using the optical amplification medium, the performance of the original Er-doped tellurite glass optical fiber amplifier align the broadband property if the wavelength-multiplexed optical transmission system and an optical CATV system with the As a result, there is an advantage that it can greatly contribute to the advancement and economy of services using these systems.

  Further, if it is used in a wavelength division multiplexing optical transmission system as a broadband amplifier, it can be expected that the transmission capacity will be remarkably increased, thereby contributing to the cost reduction of information communication. In addition, if the optical CATV system is used with the characteristic that the gain tilt is small, it is possible to distribute and relay high-quality video by wavelength multiplexing, which has been difficult in the past, and the cost reduction of the optical CATV is achieved. There is a big merit that you can. Furthermore, if it is applied as a laser device, it can contribute to cost reduction of various wavelength division multiplexing optical transmission systems and high performance of optical measurement.

First, tellurite glass containing Bi ₂ O ₃ used in the optical amplification medium in the present specification will be described. This tellurite glass
First composition (A): 0 <Bi ₂ O ₃ ≦ 20 (mol%),
0 ≦ Na ₂ O ≦ 35 (mol%),
0 ≦ ZnO ≦ 35 (mol%), and 55 ≦ TeO ₂ ≦ 90 (mol%), or the second composition (B): 1.5 <Bi ₂ O ₃ ≦ 15 (mol%),
0 ≦ Na ₂ O ≦ 35 (mol%),
0 ≦ ZnO ≦ 35 (mol%), and 55 ≦ TeO ₂ ≦ 90 (mol%),
Third composition (C): 0 <Bi ₂ O ₃ ≦ 20 (mol%),
0 ≦ LiO ≦ 25 (mol%),
0 ≦ ZnO ≦ 25 (mol%), and 55 ≦ TeO ₂ ≦ 90 (mol%)
It has a composition consisting of

FIG. 12 and FIG. 13 show composition regions in the case of the above A (B); Bi ₂ O ₃ = 5 mol%, C; Bi ₂ O ₃ = 5 mol%, which brings about stabilization of the glass.

The thermal stability of glass against fiberization can be evaluated by DSC (differential scanning calorimetry) measurement, and the Tx-Tg value (Tx: crystallization temperature, Tg: glass transition temperature) is a large value. Glass with a more stable glass. That is, when the single mode fiber is manufactured, the glass base material is heated to a temperature equal to or higher than Tg for two times of the base material drawing and drawing process. Therefore, if Tx is close to Tg, crystal nuclei grow one after another. Scattering loss increases. Conversely, if the value of Tx−Tg is large, a low-loss fiber can be manufactured. The glass in the composition region has a value of Tx−Tg of 120 ° C. or more, and can be used for producing a low-loss fiber. However, if glass having a composition deviating from the above composition is used for both the core and the clad, a low-loss fiber cannot be produced. Of these compositions, especially the addition of Bi ₂ O ₃ has a great effect on the stability of the glass. FIG. 14 shows DSC measurement results in the case of Bi ₂ O ₃ = 0, 1.5, and 5 mol% in a system containing Na ₂ O. The measurement was performed by crushing a part of the glass, filling a 30 mg piece of bulk glass into a silver gold-plated sealed container, and in an argon gas atmosphere at a heating rate of 10 ° C./min. As is apparent from this figure, the Tx-Tg value is 119.2 ° C. for Bi ₂ O ₃ = 0 glass and 121.6 ° C. for Bi ₂ O ₃ = 1.5 mol%, whereas Bi ₂ In the case of O ₃ = 5 mol%, the temperature is 167.5 ° C., and in particular, it can be seen that the thermal stability is improved by 40 ° C. or more in the composition of B. FIG. 15 shows the same DSC measurement result when Bi ₂ O ₃ = 0 or 5 mol% in a system containing Li ₂ O. As is apparent from this figure, the value of Tx−Tg is 54.6 ° C. in the case of Bi ₂ O ₃ = 0 glass, whereas in the case of Bi ₂ O ₃ = 5 mol%, the exothermic peak of crystallization is observed. In other words, Tx−Tg becomes infinite, and the thermal stability is dramatically improved. Such an effect was similarly observed when a trivalent metal oxide (Al ₂ O ₃ , La ₂ O ₃ , Er ₂ O ₃ , Nd ₂ O _3, etc.) was added.

Addition of Bi ₂ O ₃ also has an important effect in terms of refractive index control. FIG. 16 shows the Bi ₂ O ₃ addition amount dependence of the refractive index (n _D ) of TeO ₂ -based glass. As shown in the figure, when the Bi ₂ O ₃ addition amount is changed from 0 to 20 mol%, n _D increases from 2.04 to 2.22 in proportion to the addition amount.

By using this characteristic, the fiber design can be easily made from a small core-cladding relative refractive index difference of about 0.2% to a large one of about 6% by changing the amount of Bi ₂ O ₃ added. It can be carried out.

Next, an example of an optical amplification medium constituting an optical amplifier or the like will be described.

This optical amplification medium has a core glass,
A ₁ : 0 <Bi ₂ O ₃ ≦ 20 (mol%),
0 <Na ₂ O <15 (mol%),
5 ≦ ZnO ≦ 35 (mol%), and 60 ≦ TeO ₂ ≦ 90 (mol%)
Is a tellurite glass of the composition region of
Clad glass
B ₁ : 5 <Na ₂ O <35 (mol%),
0 ≦ ZnO <10 (mol%),
55 <TeO ₂ <85 (mol%); or C ₁ : 5 <Na ₂ O <35 (mol%),
10 <ZnO ≦ 20 (mol%),
55 <TeO ₂ <85 (mol%); or D ₁ : 0 ≦ Na ₂ O <25 (mol%),
20 <ZnO ≦ 30 (mol%), and 55 <TeO ₂ <75 (mol%)
An optical fiber or waveguide made of tellurite glass in the composition region is used as a rare earth host. FIG. 17 shows the composition region of B _{1 to} D ₁ that brings about glass stabilization.

  The glass in the above composition region has a Tx-Tg value (Tx: crystallization temperature, Tg: glass transition temperature) (a measure representing the thermal stability of the glass, and a glass having a large value is more thermally stable. The glass has a value of 100 ° C. or higher, and does not crystallize in a fiber manufacturing process such as a drawing process, and can be used for manufacturing a low-loss fiber. However, it is not possible to produce a low-loss fiber with a glass having a composition deviating from the above composition range.

In this specification, an embodiment of the optical amplification medium is characterized in that erbium or erbium and ytterbium are added to at least one of the tellurite glass of the core glass or the tellurite glass of the clad glass.

In the present specification, a laser device having an optical amplification medium and an excitation light source, an optical fiber using the tellurite glass doped with Er (erbium) as the optical amplifying medium, from ⁴ I _13/2 level of Er ^The most important feature is the use of a stimulated emission transition to the ⁴ I _15/2 level.

FIG. 18 is an energy level diagram of Er ³⁺ . In this figure, it is shown that light is emitted by the transition from the upper level ⁴ I _13/2 to the ground level ⁴ I _15/2 .

In addition, as shown in FIG. 1, Er ^{3+ 4} I _13/2 → ⁴ I _15/2 emission is _wider in fluoride glass than in other glasses such as quartz glass ⁴ I _13/2 → It is known to have a ⁴ I _15/2 emission band. However, as can be seen from FIG. 1, the emission intensity becomes smaller at longer wavelengths than 1.6 μm, and even when Er is in fluoride glass, optical amplification and laser oscillation at longer wavelengths of 1.6 μm or more are unlikely to occur. Become.

However, when Er is added to tellurite glass, it receives a stronger electric field than in other glasses, and as a result, it is in the level due to the Stark effect received by the ⁴ I _13/2 and ⁴ I _15/2 levels. The spread becomes large, it has a stimulated emission cross section even in a longer wavelength region, and as shown in FIG. 1, fluorescence exists even at a longer wavelength of 1.65 μm or more.

Therefore, if a tellurite glass optical fiber having at least Er added to the core is used as an optical amplifying medium, the distance from 1.5 μm to 1.7 μm, which could not be realized with an Er-added silica glass optical fiber or an Er-added fluoride glass optical fiber. Optical amplification and laser devices are possible.

When the tellurite glass contains at least one of boron, phosphorus, and a hydroxyl group, the gain coefficient and the noise figure are improved even when the ⁴ I _11/2 level is excited by 0.98 μm light. That, B-O, P-O , vibration energy of the O-H, respectively about ^{1400 cm -1,} 1200 cm -1, is 3700 cm ^-1, phonon energy of tellurite glass containing no these 600～700Cm ^-1 Therefore, it becomes more than double. For this reason, if the ⁴ I _11/2 level of Er is directly pumped with light in the vicinity of a wavelength of 0.98 μm to cause 1.5 μm optical amplification by the ⁴ I _13/2 → ⁴ I _15/2 transition, polyphony This is because it is easy to undergo relaxation due to the emission, and the excitation efficiency of the ⁴ I _13/2 level is unlikely to decrease (FIG. 18). ^{Also, 4} _{I 11/2} 4 _{I 11/2} level than direct excitation with light in the vicinity of level from ⁴ I _13/2 1.48 .mu.m to easily when ⁴ I _13/2 level occurs relaxation to level easy inversion between better to excite the ⁴ I _13/2 level After exciting position is ⁴ I _13/2 level position and ⁴ I _15/2 level is obtained, thus there is an advantage that noise characteristics are excellent.

Hereinafter, reference examples of the tellurite glass, an optical amplifying medium using the tellurite glass, a broadband optical amplifier and a laser apparatus using the optical amplifying medium, and an example of the present invention will be described in detail with reference to the drawings.

( Reference Example 1)
After melting _{TeO 2 (75mol%) - ZnO} (20mol%) - Na 2 O (5mol%), TeO 2 (77mol%) - ZnO (15.5mol%) - Na 2 O (6mol%) - Bi 2 O 3 TeO ₂ , ZnO, Na so as to be (1.5 mol%), TeO ₂ (73.5 mol%)-ZnO (15.5 mol%)-Na ₂ O (6 mol%)-Bi ₂ O ₃ (5 mol%). _A mixture of raw materials of ₂ NO ₃ and Bi ₂ O ₃ was filled in a 20 g crucible and melted at 800 ° C. for 2 hours in an electric furnace in an oxygen atmosphere. Then, it casted on the plate pre-heated to 200 degreeC, and obtained glass was annealed at 250 degreeC for 4 hours. A portion of this glass was crushed, and two samples of 30 mg of powder, 30 mg of bulk glass and powdered in an agate mortar, were filled into a silver gold-plated sealed container, and the heating rate was 10 ° C./min in an argon gas atmosphere. DSC measurement was performed. The bulk glass has a Tx-Tg value of 119.2 ° C. for Bi ₂ O ₃ = 0 glass and 121.6 ° C. for Bi ₂ O ₃ = 1.5 mol%, whereas Bi ₂ O ₃ = 5 mol%. In this case, the temperature was 167.5 ° C., and in particular, the thermal stability was improved by 40 ° C. or more in the composition in the range of B. Next, in the case of a powder-like sample, the value of Tx−Tg is 80.2 ° C. for Bi ₂ O ₃ = 0 glass and 76.3 ° C. for Bi ₂ O ₃ = 1.5 mol%. In the case of Bi ₂ O ₃ = 5 mol%, the temperature is 110.2 ° C., and the value of Tx−Tg is smaller than that measured in bulk, but the thermal stability of the glass can be measured more precisely. It was also found that the thermal stability was drastically improved by adding Bi ₂ O ₃ = 5 mol%.

  In the present specification, unless otherwise specified, the value of Tx-Tg related to the thermal stability of glass is discussed based on the measured value in bulk glass.

It has been stated that it is possible to produce a low-loss fiber by using a glass with Tx−Tg ≧ 120 ° C. based on the DSC measurement value in the bulk glass. However, the loss obtained with this range of glass is approximately 1 dB / km. It is as follows. In order to perform high-efficiency optical amplification using the optical transition of the three-level system, a more stable glass is required to obtain a fiber with a loss about one order of magnitude lower than this. As an evaluation standard at that time, the DSC measurement value in the powdery glass is effective, and if a glass satisfying this measurement Tx−Tg ≧ 100 ° C. is used, an optical fiber of up to 0.1 dB / km can be obtained.

( Reference Example 2)
As the core glass and the clad glass, those having the glass composition indicated by A or B above are used. These compositions were melted in an oxygen atmosphere using a platinum crucible or a gold crucible, and a preform was produced by a suction molding (suction casting) method. Similarly, a jacket tube was produced by the rotational molding method using the glass composition of A above. As a result of fiber drawing using these preforms and jacket tubes, the minimum loss is 0.1 dB / m or less, the cutoff wavelength is 0.5 μm to 2.5 μm, and the relative refractive index difference between the core and the clad is 0.2%. 6% tellurite glass optical fiber could be produced.

  Also, rare earth such as Er, Pr, Yb, Nd, Ce, Sm, Tm, Eu, Tb, Ho or Dy could be added to the core or clad glass by 10 wt% or less (preform, jacket tube (For the production method, see Kanamori et al., Kanamori et al., Proceeding of 9th International Symposium on Nonoxide Glasses, P. 74, 1994).

( Reference Example 3)
Those as the core glass of the glass composition shown in the above A _1, also except for using those as the cladding glass of the glass composition shown in the above B _1, C ₁ or D _1, in the same manner as in Reference Example 2 A tellurite glass optical fiber was prepared. As a result, a tellurite glass optical fiber having a minimum loss of 0.1 dB / m or less, a cutoff wavelength of 0.5 μm to 2.5 μm, and a relative refractive index difference between core and cladding of 0.2% to 6% is manufactured. I was able to.

  Further, 10 wt% or less of rare earth such as Er, Pr, Yb, Nd, Ce, Sm, Tm, Eu, Tb, Ho or Dy could be added to the core or clad glass.

( Reference Example 4)
TeO ₂ (68.6 mol%) _- Na 2 O (7.6 mole%) - ZnO (19.0 _{mole%) - Bi 2 O 3 (} 4.8 mol%) 1000 ppm added Er glass as a core material and, _TeO 2 (71 mol%) - _Na 2 O (8 mol%) - ZnO (21 mol%) of glass and a cladding material, the cut-off wavelength 1.3 .mu.m, the core-clad between the refractive index difference of 2% of the optical fiber This was used as an optical amplification medium. Using this optical amplification medium, an optical amplifier having a wavelength band of 1.5 μm to 1.7 μm was fabricated, and an amplification experiment was performed. An excitation wavelength of 0.98 μm was selected, and a DFB laser was used as a signal light source in the 1.5 μm to 1.7 μm band.

  FIG. 19 is a diagram showing a schematic configuration of the optical amplifier according to the present embodiment. The signal light source 101 and the excitation light source 102 are connected to one end of an amplification optical fiber 104 via an optical coupler 103, and an optical isolator 105 is connected to the other end of the amplification optical fiber 104. Each component is connected by the optical fiber 106.

  By an amplification experiment using the optical amplifier having such a configuration, an amplification gain could be obtained at a wavelength between 1.5 μm and 1.7 μm.

  Further, a ring laser in which the tunable narrow band-pass filter shown in FIG. 20 was inserted was configured using the same optical amplification medium. In this ring laser, instead of the signal light source 1 in FIG. 19, the output side of the optical isolator 105 is connected to the optical coupler 103 to form a ring-shaped optical resonator, and a narrow band is formed in the middle of the ring-shaped optical resonator. A band-pass filter 107 is inserted. Then, the transmission region of the narrow band-pass filter 7 was varied between 1.5 μm and 1.7 μm, and light was incident from the excitation light source 102 to perform a laser oscillation experiment. As a result, it was possible to confirm laser oscillation in the wavelength band from the output end 108.

In the above reference example, 0.98 μm was used as the excitation wavelength and the ⁴ I _11/2 level was excited. However, the ⁴ I _13/2 level may be directly excited using the wavelength of the 1.48 μm band. Needless to say. Further, a level having a higher energy than the ⁴ I _11/2 level may be excited with light having a wavelength shorter than 0.98 _μm .

( Reference Example 5)
Using the optical amplifier shown in FIG. 19, a 1.5 μm band optical amplification experiment was conducted. The excitation wavelength was 0.98 μm. As a result, amplification was possible with a noise figure of 7 dB or less in a wavelength region of 1.53 μm or more.

( Reference Example 6)
An optical fiber similar to that in Reference Example 3 was produced except that Er and Yb were added in addition to Er as a core, and used as an optical amplification medium.

Using the optical amplification medium, in the configuration of Reference Example 4 and Reference Example 5 were carried out optical amplification experiments and laser oscillation experiment. As the excitation wavelength, 1.029 μm (Yb-doped YAG laser), 1.047 μm (Nd-doped YLF laser), 1.053 μm (Nd-doped YAG laser), 1.064 (Nd-doped YAG laser), or the like was used. Thus, when Yb is co-added with Er, gain of energy transfer from Yb to Er gives a laser oscillation between 1.5 μm and 1.7 μm and 1 It was possible to confirm broadband optical amplification in the .5 μm band.

In the above reference examples 1-6, an example was shown as a composition of the optical fiber . For _{example, Cs 2 O, Rb 2 O} , K 2 O, Li 2 O, BaO, SrO, CaO, MgO, BeO, La 2 O 3, Y 2 O 3, Sc 2 O 3, Al 2 O 3, ThO 2 , HfO ₂ , ZrO ₂ , TiO ₂ , Ta ₂ O ₅ , Nb ₂ O ₅ , Wo ₃ , Tl ₂ O, CdO, PbO, In ₂ O ₃ , and Ga ₂ O ₃ together with TeO ₂ Glass may also be used (see: Glass Handbook (8th edition), edited by Sakuo Sakuo et al., Asakura Shoten, published in 1975). Further, Er or Er and Yb may be added not only to the core but also to the cladding.

Further, an optical amplifier, said optical amplifier medium, the excitation light source for exciting the light amplification medium, is not limited to the above-described configuration as long as it has an input and output means of the signal light.

The laser device, inserting said optical amplification medium in the optical resonator constituted by an optical fiber, furthermore, as long as it has an excitation light source for exciting the optical amplification medium, the present invention is not particularly limited Absent.

( Reference Example 7)
Amplification characteristics in the 1.5 μm band were measured using a fiber 4 m in which Er 1000 ppm was added to the core as an amplification fiber. Core glass compositions _TeO 2 (68.6 mol%) - ZnO (19 mol%) _- Na 2 O (7.6 _{mole%) - Bi 2 O 3 P} 2 O 5 to as (4.8 mol%) 5% by weight was added, and the clad glass composition was TeO ₂ (71 mol%)-Na ₂ O (8 mol%)-ZnO (21 mol%). The refractive index difference between the core and the clad was 2.5%, and the cutoff wavelength was 0.96 μm. When the small signal gain in the 1.5 μm band was measured using 0.98 μm light (the light source is a semiconductor laser) as a pumping light, the gain efficiency increased by a factor of 5 to 2 dB / mW compared to the case where phosphorus was not added. . Further, when the gain spectrum in the saturation region was measured with an input signal level of −10 dBm, the gain became flat with a width of 90 mm from 1530 nm to 1620 nm (excitation intensity was 200 mW). Further, the noise figure was 7 dB when phosphorus was not added, but decreased to 4 dB when phosphorus was added. By adding phosphorus as the core glass in this way, the gain coefficient and noise figure were greatly improved.

Further, even when B ₂ O ₃ was added instead of P ₂ O ₅ , improvement in gain coefficient and noise figure could be confirmed.

( Reference Example 8)
TeO ₂ (68.6 mol%) - ZnO (19 mol%) _- Na 2 O (7.6 _mole%) - _Bi 2 O 3 This 5000ppm an OH group as (4.8 mol%) of core glass, When Er was added at 1000 ppm, it was confirmed that the gain coefficient increased by a factor of 3 compared to when no OH group was added.

The degree of increase in gain coefficient is lower than that when phosphorus is added because the signal energy of the OH group has a large value of 3700 cm ⁻¹ , and the ⁴ I _13/2 level, which is the starting level of amplification, is also slightly _higher. This is because it is alleviated by phonon emission.

FIG. 21 is a diagram showing an example of a laser device that includes the optical amplification medium . In the figure, reference numerals 111 and 111 ′ are pumping semiconductor lasers (wavelength: 1480 nm), and 112 and 112 ′ are signal light and pumping light. An optical coupler that couples light, 113 and 115 are optical fibers for amplification, and 114 is an optical isolator. The signal light enters from the port A and then exits from the port B.

A ZrF ₄ fluoride glass optical fiber doped with 1000 ppm Er as an amplification fiber denoted by reference numeral 113 is used (reference: Kanamori et al, Proceeding of 9th International Synposium on Non-Oxide Glasses, P.74, 1994). As the amplification fiber 115, a TeO ₂ —Na ₂ O—Bi ₂ O ₃ —ZnO-based tellurite glass optical fiber added with 1000 ppm of Er was used.

In each optical fiber, the difference in refractive index between the core and the clad was 2.5%, the cutoff wavelength was 1.35 μm, and the fiber lengths were 10 m and 7 m, respectively. The gain spectrum in the 1.5 μm band was measured with the output light intensity of the pumping semiconductor lasers of reference numerals 111 and 111 ′ being 150 mW. The obtained gain spectrum is shown in FIG.

According to the gain spectrum shown in FIG. 22, the curve indicating the change in the value of the signal gain in the 80 nm width from the signal wavelength 1530 nm to 1610 nm is flat. That is, it can be seen that the signal gain is maintained at a value in the vicinity of 30 dB in such a wavelength band. Therefore, the gain tilt can be kept small in such a wavelength band. When the Er-doped fluoride glass optical fiber is used, the wavelength width at which the gain becomes flat is 30 nm from 1530 nm to 1560 nm, and thus the wavelength width at which the gain becomes flat has spread more than twice. In addition, in the case of an Er-doped silica glass optical fiber, the flat wavelength width is at most 10 nm, so that it has spread eight times.

In this reference example, an Er-doped ZrF ₄ -based fluoride glass optical fiber was used in the former stage, and an Er-doped tellurite glass optical fiber was used in the latter stage, but this may be reversed, and an InF ₃ -based fluoride glass optical fiber may also be used. good. Further, an Er-doped oxide multicomponent glass optical fiber may be added to the amplification optical fiber. In short, it is important to use an Er-doped tellurite glass optical fiber as one of the amplification optical fibers.

Further, the composition of the tellurite glass optical fiber is not limited to that used in the present reference example.

  It goes without saying that any one of forward pumping, backward pumping, and bidirectional pumping may be used as a pumping method for the amplification optical fiber.

( Reference Example 9)
FIG. 23 is a diagram showing a schematic configuration of another reference embodiment of a laser apparatus including an optical amplifying medium using the tellurite glass optical fiber in its configuration. In this reference example, the amplification fibers 113 and 115 used in Reference Example 8 are connected in series via a tunable bandpass filter 117 (bandwidth 3 nm), and the transmittance is 99% at 1480 nm, 1500 nm to 1630 nm. Then, a mirror 116 having a reflectance of 100% was provided, and a mirror 118 having a transmittance of 1500% to 1630 nm and a transmittance of 20% was provided at the other end for laser oscillation. As a result, it was found that laser oscillation could be confirmed in a wide range of signal wavelengths from 1500 nm to 1630 nm, and that it could be used as a broadband tunable laser that can be used at 1.5 μm.

As described above , if an optical amplifying medium made of the tellurite glass optical fiber is used, it is possible to construct an optical amplifier or a laser device from 1.5 μm to 1.7 μm, which has been impossible with an optical fiber amplifier so far. Thus, the performance of the maintenance / monitoring system used in the 1.55 μm band optical communication system can be improved, and the optical communication system can be stably operated.

  Further, if a characteristic with a wide amplification wavelength region is used, a short optical pulse such as femtosecond can be efficiently amplified, and it is also effective as an optical amplifier used in a wavelength division multiplexing optical transmission system.

( Reference Example 10)
In this reference example, the operation of the super luminescent laser was performed using the optical fiber used in the reference example 4. A laser diode of 1.48 μm was used as an excitation light source, and was incident on one end of the tellurite glass optical fiber. In order to suppress Fresnel reflection at the end of the optical fiber, the other end of the optical fiber was obliquely cut at an angle of 10 °, and the emission spectrum was measured. As a result, a broad emission spectrum from 1.46 μm to 1.64 μm was observed, indicating a broadband super It was found that it can be used as a luminescent laser device.

( Reference Example 11)
In the configuration of the optical amplifier shown in FIG. 19, after the optical isolator, a filter for equalizing the gain ( chirped fiber Bragg grating , programmable filter, Fabry-Perot etalon filter, Mach- Zender filter, etc.) is inserted. Then, the optical amplification characteristics were measured. When light with a signal intensity of −30 dBm is incident and excited at 1.48 μm (200 mW), a gain peak is observed from 1530 to 1580 nm unless the filter is inserted, but the filter is inserted to adjust the loss. As a result, it was confirmed that the peak of the gain could be canceled out, and it was possible to operate with a gain deviation of 0.2 dB or less with respect to the WDM signal in the wavelength range of 1530 nm to 1610 nm.

( Reference Example 12)
Operates as a waveguide laser and a waveguide type optical amplifier by adding Ce, Pr, Gd, Nd, Eu, Sm, Tb, Tm, Dy, Ho, Yb or Er to the core with glass in the region A as a core and cladding I let you. As a result, 0.3 μm, 1.3 μm, 0.31 μm, 1.07 μm, 0.61 μm, 0.59 μm, 0.54 μm, 1.48 μm, 3.0 μm, 1.49 μm, 1 μm, 1.55 μm band, respectively. Broadband laser oscillation and broadband optical amplification operating in

( Reference Example 13)
TeO ₂ (70 mol%)-ZnO (18 mol%)-Na ₂ O (6 mol%)-Bi ₂ O ₃ (6 mol%) glass was used as a core material and Er was added at 2000 ppm, and TeO ₂ (68 mol%) was added. %)-ZnO (22 mol%)-Na ₂ O (7 mol%)-Bi ₂ O ₃ (3 mol%) glass as a clad material, with a cutoff wavelength of 1.1 μm and a core-clad relative refractive index difference of 1 An 8% optical fiber was formed and used as an amplification medium. The fiber loss at 1.3 μm was 40 dB / km. An optical amplifier was constructed using 4 m of this optical fiber, and an amplification experiment was conducted. The excitation wavelength used was bidirectional excitation with 0.98 μm at the front and 1.48 μm at the rear. As the signal light source, a wavelength tunable laser of 1.5 μm to 1.7 μm band was used. As a result of the amplification experiment, a small signal gain of 5 dB or more was obtained in the 110 nm band of 1500 to 1630 nm. At this time, the noise figure was 5 dB or less at a wavelength of 1530 nm or more.

( Reference Example 14)
An optical amplifier was configured using 15 m of the same optical fiber as in Reference Example 13, and an amplification experiment was performed. The excitation wavelength was 1.48 μm bidirectional excitation for both front and rear. As the signal light source, a wavelength tunable laser of 1.5 μm to 1.7 μm band was used. As a result of the amplification experiment, a small signal gain of 35 dB or more was obtained particularly in the 50 nm band of 1580 to 1630 nm. At this time, the noise figure was 5 dB.

( Reference Example 15)
A laser was constructed using 15 m of the same optical fiber as in Reference Example 13. The cavity was constructed using a total reflection mirror and a fiber Bragg grating with 3% reflectivity at 1625 nm. The excitation wavelength was 1.48 μm bidirectional excitation for both front and rear. When the incident excitation intensity was 300 mW, a high output of 150 mW was obtained at 1625 nm, which could not be obtained with a silica glass optical fiber or a fluoride glass optical fiber.

( Reference Example 16)
TeO ₂ (68 mol%)-ZnO (13 mol%)-Na ₂ O (4 mol%)-Bi ₂ O ₃ (15 mol%) 3 wt% of Er is added using glass as a core material, and TeO ₂ (69 mole%) - ZnO (21 mole%) - _Na 2 O (8 _{mol%) - Bi 2 O 3 (} 2 mol%) of glass and a cladding material, the cutoff wavelength 1.4 [mu] m, between the core-clad relative refractive index difference A 5% optical fiber was formed and used as an amplification medium. A small optical amplifier was constructed using 3 cm of this optical fiber, and an amplification experiment was conducted.

  The excitation wavelength was 1.48 μm forward excitation. As the signal light source, a wavelength tunable laser of 1.5 μm to 1.7 μm band was used. As a result of the amplification experiment, a small signal gain of 20 dB or more was obtained in the 80 nm band of 1530 to 1610 nm. At this time, the noise figure was 7 dB or less.

( Reference Example 17)
In the case of the bulk glass of Reference Example 1, the quaternary glass of TeO ₂ —ZnO—Li ₂ O—Bi ₂ O ₃ is fixed to Bi ₂ O ₃ = 5 mol%, and other compositions are changed to produce 50 pieces. The thermal characteristics were measured by DSC in the same manner as above. The result is shown in FIG. As shown in this figure, a stable glass having a Tx-Tg of 120 ° C. or higher in the region A was obtained. Furthermore, in the region B, a remarkably stable glass having no crystallization exothermic peak was obtained. If an optical fiber is made using such a thermally stable glass, not only the fiber loss is low, but also a high yield optical fiber can be produced in large quantities, and the cost can be reduced. it can. Therefore, 2000 ppm of Er was added using TeO ₂ (80 mol%)-ZnO (5 mol%)-Li ₂ O (10 mol%)-Bi ₂ O ₃ (5 mol%) glass selected from the B region as a core material, and TeO was added. ₂ (75 mol%)-ZnO (5 mol%)-Li ₂ O (15 mol%)-Bi ₂ O ₃ (5 mol%) glass as a cladding material, with a cutoff wavelength of 1.1 μm and a core-clad relative refractive index difference of 2 A 5% optical fiber was formed and used as an amplification medium. The fiber loss at 1.2 μm was 20 dB / km. An optical amplifier was constructed using 3 m of this optical fiber, and an amplification experiment was conducted.

  The excitation wavelength used was bidirectional excitation with 0.98 μm at the front and 1.48 μm at the rear. As the signal light source, a wavelength tunable laser of 1.5 μm to 1.7 μm band was used. As a result of the amplification experiment, a small signal gain of 20 dB or more was obtained in the 80 nm band of 1530 to 1610 nm. At this time, the noise figure was 5 dB or less.

Further, TeO ₂ (70 mol%) — ZnO (10 mol%) — Li ₂ O (15 mol%) — Bi ₂ O ₃ (5 mol%) glass selected from the region A was used as a core material, and 2000 ppm of Er was added thereto, and TeO _{2 was} added. (70 mol%)-ZnO (7 mol%)-Li ₂ O (18 mol%)-Bi ₂ O ₃ (5 mol%) glass is used as the cladding material, the cutoff wavelength is 1.1 μm, and the core-clad relative refractive index difference is 1. A 5% optical fiber was formed and used as an amplification medium. The fiber loss at 1.2 μm was 60 dB / km. An optical amplifier was constructed using 3 m of this optical fiber, and an amplification experiment was conducted in the same manner. As a result, a small signal gain of 20 dB or more was obtained in the 80 nm band of 1530 to 1610 nm. At this time, the noise figure was 5 dB or less. From the above, it was shown that a practical broadband EDFA can be made even from the glass in the region A.

( Reference Example 18)
An optical amplifier was configured using 15 m of the optical fiber described in Reference Example 17, and an amplification experiment was performed. The excitation wavelength was 1.48 μm bidirectional excitation for both front and rear. As the signal light source, a wavelength tunable laser of 1.5 μm to 1.7 μm band was used. As a result of the amplification experiment, a small signal gain of 20 dB or more was obtained particularly in the 50 nm band of 1580 to 1630 nm. At this time, the noise figure was 5 dB or less.

( Reference Example 19)
A laser was constructed using 15 m of the optical fiber described in Reference Example 17. The cavity was constructed using a total reflection mirror and a fiber Bragg grating with 3% reflectivity at 1625 nm. The excitation wavelength was 1.48 μm bidirectional excitation for both front and rear. When the incident excitation intensity was 300 mW, a high output of 150 mW was obtained at 1625 nm, which could not be obtained with a silica- based glass optical fiber or a fluoride glass optical fiber.

( Reference Example 20)
TeO ₂ (68 mol%)-ZnO (13 mol%)-Na ₂ O (4 mol%)-Bi ₂ O ₃ (15 mol%) 3 wt% of Er is added using glass as a core material, and TeO ₂ (69 mol%)-ZnO is added. _{(21mol%) - Na 2 O} (8mol%) - Bi 2 O 3 (2mol%) of glass and the clad material, to form a cut-off wavelength 1.4 [mu] m, a core-clad between relative refractive index difference of 5% fiber This was used as an amplification medium. A small optical amplifier was constructed using 3 cm of this optical fiber, and an amplification experiment was conducted.

  The excitation wavelength was 1.48 μm forward excitation. As the signal light source, a wavelength tunable laser of 1.5 μm to 1.7 μm band was used. As a result of the amplification experiment, a small signal gain of 20 dB or more was obtained in the 80 nm band of 1530 to 1610 nm. At this time, the noise figure was 5 dB.

( Reference Example 21)
After melting _{TeO 2 (73.5mol%) - ZnO} (20mol%) - Na 2 O (5mol%) - Bi 2 O 3 (1.5mol%), TeO 2 (73mol%) - ZnO (20mol%) - Na 90 g of crucible is charged with a mixture of TeO ₂ , ZnO, Na ₂ CO ₃ and Bi ₂ O ₃ raw materials so that ₂ O (5 mol%)-Bi ₂ O ₃ (2 mol%) is obtained. It was melted at 800 ° C. for 2 hours in an oxygen atmosphere. Thereafter, the melt was cast into a cylindrical hollow mold preheated to 250 ° C., and the lid was immediately used as a melt inlet, and then the mold was laid down horizontally at 2000 rpm and kept for 3 minutes. Thereafter, it was gradually cooled to room temperature. The obtained tellurite glass was a cylindrical tube having an outer diameter of 15 mmφ, an inner diameter of 5 mmφ, a length of 130 mm, and a bottom at the bottom. When the entire obtained two glass tubes were examined in detail using a microscope, a large amount of crystallization was observed near the outer wall in the case where 1.5 mol% of Bi ₂ O ₃ was added, whereas Bi ₂ Such crystallization was not observed in the case where 2 mol% of O ₃ was added. Part of these two glasses are crushed, and two kinds of powder 30mg powdered in an agate mortar are filled into a silver gold-plated sealed container, and DSC measurement is performed in an argon gas atmosphere at a heating rate of 10 ° C / min. went. FIG. 25 shows the measurement results.

Figure 25 is in the composition _{73.5TeO 2 -20ZnO-5Na 2 O-} 1.5Bi 2 O 3 glass (in the figure, a line) and _{73TeO 2 -20ZnO-5Na 2 O-} 2Bi 2 O 3 glass (Fig., B It is a measurement figure of each DSC at the time of using a line. In the glass to which 1.5 mol% of Bi ₂ O ₃ was added, the crystallization peak started from around 350 ° C., and the value of Tx−Tg was 69.2 ° C. On the other hand, in the glass to which 2 mol% of Bi ₂ O ₃ was added, the crystallization peak started from around 390 ° C., and the value of Tx−Tg was 110.4 ° C. That is, compared with the case where 1.5 mol% of Bi ₂ O ₃ is added, the glass with 2 mol% added has dramatically improved thermal stability.

The tellurite glass of the above Reference Examples 1 to 21 is characterized by being a quaternary system containing Bi ₂ O ₃ . Such tellurite glass has a high thermal stability, loss upon optical fiber of can be kept low, by further refractive index control optical fiber high Δn for their ease can be prepared, less efficient 3 The amplification band of the level EDFA can be expanded.

As a conventionally known tellurite glass capable of forming an optical fiber, there is a tellurite glass such as Sintzer et al. (US Pat. No. 5,251,062) described in the prior art. It differs from No. 062 tellurite glass in the presence or absence of Bi ₂ O ₃ , that is, whether it is a ternary system or a quaternary system.

As described above, the ternary tellurite glass described in US Pat. No. 5,251,062 has a lower thermal stability than the quaternary tellurite glass disclosed in the present specification. While the loss at 1.55 μm can only be reduced to 1500 dB / km, as a result of examining various compositions for the purpose of reducing the loss, a quaternary system including Bi ₂ O ₃ can reduce the loss. I found it effective. Furthermore, since this quaternary glass is easy to control the refractive index, an optical fiber having a high Δn can be produced, and a tellurite EDFA has been realized for the first time together with a low loss. In US Pat. No. 5,251,062, it is difficult to realize an inefficient three-level EDFA in the ternary tellurite glass of US Pat. No. 5,251,062. It is also clear from the fact that the submitted Optics Letters and Optical Materials do not have any specific description regarding the realization of EDFA.

More specifically, in U.S. Pat. No. 5,251,062, Snitzer et al. Require that an optical fiber structure with a core and cladding be used for optical amplification, whereas lasers can also be realized in bulk glass. The composition range of the ternary tellurite glass was shown as the tellurite glass that can be made into an optical fiber. Therefore, it is clear that the purpose is realization of optical amplification, but these three documents only describe a fiber laser using neodymium in the Optics Letters. Moreover, in the field of optical amplification, neodymium was initially expected to be applied to amplification in the 1.3 μm band. However, as described in the optical materials, 1.3 μm is used for absorption of excited states. It is a well-known fact that application to band amplification is difficult.

The tellurite glass containing Bi ₂ O ₃ contains 72% Te ₂ O ₃ -18% Bi ₂ O ₃ and 80% Te ₂ O ₃ -10% Bi ₂ O ₃ -10% TiO in the optical materials. _Although these are descriptions of ₂ , these have completely different compositions from the quaternary system disclosed in the present specification , and further, there is no description regarding thermal stability and loss of these glasses in the optical materials.

Further, a quaternary tellurite glass having a core composition of 77% TeO ₂ -6.0% Na ₂ O-15.5% ZnO-1.5% Bi ₂ O _{3 in} the optical materials and the optical letters. In particular, the optical materials describe the loss up to the loss, but the loss is as high as 1500 dB / km in the 1.55 μm band, and even more about the thermal stability improvement by adding Bi ₂ O _3. In addition, there is no description reminiscent of improving thermal stability. In the field of optical fibers, it is known to add a refractive index control material to glass for refractive index control, and the addition of Bi ₂ O ₃ in the optical fiber is considered to be for that reason.

As described in detail in Reference Examples and the like, as a result of various investigations on the composition of tellurite glass with the aim of reducing the loss of tellurite glass optical fiber according to the disclosure of the present specification, quaternary tellurite added with Bi ₂ O ₃ was obtained. It was clarified that glass was effective. Although this has already been described in the reference examples, especially when the Bi ₂ O ₃ concentration exceeds 1.5%, the thermal stability has been dramatically improved, and the loss of the tellurite glass optical fiber has been successfully reduced. Further secondarily can produce high Δn optical fiber since the Δn of the optical fiber by adjusting the core and the cladding of the Bi ₂ O ₃ amount can be freely controlled, low-efficiency three-level system of the EDFA by these synergistic effects Succeeded in expanding the amplification band.

Next, the glass composition that makes the gain spectrum of the tellurite EDFA flatter will be examined. The following reference examples are characterized mainly by adding Al as a host to tellurite glass or tellurite glass optical fiber. If adding Al to the SiO ₂ based glass, eliminates the indentations between 1.53μm and 1.56 .mu.m of stimulated emission cross-section of Er added to SiO ₂ based glass optical fiber, 1.56 .mu.m from 1.54μm (Erbium-Doped Fiber Amplifiers, Emmanuel Desurvire, publisher John Wiley & Sons, 1994).

However, this is an effect of adding Al to the silica-based glass optical fiber, and the effect is not known for the tellurite glass optical fiber. As shown in the reference examples below, the present inventors eliminated dents in the stimulated emission cross sections of 1.53 μm and 1.56 μm and added 1.6 μm band by adding Al to the tellurite glass optical fiber . stimulated emission cross section changing the (increasing) that can, as a result, found that it is possible to reduce the gain deviation between 1.55μm band and 1.6μm band.

( Reference Example 22)
FIG. 26 shows (74) TeO ₂ — (16) ZnO— (6) Na ₂ O— (4 mol%) Bi ₂ O ₃ glass, and (73) TeO ₂ — (15) ZnO— (6) Na ₂ O. _{- (3) Bi 2 O 3} - (3 mol%) _Al 2 _{O 3} glass and _{(79) TeO 2 - (3} ) ZnO- (12) Li 2 O- (3) Bi 2 O 3 - (3 mol% ) Shows a 1.5 μm emission spectrum of Er in Al ₂ O ₃ glass. Intensity around 1.6μm of the emission spectrum of the glass containing _Al 2 _{O 3} As is apparent from the figure strongly compared to those not containing _Al 2 _{O 3,} also between 1.53μm and 1.56μm The depth of the valley is also shallow.

This Al ₂ O ₃ -containing glass (TeO ₂ —ZnO—Na ₂ O—Bi ₂ O ₃ -based glass) is used as an Er-doped tellurite optical fiber (cutoff wavelength: 1.3 μm, Er concentration: 4000 ppm, length: 0.9m) and excitation (200 mW) at 1.48 μm, the gain deviation between 1.56 μm and 1.69 μm could be reduced to 10 dB or less.

When this optical fiber was used as an amplification medium and an EDFA was configured using a fiber Bragg grating as a gain equalizer, an EDFA having a gain deviation of 1 dB or less from 1.53 μm to 1.60 μm could be realized. In the case of using an optical fiber not containing Al ₂ O ₃ , the gain deviation between 1.53 μm and 1.60 μm is 15 dB or more, and even if the gain is corrected using a gain equalizer, the gain deviation extends over a bandwidth of 70 nm. It was difficult to make it 1 dB or less. It was only possible to use the Al ₂ O ₃ -containing glass of this reference example for a fiber host.

The effect of addition of Al ₂ O _{3 on} the gain characteristics is as follows: TeO ₂ —ZnO—Na ₂ O—Bi ₂ O ₃ composition (55 ≦ TeO ₂ ≦ 90, 0 ≦ ZnO) described in Japanese Patent Application No. 9-226890 ≦ 35, 0 ≦ Na ₂ O ≦ 35, 0 <Bi ₂ O ₃ ≦ 20, unit mol%).

( Reference Example 23)
The effect of addition on the gain characteristics of Al ₂ O ₃ was confirmed for TeO ₂ —ZnO—Li ₂ O—Bi ₂ O ₃ glass. That is, (80) TeO _2- (3) ZnO— (12) Li ₂ O— (5 mol%) Bi ₂ O ₃ glass and (79) TeO ₂ — (3) ZnO— (12) Li ₂ O— ( 3) The emission spectrum of 1.5 μm band of Er in Bi ₂ O ₃ — (3 mol%) Al ₂ O ₃ glass was compared, and in the case of glass containing Al ₂ O ₃ as in Reference Example 22 , The emission intensity in the 1.6 μm band was stronger than that not contained, and there was no valley formed between 1.53 μm and 1.56 μm.

An Er-added tellurite glass optical fiber (cutoff wavelength: 1.3 μm, Er concentration: 4000 ppm, length: 0.9 m) is produced using this Al ₂ O ₃ -containing glass as a core composition, and excited at 1.48 μm (200 mW) As a result, the gain deviation between 1.56 μm and 1.60 μm could be reduced to 10 dB or less.

When this optical fiber is used as an amplifying medium and a Mach-Zehnder type filter (loss medium) is used as a gain equalizer, an EDFA having a gain deviation of 1 dB or less from 1.53 μm to 1.60 μm can be realized. did it. In the case of using an optical fiber not containing Al ₂ O ₃ , the gain deviation between 1.56 μm and 1.60 μm is 15 dB or more, and even if the gain is corrected using a gain equalizer, the gain deviation extends over a bandwidth of 70 nm. It was difficult to make it 1 dB or less.

The measured amplification spectrum using the optical fiber of 2m length for the optical fiber having Er doping concentration 1000 ppm, between 1.53μm and 1.56μm observed in the optical fiber not containing _Al 2 _{O 3} It was found that a gain with good uniformity was obtained from 1.53 μm to 1.56 μm, which is advantageous for WDM transmission applications in the same wavelength region. Moreover, this phenomenon was confirmed also in the _{TeO 2 -ZnO-Na 2 O-} Bi 2 O 3 -Al 2 O 3 system of the optical fiber.

The effect of addition of Al ₂ O _{3 on} the gain characteristics is as follows: the composition of TeO ₂ —ZnO—Li ₂ O—Bi ₂ O ₃ (70 ≦ TeO ₂ ≦ 90, 0 ≦ ZnO ≦ 24, 0 ≦ Li ₂ O ≦ 30). , 0 <Bi ₂ O ₃ ≦ 10, unit mol%), that is, a composition that can form an optical fiber stably was confirmed.

In the above reference examples, the concentration of Al ₂ O ₃ was 3 mol%, but the concentration is not limited to this. If the concentration is higher than 0 mol%, the effect of adding Al ₂ O ₃ can be confirmed. It was.

( Reference Example 24)
However, it is not preferable to increase the concentration more than necessary, because the composition conditions that allow stable fiber formation are ignored.

In this reference example, the effect of adding Al ₂ O _{3 to} the gain characteristics of TeO ₂ —ZnO ₂ —M ₂ O—Bi ₂ O ₃ (M is an alkali element other than Li and Na) -based glass was confirmed. That is, when M is K, Cs, Rb, the gain deviation between 1.56 μm and 1.60 μm can be reduced to 10 dB or less by adding Al ₂ O ₃ as in Reference Examples 22 to 23, In addition, an EDFA is configured by using a gain equalizer to realize an EDFA with a gain deviation of 1 dB or less over a 70 nm of 1.53 μm to 1.60 μm, and a uniform gain of 1.53 μm to 1.56 μm. I was able to.

( Reference Example 25)
In this reference example, the effect of adding Al ₂ O _{3 to} the gain characteristics of TeO ₂ —ZnO ₂ —M ₂ O—Bi ₂ O ₃ (M is an alkali element and containing two or more types) glass was confirmed. That is, even when two or more kinds of alkali elements are included as M, the gain deviation between 1.56 μm and 1.60 μm is made 10 dB or less by adding Al ₂ O ₃ as in Reference Examples 22 to 23. And an EDFA can be configured using a gain equalizer to realize an EDFA with a gain deviation of 1 dB or less over a 70 nm of 1.53 μm to 1.60 μm, and a gain of 1.53 μm to 1.56 μm Can be made uniform.

( Reference Example 26)
In the above reference examples, the effect of addition of Al ₂ O _{3 on} the gain characteristics with respect to TeO ₂ —ZnO—R ₂ O—Bi ₂ O ₃ (R is an alkali element) glass was described. However, the addition effect of Al ₂ O ₃ is not only effective for these glass systems, but also other tellurium such as TeO ₂ —WO ₃ system, regardless of the composition other than TeO ₂ and Al ₂ O _3. It was confirmed that light glass (for example, TeO ₂ —WO ₃ —La ₂ O ₃ —Bi ₂ O ₃₎ is effective for realizing a broadband / gain flat EDFA.

  In the following, further discussion will be made on ternary glass.

( Reference Example 27)
In the ternary glass of TeO ₂ —ZnO—Li ₂ O—Na ₂ O—Bi ₂ O ₃ , when fixed to TeO ₂ = 75 mol% and Bi ₂ O ₃ = 5 mol%, TeO ₂ = 80 mol %, Bi ₂ O ₃ = 5 mol%, and 100 glasses were prepared by changing other compositions. A sample of 30 mg of powdered powder in a glass mortar was filled in a gold-plated silver sealed container, and DSC measurement was performed in an argon gas atmosphere at a heating rate of 10 ° C./min. As a result, a stable glass having a Tx-Tg of 120 ° C. or higher was obtained in the region B seen in FIGS. Optical fibers can be produced in large quantities using such thermally stable glass, and a reduction in cost can be realized. Therefore, TeO ₂ (75 mol%)-ZnO (5 mol%)-Li ₂ O (12 mol%)-Na ₂ O (3 mol%)-Bi selected from the region A (fiber optimum region) in FIG. ₂ O ₃ (5 mol%) glass in the core material with Er added 2000ppm by, _TeO 2 (75 mol%) - ZnO (2 mol%) _- Li 2 O (15 mole%) - _Na 2 O (3 mol %)-Bi ₂ O ₃ (5 mol%) glass as a clad material, an optical fiber having a cutoff wavelength of 1.1 μm and a core-clad relative refractive index difference of 1.6% is formed, and this is used as an amplification medium . The fiber loss at 1.2 μm was 0.015 dB / m. An optical amplifier was constructed using 3 m of this optical fiber, and an amplification experiment was conducted.

In the amplification experiment, bidirectional excitation with an excitation wavelength of 0.98 μm at the front and 1.48 μm at the rear was employed. As the signal light source, a wavelength tunable laser in the 1.5 μm to 1.7 μm band was used. As a result of the amplification experiment, a small signal gain of 20 dB or more was obtained in the 80 nm band of 1530 to 1610 nm. At this time, the noise figure was 5 dB or less. Further, FIG. 28 _TeO selected from the region of the (fiber region) 2 (80 mol%) - ZnO (6 mol%) - _Li 2 O (4 mol%) - _Na 2 O (5 mol%) - _Bi 2 O ₃ (5 mol%) glass core material with Er added 2000ppm by, _TeO 2 (80 mol%) - ZnO (2 mol%) - _Li 2 O (6 mole%) - _Na 2 O (7 mol%) -Bi ₂ O ₃ (5 mol%) as the glass clad material, cut-off wavelength 1.1 .mu.m, to form a core-clad between relative refractive index difference of 1.5% of the optical fiber, and an amplifying medium so. The fiber loss at 1.2 μm was 0.07 dB / m. An optical amplifier was constructed using 3 m of this optical fiber, and an amplification experiment was conducted in the same manner. As a result, a small signal gain of 20 dB or more was obtained in the 80 nm band of 1520 to 1620 nm. At this time, the noise figure was 4 dB. From the above, it was shown that a practical broadband EDFA can be produced without any problem from the glass in the region B.

( Reference Example 28)
An optical amplifier was constructed using 15 m of the same optical fiber as in Reference Example 27, and an amplification experiment was conducted. The excitation wavelength was 1.48 μm bidirectional excitation for both front and rear. A tunable DFB laser in the 1.5 μm to 1.7 μm band was used as the signal light source. As a result of the amplification experiment, a small signal gain of 20 dB or more was obtained particularly in the 70 nm band of 1560 to 1630 nm. At this time, the noise figure was 5 dB or less.

( Reference Example 29)
A laser was constructed using 15 m of the same optical fiber as in Reference Example 27. The cavity was constructed using a total reflection mirror and a fiber Bragg grating with a reflectance of 3% at 1625 nm. The excitation wavelength was 1.48 μm bidirectional excitation for both front and rear. When the incident excitation intensity was 300 mW, a high output of 150 mW at 1625 nm, which could not be obtained with a silica glass optical fiber or a fluoride glass optical fiber, was obtained.

( Reference Example 30)
In the ternary glass of TeO ₂ —ZnO—Li ₂ O—Al ₂ O ₃ —Bi ₂ O ₃ , Al ₂ O ₃ = 2 mol%, Li ₂ O = 12 mol is fixed, and other compositions are changed. Fifty glasses were produced. A sample of 30 mg of powder, in which a part of these glasses was shattered in an mortar, was filled in a silver gold-plated sealed container and subjected to DSC measurement in an argon gas atmosphere at a heating rate of 10 ° C./min. As a result, a stable glass having a Tx-Tg of 120 ° C. or higher was obtained in the region A shown in FIG. If an optical fiber is manufactured using such a thermally stable glass, a reduction in loss of 0.1 dB / m or less can be realized. In addition, due to the effect of the addition of Al ₂ O ₃ , the stimulated emission cross-sectional area is widened, so that the amplification band of EDFA can be widened. Therefore, _TeO 2 (82 mol%) chosen from the region of Figure 29 - ZnO (1 mole%) _- Li 2 O (12 _mole% -Al _{2 O} 3 _{(2 mol%) - Bi 2 O 3 (} 3 mol% ) Glass is used as a core material, Er is added at 2000 ppm, TeO ₂ (75 mol%)-ZnO (3 mol%)-Li ₂ O (18 mol%)-Bi ₂ O ₃ (4 mol%) glass is clad material and then, cut-off wavelength 1.1 .mu.m, to form a core-cladding between ratios optical fiber having a refractive index difference of 1.6%, fiber loss in .1.2μm that the amplifying medium of which was 0.07 dB / m An optical amplifier was constructed using 3 m of this optical fiber, and an amplification experiment was conducted.

  The excitation wavelength used was bidirectional excitation with 0.98 μm at the front and 1.48 μm at the rear. As the signal light source, a wavelength tunable laser of 1.5 μm to 1.7 μm band was used. As a result of the amplification experiment, a small signal gain of 20 dB or more was obtained in the 80 nm band region of 1530 to 1610 nm. At this time, the noise figure was 5 dB or less.

( Reference Example 31)
A wavelength tunable ring laser was configured using 4 m of the same optical fiber as in Reference Example 30. The filter used was a wavelength tunable filter in the 1.5 μm to 1.7 μm band. The excitation wavelength was 1.48 μm bidirectional excitation for both front and rear. When the incident excitation intensity was 300 mW, broadband laser characteristics of 5 mW or more were observed in the 135 nm band of 1500-1635 nm, which could not be obtained with quartz glass optical fibers or fluoride glass optical fibers.

( Reference Example 32)
TeO ₂ (79.5-x mol%) - ZnO (14.5 mole%) - _Na 2 O (6 _{mole%) - Bi 2 O 3 (} x mol%) (x = 4,4.2,5. 4, 6.8, 7) Glass is used as a core material, Er is added at 500 ppm, and TeO ₂ (75 mol%)-ZnO (19 mol%)-Na ₂ O (5 mol%)-Bi ₂ O ₃ (2 .5 mol%) glass and cladding material, the cutoff wavelength 1.1 .mu.m, respectively the ones of length 800m a core-clad between relative refractive index difference from 1.3 to 2.2% of the optical fiber to produce five. In an optical fiber with x = 4 and 7 mol%, the distance between scattering points (the point where light is scattered by a foreign substance such as a crystal and the loss increases remarkably) is 15 m or less, and 1.2 μm of the portion not including the scattering point The fiber loss at was 0.07 dB / m. On the other hand, in the case of optical fibers with x = 4.2, 5.4, and 6.8 mol%, the distance between the scattering points is 100 m or more, and the fiber loss at 1.2 μm in the portion not including the scattering points is 0.02 dB / km. It was the following. In configuring the EDFA, the optical fiber length needs to be around 10 m. With x = 4 and 7 mol% optical fibers, only 20 or less 10 m optical fibers could be taken from 800 m optical fibers, whereas x = 4.2, 5.4, 6.8 mol% optical fibers. Then, more than 70 optical fibers from 800m to 10m were taken, and the yield rate improved dramatically.

In the following Reference Examples 33 to 40, a tellurite EDFA having a low wavelength dispersion characteristic that improves the wavelength dispersion characteristic of the conventional tellurite EDFA will be described in view of the above-described characteristics of the tellurite glass optical fiber.

  In an optical amplifier using tellurite glass as an amplifying medium, a structure in which a dispersion medium that compensates for dispersion with a chromatic dispersion value different from the chromatic dispersion value of the tellurite EDFA is inserted in front of or behind the tellurite EDFA that is an amplifying medium. The main feature is to take. Examples of media for controlling chromatic dispersion include optical fibers and fiber Bragg gratings.

  Since the conventional tellurite EDFA does not have a medium for compensating the chromatic dispersion of the tellurite EDFA, the chromatic dispersion in the optical amplifier increases, and as a result, the error rate increases when a high-speed optical signal is amplified. There was a problem. On the other hand, the chromatic dispersion value in the amplifier can be lowered by adopting the structure of the following embodiment, and even when a high-speed optical signal is amplified, the error rate does not increase and the communication quality is maintained. be able to.

( Reference Example 33)
FIG. 30 is a diagram illustrating a configuration example of an optical amplifier that includes an optical amplifying medium using a tellurite glass optical fiber . In the optical amplifier shown in the figure, an optical signal is configured to enter from the left side and to exit to the right side. The incident signal light passes through the optical isolator 201 a and is then combined with the excitation light from the excitation light source 202 by the optical coupler 203. The signal light combined with the pumping light passes through the dispersion medium 204, enters the amplification optical fiber 205, and is amplified. The signal light amplified by the optical fiber 205 passes through the optical isolator 201b and is output.

In the optical amplifier of this reference example, a semiconductor laser having a signal wavelength of 1.55 μm and an oscillation wavelength of 1.48 μm was used as the excitation light source 202. Further, as the amplification optical fiber 205, the Er concentration in the core is 200 ppm, the cutoff wavelength is 1.3 μm, and the optical refractive index difference (Δh) between the core and the clad is 1.4%. A tellurite glass optical fiber having a length of 10 m was used. The chromatic dispersion value of this optical fiber 205 at 1.55 μm was −1.3 ps / nm. Further, as the dispersion medium 204, a 1.3 μm zero-dispersion silica single mode optical fiber (so-called standard single mode optical fiber) having a chromatic dispersion value of 1.5 ps at 17 ps / km / nm was used. The length of this single mode optical fiber was 76 m.

  In this configuration, the chromatic dispersion of the dispersion medium 204 and the amplification optical fiber 205 as a whole was measured and found to be 0.1 ps / nm or less.

  When a 40 Gbit / s high-speed optical signal having a wavelength of 1.55 μm was amplified using such an optical amplifier, no distortion of the pulse wavelength due to chromatic dispersion was observed. Therefore, it was found that the optical amplifier having this configuration can be used as a booster amplifier, a relay amplifier, or a preamplifier without significantly degrading the communication quality even when used in a high-speed optical communication system. For comparison, when a 40 Gbit / s high-speed pulse with a wavelength of 1.55 μm was amplified without inserting the dispersion medium 204, distortion of the pulse waveform was observed and applied to a high-speed optical communication system. I found it difficult to do.

In this reference example, was placed dispersion medium 204 between the optical coupler 203 and the amplification of the Er-doped tellurite glass optical fiber 205, the installation location is not limited here. For example, it may be the front stage of the optical isolator 201a, between the optical isolator 201a and the optical coupler 203, between the amplification optical fiber 205 and the optical isolator 201b, or after the optical isolator 201b.

Further, in the present reference example, as a dispersion medium 204, was used a standard single-mode optical fiber, it is not limited thereto, having a wavelength dispersion value of the chromatic dispersion and opposite sign of the tellurite glass optical fiber 205 Any optical fiber can be used.

Further, the dispersion medium 204 is not limited to an optical fiber but may be a chirped fiber Bragg grating (“KOHill CLEO / PACIFIC RIM SHORT COURSE '97“ Photosensitivity and Bragg Gratings in Optical Waveguide ”).

In the above description, the dispersion medium 204 is inserted into one of the front and rear of the amplification optical fiber 205, but the installation configuration of the dispersion medium 204 is not limited to this. That is, when an optical fiber is used as the dispersion medium 204, the optical fiber may be divided and installed at appropriate positions before and after the amplification optical fiber 205, or an optical fiber having a plurality of different characteristics may be disposed at an appropriate position. It may be installed in. A plurality of optical fibers and chirped fibers, Braggs, and gratings may be used in combination.

( Reference Example 34)
In this reference example, as the amplification optical fiber 205 in FIG. 30, Pr (praseodymium) is added to the core in an amount of 500 ppm, the cutoff wavelength is 1.0 μm, Δn is 1.4%, and the fiber length is 15 m. The tellurite glass optical fiber was used. Further, as the excitation light source 2, an Nd (neodymium) -added YLF laser was used. Further, a chirped fiber Bragg grating was used as the dispersion medium 4.

At this time, the chromatic dispersion at 1.31 μm of the tellurite glass optical fiber was −3.15 ps / nm. Therefore, the chromatic dispersion value of the chirped fiber Bragg grating was set to 3.15 ps / nm, and a high-speed optical signal having a wavelength of 1.31 μm was amplified by the amplifier having this configuration.

As a result, even when a 40 Gbit / s high-speed optical signal having a wavelength of 1.31 μm was amplified, no distortion of the pulse waveform due to wavelength dispersion was observed, and it was confirmed that it could be applied to a high-speed optical communication system. On the other hand, in the case of an amplifier configuration that does not use the dispersion medium 4 as a reference comparative example, distortion of the pulse waveform occurs when a high-speed optical signal is amplified, making it difficult to apply the high-speed optical communication system.

( Reference Example 35)
In this reference example, TeO ₂ —ZnO—M ₂ O—Bi ₂ O ₃ glass (where M is one or more alkali elements) is used as a base material as the amplification optical fiber 205, and Er, An optical fiber constituted by adding Pr, Tm (for 1.48 μm or 1.65 μm band amplification) or Nd (for 1.06 μm or 1.33 μm band amplification) was used. As the dispersion medium 204, or silica-based glass optical fiber with chirped fiber Bragg grating, the wavelength dispersion of the optical fiber, in particular, to compensate for chromatic dispersion in the amplification wavelength of the rare earth elements, high-speed optical pulse As a result of amplification, it was confirmed that the distortion of the optical pulse waveform that occurred when the dispersion medium 204 was not present was suppressed, and that it could be used in a high-speed optical communication system.

( Reference Example 36)
In this reference example, as the amplification optical fiber 205, the _TeO 2 composition _{-ZnO-Na 2 O-Bi 2} O 3 (55 ≦ TeO 2 ≦ 90,0 ≦ ZnO ≦ 35,0 ≦ Na 2 O ≦ 35 , 0 <Bi ₂ O ₃ ≦ 20, unit mol%), and an optical fiber constituted by adding Er, Pr, Tm or Nd to the core as a base material was used. Further, when the dispersion medium 204 is a silica- based glass optical fiber or a chirped fiber Bragg grating and compensates for chromatic dispersion at each amplification wavelength and amplifies the high-speed optical pulse, It was confirmed that the distortion of the optical pulse waveform that occurred when there was not, was suppressed, and that it could be used in a high-speed optical communication system.

( Reference Example 37)
In this reference example, as the amplification optical fiber 205, the _TeO 2 composition _{-ZnO-Li 2 O-Bi 2} O 3 (55 ≦ TeO 2 ≦ 90,0 ≦ ZnO ≦ 25,0 ≦ Li 2 O ≦ 25 , 0 <Bi ₂ O ₃ ≦ 20, unit mol%), and an optical fiber constituted by adding Er, Pr, Tm or Nd to the core as a base material was used. An optical fiber or chirped fiber Bragg grating is used as the dispersion medium 204 to compensate for chromatic dispersion at each amplification wavelength, and when high-speed optical pulses are amplified, this occurs when the dispersion medium 204 is not present. It was confirmed that the distortion of the optical pulse waveform was suppressed and that it could be used in a high-speed optical communication system.

Further, as the amplification optical fiber _{5, TeO 2 -ZnO-M 2} O-Bi 2 O 3 -Al 2 O 3 based glass (where, M is one or more alkali elements) using an optical fiber which is constructed from Even in this case, the above effect could be confirmed.

( Reference Example 38)
In this reference example, a tellurite glass single-mode optical fiber (cut-off wavelength 1.3 μm, Δn1.4) is formed by using the glass system in the reference example 37 as a base material and adding neither a rare earth element nor a transition metal element. %, Length 1 km), and Raman amplification was performed. The excitation wavelength was 1.48 μm, and 1.5 μm band optical amplification was performed.

At this time, the chromatic dispersion at the signal wavelength of the tellurite glass single mode optical fiber was -130 ps / nm. A standard quartz single mode optical fiber was used as the dispersion medium 204.

The dispersion medium 204 was placed in the subsequent stage of the tellurite glass single mode optical fiber (amplifying optical fiber) 205 to perform optical amplification. When this standard quartz single mode optical fiber 205 for amplification is used with a length of 7.6 km, the waveform distortion of the 1.5 μm band optical pulse (due to the chromatic dispersion of the tellurite glass single mode optical fiber) is suppressed. I was able to.

( Reference Example 39)
In the present reference example, each of the amplification optical fibers 205 formed by adding Cr, Ni, or Ti to the core of the tellurite glass optical fiber having the composition of the reference examples 35 and 36, each 1.5 μm. Band, 1.5 μm band, and 1 μm band optical amplification was performed. When a standard quartz single-mode optical fiber was connected as a dispersion medium 204 to the subsequent stage of the amplification optical fiber 205 and high-speed optical pulses were amplified, optical amplification could be performed without waveform distortion of the optical pulses.

In the above Reference Example, the light amplification medium has been described for the case where an optical fiber, the optical amplification medium, but includes a planar optical waveguide as well as an optical fiber. In the disclosure of the present specification , even when the optical amplifying medium is a planar optical waveguide, the same effects of the present invention as confirmed in the respective reference examples are realized.

Hereinafter, reference examples when the optical amplifying medium is a planar optical waveguide will be described.

( Reference Example 40)
In this reference example, a planar optical waveguide in which TeO ₂ —ZnO—M ₂ O—Bi ₂ O glass (where M is one or more alkali elements) is used as a base material and Er is added to the core is used. An amplification medium was used instead of the optical fiber 205 of FIG. The dispersion of the optical waveguide was corrected using an optical fiber or a fiber Bragg grating as the dispersion medium 204. As a result, it was possible to amplify the light in the 1.5 μm band so as to reduce the distortion of the pulse waveform as compared with the case where the dispersion medium 204 was not used.

  Even when Pr, Tm, Nd, Ni, Ti, and Cr were used as dopants added to the optical waveguide, it was possible to amplify the light with small distortion of the pulse waveform.

As described above, in the optical amplifier using the tellurite glass optical fiber as the amplification medium, by adopting the optical amplifier structure of the reference examples 33 to 40, the tellurite glass optical fiber itself that is the amplification medium has a wavelength dispersion. Generation of distortion of the optical pulse waveform can be suppressed.

In the following Examples 41 to 45 of the present invention , the purpose is to expand the amplification band of the conventional tellurite EDFA to a shorter wavelength side than 1.53 μm and to a longer wavelength side from 1.56 μm.

In order to realize this, in the following examples, an Er-doped tellurite glass optical fiber is used as at least one connected optical fiber, and the Er-doped tellurite glass optical fiber has a shorter length (or an Er concentration) in front of the Er-doped tellurite glass optical fiber. In addition, an Er-doped tellurite glass optical fiber having a small fiber length product or an Er-doped optical fiber hosted from a different material is connected to form an amplification medium. As the different materials, fluoride glass (Er-added ZrF ₄ -based fluoride glass or InF ₃ -based fluoride glass), quartz-based glass, fluorophosphate- based glass, phosphate- based glass, and chalcogenite- based glass can be used.

  By adopting such an amplifier structure, it is possible to realize an EDFA that can operate with low noise in a wider wavelength range than a conventional tellurite EDFA.

(Invention Example 41)
FIG. 31 is a diagram showing a configuration example of an optical amplifier according to the present invention. In the figure, 201a, 201b and 201c are optical isolators, 202a and 202b are optical couplers for introducing pumping light, 203a and 203b are pumping light sources, and 204 and 205 are optical fibers for amplification.

In this embodiment, as the amplification optical fiber 204, an Al (aluminum) -added silica glass optical fiber (length: 25 m, cutoff wavelength: 1.2 μm, Er concentration fiber length product: 2500 m · ppm) having an Er concentration of 100 ppm is used. It was. A semiconductor laser having an oscillation wavelength of 1.48 μm was used as the excitation light source 203a. Further, the composition of TeO ₂ —ZnO—Na ₂ O—Bi ₂ O ₃ (55 ≦ TeO ₂ ≦ 90, 0 ≦ ZnO ≦ 35, 0 ≦ Na ₂ O ≦ 35, 0 <Bi _{2) is used} as the amplification optical fiber 205. O ₃ ≦ 20, the glass of the unit mol%) as a base material, with Er doping concentration 500 ppm, the length was 12m (Er concentration fiber length product 6000 m · ppm), tellurite glass is 1.3μm cut-off wavelength An optical fiber was used. A semiconductor laser having an oscillation wavelength of 1.48 μm was used as the excitation light source 203b.

  When the excitation light quantity of the light source 203a was 70 mW and the excitation light quantity of the light source 203b was 150 mW, a gain of 20 dB or more and a noise figure of 5 dB or less could be confirmed in the 85 nm band from a wavelength of 1.525 μm to 1.610 μm. .

  Such an EDFA that operates in a wide band with low noise has not been realized with a conventional configuration.

  When the amplification optical fiber 204 is not used, the noise figure is higher than 5 dB at a wavelength shorter than 1.54 μm, 10 dB or more at 1.525 μm, and the gain of 20 dB or more starts from 1.53 μm. It was obtained only in the 80 nm band of 1.61 μm.

In this example, the low noise band was extended to a short wavelength, and as a result, the operating wavelength band of the EDFA was expanded because an optical fiber for amplification with a small Er-concentration fiber long product was placed in front of the tellurite glass optical fiber. This is because amplification of the tellurite glass optical fiber is caused after amplification of a wavelength of 1.525 μm to 1.54 μm with low gain.

  Next, a modification of the present embodiment will be described.

As an optical fiber 204 for amplification, an Al (aluminum) -added silica glass optical fiber with an Er concentration of 1000 ppm (length: 12 m, cutoff wavelength: 1.2 μm, Er- concentration fiber length product: 12,000 m · ppm, this product is erbium-added Larger than that of tellurite glass optical fiber).

  When the excitation light amount of the light source 203a was 70 mW and the excitation light amount of the light source 203b was 150 mW, a gain of 20 dB or more and a noise figure of 5 dB or less could be confirmed in a 75 mm band from a wavelength of 1.535 μm to 1.610 μm. .

  Such an EDFA that operates in a wide band with low noise has not been realized with a conventional configuration.

( Invention Example 42)
In this embodiment, a ZrF ₄ fluoride glass optical fiber (cutoff wavelength: 1.2 μm, Er concentration fiber length product: 3500 m · ppm) having an Er concentration of 100 ppm and a fiber length of 3.5 m is used as the amplification optical fiber 204. A semiconductor laser having an oscillation wavelength of 1.48 μm was used as the light source 203. Further, as the amplification optical fiber 205, the composition of TeO ₂ —ZnO—Li ₂ O—Bi ₂ O ₃ (55 ≦ TeO ₂ ≦ 90, 0 ≦ ZnO ≦ 25, 0 ≦ Li ₂ O ≦ 25, 0 <Bi ₂ O ₃ ≦ 20 (unit mol%) glass as a base material, tellurite glass optical fiber having an Er addition concentration of 500 ppm, a length of 12 m, and a cutoff wavelength of 1.3 μm (Er concentration fiber length product 6000 m · ppm) Was used. Further, a semiconductor laser having an oscillation wavelength of 1.48 μm was used as the excitation light source 203b.

  When the excitation light quantity of the light source 203a was 70 mW and the excitation light quantity of the light source 203b was 150 mW, a gain of 20 dB or more and a noise figure of 5 dB or less could be confirmed in the 85 nm band from a wavelength of 1.525 μm to 1.610 μm. . When the amplification optical fiber 304 is not used, the noise figure is higher than 5 dB at a wavelength shorter than 1.54 μm, 10 dB or more at 1.525 μm, and the gain of 20 dB or more starts from 1.53 μm. It was obtained only in the 80 nm band of 1.61 μm.

( Invention Example 43)
In this embodiment, the amplification optical fibers 204 and 205 are composed of the above TeO ₂ —ZnO—Na ₂ O—Bi ₂ O ₃ (55 ≦ TeO ₂ ≦ 90, 0 ≦ ZnO ≦ 35, 0 ≦ Na ₂ O ≦ 35). , 0 <Bi ₂ O ₃ ≦ 20, unit mol%), a tellurite glass optical fiber having an Er addition concentration of 500 ppm and a cutoff wavelength of 1.3 μm was used. The amplification optical fiber 4 has a fiber length of 3 m, and the amplification optical fiber 205 has a fiber length of 12 m. A semiconductor laser with an oscillation wavelength of 0.98 μm was used as the excitation light source 203a, and a semiconductor laser with an oscillation wavelength of 1.48 μm was used as the light source 203b.

  When the excitation light quantity of the light source 203 was 100 mW and the excitation light quantity of the light source 203b was 150 mW, a gain of 20 dB or more and a noise figure of 5 dB or less could be confirmed in a 85 nm band from a wavelength of 1.525 μm to 1.610 μm. . When the amplification optical fiber 304 is not used, the noise figure is higher than 5 dB at a wavelength shorter than 1.54 μm, 10 dB or more at 1.525 μm, and the gain of 20 dB or more starts from 1.53 μm. It was obtained only in the 80 nm band of 1.61 μm.

  In the above embodiments, the amplification optical fibers 204 and 205 are all forward pumped and backward pumped, respectively. However, the pumping method is not particularly limited to these, and any pumping method including bidirectional pumping can be used. May be.

( Invention Example 44)
In this embodiment, the amplification optical fiber 4 is the same as that of Examples 41 to 43, and the amplification optical fiber 205 is TeO ₂ —ZnO—M ₂ O—Bi ₂ O ₃ —Al ₂ O ₃ (M Used an Er-added tellurite glass optical fiber (Er concentration: 500 ppm, length: 14 m) based on a glass of one or more alkali elements. Also in this case, by using the amplification optical fiber 4, it was possible to confirm the expansion of the amplification band with lower noise than when not using it.

( Invention Example 45)
In this embodiment, as the amplification optical fiber 204, Er is added, fluorophosphate glass fiber, phosphate glass optical fiber, a chalcogenide glass optical fiber was used. When the Er concentration fiber length product of the amplification optical fiber 204 is smaller than the tellurite glass optical fiber of the amplification optical fiber 205, it was confirmed that the amplification band was expanded with low noise. That is, the material of the amplification optical fiber 204 is not a big problem in order to exhibit the effects of the present invention, and the Er concentration fiber length product is an important parameter.

In the above Examples 41 to 45 of the present invention , the two optical fibers having different Er addition concentration fiber length products are used as the amplifying medium, but three or more optical fibers may be used. At this time, the optical fiber having the smallest Er-doped optical fiber length product may be in any position other than the rearmost stage, but preferably the frontmost stage.

Next, in an optical amplifier in which a plurality of optical amplifying media are arranged in series, a non-silica glass optical fiber and a silica glass optical fiber, or non-silica glass optical fibers having different core refractive indexes are securely connected. A structure for connecting with low loss and low reflection will be described.

Figure 32 is a schematic view for explaining the configuration of the connection portion of the non-silica-based glass optical fiber and silica glass optical fibers constituting the optical amplification medium according to the present invention. In the figure, reference numeral 301 is a non-silica glass optical fiber, 302 is a silica glass optical fiber, and 303a and 303b are optical fiber holders for holding the ends of the non-silica glass optical fiber and the silica glass optical fiber 2, respectively. Cases 304a and 304b are connection end faces of the optical fiber holding cases 303a and 303b, 305 is an optical adhesive, and the non-quartz glass optical fiber 301 and the silica glass optical fiber 302 are respectively connected end faces 304a and 304b. Are held at different angles θ ₁ and θ ₂ with respect to the vertical axis. In this case, the low-loss connection between the non-silica glass optical fiber 301 and the silica glass optical fiber 302 is realized when the angles θ ₁ and θ ₂ [rad] satisfy the Snell formula shown in the equation (1). it can. Further, reflection attenuation amounts R ₁ and R _{2 at} the connection portion between the non-quartz glass optical fiber 301 and the silica glass optical fiber 302 are expressed by the following equations (5) and (6), respectively.

(The above equation is based on the literature [HM Presby, et. Al, “Bevelled-microlensed taper connectors for laser and fiber back-reflections”, Electron. Lett., Vol. 24, pp. 1162-1163, 1988]) _Where n _UV is the refractive index of the optical adhesive 305, λ is the signal wavelength (wavelength used), and ω ₁ and ω ₂ are the mode field radii of the non-quartz glass optical fiber 301 and the silica glass optical fiber 302, respectively. . Therefore, by adjusting the angles θ ₁ and θ ₂ from the above equations (5) and (6), a low reflection connection greater than the desired return loss can be realized. For example, non-quartz glass optical fiber 301 (Zr fluoride glass optical fiber: core refractive index 1.55, In fluoride glass optical fiber: core refractive index 1.65, chalcogenide glass optical fiber (glass composition As- S): Core refractive index 2.4, Tellurite glass optical fiber: Angle θ ₁ necessary for realizing desired return loss R ₁ with respect to core refractive index 2.1), and silica-based glass optical fiber The angle θ ₂ necessary for realizing a desired return loss with respect to 302 can be calculated by the following equations (7) and (8) obtained by modifying equations (5) and (6).

The refractive index n _UV of the optical adhesive 5 is 1.5, the signal wavelength λ is 1.3 μm, and the spot sizes (radius) ω ₁ and ω ₂ of the non-quartz glass optical fiber 1 and the silica glass optical fiber ₂ are 5 μm. Table 1 shows θ ₁ and θ ₂ for realizing R ₁ = 40 dB, 50 dB, 60 dB and R ₂ = 40 dB, 50 dB, 60 dB. Here, the angle θ ₂ necessary for realizing the return loss R ₂ = 40 dB, 50 dB, and 60 dB with respect to the silica-based glass optical fiber 2 is 0, which is the refraction of the optical adhesive. This is because the refractive index n _UV is the same as the core refractive index of the silica glass optical fiber 2. As a result, for example, a low loss and 50 dB return loss connection between a tellurite glass optical fiber and a silica-based glass optical fiber can be achieved by setting θ ₁ to 3.2 [deg] and θ ₂ to 4.5 [deg]. (The angle of θ ₂ is derived from equation (1)).

As described above, the connecting portion according to the present invention is
1) without the optical axis collinear with non silica-based glass optical fiber and silica glass optical fibers constituting the optical amplification medium, it is in relation to both the relationship between the optical axis satisfies the official Snell,
2) No need for a dielectric film for antireflection which is required in the prior art;
3) The inclination angle of the optical axis of the non-quartz glass optical fiber constituting the optical amplifying medium with respect to the vertical axis of the optical fiber holding housing / connection end surface, and the optical fiber holding housing / connection end surface of the optical axis of the silica glass optical fiber. The angle of inclination with respect to the vertical axis differs greatly from the conventional one.

In the above description, the optical fiber is not provided between the connection end faces 304a and 304b of the optical fiber holding housings 303a and 303b that hold the ends of the non-quartz glass optical fiber 301 or the silica glass optical fiber 302 constituting the optical amplification medium. Although the connection is made via the adhesive 305, both connection end faces may be brought into close contact as shown in FIG. However, in this case, the optical fiber holding housings 303a and 303b are fixed with an adhesive 306 between the both sides thereof (referred to as gripping fixation in the following embodiments of the present invention ). In this case, equation (5), the _{u UV} to _{n 2,} changing equation _{u UV} in (6) to _{n 1,} formula (7) and _{u UV} in (8), respectively _{n 2} and _{n 1} Thus, the angle θ ₂ required to realize the return loss R ₁ = 40 dB, 50 dB, and 60 dB with respect to the non-quartz glass optical fiber 1 can be calculated.

In the above description, the low-loss / low-reflection connection between the non-quartz glass optical fiber and the silica-based glass optical fiber constituting the optical amplifying medium has been described. However, the present invention provides two non-quartz glass lights made of different glasses. This also works effectively for all combinations of connections between fibers, for example, between chalcogenide glass fibers and In-based fluoride glass optical fibers.

( Invention Example 46)
This embodiment will be described with reference to FIGS. FIG. 34 is a top view of the connecting portion, and FIG. 35 is a cross-sectional view of the connecting portion. Reference numeral 301 denotes an Er-doped tellurite glass optical fiber (glass composition is TeO ₂ —ZnO—Na ₂ O—Bi ₂ O ₃ , core refractive index is 2.1, mode field radius is 5 μm, Er addition concentration is 4000 ppm, fiber 2 is silica glass optical fiber (core refractive index is 1.5, mode field radius is 5 μm, coating is UV resin), 307a and 307b hold the ends of optical fibers 301 and 302 , respectively. Each of the optical fibers 301 and 302 is positioned by the V-groove substrate 8, and is bonded to the V-groove optical fiber holding casings 307a and 307b by the adhesive 310 and the optical fiber fixing plate 309. Fixed. However, the materials of the V-groove type optical fiber holding housings 307a and 307b, the V-groove substrate 308, and the optical fiber fixing plate 309 were made of Pyrex (registered trademark) glass. Further, 311a and 311b are connection end faces of the V-groove optical fiber holding housings 307a and 307b, respectively, and 305 is an optical adhesive (in this embodiment, an epoxy UV adhesive is used. The refractive index is 1.5. The Er-added tellurite glass optical fiber 301 and the silica-based glass optical fiber 302 have θ ₁ = 18 [deg] and θ ₂ = 25 [deg] with respect to the vertical axes of the connection end faces 311a and 311b, respectively. Held in. With this connection, the Er-doped tellurite glass optical fiber 301 and the silica-based glass optical fiber 302 could be connected with a connection loss of 0.2 dB. However, the connection loss was measured at 1.3 μm without absorption of Er ions in the Er-doped tellurite glass optical fiber 301. Next, the return loss at a wavelength of 1.3 μm was measured using a commercially available return loss measuring device. The reflection attenuation measured from the Er-doped tellurite glass optical fiber 301 and the silica-based glass optical fiber 302 showed high performance characteristics exceeding the measurement limit of 60 dB, which is the limit of this apparatus. Also, the angles of the connection end faces 311a and 311b of the Er-doped tellurite optical fiber 1 and the silica-based glass optical fiber 302 with respect to the vertical axis are {θ ₁ = 8 [deg], θ ₂ = 11.2 [deg]}. Even when {θ ₁ = 14 [deg], θ ₂ = 20 [deg]}, the connection loss between the Er-doped tellurite glass optical fiber 301 and the silica-based glass optical fiber 302 is 0.2 dB (measurement wavelength 1 .3 μm), the return loss measured from the Er-added tellurite glass optical fiber 301 and the silica-based glass optical fiber 302 side was 60 dB or more at the measurement limit.

As can be seen from the values of the angles θ ₁ and θ ₂ described above, the value of sin θ ₁ / sin θ ₂ does not necessarily exactly match the value of n ₂ / n ₁ . This is because it is actually influenced by the equivalent refractive index of the core of the optical fiber. For practical problems, the value of sin θ ₁ / sin θ ₂ may be within a range of ± 10% of n ₂ / n ₁ .

However, the angles of the connection end faces 311a and 311b of the Er-doped tellurite glass optical fiber 301 and the silica-based glass optical fiber 302 with respect to the vertical axis are {θ ₁ = 5 [deg], θ ₂ = 7 [deg]}. In this case, the connection loss between the Er-doped tellurite glass optical fiber 1 and the silica glass optical fiber 2 is 0.2 dB (measurement wavelength: 1.3 μm), and the return loss measured from the silica glass optical fiber 2 side is 60 dB. As described above, the return loss measured from the Er-added tellurite glass optical fiber 1 side is 55 dB. As a result, the value of sin θ ₁ / sin θ ₂ is within the range described above with respect to the value of n ₂ / n _1. even the inner, low loss Er-doped tellurite glass optical fiber and the silica-based glass optical fiber, and low reflection for both directions (return loss 60dB or more To connect the), the tellurite glass optical fiber, is 8 [deg] or more angles were found to be required with respect to the vertical axis of the connection end face.

  Even when the optical adhesive 5 having a refractive index of 1.55 was used, the same result as that obtained when an optical adhesive having a refractive index of 1.5 was used was obtained.

( Invention Example 47)
Next, this embodiment will be described with reference to FIGS. 36 is a top view of the connection portion, and FIG. 37 is a cross-sectional view of the connection portion. Reference numeral 301 denotes an Er-doped tellurite glass optical fiber (glass composition is TeO ₂ —ZnO—Na ₂ O—Bi ₂ O ₃ , core refractive index is 2.1, mode field radius is 5 μm, Er addition concentration is 4000 ppm, fiber ) Is a silica-based glass optical fiber (core refractive index is .about.1.5, mode field radius is 5 .mu.m, coating is UV resin), and optical fibers 301 and 302 are the same as in Example 45. These ends were held by V-groove optical fiber holding housings 307a and 307b, respectively. However, in this embodiment, the V-groove type optical fiber holding housings 307a and 307b are connected in close contact with each other without using an optical adhesive between the connection end faces 311a and 311b. The casings 307a and 307b were fixed with the adhesive 306 between the sides (gripping and fixing). The angles of the Er-added tellurite glass optical fiber 301 and the silica-based glass optical fiber 302 with respect to the vertical axes of the connection end faces 311a and 311b are θ ₁ = 18 [deg] and θ ₂ = 25 [deg]. Even this embodiment 46, the connection loss between the Er-doped tellurite glass optical fiber 301 and the silica glass optical fiber 302 is 0.2 dB (measuring wavelength 1.3 .mu.m), Er-doped tellurite glass optical fiber 301 and the silica-based The return loss measured from the glass optical fiber 302 side was 60 dB or more. Similarly to Example 45, an Er-added tellurite glass optical fiber is used to connect an Er-added tellurite glass optical fiber and a silica-based glass optical fiber with low loss and low reflection (reflection attenuation of 60 dB or more). It has been experimentally found that an angle of 8 [deg] or more is required with respect to the vertical axis of the connection end face.

( Invention Examples 48 and 49)
Next, Examples 48 and 49 will be described with reference to FIGS. 38 and 40 are top views of the connecting portion, respectively, and FIGS. 39 and 41 are cross-sectional views of the connecting portion, respectively. In these drawings, reference numeral 301 is an Er-doped tellurite glass optical fiber (glass composition is TeO ₂ —ZnO—Na ₂ O—Bi ₂ O ₃ , core refractive index is 2.1, mode field radius is 5 μm, Er addition is performed) The concentration is 4000 ppm, and the coating of the fiber is UV resin. In Examples 48 and 49 , glass ferrules 312a and 312b are applied as optical fiber holding cases. The connection end faces 313a and 313b are realized by obliquely polishing the glass ferrules 312a and 312b.

The Er-added tellurite glass optical fiber 301 and the silica-based glass optical fiber 302 were fixed to the glass ferrules 312a and 312b using an adhesive 310 (using a UV adhesive). In Example 48 shown in FIG. 38 and FIG. 39, an optical adhesive 305 is used between the connecting end faces 313a and 313b (with two refractive indexes of 1.5 and 1.55). In addition, in the embodiment 49 shown in FIGS. 40 and 41, the connection end faces 313a and 313b are brought into close contact with each other and connected. In Examples 38 and 39, the angles of the connection end faces 313a and 313b of the Er-doped tellurite glass optical fiber 301 and the silica-based glass optical fiber 302 with respect to the vertical axis are θ ₁ = 12 [deg] and θ ₂ = 17 [ deg], the connection loss between the Er-doped tellurite glass optical fiber 301 and the silica-based glass optical fiber 302 is 0.2 dB (measurement wavelength 1.3 μm), the Er-added tellurite glass optical fiber 301 and the silica-based glass optical fiber 302. The return loss measured from the side was 60 dB or more (in Example 48 , the refractive index of the optical adhesive was 1.5 and 1.55, but the results were the same). Similarly to Examples 46 and 47, the tellurite glass optical fiber required for connecting the Er-doped tellurite glass optical fiber and the silica glass optical fiber with low loss and low reflection (reflection attenuation of 60 dB or more) The angle between the connection end face and the vertical axis was 8 [deg] or more.

Further, according to the connection method shown in Examples 46 to 49 of the present invention, Er-doped tellurite glass optical fiber 1 (glass composition is TeO ₂ —ZnO—Na ₂ O, core refractive index is 2.1, and mode field radius is A silica-based glass optical fiber was connected to both ends of 5 μm, Er addition concentration was 4000 ppm, fiber length was 1 m, and the coating was UV resin. Thus, an optical fiber amplifier shown in FIG. 42 was constructed. 314a and 314b are pumping light source units for generating pumping light to the Er-doped tellurite glass optical fiber 301. A semiconductor laser having an oscillation wavelength of 1.48 μm and an output of 200 mW, 315a and 315b are generated by the signal light and pumping light source units 314a and 314b. Multiplexers 316a and 316b that multiplex the pumped light are optical isolators for suppressing oscillation of the optical amplifier. Reference numerals 317a and 317b denote connection portions of the present invention. Example 46 (the refractive index of the optical adhesive is 1.55), Example 47 and Example 48 (the refractive index of the optical adhesive is 1.55), And all methods shown in Example 49 were applied. However, in the connection portions shown in Examples 46 and 47, the angles of the connection end faces 311a and 311b of the Er-doped tellurite glass optical fiber 301 and the silica-based glass optical fiber with respect to the vertical axis are θ ₁ = 14 [deg] and θ ₂ = 20 [deg], in the connection portions shown in Examples 48 and 49, the angles of the Er-added tellurite glass optical fiber 1 and the silica-based glass optical fibers with respect to the vertical axes of the connection end faces 313a and 313b are θ ₁ = 12 [deg], θ ₂ = 17 [deg] was adopted. By using all the connection methods shown in Example 45, Example 46, Example 47, and Example 48, the signal gain of the optical fiber amplifier is 40 dB or more, and no ghost is generated in the optical fiber amplifier. It was. FIG. 43 shows an example of amplification characteristics of the present optical fiber amplifier. As a connection method, the method of Example 46 was adopted.

(Invention Example 50)
Various non-silica glass optical fibers were connected to the silica glass optical fibers according to the present invention.

Tables 2 and 3 summarize the results. As the non-quartz optical fiber 301,
1. Tellurite glass optical fiber (shown as non-quartz optical fiber A in Table 2)
Glass _{composition: TeO 2 -ZnO-Na 2 O} -Bi 2 O 3,
Core refractive index: 2.1
2. Zr fluoride glass optical fiber (indicated as non-quartz optical fiber B in Table 2)
Glass _{composition: ZrF 4 -BaF 2 -LaF 3 -YF} 3 -AlF 3 -
LiF-NaF,
Core refractive index: 1.55, mode field radius: 4 μm,
Coating: UV resin In-based fluoride glass optical fiber (shown as non-quartz optical fiber C in Table 3)
Glass _{composition: InF 3 -GaF 3 -ZnF 2 -PbF} 2 -BaF 2 -
SrF ₂ -YF ₃ -NaF,
Core refractive index: 1.65, mode field radius: 4.5 μm
Coating: UV resin Chalcogenide glass optical fiber
(In Table 3, indicated as non-silica optical fiber D)
Glass composition: As-S, core refractive index: 2.4,
Mode field radius: 3 μm, Coating: UV resin was used.
In the non-quartz glass optical fibers A, B, C, and D, the rare earth elements Er (addition concentration 1000 ppm), Pr (addition concentration 500 ppm), Tm (addition concentration 2000 ppm), Ho (addition concentration 1000 ppm), Yb (Addition concentration 500 ppm), Tb (addition concentration 2000 ppm), Nd (addition concentration 1000 ppm), and Eu (addition concentration 2000 ppm) were added for one or two or more, and those not added. The mode field radius of the silica-based glass optical fiber to be connected (core refractive index is 1.5) is the same as that of each of the non-silica-based glass optical fibers, and the connection mode is any one of Examples 46 to 49. Applied. In addition, the refractive index of the optical adhesive 5 between the connection end surfaces 13-1 and 13-2 used at the time of application of the connection form of Example 45 and Example 46 is 1.5. The splice loss and return loss were not related to the presence or absence of rare earth elements and the type of rare earth elements added.

As shown in Table 2 and Table 3, by using the connection method of the present invention, a non-quartz glass optical fiber could be connected with low loss and low reflection. Tables 2 and 3 show examples of low reflection (reflection attenuation of 60 dB or more). However, in the Zr-based fluoride glass optical fiber, θ ₁ <3 [deg], and the In-based fluoride glass optical fiber is used. Then, θ ₁ <4 [deg], and the chalcogenide glass optical fiber cannot achieve a return loss of 60 dB or more in both directions at θ ₁ <8 [deg]. In order to achieve a return loss of 60 dB or more in both directions, An angle θ ₁ greater than this value was required.

A 1.3 μm band optical fiber amplifier was constructed using the Pr-doped In-based fluoride glass optical fiber (shown as non-quartz glass optical fiber D in Table 3), and an amplifier with a signal gain of 30 dB or more was realized. However, the connection form is Example 47, θ ₁ is 5 [deg], θ ₂ is 5.5 [deg], and a 1.047 μm oscillation Nd-YLF laser is used as the excitation light source. There was no ghost problem.

In the above embodiment, the connection between the non-silica glass optical fiber and the silica glass optical fiber has been described. Here, the connection result between the non-quartz glass optical fibers which consist of two different glass is demonstrated. As the non-quartz glass optical fiber used, the four types of non-quartz glass optical fibers A, B, C, and D described in Example 50 were used. Rare earth elements are not added. Table 4 shows the results. The relationship between the core refractive index and the connection angle of each optical fiber is in the range described in the above embodiment. As shown in Table 4, by using the connection method of the present invention, non-quartz glass optical fibers could be connected with low loss and low reflection.

When combining the characteristics of the optical amplifying medium, optical amplifier and laser device using the optical amplifying medium described in Examples 46 to 50 above, and the wideband characteristics inherent in the Er-doped tellurite glass optical fiber amplifier, the wavelength division multiplexing optical transmission system As a result, the optical CATV system can be improved in performance, and as a result, there is an advantage that it can greatly contribute to the advancement and economy of services using these systems.

  Further, if it is used in a wavelength division multiplexing optical transmission system as a broadband amplifier, it can be expected that the transmission capacity will be remarkably increased, thereby contributing to the cost reduction of information communication. In addition, if the optical CATV system is used with the characteristic that the gain tilt is small, it is possible to distribute and relay high-quality video by wavelength multiplexing, which has been difficult in the past, and the cost reduction of the optical CATV is achieved. There is a big merit that you can. Furthermore, if it is applied as a laser device, it can contribute to cost reduction of various wavelength division multiplexing optical transmission systems and high performance of optical measurement.

( Invention Example 51)
In the present invention, a case where an Er-doped tellurite glass optical fiber or an optical waveguide is used as an ASE (Amplifier Spontaneous Emission) light source will be described. Normally, when an Er-doped tellurite glass optical fiber is excited, an ASE having a spectrum represented by a solid line in FIG. 46 is obtained from the fiber, and this can be used as a light source of 1.5 to 1.6 μm. Even the spectrum of this solid line can be used as a light source. However, if the spectral wavelength dependence is eliminated and the spectrum becomes flat, the application range is expanded.

In this example, an ASE light source was fabricated with the configuration shown in FIG. The Er-doped tellurite glass optical fiber 402 is made of TeO ₂ —ZnO—M ₂ O—Bi ₂ O ₃ (M is one or more alkali elements) glass or TeO ₂ —ZnO—M ₂ O—Bi ₂ O ₃ —Al. ₂ O ₃ -based (M is one or more alkali elements) -based glass was used as a material. The Er concentration in the core was 2,000 ppm, the fiber length was 4 m, the cutoff wavelength was 1.3 μm, and Δn was 1.5%.

In the figure, reference numeral 401 is an optical coupler for combining and demultiplexing excitation light (wavelength 1.48 μm) and a wavelength of 1.5 μm or more, and 403 is light having a long wavelength and a short wavelength centered at 1.56 μm. , Optical couplers 404 and 405 are optical attenuators, and 406 and 408 are reflectors. Of the ASE generated in the Er-doped tellurite glass optical fiber indicated by reference numeral 2, light having a wavelength longer than 1.56 μm passes through the optical attenuator 404, is reflected by the reflector 406, and then travels backward. Then, the light is again amplified through the Er-doped tellurite glass optical fiber 402 and emitted from one end of the optical coupler 401. Further, light having a wavelength shorter than 1.56 μm passes through the optical attenuator 405, is reflected by the reflector 408, travels backward, passes through the Er-doped tellurite glass optical fiber 402, and is amplified again. The amplified light was emitted from one end of the optical coupler 401.

  When the reflectivity of the reflector is as shown in FIG. 45, that is, the reflectivity is reduced near the peak of ASE and increased with increasing distance from the peak wavelength, from 1.53 μm as shown by the broken line in FIG. An ASE spectrum with small wavelength dependency of intensity was obtained over 60 μm. At this time, the attenuation amount of the optical attenuators 404 and 405 was optimized. Even when an optical waveguide was used as an amplifying medium, an ASE spectrum having a small wavelength dependency of intensity could be obtained.

( Invention Example 52)
In this example, the optical amplification characteristics were evaluated with the configuration of FIG. This configuration is based on the configuration of FIG. 44, in which an optical circulator 409 is coupled to the signal input end of the optical coupler 401a, and an excitation optical coupler 401b is coupled to the subsequent stage of the Er-doped tellurite optical fiber. Excitation light having a wavelength of 0.98 μm or 1.48 μm was used, which was incident from the front of 0.98 μm, and incident from 1.48 μm from the rear. In addition, light amplification using 1.48 μm light was performed for both the forward and backward pumping light.

  As a result, a gain spectrum having a small wavelength dependence of gain was obtained between 1.53 μm and 1.60 μm. At this time, the attenuation amount of the optical attenuators 404 and 405 was optimized.

Normally, in order to flatten the gain spectrum having a large wavelength dependency as shown in FIG. 43, the gain peak seen from 1.53 μm to 1.57 μm is applied to the optical amplifier by a filter such as a fiber Bragg grating. Cutting and flattening by giving a loss. However, this method has the disadvantage that the quantum efficiency of the optical amplifier is lowered and the gain after flattening is unified to a low value (in FIG. 43, the gain value near 1.58 μm). However, in this embodiment, the decrease in quantum efficiency is not fundamental, and there is an advantage that the gain after flattening is unified to a high value instead of the original low value.

For the reflectors 406 and 408, a dielectric multilayer film, a fiber Bragg grating, or the like can be used. Further, the gain flattening effect could be confirmed by using not only an Er-doped tellurite glass optical fiber but also a quartz glass optical fiber or a fluoride glass optical fiber as an amplification optical fiber. Moreover, the same effect was confirmed even if the optical waveguide was used.

It is a diagram representing the ⁴ I _13/2 → ⁴ I _15/2 emission spectra of Er in the tellurite glass. It is an energy level diagram of a three-level system (Er ³⁺ near 1.54 μm) (where N ₁ ≠ 0 in a three-level system). It is an energy level diagram (N ₁ = 0 in a 4-level system) of a 4-level system (Nd ³⁺ near 1.06 μm). It is a figure which shows the ideal amplification characteristic of the quartz EDFA which used the tellurite glass (solid line) and quartz glass (dashed line) as a host. It is explanatory drawing of the difference in the amplification zone | band by the magnitude of a loss, and when a loss becomes large, an amplification zone | band will also reduce large with a decrease in gain. It is a figure explaining the conventional connection of a non-quartz glass optical fiber and a silica glass optical fiber. It is a figure explaining the conventional connection of a non-quartz glass optical fiber and a silica glass optical fiber. It is a figure explaining the ghost generation | occurrence | production by the reflection of a connection surface. It is a figure explaining the conventional connection of a non-quartz glass optical fiber and a silica glass optical fiber. It is a figure explaining the conventional connection of a non-quartz glass optical fiber and a silica glass optical fiber. It is a figure explaining the conventional connection of a non-quartz glass optical fiber and a silica glass optical fiber. Bi ₂ O ₃ is a schematic diagram showing a _TeO 2 _-Na 2 stable vitrification range of O-ZnO-based glass when 5 mol%. Bi ₂ O ₃ is a schematic diagram showing a _TeO 2 _-Li 2 stable vitrification range of O-ZnO-based glass when 5 mol%. 75TeO ₂ -20ZnO-5Na ₂ O (Bi ₂ O ₃ free) glass (upper line), 77TeO ₂ 15.5ZnO-6Na ₂ O-1.5Bi ₂ O ₃ glass (middle line), 73.5TeO is a DSC measurement chart when the _{2 -15.5ZnO-6Na 2 O-5Bi} 2 O 3 glass (lower line). 83TeO ₂ -5ZnO-12Li ₂ O (upper line) and _{78TeO 2 -5ZnO-12Li 2 O-} 5Bi 2 O 3 ( lower line) is a DSC measurement view of the glass. TeO is a diagram illustrating a _Bi 2 _{O 3} added amount dependency of _{2 -Na 2 O-ZnO-Bi} 2 O 3 based refractive index of the glass _{(n D).} TeO is a schematic diagram showing a stable vitrification range of ₂ -Na ₂ O-ZnO-based glass. It is an energy level diagram of Er ³⁺ . It is a figure which shows typically the example of 1 structure of the optical amplifier based on this specification . It is a block diagram which shows an example of the laser apparatus based on this specification . It is a block diagram which shows an example of the laser apparatus based on this specification . It is a figure showing the gain spectrum obtained in Reference Example 8. It is a block diagram which shows the other example of the laser apparatus based on this specification . Bi ₂ O ₃ is 5 mol% _TeO 2 _-Li 2 O-ZnO-based stabilizer vitrification range of the glass when the (A: Tx-Tg> 120 ℃, B: Crystallization no peak) is a schematic view showing a. Composition _{73.5TeO 2 -20ZnO-5Na 2 O-} 1.5Bi 2 O 3 glass (in the figure, a line) use the and _{73TeO 2 -20ZnO-5Na 2 O-} 2Bi 2 O 3 glass (in the figure, b line) It is a measurement figure of each DSC when there is. _{TeO 2 -ZnO-Na 2 O-} Bi 2 O 3 based glass and _{TeO 2 -ZnO-Na 2 O-} Bi 2 O 3 -Al 2 O 3 based glass and _{TeO 2 -ZnO-Li 2 O 3} -Bi 2 O ₃ is a diagram showing a 1.5μm band emission spectrum of the Er of -Al ₂ O ₃ system glass. Is a schematic diagram showing a TeO ₂ = 75 mol% and _Bi 2 _O 3 = 5 _{mole% TeO 2 -ZnO-LiO-Na} 2 O-Bi 2 stable vitrification range of quinary glass _{O 3} in the case of. Is a schematic diagram showing a TeO ₂ = 80 mol% and _Bi 2 _O 3 = 5 _{mole% TeO 2 -ZnO-LiO-Na} 2 O-Bi 2 stable vitrification range of quinary glass _{O 3} in the case of. Stabilized vitrification range of TeO ₂ —ZnO—Li ₂ O—Al ₂ O ₃ —Bi ₂ O ₃ ternary glass when Al ₂ O ₃ = 2 mol% and Li ₂ O ₃ = 12 mol% It is a schematic diagram shown. It is a figure which shows one structural example of the optical amplifier which used the tellurite glass optical fiber as an amplification medium. It is a figure which shows one structural example of the optical amplifier which used the tellurite glass optical fiber as an amplification medium. It is a figure for demonstrating one structural example of the connection part of the non-quartz type glass optical fiber which comprises the optical amplification medium based on this invention, and a silica type glass optical fiber. It is a figure for demonstrating one structural example of the connection part of the non-quartz type glass optical fiber which comprises the optical amplification medium based on this invention, and a silica type glass optical fiber. It is a figure for demonstrating one structural example of the connection part of the non-quartz type glass optical fiber which comprises the optical amplification medium based on this invention, and a silica type glass optical fiber. It is sectional drawing of the connection part shown in FIG. It is a figure for demonstrating one structural example of the connection part of the non-quartz type glass optical fiber which comprises the optical amplification medium based on this invention, and a silica type glass optical fiber. It is sectional drawing of the connection part shown in FIG. It is a figure for demonstrating one structural example of the connection part of the non-quartz type glass optical fiber which comprises the optical amplification medium based on this invention, and a silica type glass optical fiber. It is sectional drawing of the connection part shown in FIG. It is a figure for demonstrating one structural example of the connection part of the non-quartz type glass optical fiber which comprises the optical amplification medium based on this invention, and a silica type glass optical fiber. It is sectional drawing of the connection part shown in FIG. It is a schematic diagram for demonstrating the optical fiber amplifier to which the connection part of the non-silica-type glass optical fiber and the silica-type glass optical fiber which comprise the optical amplification medium based on this invention is applied. FIG. 43 is a diagram showing a relationship between gain and wavelength in the optical fiber amplifier shown in FIG. 42. It is a schematic diagram for demonstrating the schematic structure of the ASE light source based on this invention. It is a graph which shows the relationship between the intensity | strength of the spectrum of the ASE light source shown in FIG. 44, and the reflectance of a reflector. It is a spectrum figure of an ASE light source. It is a schematic diagram for demonstrating the schematic structure of an example of the fiber amplifier based on this invention.

Explanation of symbols

111,111 ′ pumping semiconductor laser (wavelength: 1480 nm)
112, 112 'Optical coupler 113, 115 Amplifying optical fiber 114 Optical isolator 116 Mirror 117 Filter 118 Mirror 201 Optical isolator 202 Excitation light source 203 Optical coupler 204 Dispersion medium 205 Optical fiber 301 Non-silica glass optical fiber 302 Silica glass optical fiber 303 Optical Fiber Holding Case 304 Connection End Surface 305 Optical Adhesive Material 401 Optical Coupler 402 Optical Fiber 403 Optical Coupler 404 Optical Attenuator 405 Optical Attenuator 406 Reflector 408 Reflector 409 Optical Circulator

Claims (4)

An optical amplifier in which a plurality of optical amplifying units including an optical fiber doped with erbium as an optical amplifying medium are arranged in series,
The first optical fiber, which is a non-quartz glass optical fiber constituting the optical amplification medium, and the end portion of the second optical fiber made of glass having a different refractive index of the core are respectively connected to the first optical fiber. Held in the first and second casings, and the first casing and the second casing are aligned so that the optical axes of the first optical fiber and the second optical fiber coincide with each other. When the connection end surfaces of the first housing and the second housing are connected, the optical axes of the first optical fiber and the second optical fiber are different from each other with respect to the vertical axis of the connection end surface. in is inclined, also, the first optical fiber connecting end faces of the optical axis of the tilt angle theta ₁ and the second optical fiber with respect to the vertical axis of the connection end face of the optical axis of the tilt angle theta ₂ with respect to the vertical axis relationship, the refractive index of the core of the first optical fiber n _1, the core of the second optical fiber When was the _{n 2} Oriritsu,



Connected to meet the Snell formula of
As the first optical fiber , a tellurite glass optical fiber is used as an optical fiber material, and the optical amplifying unit before the optical amplifying unit made of the tellurite glass optical fiber has an erbium addition concentration and an optical fiber length product as described above. Tel Er doping concentration and smaller erbium-doped fiber than optical fiber length product of the light glass optical fibers have been found using,
The optical amplifier, wherein the second optical fiber is a silica-based glass optical fiber, and the angle θ ₁ is 8 degrees or more.
The tellurite glass is TeO ₂ —ZnO—M ₂ O—Bi ₂ O ₃ , or TeO ₂ —ZnO—M ₂ O—Bi ₂ O ₃ —Al ₂ O ₃ (wherein M is one or more kinds of alkalis). _2. The optical amplifier according to claim 1 , wherein the optical amplifier has a composition composed of TeO ₂ —WO ₃ —La ₂ O ₃ —Bi ₂ O ₃ —Al ₂ O ₃ .
3. The optical amplifier according to claim 1, wherein connection end surfaces of the first casing and the second casing are connected via an optical adhesive.
4. The optical amplifier according to claim 1, wherein the connection surfaces of the first casing and the second casing are connected in close contact with each other. 5.