JP2003046174A - Broadband composite optical amplifier - Google Patents

Abstract

(57) Abstract: A broadband composite optical amplifier capable of continuously amplifying signal light in a wide wavelength band is provided. A first optical fiber amplifier 1 uses an EDF as a gain medium, multiplexes a signal light and a pump light having a wavelength of 980 nm into the medium, and enters the multiplexed light into a gain medium having a wavelength band from 1530 nm to 1565 nm. An EDFA that amplifies signal light. Second
Is an optical fiber amplifier which uses a TDF as a gain medium, multiplexes signal light and pump light into the gain medium, and amplifies the signal light in a wavelength band from 1460 nm to 1530 nm.
FA. The first optical fiber amplifier 1 and the second optical fiber amplifier 2 are connected in series to form a broadband composite optical amplifier.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an optical amplifier,
In particular, an optical fiber (hereinafter referred to as "T
An optical amplifier (hereinafter abbreviated as "DF") as a gain medium (hereinafter abbreviated as "TDFA") and an optical amplifier having an optical fiber having erbium added to a core (hereinafter abbreviated as "EDF") as a gain medium (hereinafter And abbreviated as “EDFA”).

[0002]

2. Description of the Related Art In the wavelength band used or being considered for use in the optical communication field, wavelengths from 1460 nm to 1530 n
Wavelength band up to m (hereinafter abbreviated as "S-band"),
Wavelength band from 1530nm to 1565nm (hereinafter referred to as "C-
Band)) and a wavelength band from 1565 nm to 1625 nm (hereinafter abbreviated as "L-band"). As an amplification technique for transmitting and amplifying light in these bands in one optical fiber, as shown in FIG. 10, a method of separating the signal lights for each wavelength band, amplifying them, and then combining them Was studied and used, and this technique is disclosed in OAA'99WC-2.
In FIG. 10, reference numeral 51 is an optical transmission line, which is connected to the input end of the first WDM coupler 55. WDM coupler 55
The S-band optical amplifier 52 is connected to the output terminal of the above, and the second WDM coupler 56 is connected to the other output terminal. The output terminal of the second WDM coupler 56 is connected to the C-band optical amplifier 53, and the other output terminal is connected to the L-band optical amplifier 54. The C-band optical amplifier 53 and the L-band optical amplifier 54 are the third WDM
The third WDM coupler 5 is connected to the input end of the coupler 57.
The output terminal of 7 is connected to the input terminal of the fourth WDM coupler 58. The S-band optical amplifier 52 is connected to the other input terminal of the fourth WDM coupler 58.

In the optical amplifier shown in FIG. 10, the signal light sent from the optical transmission line 51 is the first WDM coupler 55.
The light in the wavelength band of the S-band is demultiplexed by the optical amplifier 52 for S-band. Then the second
WDM coupler 56 demultiplexes the light in the C-band wavelength band into the light in the L-band wavelength band, and the C-band optical amplifier 53 optically amplifies the light in the C-band wavelength band. The light in the wavelength band of the L-band is optically amplified by the L-band optical amplifier 54. The light of each wavelength band that has been optically amplified is multiplexed by the third WDM coupler 57 and the fourth WDM coupler 58.

[0004]

However, according to this amplification technique, it is necessary to use an optical coupler for multiplexing and demultiplexing the light, and further, it is added to the optical fiber used for S-band amplification. The rare earth elements used are different from the rare earth elements added to the optical fiber used for C-band amplification. Therefore, as shown in FIG. 11, there is a problem that the amplification characteristic is not continuous over the used wavelength band, and it is not possible to manufacture a seamless optical amplifier that can obtain a continuous gain for the used wavelength band.
As a method of solving this problem, a technique for collectively amplifying C-band and L-band signal lights is described in Electron. Lett. 34.
-18 (1998) 1747-1748. But,
No technique has been reported for collectively amplifying signal light of S-band and C-band. The present invention has been made in view of such circumstances, and an object of the present invention is to provide a broadband composite optical amplifier capable of continuously amplifying signal light in a wide wavelength band.

[0005]

In order to solve the above-mentioned problems, the invention according to claim 1 uses a first optical fiber having erbium added to a core as a gain medium, and a signal is transmitted to the first optical fiber. A first optical fiber amplifier that amplifies the signal light in the wavelength 1550 nm band by injecting the light and the excitation light in the wavelength 980 nm band and makes it incident, and a second optical fiber in which thulium is added to the core as a gain medium. , A signal light and a pump light are combined and incident on the second optical fiber, and a second optical fiber amplifier for amplifying the signal light in the wavelength band of 1480 nm is connected in series in multiple stages in an arbitrary order. It is a wideband compound optical amplifier characterized by the following. According to a second aspect of the present invention, in the first aspect of the invention, a first optical fiber amplifier is arranged at an input portion of the signal light, and a second optical fiber amplifier is provided at an output portion of the first optical fiber amplifier. It is characterized by being connected. According to a third aspect of the present invention, in the first aspect of the invention, a second optical fiber amplifier is arranged at an input portion of the signal light, and a first optical fiber amplifier is provided at an output portion of the second optical fiber amplifier. It is characterized by being connected. The invention according to claim 4 is the invention according to claim 1, 2 or 3, wherein the second optical fiber is a silica optical fiber or a fluoride optical fiber. According to a fifth aspect of the present invention, in the first, second, third, or fourth aspect of the invention, the second optical fiber is excited by excitation light having a wavelength of 1050 nm band, 1150 nm band, or 1400 nm band. . The invention according to claim 6 is the invention according to claim 1, 2, 3 or 4.
In the described invention, the second optical fiber has a wavelength of 1050n.
It is characterized in that it is excited by combining two or more of any one of the excitation lights in the m band, 1150 nm band, 1400 nm band and 1600 nm band. The invention according to claim 7 is,
In the invention described in 4, 5, or 6, the first optical fiber amplifier and the second optical fiber amplifier signal forward pumping light that pumps pumping light in the same direction as the traveling direction of signal light and pumps pumping light. Either backward pumping, which is excited by being incident in the direction opposite to the traveling direction of light, or bidirectional pumping, which is that the pumping light is incident by exciting it in both directions, which are opposite to the same direction as the traveling direction of the signal light. It is characterized in that the signal light is amplified by the pumping means. The invention described in claim 8 is,
In the invention described in 3, 4, 5, 6 or 7, the first optical fiber amplifier reflects the signal light and the pumping light incident on the first optical fiber on the emission side of the first optical fiber,
It is characterized in that it is provided with means for making the returned light to enter the first optical fiber again. According to a ninth aspect of the invention, in the first, second, third, fourth, fifth, sixth, seventh or eighth aspect of the invention, the second optical fiber amplifier pumps the signal light incident on the second optical fiber and pumps the signal light. It is characterized in that it is provided with means for reflecting light and light on the emission side of the second optical fiber and for making the returned light to enter the second optical fiber again. Claim 1
The invention described in 0 is claim 1, 2, 3, 4, 5, 6 or 7
In the invention described above, an optical isolator for suppressing reflected light is provided at an input / output end of one or both of the first optical fiber and the second optical fiber. Claim 1
The invention according to claim 1 is defined by claims 1, 2, 3, 4, 5, 6, 7,
The invention described in 8, 9, or 10 is characterized in that a gain equalizer is provided in one or both of the first optical fiber amplifier and the second optical fiber amplifier. The invention according to claim 12 is the invention according to claims 1, 2, 3, 4, 5, 6, 7, 8,
In the invention described in 9, 10, or 11, a third optical fiber amplifier for amplifying signal light in a wavelength band of 1600 nm with respect to a series connection of a first optical fiber amplifier and a second optical fiber amplifier. Are connected in parallel.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
FIG. 1 is a diagram showing an example of a broadband composite optical amplifier of the present invention. In FIG. 1, reference numeral 1 is a first optical fiber amplifier,
The EDF is used as the gain medium, and the signal light and the excitation light in the wavelength of 980 nm are multiplexed and incident on the gain medium, and the wavelength is changed from 1530 nm to
It consists of an EDFA that amplifies signal light in the wavelength band up to 1565 nm. Reference numeral 2 is a second optical fiber amplifier, which uses a TDF as a gain medium and multiplexes the signal light and the pumping light to enter the gain medium to amplify the signal light in the wavelength band from the wavelength 1460 nm to the wavelength 1530 nm. It consists of TDFA. The first optical fiber amplifier 1 and the second optical fiber amplifier 2 are connected via an optical transmission line 3. The connection order may be such that the output end of the first optical fiber amplifier 1 is connected to the input end of the second optical fiber amplifier 2 as shown in FIG. As described above, the first optical fiber amplifier 1 is connected to the output end of the second optical fiber amplifier 2.
You may connect the input end of. According to this example, TDFA
And EDFA are connected in series, and by exciting the EDF with pumping light in the wavelength of 980 nm, it is possible to continuously amplify the signal light in a wide wavelength band spanning S-band and C-band. An optical amplifier can be realized. Further, since the TDFA and the EDFA are connected in series to configure the wideband composite optical amplifier, the number of parts can be reduced and the wideband composite optical amplifier can be realized.

FIG. 2 shows an example of a wide band composite optical amplifier in which at least one first optical fiber amplifier 1 and at least one second optical fiber amplifier 2 are connected in series in multiple stages. FIG. 2A shows an example in which a first optical fiber amplifier 1, a first optical fiber amplifier 1 and a second optical fiber amplifier 2 are connected in series in this order, and FIG. 2B shows a first optical fiber amplifier 1.
Is an example in which the optical fiber amplifier 1, the second optical fiber amplifier 2, and the first optical fiber amplifier 1 are connected in series in this order.
The number of optical fiber amplifiers to be connected and the order of the optical fiber amplifiers to be connected are not limited to the example shown in FIG.

FIG. 3 is a diagram showing the configuration of the TDFA which is the second optical fiber amplifier used in this example. Figure 3
(A) shows that TDFA is configured by a pumping method (hereinafter abbreviated as “forward pumping”) in which pumping light is incident in the same direction as the traveling direction of signal light to pump, and two pumping light sources with different wavelengths are used. This is an example in which the TDFA is configured by an excitation method (hereinafter abbreviated as “two-wave excitation”) in which excitation is performed. In FIG. 3A, reference numeral 11 indicates an optical transmission line for transmitting signal light. This optical transmission line 11 includes the first WDM coupler 1
It is connected to 2 input ports. The first pumping light source 13 is connected to the other input port of the first WDM coupler 12, and the output port of the first WDM coupler 12 is connected to the input port of the second WDM coupler 14. .
The second pumping light source 15 is connected to the other input port of the second WDM coupler 14. Second WDM coupler 1
The output port of No. 4 is connected to one end of a TDF 16 which is a gain medium, and the other end of the TDF 16 is connected to the optical transmission line 11. In this example, the connections between the optical components are made by fusion splicing. A silica-based fiber or a fluoride-based fiber may be used as the TDF 16. Next, the operation of the first optical fiber amplifier by this forward pumping will be described. The signal light sent from the optical transmission line 11 is first
Of the first pumping light from the second pumping light source 13 is combined with the first pumping light having the wavelength of 1050 nm and sent to the second WDM coupler 14, where the second pumping light from the second pumping light source 15 has the wavelength of 1600 nm. Is combined with. The signal light and the first and second pumping lights are input to one end of the TDF 16, where they are optically amplified and output from the other end of the TDF 16 to the optical transmission line 11.

FIG. 3 (b) shows an example in which the TDFA is constructed by a pumping method (hereinafter abbreviated as "rearward pumping") in which pumping light is incident and excited in a direction opposite to the traveling direction of the signal light. The optical transmission line 11 is connected to one end of the TDF 16, and the other end of the TDF 16 is connected to the first WDM coupler 12.
Is connected to the input port of. The first pumping light source 13 is connected to the other input port of the first WDM coupler 12, and the output port of the first WDM coupler 12 is the second
Is connected to the input port of the WDM coupler 14. The second pumping light source 15 is connected to the other input port of the second WDM coupler 14. Second WDM coupler 14
The output port of is connected to the optical transmission line 11. The operation of the first optical fiber amplifier by the backward pumping is performed by the first WDM coupler 12 and the second WDM coupler 14 by multiplexing the first pumping light and the second pumping light.
It is input to one end of F16, where it is optically amplified and TDF1
Output from the other end of 6 to the optical transmission line 11 is the same as in the case of forward pumping, but in the case of forward pumping, pumping light is incident in the direction opposite to the traveling direction of the signal light. Is different from

FIG. 3C shows a pumping method (hereinafter abbreviated as “bidirectional pumping”) in which pumping light is incident from two directions, which are opposite to the traveling direction of the signal light, in opposite directions. It is an example which constituted TDFA. This optical transmission line 11 is
It is connected to the input port of the first WDM coupler 12. The first pumping light source 13 is connected to the other input port of the first WDM coupler 12, and the output port of the first WDM coupler 12 is connected to the input port of the second WDM coupler 14. . The second pumping light source 15 is connected to the other input port of the second WDM coupler 14. The output port of the second WDM coupler 14 is TDF1
6 is connected to one end of the TDF 16 and the other end of the TDF 16 is connected to the third W
It is connected to the input port of the DM coupler 17. The third pumping light source 18 is connected to the other input port of the third WDM coupler 17, and the output port of the third WDM coupler 17 is connected to the input port of the fourth WDM coupler 19. . The fourth pumping light source 20 is connected to the other input port of the fourth WDM coupler 19. 4th W
The output port of the DM coupler 19 is connected to the optical transmission line 11. The operation of the first optical fiber amplifier by this bidirectional pumping is that the first pumping light and the second pumping light are multiplexed by the first WDM coupler 12 and the second WDM coupler 14, and the TDF 16 is operated. It is input to one end, and the third pumping light and the fourth pumping light are multiplexed by the third WDM coupler 17 and the fourth WDM coupler 19 to generate TD.
It is input to one end of F16, where it is optically amplified and TDF1
It is output from the other end of 6 to the optical transmission line 11. The first pumping light and the third pumping light have the same wavelength, and the second pumping light and the fourth pumping light have the same wavelength.

In FIG. 3D, the signal light and the pumping light that have entered the first optical fiber 16 are reflected at the exit side of the first optical fiber 16, and the return light is reflected by the first optical fiber 16.
A method of re-incident light injection and amplification (hereinafter referred to as "reflection-type excitation")
Is abbreviated). In FIG. 3D, the first WDM coupler 12, the second WDM
The DM coupler 14 and the TDF 16 are connected to the optical transmission line 11 as in the case of FIG. Also, the first
Pumping light source 13 is connected to the first WDM coupler 12,
The second pumping light source 15 is connected to the second WDM coupler 14 as in the case of FIG. 3A. Reference numeral 22
Is a loop mirror connected to the other end of the TDF 16 and reflects the signal light and the pump light from the TDF 16 to reflect the TD.
It is for returning to F16. As the loop mirror 22, for example, a total reflection loop mirror using a 3 dB coupler is used, but it is not limited to the total reflection loop mirror, and other components such as a fiber grating may be used as long as they have a reflection function. Used. Reference numeral 23 is
It is a non-reflection end portion for suppressing the influence of reflection at the exit end of the loop mirror, and is composed of, for example, a fusion-bonded coreless fiber. A coreless fiber is a fiber that has no core, and it is possible to suppress light reflection by fusion-splicing this fiber. Reference numeral 21 is an optical circulator, which is connected to the optical transmission line 11 connected to the output port of the return light of the first WDM coupler 12. Also in this example, the connection between the optical components is performed by fusion splicing. The signal light sent from the optical transmission line 11 is the first
In the WDM coupler 12, the first pumping light from the first pumping light source 13 is combined and sent to the second WDM coupler 14, where the second pumping light from the second pumping light source 15 Combined. The signal light and the first and second pumping lights are input to one end of the TDF 16, where they are optically amplified and then reflected by the mirror 22. The reflected return light is input again to one end of the TDF 16 and is optically amplified, so that the second W
After passing through the DM coupler 14 and the first WDM coupler 12, it is taken out as output light by the optical circulator 21 and sent out to the optical transmission line 11.

Although FIG. 3 (d) shows only the case of forward pumping, the present invention is not limited to this, and the backward pumping and the bidirectional pumping are also constituted by reflection pumping. Is possible. Also, FIG.
In the description of the TDFA shown in (a), (b), (c), and (d), the wavelength of the first pumping light sent from the first pumping light source 13 is set to the 1050 nm band, and the second pumping light source is used. The wavelength of the second pumping light sent from 15 is in the 1600 nm band, but it is not limited to this, and other wavelengths are also possible.
It is possible to use a combination of excitation light sources that emit excitation light in the 1150 nm band and the wavelength 1400 nm band. Also, the number of pumping light sources is not limited to two-wave pumping, and the wavelength of 1050
It is also possible to excite by using only one excitation light source that emits excitation light in the nm band, the wavelength 1150 nm band, and the wavelength 1400 nm band.

FIG. 4 is a diagram showing the configuration of the EDFA which is the first optical fiber amplifier used in this example. Figure 4
(A) is an example in which the EDFA is configured by forward excitation. In FIG. 4A, reference numeral 31 is an optical transmission line, and this optical transmission line 31 is connected to the input port of the WDM coupler 32. The pump light source 33 is connected to the other input port of the WDM coupler 32, and the output port of the WDM coupler 32 is connected to one end of the EDF 34 that is a gain medium. The other end of the EDF 34 is connected to the optical transmission line 31. Also in this example, the connection between the optical components is performed by fusion splicing. The signal light sent from the optical transmission line 31 is combined with the pumping light of the wavelength 980 nm band from the pumping light source 33 in the WDM coupler 32. The signal light and the pumping light are input to one end of the EDF 34, optically amplified here, and output to the optical transmission line 31 from the other end of the EDF 34.

FIG. 4B shows the EDF by backward excitation.
It is the example which constituted A. In FIG. 4B, the optical transmission line 31
Is connected to one end of the EDF 34, and the other end of the EDF 34 is connected to the input port of the WDM coupler 32. A pumping light source 33 is connected to the other input port of the WDM coupler 32. The output port of the WDM coupler 32 is connected to the optical transmission line 31. The operation of the second optical fiber amplifier by the backward pumping is that the pumping light is multiplexed by the WDM coupler 32 and input to one end of the EDF 34, where it is optically amplified and is transmitted from the other end of the EDF 34 to the optical transmission line 31. The output is the same as in the case of forward pumping, but differs from the case of forward pumping in that pumping light is incident in the direction opposite to the traveling direction of the signal light.

FIG. 4C shows the EDF by bidirectional excitation.
It is the example which constituted A. In FIG. 4C, the optical transmission line 31
Are connected to the input port of the first WDM coupler 32. The first pump light source 33 is connected to the other input port of the WDM coupler 32, and the output port of the WDM coupler 32 is connected to one end of the EDF 34. Further, the other end of the EDF 34 is connected to the input port of the second WDM coupler 35. This second WDM coupler 3
The second pumping light source 36 is connected to the other input port of 5. The output port of the second WDM coupler 35 is connected to the optical transmission line 31. The operation of the second optical fiber amplifier by the bidirectional pumping is performed by the first WDM coupler 3
2, the first pumping light is multiplexed and input to one end of the EDF 34, and the second WDM coupler 35 multiplexes the second pumping light and is input to the other end of the EDF 34. The light is amplified and output from the other end of the EDF 34 to the optical transmission line 31. The wavelengths of the first excitation light and the second excitation light are both 980 nm.

FIG. 4D shows the EDF by the reflection type excitation.
It is the example which constituted A. In FIG. 4D, the WDM coupler 32 and the EDF 34 are connected to the optical transmission line 31, as in the case of FIG. 4A. Also, the excitation light source 3
3 is also connected to the WDM coupler 32, as shown in FIG.
It is similar to the case of. Reference numeral 38 is a loop mirror connected to the other end of the EDF 34, and reference numeral 39 is a non-reflection end portion for suppressing the influence of reflection at the exit end of the loop mirror. Reference numeral 37 is an optical circulator, WD
It is connected to the optical transmission line 31 connected to the output port of the return light of the M coupler 32. Also in this example, the connection between the optical components is performed by fusion splicing. Optical transmission line 3
In the WDM coupler 32, the signal light sent from No. 1 is multiplexed with the pumping light of the wavelength 980 nm band from the pumping light source 33. The signal light and the pumping light are input to one end of the EDF 34, where they are optically amplified and then reflected by the loop mirror 38. The reflected return light is input again to one end of the EDF 34, is optically amplified, passes through the WDM coupler 32, is taken out as output light by the optical circulator 37, and is sent to the optical transmission path 31. In addition, in FIG. 4D, only the case of forward excitation is illustrated, but the present invention is not limited to this, and the backward excitation and the bidirectional excitation also have a configuration of reflection type excitation. Is possible.

FIG. 5 shows an example in which an optical isolator 40 is inserted at the input and output ends of the EDF 34 to form an EDFA. In this example, by inserting the optical isolator 40, reflection of light at the input / output end of the EDF can be suppressed. 5A shows the case of forward excitation, FIG. 5B shows the case of backward excitation, and FIG. 5C shows the case of bidirectional excitation. The example of forming the optical fiber amplifier by inserting the optical isolator 40 is not limited to the EDFA, and the same applies to the TDFA. FIG. 6 is an example in which a gain equalizer 41 is inserted in the EDF to configure the EDFA. In this example, the gain by the EDF can be flattened by inserting the gain equalizer 41. A fiber grating is used as the gain equalizer 41, but is not limited to this. Similarly, by inserting the gain equalizer 41 into the TDF to configure the TDFA, the gain due to the TDF can be flattened.

FIG. 7 shows a first optical fiber amplifier 1 and a second optical fiber amplifier 1.
For those connected in series with the optical fiber amplifier 2 of
This is an example in which a wideband composite optical amplifier is configured by connecting in parallel a third optical fiber amplifier for amplifying signal light in a wavelength band from a wavelength of 1565 nm to a wavelength of 1625 nm. In FIG.
Reference numeral 3 is an optical transmission line, which is connected to the input end of the first WDM coupler 5. The first optical fiber amplifier 1 and the second optical fiber amplifier 2 are connected in series to the output end of the first WDM coupler 5, and the third optical fiber amplifier 2 is connected to the other output end of the first WDM coupler 5. The fiber amplifier 4 is connected.
Second optical fiber amplifier 2 and third optical fiber amplifier 4
Is connected to the input end of the second WDM coupler 6.
In this example, the first WDM coupler 5 causes L-
The light in the band wavelength band is demultiplexed and optically amplified by the third optical fiber amplifier 4. Light in the S-band and C-band wavelength bands is optically amplified by the first optical fiber amplifier 1 and the second optical fiber amplifier 2. The light in each wavelength band that has been optically amplified is multiplexed by the second WDM coupler 6. According to this example, in the wide band composite optical amplifier capable of continuously amplifying in the S-band and the C-band, it becomes possible to additionally amplify the L-band light.

(Examples) Specific examples are shown below. The broadband composite optical amplifier shown in FIG. 1 was manufactured. The EDF used in the first optical fiber amplifier contains 1020 wtp of erbium.
An optical fiber containing 11700 wtppm of pm and aluminum was used. The mode field diameter of this optical fiber was 5.1 μm, the core diameter was 2.7 μm, and the length was 6 m. . A semiconductor laser having a pumping power of 165 mW was used as a pumping light source that emits pumping light having a wavelength of 980 nm band. Thulium is 1000w in the TDF used in the second optical fiber amplifier.
An optical fiber made of silica glass doped with tppm was used. The mode field diameter of this optical fiber is 5.0μ
m, the core diameter was 3.3 μm, and the length was 10 m. This TDF
Was excited by two-wave excitation and reflection type excitation. Wavelength 1
A fiber laser light source having a pumping power of 2 W was used as the pumping light source that emits the pumping light in the 050 nm band, and a semiconductor laser having a wavelength of 1610 nm and a pumping power of 115 mW was used as the pumping light source that emitted the pumping light in the wavelength 1600 nm band.

FIG. 8 shows the gain characteristic of this wide band composite optical amplifier. The EDFA alone does not provide sufficient gain in the S-band wavelength band, and the TDFA alone does not provide C-band wavelength band gain, whereas the TDFA does not.
In the broadband composite optical amplifier of the present invention in which the EDFA and the EDFA are connected in series, by pumping the EDF with pumping light in the wavelength of 980 nm band, gain is obtained in the wavelength band longer than 1470 nm, and loss is caused only by TDFA. EDF is generated even in the wavelength band longer than 1535 nm.
Is compensated for by the loss. 1480nm to 1560n
A gain of 10 dB or more is obtained in the wavelength band up to m. FIG. 9 shows the result of gain equalization using the gain equalizer. Two long-period fiber gratings shown in Table 1 were used as gain equalizers. FIG. 12 shows the loss spectrum of this long-period fiber grating.

[Table 1] By gain equalization, a gain of 10 dB or more is almost continuously obtained in the wavelength band from 1480 nm to 1560 nm, and the flatness of the gain, which is the difference between the maximum value and the minimum value of the gain over this wavelength band, is 1.5 dB or less. Has become.

[0021]

As described above, according to the present invention,
A first optical fiber amplifier made of EDFA and a second optical fiber amplifier made of TDFA are connected in series to obtain ED
By exciting F with excitation light in the wavelength of 980 nm band, S
It is possible to realize a wideband composite optical amplifier capable of continuously amplifying a signal light of a wide wavelength band spanning the − band and the C-band. Further, since the wideband composite optical amplifier is configured by connecting the first optical fiber amplifier and the second optical fiber amplifier in series, it is possible to realize the wideband composite optical amplifier with a reduced number of parts. Further, according to the present invention, a wavelength of 1600n is obtained for a serial connection of the first optical fiber amplifier and the second optical fiber amplifier.
In a wideband composite optical amplifier capable of continuously amplifying in S-band and C-band by connecting in parallel a third optical fiber amplifier for amplifying m-band signal light, L-band It is possible to additionally amplify the light.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a broadband composite optical amplifier of the present invention.

FIG. 2 is a diagram showing an example in which a TDFA and EDFA are connected in series in multiple stages to configure a wideband composite optical amplifier.

FIG. 3 is a diagram showing a configuration of TDFA.

FIG. 4 is a diagram showing a configuration of an EDFA.

FIG. 5 is a diagram showing an example in which an EDFA is configured by inserting an isolator into an input / output end of an optical fiber.

FIG. 6 is a diagram showing an example in which a wideband composite optical amplifier is configured using a gain equalizer.

[FIG. 7] A wideband composite optical amplifier configured by connecting in parallel optical fiber amplifiers for amplifying signal light in a wavelength band from wavelength 1565 nm to wavelength 1625 nm, in which an EDFA and TDFA are connected in series. It is a figure which shows the example.

FIG. 8 is a diagram showing a gain characteristic of an EDFA, a gain characteristic of a TDFA, and a gain characteristic of a broadband composite optical amplifier of the present invention.

FIG. 9 is a diagram showing a result of gain equalization using a gain equalizer.

FIG. 10 is a diagram showing a configuration of a conventional wideband composite optical amplifier.

FIG. 11 is a diagram showing an amplification characteristic of a conventional broadband composite optical amplifier.

FIG. 12 is a diagram showing a loss spectrum of a long-period fiber grating.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... 1st optical fiber amplifier, 2 ... 2nd optical fiber amplifier, 4 ... 3rd optical fiber amplifier, 13 ... 1st excitation light source, 15 ... 2nd excitation light source, 16 ... TDF, 33 ... Excitation Light source, 34 ... EDF, 40 ... Isolator, 41 ... Gain equalizer,

Continued front page    (72) Inventor Tetsuya Sakai             Fuji Co., Ltd. 1440 Rokuzaki, Sakura City, Chiba Prefecture             Kura Sakura Office (72) Inventor Akira Wada             Fuji Co., Ltd. 1440 Rokuzaki, Sakura City, Chiba Prefecture             Kura Sakura Office F term (reference) 5F072 AB07 AB09 AK06 JJ20 KK30

Claims (12)

[Claims] 1. A first optical fiber having erbium added to a core is used as a gain medium, and a signal light and a pumping light in a wavelength of 980 nm are multiplexed and incident on the first optical fiber to obtain a wavelength of 1
The first optical fiber amplifier that amplifies the signal light in the 550 nm band and the second optical fiber in which thulium is added to the core are used as the gain medium, and the signal light and the pump light are combined with this second optical fiber. The second which amplifies the signal light of wavelength 1480nm band
A wide-band compound optical amplifier, characterized in that the optical fiber amplifiers of (1) and (2) are connected in series in multiple stages in an arbitrary order. 2. The first optical fiber amplifier is arranged in a signal light input section, and the second optical fiber amplifier is connected to an output section of the first optical fiber amplifier. The broadband composite optical amplifier according to claim 1. 3. The second optical fiber amplifier is arranged at the input part of the signal light, and the first optical fiber amplifier is connected to the output part of the second optical fiber amplifier. The broadband composite optical amplifier according to claim 1. 4. The broadband composite optical amplifier according to claim 1, wherein the second optical fiber is a silica optical fiber or a fluoride optical fiber. 5. The second optical fiber has a wavelength of 1050 nm.
5. The broadband composite optical amplifier according to claim 1, wherein the broadband composite optical amplifier is excited by pumping light in a band, a 1150 nm band, or a 1400 nm band. 6. The second optical fiber has a wavelength of 1050 nm.
5. The broadband composite optical amplifier according to claim 1, wherein the pump is a combination of two or more pumping lights in the band, 1150 nm band, 1400 nm band, or 1600 nm band. 7. The first optical fiber amplifier and the second optical fiber amplifier.
In the optical fiber amplifier, the pump light is incident in the same direction as the traveling direction of the signal light to excite it in the forward direction, and the pump light is incident in the opposite direction to the traveling direction of the signal light to excite it. Amplification of the signal light by either directional pumping or bidirectional pumping that pumps the pumping light by bidirectionally pumping the pumping light in the opposite direction to the traveling direction of the signal light. Claims 1, 2, 3,
7. The broadband composite optical amplifier according to 4, 5, or 6. 8. The first optical fiber amplifier reflects the signal light and the pumping light incident on the first optical fiber on an emission side of the first optical fiber, and returns the return light. 8. A means for re-entering the first optical fiber, further comprising means for 1, 2, 3, 4, 5, 6 or 7.
2. A wideband composite optical amplifier according to. 9. The second optical fiber amplifier reflects the signal light and the pumping light incident on the second optical fiber at an emission side of the second optical fiber, and returns the returned light. 9. The broadband composite optical amplifier according to claim 1, further comprising means for re-entering the second optical fiber. 10. An optical isolator for suppressing reflected light is provided at an input / output end of one or both of the first optical fiber and the second optical fiber.
2. The broadband composite optical amplifier according to 2, 3, 4, 5, 6 or 7. 11. A gain equalizer is provided in one or both of the first optical fiber amplifier and the second optical fiber amplifier. ,
A wideband composite optical amplifier according to 7, 8, 9 or 10. 12. The serial connection of the first optical fiber amplifier and the second optical fiber amplifier,
13. A third optical fiber amplifier for amplifying signal light having a wavelength of 1600 nm band is connected in parallel, wherein the third optical fiber amplifier is connected in parallel. 2. A wideband composite optical amplifier according to.