JPH05127199A - Amplifying waveguide element and optical signal amplifier - Google Patents

Abstract

(57) [Summary] [Object] An object of the present invention is to provide an optical signal amplifier having a simple configuration and exhibiting high amplification characteristics, and an amplification waveguide element used in this amplifier. The amplification waveguide element of the present invention has a portion containing neodymium and a portion containing ytterbium, which absorbs fluorescence in the 1.06 μm band from neodymium and is arranged separately from the portion containing neodymium. It has an optical waveguide.
The optical signal amplifier of the present invention includes the amplification waveguide element, a signal light source and a pumping light source connected to one end of the amplification waveguide element via an optical coupler, and the amplification waveguide element. And a spectrum analyzer connected to the other end of the.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amplifying waveguide element having an optical waveguide structure containing two or more kinds of rare earth ions and capable of highly efficient optical amplification, and an optical signal amplifier using the waveguide element.

[0002]

2. Description of the Related Art In recent years, in the field of optical communication, a method for amplifying an optical signal by using light emitted by photoexcitation of ions doped in an optical waveguide has begun to be studied. The principle is
It is based on the fact that when the ions in the optical waveguide are excited by light and are in a population inversion state, the light emission from the population inversion has the effect of amplifying the signal light of the same wavelength as this light emission. Therefore, in order to obtain the high amplification characteristic, it is sufficient to efficiently realize the population inversion state. In this sense, it is the same as the design of the waveguide structure or its composition for increasing the laser oscillation efficiency.

[0003]

However, the optical signal amplifier using rare earth ions generally has the following problems. That is, when the rare earth ion involved in amplification has fluorescence in a wavelength band other than the amplification wavelength band, the fluorescence in the wavelength band other than the amplification wavelength band may cause laser oscillation. In particular, when fluorescence in the amplification wavelength band and fluorescence other than that emit light from the same energy level, laser oscillation in the fluorescence band other than the amplification wavelength band hinders optical amplification in the amplification wavelength band that should be originally performed.

Here, this problem will be described below by taking an optical fiber having a core doped with neodymium, which is expected as an optical fiber amplifier or an optical fiber laser in the 1.3 μm band, as an example.

The fluorescence intensity of neodymium ion is 1.3 μnm
1.06 μm is essentially larger than the band. Therefore, when reflection of 1.06 μm band light occurs in the optical amplifier,
The spontaneous amplification oscillation of 1.06 μm occurs preferentially, and as a result, the amplification of 1.3 μ band is suppressed. To solve this problem, for example, a method in which dielectric mirrors having high transmittance of 1.06 μm light and high reflectance of 1.3 μm band are closely attached to both ends of the fiber (W. J. Minisca).
lco et al. , Electron. Lett.
1988, 24, 28-29, M.I. C. Brierle
y et al. , Electron. Lett. 19
88, 24, 438-439, F.I. Hakimi, et
al. , Optics Lett. 1989, 14,
1060-1061, S.I. G. Grubb, Select
ron. Lett. (1990, 26, 121-122)
Or 1.0 using a wavelength-selective fiber coupler
A method of extracting only the fluorescence in the 6 μm band to the outside of the system of the optical amplifier (Y. Miyajima, et al. Electro.
n. Lett. , 1990, 26, 1397-139.
8) has been proposed. Alternatively, a method in which a wavelength-selective dielectric multilayer film is directly vapor-deposited on the end face of the fiber and antireflection coating is performed is considered.

However, in any of the above methods, the structure of the optical amplifier is complicated, and a simpler method has been desired. One possible solution to this is to co-dope ytterbium as ions that selectively absorb 1.06 μm fluorescence in the core containing neodymium.

However, in this method, as the concentrations of both neodymium and ytterbium are increased, as shown in FIG. 1, ytterbium ² F _5/2 and nedium ⁴ F are added.
The probability of non-radiative energy transfer with _3/2 increases and the number of neodymium in the excited state decreases, resulting in 1.3
There is a problem in that the fluorescence intensity of μm decreases and high amplification characteristics cannot be obtained.

The present invention has been made in order to solve the above technical problems, and an object thereof is an optical signal amplifier having a simple structure and exhibiting high amplification characteristics, and an amplification used in this amplifier. It is to provide a waveguide element for use.

[0009]

In order to achieve the above object, the amplification waveguide device of the present invention comprises a portion containing neodymium and a portion absorbing the fluorescence of 1.06 μm band from neodymium and containing said neodymium. And an ytterbium-containing portion disposed separately from the optical waveguide. Further, the optical waveguide is a double optical waveguide whose cross section is concentric, and the optical waveguide inside the double optical waveguide contains either one of neodymium and ytterbium, and the outside of the double optical waveguide. The optical waveguide may include one of neodymium and ytterbium. Further, the portions containing the neodymium and the portions containing the ytterbium may be alternately arranged.

Further, the optical signal amplifier of the present invention comprises the above-mentioned amplification waveguide element, a signal light source and a pumping light source which are respectively connected to one end of the amplification waveguide element through an optical coupler, and the amplification. And a spectrum analyzer connected to the other end of the waveguide element for use.

[0011]

In the amplification waveguide element of the present invention, the neodymium-containing portion and the ytterbium-containing portion are separately arranged in the optical waveguide, so that 1.06 μm fluorescence from neodymium can be efficiently emitted by the ytterbium. Be absorbed. As a result, the spontaneous amplification oscillation of 1.06 μm is suppressed, so that the fluorescence intensity in the 1.3 μm band is increased and a high amplification characteristic is obtained.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in more detail below with reference to the drawings.

The inventors examined the amplification characteristics of 1.3 μm band signal light in a zirconium fluoride fiber having neodymium dispersed therein. That is, when the core of the fiber has a double structure as shown in FIG. 1 and neodymium and ytterbium are dispersed in different parts in the double core,
It has been found that the optical signal amplification is significantly improved without using a wavelength-selective fiber coupler for outputting 1.06 μm light out of the amplifier system. In FIG. 1, reference numeral 1 is an optical fiber type waveguide device. The device 1 includes a core 2 and a clad 3. The core 2 is a concentric double core, and is composed of an inner core 2a and an outer core 2b. The inner core 2a is doped with either neodymium or ytterbium, and the outer core 2b is doped with the other.

The base material used for the amplifying waveguide device of the present invention is not limited to the above-mentioned fluoride glass, but glass of other compositions such as silicate glass, phosphate glass, and fluorophosphate glass. Etc. can also be used suitably. Even if the glass having these other compositions is used, the amplification characteristics can be greatly improved substantially in the same manner as in the case of the above-mentioned fluoride glass, although the wavelength region showing the amplification characteristics is slightly different.

FIG. 2 and FIG. 3 respectively show the structure of an optical waveguide type device having alternating portions containing neodymium and portions containing ytterbium. In FIG. 2, reference numeral 4 is a thin film type waveguide device. This element 4 includes a long core 5 having a rectangular cross section and a clad 6 sandwiched by sandwiching the core 5. This core 5 is a portion 5a containing neodymium
The neodymium portion 5a includes a portion 5b containing ytterbium, which is divided and arranged in the length direction of the core 5.
FIG. 2 shows a part of the thin film type waveguide element 4, and actually the neodymium portions 5a and the ytterbium portions 5b of the core 5 are alternately arranged along the length direction of the core 5.

Reference numeral 7 in FIG. 3 is an optical fiber type waveguide device. The element 7 includes a cylindrical core 8 and a cylindrical clad 9. The core 8 includes a portion 8a containing neodymium and a portion containing ytterbium which is divided and arranged in the length direction of the core 8 from the neodymium portion 8a.
Similar to FIG. 2, FIG. 3 shows a part of the optical fiber type element 7. In reality, the neodymium portion 8a and the ytterbium portion 8b of the core 8 are alternately arranged along the length direction of the core 8. Has been done.

As shown in FIGS. 2 and 3, an optical signal amplifier including an optical waveguide element having a structure in which a portion containing neodymium and a portion containing ytterbium in the optical waveguide are alternately provided is also shown in FIG. Similar to the case of the amplifier, a remarkable improvement in the amplification characteristic is recognized as compared with the case of the amplifier using the amplifying fiber containing only neodymium.

The effect of improving the amplification characteristics will be described below by taking a system using a fluoride glass as a matrix.

FIG. 4 shows a loss spectrum of an optical fiber in which only neodymium is dispersed. In addition, in FIG. 5, neodymium is used for the outer core 2b of the double core 2 of FIG. 1, ytterbium is used for the inner core 2a of the double core 2, and the concentration ratio of neodymium to ytterbium is set to 1:10. The loss spectrum of a waveguide element for amplification is shown. As can be seen from FIG. 5, ytterbium absorption exists near 1.06 μm, which is the fluorescence wavelength of neodymium. 7 and 8 show the results of measuring the fluorescence intensity in these two types of optical fibers using the evaluation system shown in FIG. Here, FIGS. 7 and 8 are normalized by the fluorescence intensities of 1.06 μm band and 1.3 μm band, respectively. In FIG. 6, reference numeral 10 is an ion-doped optical fiber as an amplification fiber.
A signal light LD 12 and a pumping LD 1 are provided at an incident end (on the left side in FIG. 8) of the optical fiber 10 via an optical coupler 11.
3 and 3 are branched from the optical coupler 11 and connected.
Further, another optical coupler 14 is provided at the emission end of the optical fiber 10.
The spectrum analyzer 15 is further connected to the spectrum analyzer 15 via the, and the computer 16 is sequentially connected to the spectrum analyzer 15.

As can be seen from FIGS. 7 and 8, the fluorescence spectrum intensity in the 1.3 μm band indicated by the arrow in the figure is remarkably increased by providing the ytterbium-doped portion outside the neodymium-doped portion. There is. Comparing the fluorescence intensity of the 1.06 μm band and the fluorescence intensity of the 1.3 μm band of neodymium in such a doped system, 1.3 μm is obtained based on the difference in the absorption intensity of ytterbium in both wavelength regions.
The fluorescence intensity in the m band becomes relatively stronger. FIG. 9 shows a graph of amplification characteristics with respect to signal light intensity. As is clear from FIG. 9, an amplification characteristic of 20 dB or more was obtained for the signal light of 20 dBm.

As explained above, the feature of the present invention is that the core has a double structure in which neodymium which is a phosphor of 1.3 μm and ytterbium which is an absorber of 1.06 μm are separated in separate cores. It is in the point that I arranged. This will be described in more detail. In a co-doped amplification waveguide element as a comparative example in which neodymium and ytterbium are uniformly dispersed in the same core, the energy shown in FIG. 10 increases as the concentration of each rare earth element increases. The probability of non-radiative energy transfer between ytterbium ² F _5/2 and neodymium ⁴ F _3/2 in the level diagram increases, and it is in the ⁴ F _3/2 state which is the initial state of 1.3 μm fluorescence. The phenomenon that the number of neodymium is reduced and, as a result, the fluorescence intensity of 1.3 μm is reduced becomes remarkable.

Therefore, in the amplification waveguide element of the present invention,
By doping neodymium and ytterbium into separate cores, the above energy transfer does not occur at all 1.06μ
Ytterbium can be used only as the absorber of m, and efficient amplification characteristics can be obtained without adding any device to the optical signal amplifier. Further, this is not limited to an optical signal amplifier having an optical waveguide having a double structure, and the same logic is applied to an optical signal amplifier in which neodymium-containing portions and ytterbium-containing portions are alternately arranged. It is clear that a very large effect will occur. On the other hand, the concentration of the rare earth element may be any concentration as long as energy transfer between ions does not occur, and should be determined in consideration of the loss characteristics of the matrix used. To determine the concentration that causes energy transfer,
The measurement was performed by measuring the concentration dependency of the fluorescence intensity from the ion or the fluorescence lifetime. On the other hand, the glass composition is not limited to fluoride glass. Obviously, any glass composition can be used as long as it can disperse the ions used and can form an optical waveguide structure. However, in the case where a glass having a low glass transition point is used as a matrix, when producing a concentric optical waveguide structure as shown in FIG. 1, both ions are contacted at a portion where a portion containing neodymium and a portion containing ytterbium are in contact with each other. It is conceivable that an interaction will occur between both ions due to the diffusion of. In order to prevent this interaction, interposing an insulator layer not containing both ions in advance between both ion-containing portions is also an effective means. It goes without saying that the thickness of this insulator layer depends on the optical waveguide structure manufacturing conditions or the glass composition used.

Hereinafter, the amplification waveguide element of the present invention having a portion containing neodymium and a portion containing ytterbium will be described in more detail based on examples, but the present invention is not limited to these examples. Absent.

Example 1 A single mode optical fiber having a matrix of alkali aluminum phosphate glass containing 300 ppm of neodymium in the inner core of the double core and 2% by weight of ytterbium in the outer core of the double core was prepared.
When the optical signal amplification characteristic of this 5 m optical fiber was measured using the measurement system shown in FIG. 6, the amplification characteristic of 20 dB was observed for the signal light having a wavelength of 1350 nm and an intensity of 0 dBm.

On the other hand, when a similar experiment was conducted with a fiber containing only neodymium in the core, only 2 dB amplification was observed. As described above, it was confirmed that doping of neodymium and ytterbium into separate cores in the dual core significantly improved the optical signal amplification characteristics.

Example 2 A single mode optical fiber having a matrix of fluorophosphate glass containing 300 ppm of neodymium in the outer core of the double core and 2% by weight of ytterbium in the inner core of the double core was prepared. When the optical signal amplification characteristic of this 5 m optical fiber was measured using the measurement system shown in FIG. 6, the wavelength was 1330 nm and the intensity was 0 dBm.
An amplification characteristic of 22 dB was observed for the signal light of.

On the other hand, when a similar experiment was conducted with a fiber containing only neodymium in the core, only 2 dB amplification was observed. As described above, it was confirmed that doping of neodymium and ytterbium into separate cores in the dual core significantly improved the optical signal amplification characteristics.

[0028]

As described above, according to the amplifying waveguide element of the present invention, it is possible to efficiently absorb 1.06 μm fluorescence of neodymium into ytterbium. If this amplifying waveguide element is used, As compared with the conventional method, it is possible to obtain an optical signal amplifier whose design is easy and whose amplification characteristic is stable.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a cross-sectional structure of an embodiment of an amplification waveguide device of the present invention.

FIG. 2 is a perspective view showing the structure of another embodiment of the amplification waveguide device according to the present invention.

FIG. 3 is a perspective view showing the structure of still another embodiment of the amplifying waveguide device according to the present invention.

FIG. 4 is a characteristic diagram showing loss characteristics of a fluoride fiber doped with neodymium.

5 is a characteristic diagram showing a loss characteristic of a fluoride fiber as an example of the amplification waveguide element of the present invention shown in FIG.

FIG. 6 is a configuration diagram of an embodiment of an optical signal amplifier of the present invention for measuring a loss spectrum or a fluorescence spectrum of an optical fiber sample.

7 is a diagram showing a fluorescence spectrum of the optical fiber shown in FIG. 4 when excited at 800 nm.

FIG. 8 is a schematic view of the amplification waveguide element 80 of the present invention shown in FIG.
It is a figure which shows the fluorescence spectrum when excited by 0 nm.

9 is a characteristic diagram showing amplification characteristics with respect to signal light intensity in an optical fiber as an example of the amplification waveguide element of the present invention shown in FIG.

FIG. 10 is an energy level diagram showing energy levels of neodymium and ytterbium.

[Explanation of symbols]

 1 Optical Fiber Waveguide Element 2 Core 2a Inner Core 2b Outer Core 3 Cladding 4 Thin Film Type Waveguide Element 5 Core 5a Neodymium Part 5b Ytterbium Part 6 Cladding 7 Optical Fiber Type Waveguide Element 8 Core 8a Neodymium Part 8b Ytterbium Part 9 Cladding 10 ion-doped optical fiber 11 optical coupler 12 signal light LD 13 pumping LD 14 optical coupler 15 spectrum analyzer 16 computer

Front Page Continuation (72) Inventor Elijah Snitz Tour, Latgas University, Bretted and Bowser Road, Piscataway, New Jersey, USA

Claims (4)

[Claims] 1. An optical waveguide having a portion containing neodymium and a portion containing ytterbium, which is arranged separately from the portion containing neodymium and absorbing the fluorescence in the 1.06 μm band from the neodymium. A characteristic waveguide element for amplification. 2. The optical waveguide is a double optical waveguide having a concentric cross section, and the optical waveguide inside the double optical waveguide contains at least one of neodymium and ytterbium, and 2. The amplification waveguide element according to claim 1, wherein the optical waveguide outside the waveguide contains one of neodymium and ytterbium. 3. The amplifying waveguide device according to claim 1, wherein the portions containing the neodymium and the portions containing the ytterbium are alternately arranged. 4. The amplification waveguide element according to claim 1, a signal light source and a pumping light source connected to one end of the amplification waveguide element via an optical coupler, respectively, and the amplification waveguide element. And a spectrum analyzer connected to the other end of the optical signal amplifier.