JP4071869B2 - Optical amplifier - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical amplifier used in an optical transmission system.
[0002]
[Prior art]
The optical amplifier supplies excitation light of a predetermined wavelength to a silica-based optical waveguide to which a rare earth element such as Er (erbium) element is added, optically amplifies the signal light input to the optical waveguide, and the optical amplification is performed. This is one of important optical components in an optical transmission system. The optical amplifier is required to have a large optical amplification gain with respect to the signal light, and is also required to have a low output level of spontaneous emission light that becomes noise. In particular, when the input signal light is weak, the above two requirements are particularly great.
[0003]
For example, if the input signal light is extremely weak, a signal light amplification gain of 45 dB may be required. Such a high signal light amplification gain is difficult to obtain with a single light amplifying optical waveguide, and is usually obtained by cascading a plurality of light amplifying optical waveguides. If an optical filter that removes spontaneously emitted light is also used, a 45 dB signal light amplification gain can be obtained by cascading the optical filter and two optical amplifying optical waveguides.
[0004]
[Problems to be solved by the invention]
If the signal light has only one wavelength, it is easy to realize a band pass filter that transmits only the signal light of one wavelength with low loss and blocks light of other wavelengths (spontaneously emitted light). The construction of a simple optical amplifier is relatively easy. On the other hand, when the signal light has multiple wavelengths, it is necessary to use an optical filter that transmits each of the multi-wavelength signal lights with low loss and blocks light having a wavelength other than the wavelength of each of the multi-wavelength signal lights (spontaneously emitted light). There is. As an optical filter having such transmission characteristics, a multilayer filter, a combination of a coupler and a grating, and an optical circulator can be considered.
[0005]
However, it is difficult to manufacture an optical filter configured to have the above transmission characteristics by a multilayer filter with a flat light transmittance in the transmission wavelength band. A combination of a coupler and a grating has a large number of parts. In addition, since these have insertion loss, they are not appropriate when optically a weak light is amplified. Those using an optical circulator are generally expensive and have a large number of parts.
[0006]
The present invention has been made in order to solve the above-described problems, has a simple configuration, and has a large signal light amplification gain and a low output level of spontaneous emission light even if the input multi-wavelength signal light is weak. An object is to provide an optical amplifier.
[0007]
[Means for Solving the Problems]
The optical amplifier for intersatellite communication according to the present invention is (1) set so that the inversion distribution is 70%, and in each of the first and second transmission wavelength bands that do not overlap each other among the optical amplification wavelength bands. A plurality of optical waveguides that optically amplify light having a wavelength that matches the gain peak of the amplifier, and (2) a chirp formed in the optical waveguide provided between the plurality of optical waveguides and connected in cascade. An optical notch filter comprising a grating and transmitting light having a gain peak and removing light included in a cutoff wavelength band between the first and second transmission wavelength bands; and (3) output from a plurality of optical waveguides. A branch coupler for branching light; (4) a first bandpass filter that selectively transmits signal light included in the first transmission wavelength band in the first branch path of the branch coupler; and (5) Second to the second branch of the branch coupler And a second band-pass filter that selectively transmits signal light included in the transmission wavelength band.
[0008]
According to this optical amplifier, the light included in the optical amplification wavelength band is optically amplified by the optical waveguide provided in front of the optical notch filter, and the optically amplified light and the spontaneous emission light generated in the optical waveguide are Is output. Of the light output from the preceding optical waveguide, the light included in the first or second transmission wavelength band has a low loss (including no loss ) through an optical notch filter formed of a chirped grating formed in the optical waveguide. ) And is included in the cutoff wavelength band between the first and second transmission wavelength bands is removed by the optical notch filter. Then, the light that has passed through the optical notch filter is optically amplified and output by an optical waveguide provided at the subsequent stage of the optical notch filter. That is, the signal light included in each of the first and second transmission wavelength bands is optically amplified and output with a high optical amplification gain, and the output intensity of the light included in the cutoff wavelength band is extremely weak. Output light from a plurality of optical waveguides is branched by a branch coupler. The signal light included in the first transmission wavelength band is selectively transmitted through the first bandpass filter provided in the first branch path of the branch coupler. Further, the signal light included in the second transmission wavelength band is selectively transmitted through the second band pass filter provided in the second branch path of the branch coupler.
[0009]
The optical amplifier according to the present invention is characterized in that the optical waveguide is of a quartz type to which an Er element and an Al element are added. In this case, the width of the optical amplification wavelength band is wide and the interval between the first and second transmission wavelength bands can be widened, which is preferable in terms of signal light separation.
[0010]
In the optical amplifier according to the invention, the cutoff wavelength band of the optical notch filter includes a wavelength band of 1535 nm to 1554 nm. In this case, the signal light near the gain peak wavelength of the optical waveguide is optically amplified with a high optical amplification gain. At this time, the signal light output intensity and the noise figure are not deteriorated, and the intensity of the pumping light supplied to the subsequent optical waveguide can be greatly reduced, which is preferable.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. In the following, a quartz-based optical fiber (EDF: Erbium-Doped Fiber) to which an Er (erbium) element, which is a rare earth element, is added will be described as an optical waveguide for optically amplifying light included in the optical amplification wavelength band. .
[0012]
FIG. 1 is a configuration diagram of an optical amplifier according to the present embodiment. The optical amplifier includes, in order from the signal light input side, an optical connector 11, an optical isolator 21, an EDF 31, a WDM coupler 41, an optical isolator 22, an optical notch filter 51, an optical isolator 23, a WDM coupler 42, an EDF 32, an optical isolator 24, and the like. A branch coupler 71 is connected in cascade. Further, in this optical amplifier, a band pass filter 82, a branch coupler 72, and an optical connector 12 are connected in cascade from one output end of the two output ends of the branch coupler 71, and a band pass filter 83 in order from the other output end. The branch coupler 73 and the optical connector 13 are connected in cascade. Further, an excitation light source 61 is connected to the WDM coupler 41, and an excitation light source 62 is connected to the WDM coupler 42. A light receiving element 92 is connected to the branch coupler 72, and a light receiving element 93 is connected to the branch coupler 73.
[0013]
The optical isolator 21, EDF 31, WDM coupler 41, optical isolator 22, and pumping light source 61 constitute an upstream optical amplification unit. The optical isolator 23, the WDM coupler 42, the EDF 32, the optical isolator 24, and the pumping light source 62 constitute a subsequent optical amplification unit. The optical notch filter 51 is located between the upstream optical amplifier and the downstream optical amplifier.
[0014]
Each of the optical isolators 21 to 24 allows light to pass in the forward direction but does not pass in the reverse direction. That is, the optical isolator 21 allows the light reaching from the optical connector 11 to pass to the EDF 31 but does not allow light to pass in the reverse direction. The optical isolator 22 allows the light reaching from the WDM coupler 41 to pass to the optical notch filter 51 but does not allow light to pass in the reverse direction. The optical isolator 23 allows the light reaching from the optical notch filter 51 to pass to the WDM coupler 42 but does not allow light to pass in the reverse direction. The optical isolator 24 allows the light reaching from the EDF 32 to pass to the branch coupler 71 but does not allow the light to pass in the reverse direction.
[0015]
Each of the EDFs 31 and 32 is a silica-based optical fiber to which an Er element is added. When excitation light having a predetermined wavelength is supplied, the light contained in the input optical amplification wavelength band is optically amplified and output. . Each of the EDFs 31 and 32 has a wavelength-dependent signal light amplification gain characteristic. The light included in a predetermined light amplification wavelength band is amplified with a high gain, but the other light has a low gain or light. Does not amplify. The signal light amplification gain characteristics of each of the EDFs 31 and 32 depend on the composition and length, but the width of the light amplification wavelength band is broadened by co-adding an Al (aluminum) element.
[0016]
The WDM coupler 41 allows the excitation light output from the excitation light source 61 to reach the EDF 31 and allows the signal light output from the EDF 31 to reach the optical isolator 22. That is, the upstream optical amplification unit has a reverse excitation configuration. The WDM coupler 42 passes the pumping light that is output from the pumping light source 62 and reaches the EDF 32, and passes the signal light that arrives from the optical isolator 23 toward the EDF 32. That is, the subsequent optical amplification unit has a forward pumping configuration.
[0017]
The optical notch filter 51 transmits light included in either the first transmission wavelength band or the second transmission wavelength band that does not overlap each other among the optical amplification wavelength bands of the EDFs 31 and 32 with low loss (including no loss). The light included in the cutoff wavelength band between the first and second transmission wavelength bands is removed. Such an optical notch filter 51 can be easily realized by a chirped grating formed in an optical waveguide such as an optical fiber. In the chirped grating, the grating period is not constant, and the grating period changes over a certain range so as to Bragg reflect light included in the cutoff wavelength band.
[0018]
The branch coupler 71 splits the light that has arrived from the optical isolator 24 into two branches, outputs one of the two branches toward the bandpass filter 82, and outputs the other toward the bandpass filter 83. The band pass filter 82 selectively transmits the signal light included in the first transmission wavelength band among the light reaching from the branch coupler 71. The branching coupler 72 passes most of the signal light output from the bandpass filter 82 to the optical connector 12 and outputs a part thereof to the light receiving element 92. The light receiving element 92 detects the intensity of light reaching from the branch coupler 72. On the other hand, the band pass filter 83 selectively transmits the signal light included in the second transmission wavelength band among the light reaching from the branch coupler 71. The branching coupler 73 passes most of the signal light output from the bandpass filter 83 to the optical connector 13 and outputs a part thereof toward the light receiving element 93. The light receiving element 93 detects the intensity of light reaching from the branch coupler 73.
[0019]
FIG. 2 is an explanatory diagram of the characteristics of each element of the optical amplifier according to the present embodiment. 2A shows the signal light amplification gain characteristics of the EDF 31 and the EDF 32, and FIG. 2B shows the transmission characteristics of the optical notch filter 51. 2C shows the transmission characteristic of the bandpass filter 82, and FIG. 2D shows the transmission characteristic of the bandpass filter 83.
[0020]
As shown in FIG. 2A, the EDF 31 and the EDF 32 have a signal light amplification gain of a certain value or more within the optical amplification wavelength band (λ1 to λ4), and light included in the optical amplification wavelength band. Amplify light. As shown in FIG. 2B, the optical notch filter 51 includes a first transmission wavelength band (λ1 to λ2) and a second transmission wavelength band (λ3 to λ4) that do not overlap each other among the optical amplification wavelength bands. The transmittance is high in each, and the transmittance is low in the cutoff wavelength band (λ2 to λ3) between the first and second transmission wavelength bands. When the optical notch filter 51 is made of chirped grating, the insertion loss can be set to 0 dB, so that the transmission loss in the first and second transmission wavelength bands can be set to about 0 dB. . Further, the transmission loss in the cutoff wavelength band can be reduced to about 15 dB. Note that a loss due to the coupling between the core mode light and the cladding mode light may occur on the shorter wavelength side than the Bragg wavelength. In this case, the first transmission wavelength band on the shorter wavelength side is the first wavelength on the longer wavelength side. The transmission loss is about 3 dB larger than the transmission wavelength band of 2.
[0021]
As shown in FIG. 2C, the bandpass filter 82 has a high transmittance only in the vicinity of the wavelength λa of the signal light included in the first transmission wavelength band (λ1 to λ2). Further, as shown in FIG. 2D, the bandpass filter 83 has a high transmittance only in the vicinity of the wavelength λb of the signal light included in the second transmission wavelength band (λ3 to λ4). The full width at half maximum of the transmission characteristics of each of the bandpass filters 82 and 83 is, for example, 0.2 nm.
[0022]
Next, the operation of the optical amplifier according to this embodiment will be described. The pumping light output from the pumping light source 61 is supplied to the EDF 31 via the WDM coupler 41, so that the EDF 31 performs an optical amplification function, and the pumping light output from the pumping light source 62 passes to the EDF 32 via the WDM coupler 42. By being supplied, the EDF 32 exhibits an optical amplification function.
[0023]
The signal light input to the optical connector 11 is input to the EDF 31 through the optical isolator 21 and is optically amplified by the EDF 31. The light output from the EDF 31 is input to the optical notch filter 51 through the WDM coupler 41 and the optical isolator 22. Of the light input to the optical notch filter 51, light included in one of the first and second transmission wavelength bands passes through the optical notch filter 51 with low loss, and light included in the cutoff wavelength band is optical notch filter. 51 to remove. The light transmitted through the optical notch filter 51 is input to the EDF 32 through the optical isolator 23 and the WDM coupler 42 and is optically amplified by the EDF 32. The light output from the EDF 32 is input to the branch coupler 71 through the optical isolator 24 and branched into two by the branch coupler 71.
[0024]
Of the light reaching the bandpass filter 82 from the branch coupler 71, the signal light included in the first transmission wavelength band is transmitted through the bandpass filter 82, and most of the light passes through the branch coupler 72, so that the optical connector 12. Is output from. On the other hand, of the light reaching the band pass filter 83 from the branch coupler 71, the signal light included in the second transmission wavelength band is transmitted through the band pass filter 83, and most of the light passes through the branch coupler 73. Output from the connector 13. The intensity of light output from each of the optical connectors 12 and 13 is monitored by the light receiving elements 92 and 92. Based on the monitoring result, the excitation light output intensity of the excitation light source 62 is controlled so that the intensity of the light output from each of the optical connectors 12 and 13 becomes a constant value.
[0025]
As described above, the wavelength dependence of the light output from the optical connector 12 out of the light input to the optical connector 11 includes the signal light amplification gain characteristics in the EDFs 31 and 32, the transmission characteristics in the optical notch filter 51, and the bandpass filter 82. This is in accordance with the transmission characteristics. Therefore, the signal light included in the first transmission wavelength band is optically amplified by the EDFs 31 and 32 and output from the optical connector 12 at a high output level.
[0026]
Similarly, the wavelength dependence of the light output from the optical connector 13 out of the light input to the optical connector 11 includes signal light amplification gain characteristics in the EDFs 31 and 32, transmission characteristics in the optical notch filter 51, and transmission in the bandpass filter 83. It depends on the characteristics. Therefore, the signal light included in the second transmission wavelength band is optically amplified by the EDFs 31 and 32 and output from the optical connector 13 at a high output level.
[0027]
On the other hand, the spontaneous emission light generated in the optical amplification unit in the previous stage is removed by the optical notch filter 51 in the cut-off wavelength band. Also, those having wavelengths other than the wavelength of the signal light are removed by the bandpass filters 82 and 83, respectively. Accordingly, light having a wavelength other than the wavelength of the signal light is output from each of the optical connectors 12 and 13 at an extremely low output level.
[0028]
Next, a specific example of the optical amplifier according to the present embodiment will be described. Here, it is assumed that the intensity of the signal light input to the optical connector 11 is −45 dBm, and the signal light near the wavelength of 1530 nm and near the wavelength of 1560 nm is optically amplified.
[0029]
The excitation light source 61 is a semiconductor laser light source that outputs a laser beam having a wavelength of 0.98 μm as excitation light to be supplied to the EDF 31, and its output intensity is constant at 50 mW. The excitation light source 62 is a semiconductor laser light source that outputs laser light having a wavelength of 1.48 μm as excitation light to be supplied to the EDF 32, and the excitation light output intensity is such that the light intensity monitored by each of the light receiving elements 92 and 93 becomes a constant value. Shall be controlled. Each of the EDFs 31 and 32 is Al-added, and the EDF 31 wavelength 1.53 μ-band absorption strip length product is 40 dB, and the EDF 32 wavelength 1.53 μ-band absorption strip length product is 100 dB. Each of the EDFs 31 and 32 optically amplifies the signal light in the optical amplification wavelength band 1520 nm to 1570 nm.
[0030]
The optical notch filter 51 is made of a chirped grating formed in an optical fiber. As shown in the transmission characteristic diagram of the optical notch filter 51 in FIG. 3, the optical notch filter 51 has a steep transmission characteristic, and has a transmission loss of 15 dB in the cut-off wavelength band 1538 nm to 1557 nm, and the first transmission wavelength band. The transmission loss at 1520 nm to 1538 nm and shorter wavelength side is 3 dB, and the transmission loss at the second transmission wavelength band 1557 nm to 1570 nm and longer wavelength side is 0 dB.
[0031]
Further, as shown in the transmission characteristic diagram of the bandpass filter 82 in FIG. 4, the center wavelength of the bandpass filter 82 is set to 1535 nm, and the center wavelength of the bandpass filter 83 is set to 1560 nm. Each of the bandpass filters 82 and 83 has a full width at half maximum of 0.2 nm, a transmission loss at the center wavelength of 0 dB, and a transmission loss at wavelengths other than the vicinity of the center wavelength of 25 dB.
[0032]
As an optical amplifier having such a specific configuration, signal lights having wavelengths of 1535 nm and 1560 nm are input to the optical connector 11. Further, the excitation light output intensity of the excitation light source 62 is controlled so that the intensity of the light output from each of the optical connectors 12 and 13 becomes a constant value of +1 dBm. FIG. 5 is a table summarizing the signal light output intensity, the noise figure, and the intensity of the excitation light supplied to the EDF 32 at the subsequent stage.
[0033]
Although the intensity of light output from each of the optical connectors 12 and 13 is controlled to be a constant value of +1 dBm, since this light is composed of signal light and spontaneous emission light, the output intensity of signal light having a wavelength of 1535 nm Is -1.76 dBm, and the output intensity of signal light having a wavelength of 1560 nm is −1.81 dBm, both of which are less than 0 dBm. This depends on the transmission characteristics of the bandpass filters 82 and 83, and does not depend on the transmission characteristics of the optical notch filter 51.
[0034]
The noise figure at a wavelength of 1535 nm is 4.40 dB, and the noise figure at a wavelength of 1560 nm is 4.24 dB. However, considering the insertion loss of 1 dB in the optical connector 11, the noise figure is reduced to close to the quantum limit of 3 dB.
[0035]
The intensity of the excitation light supplied to the subsequent EDF 32 is 47.0 mW in the case of signal light having a wavelength of 1535 nm, and 79.7 mW in the case of signal light having a wavelength of 1560 nm. In general, the maximum output intensity of a laser light source with a wavelength of 1.48 μm is about 100 mW. Therefore, if this is used as the excitation light source 62, the intensity of the excitation light to be supplied to the EDF 32 at the subsequent stage can be obtained.
[0036]
As described above, the optical amplifier according to the present embodiment can have sufficiently good characteristics by using the optical notch filter 51 having the transmission characteristic diagram shown in FIG.
[0037]
Each of the EDFs 31 and 32 is an Al-added EDF. In this case, as shown in the gain spectrum in FIG. 6, gain peaks are generated in the vicinity of the wavelengths 1531 nm and 1558 nm in a state of being saturated to some extent during actual use. . On the other hand, in the case of EDF without addition of Al, as shown in the gain spectrum in FIG. As can be seen from FIGS. 6 and 7, the gain peak wavelength interval is about 15 nm in the case of Al-free EDF, whereas the gain peak wavelength interval is about 27 nm in the case of Al-added EDF. . Therefore, it is preferable to use Al-added EDF as each of the EDFs 31 and 32 in terms of signal light separation.
[0038]
Next, a specific example of an optical amplifier in the case of optically amplifying signal lights having wavelengths of 1531 nm and 1558 nm, which are gain peak wavelengths of the Al-added EDF, will be described. In this case, as shown in FIG. 8, the optical notch filter 51 has a steep transmission characteristic, a transmission loss of 15 dB in the cutoff wavelength band 1535 nm to 1554 nm, and the first transmission wavelength band 1520 nm to 1535 nm. The transmission loss on the shorter wavelength side is 3 dB, and the transmission loss on the second transmission wavelength band 1554 nm to 1570 nm and the longer wavelength side is 0 dB. Then, the excitation light output intensity of the excitation light source 62 is controlled so that the intensity of the light output from each of the optical connectors 12 and 13 becomes a constant value of +1 dBm. FIG. 9 is a table summarizing the signal light output intensity, the noise figure, and the intensity of the excitation light supplied to the EDF 32 at the subsequent stage.
[0039]
In this case as well, the intensity of the light output from each of the optical connectors 12 and 13 is controlled to be a constant value of +1 dBm. However, since this light is composed of signal light and spontaneous emission light, signal light having a wavelength of 1531 nm is used. Output intensity is −1.62 dBm, and the output intensity of signal light having a wavelength of 1558 nm is −1.68 dBm, both of which are less than 0 dBm. The noise figure at the wavelength of 1531 nm is 4.45 dB, and the noise figure at the wavelength of 1558 nm is 4.24 dB. The intensity of the excitation light supplied to the subsequent EDF 32 is 24.2 mW in the case of signal light having a wavelength of 1531 nm, and 57.5 mW in the case of signal light having a wavelength of 1558 nm. When this is compared with FIG. 5, the signal light output intensity is improved by 0.1 dB or more, the noise figure is increased to 0.1 dB or less, which is within the measurement error range, and the intensity of the excitation light supplied to the EDF 32 in the subsequent stage is It is greatly reduced.
[0040]
As described above, in the case of optically amplifying the signal lights having wavelengths of 1531 nm and 1558 nm, which are the gain peak wavelengths of the Al-added EDF, by using the optical notch filter 51 having the transmission characteristic diagram shown in FIG. The intensity of the excitation light supplied to the subsequent EDF 32 can be greatly reduced without causing deterioration of the output intensity and noise figure.
[0041]
【The invention's effect】
As described above in detail, according to the present invention, light included in the optical amplification wavelength band is optically amplified by the optical waveguide provided in the front stage of the optical notch filter, and the optically amplified light and the optical waveguide are provided. Spontaneous emission light generated in is output. Of the light output from the preceding optical waveguide, the light included in the first or second transmission wavelength band passes through the optical notch filter with low loss, and is blocked between the first and second transmission wavelength bands. The light included in the wavelength band is removed by the optical notch filter. Then, the light that has passed through the optical notch filter is optically amplified and output by an optical waveguide provided at the subsequent stage of the optical notch filter. That is, the signal light included in each of the first and second transmission wavelength bands is optically amplified and output with a high optical amplification gain, and the output intensity of the light included in the cutoff wavelength band is extremely weak.
[0042]
Thus, by using the optical notch filter, the configuration is easy, and even if the input multi-wavelength signal light is weak, the signal light amplification gain is large and the output level of the spontaneous emission light is small. Therefore, for example, it can be suitably used as an optical amplifier in intersatellite optical communication.
[0043]
In addition, when the optical waveguide is of a quartz system to which an Er element and an Al element are added, the width of the optical amplification wavelength band is wide, the interval between the first and second transmission wavelength bands can be widened, and the signal light It is preferable in terms of separation.
[0044]
When the cutoff wavelength band of the optical notch filter includes the wavelength band of 1535 nm to 1554 nm, the signal light near the gain peak wavelength of the optical waveguide is optically amplified with a high optical amplification gain. At this time, the intensity of the pumping light supplied to the subsequent optical waveguide can be significantly reduced without causing deterioration of the signal light output intensity and noise figure.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an optical amplifier according to an embodiment.
FIG. 2 is an explanatory diagram of characteristics of each element of the optical amplifier according to the present embodiment.
FIG. 3 is a transmission characteristic diagram of an optical notch filter.
FIG. 4 is a transmission characteristic diagram of a bandpass filter.
FIG. 5 is a chart summarizing signal light output intensity, noise figure, and intensity of pumping light supplied to a subsequent EDF.
FIG. 6 is a gain spectrum diagram of an Al-added EDF.
FIG. 7 is a gain spectrum diagram of an Al-free EDF.
FIG. 8 is a transmission characteristic diagram of an optical notch filter.
FIG. 9 is a table summarizing signal light output intensity, noise figure, and intensity of pumping light supplied to a subsequent EDF.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11-13 ... Optical connector, 21-24 ... Optical isolator 31, 32 ... EDF, 41, 42 ... WDM coupler, 51 ... Optical notch filter, 61, 62 ... Excitation light source, 71-73 ... Branch coupler, 82, 83 ... band-pass filter, 92, 93 ... light receiving element.

Claims (3)

Light having a wavelength that is set to have an inversion distribution of 70% and is included in each of the first and second transmission wavelength bands that do not overlap each other in the optical amplification wavelength band and that matches the gain peak of the amplifier A plurality of optical waveguides to be amplified;
The chirped grating formed between the plurality of optical waveguides and cascaded to each other and formed in the optical waveguide, transmits light having the gain peak, and has the first and second transmission wavelength bands. An optical notch filter that removes light included in the cutoff wavelength band between,
A branch coupler for branching output light from the plurality of optical waveguides,
A first band pass filter that selectively transmits signal light included in the first transmission wavelength band to the first branch path of the branch coupler;
An optical amplifier for intersatellite communication, comprising: a second bandpass filter that selectively transmits signal light included in the second transmission wavelength band in the second branch path of the branch coupler.   2. The optical amplifier according to claim 1, wherein the optical waveguide is of a quartz type to which an Er element and an Al element are added.   3. The optical amplifier according to claim 2, wherein the cutoff wavelength band of the optical notch filter includes a wavelength band of 1535 nm to 1554 nm.

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