JP2012114235A - Optical amplifier and optical amplification method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical amplifier of simple configuration capable of amplifying a U-band signal.SOLUTION: An optical amplifier of the present invention comprises a tellurite glass fiber for amplifying signal light of a U-band, a 1480 nm band semiconductor laser which directly generates the exciting light for exciting the tellurite glass fiber, and a multiplexer which multiplexes the exciting light generated by the 1480 nm band semiconductor laser and the signal light of the U-band before inputting the multiplexed light to the tellurite glass fiber.

Description

  The present invention relates to an optical amplifier that amplifies an optical signal.

  In the backbone transmission system, in order to expand the capacity, a high-density wavelength division multiplexing (DWDM) transmission technique that simultaneously transmits optical signals of a plurality of wavelengths is introduced. The optical fiber used for the transmission line of the DWDM system has a loss coefficient spectrum as shown in FIG. 13, and 1300-1700 nm is a wavelength range suitable for long-distance transmission with low loss. However, since an optical amplifier is used as a repeater in the long-distance DWDM system, the amplification band of the optical amplifier limits the usable wavelength range of the system.

  In a conventional DWDM system, an Er-doped fiber amplifier (EDFA) operating in the C band (1530-1565 nm) and L band (1565-1625 nm), which are low loss bands of transmission fibers, is used as a repeater. Since the EDFA essentially has a wavelength dependency of gain, an optical filter is added to flatten the gain spectrum (gain flattening). However, when the EDFA is gain flattened with an optical filter, the amplification band is approximately 1530-1560 nm in the C band and approximately 1570-1610 nm in the L band. Therefore, the transmission band of the DWDM system is limited to the amplification band of this EDFA.

  On the other hand, as shown in FIG. 13, the loss of the transmission fiber is sufficiently small even in the U band (1625-1675 nm) on the longer wavelength side of the L band. By using an optical amplifier having an amplification band in the U band and using the U band simultaneously with the C band and the L band, it is considered that the transmission capacity can be increased.

H. Masuda, et al., “1.65-μm band fiber Raman amplifier pumped by wavelength-tunable broad-linewidth light source,” Electronics Letters, vol. 34, no. 24, pp. 2339-2340, 1998. T. Tsuzaki et al., “Broadband discrete fiber Raman amplifier with high differential gain operating over 1.65 μm-band,” Proc. OFC2001, 2001, MA3. P. C. Reeves-Hall et al., “Dual wavelength pumped L- and U-band Raman amplifier,” Electronics Letters, vol. 37, no. 14, pp. 883-884, 2001. http://www.anritsu.co.jp/Devices/Products/ OPT-products.asp http://www.furukawa.co.jp/fitel/eng/active/ pumping.html

  Several optical amplifiers having a wide amplification band that can be used for DWDW signal transmission in the U band have been reported so far (Non-Patent Documents 1, 2, and 3). However, these optical amplifiers are fiber Raman amplifiers using silica-based fibers, and pump light of about 1530 to 1570 nm is used to amplify U band signals. However, in order to generate this excitation light, it has a complicated configuration of an excitation light source system using an Er-doped fiber.

  The present invention has been made in view of the above circumstances, and provides an optical amplifier having a simple configuration capable of amplifying a U-band signal.

  In order to achieve the above object, according to the present invention, the invention described in claim 1 directly includes tellurite glass fiber for amplifying U-band signal light and excitation light for exciting the tellurite glass fiber. 1480 nm band semiconductor laser to be generated at the same time, and a multiplexer for combining the excitation light generated by the 1480 nm band semiconductor laser and the U band signal light and inputting them to the tellurite glass fiber as an amplification unit It is characterized by that.

  The invention described in claim 2 is the optical amplifier according to claim 1, wherein in the amplification unit, the 1480 nm band semiconductor laser is a backward pumping light source, and a tellurite glass fiber is used for the multiplexer. The U-band signal light is input to the tellurite glass fiber, and the amplified signal light is output via the multiplexer.

  The invention described in claim 3 is the optical amplifier according to claim 1, wherein in the amplification unit, the 1480 nm band semiconductor laser is a forward pumping light source, and a tellurite glass fiber is used for the multiplexer. The U-band signal light is input to the multiplexer, and the amplified signal light is output from the tellurite glass fiber.

  The invention according to claim 4 is the optical amplifier according to claim 1, wherein the amplification unit is bi-directionally pumped, and uses the two 1480 nm band semiconductors as a forward pumping light source and a backward pumping light source. Two couplers, a laser, a forward multiplexer to which the front pumping light source is connected, and a rear multiplexer to which the rear pumping light source is connected, the front multiplexer and the rear multiplexer The U-band signal light is input to the forward multiplexer, and forward-excited from the forward multiplexer by the tellurite glass fiber. Amplified by light and backward pumping light from the backward multiplexer, and the amplified signal light is output from the backward multiplexer.

  The invention according to claim 5 is the optical amplifier according to claim 4, wherein the tellurite glass fiber in the amplification unit has gain equalization that does not block the forward pumping light and the backward pumping light. A filter is inserted, and the gain equalization filter performs gain equalization for amplification in the tellurite glass fiber.

  The invention according to claim 6 is the optical amplifier according to any one of claims 1 to 5, comprising a plurality of the amplifying units, wherein the amplifying units are connected in cascade. .

  The invention according to claim 7 is the optical amplifier according to any one of claims 1 to 6, wherein at least one of the one or a plurality of amplification units is provided at a subsequent stage. A gain equalizing filter for equalizing the gain of the signal light amplified by the amplification unit is further provided.

  The invention according to claim 8 is the optical amplifier according to any one of claims 1 to 7, further comprising an optical isolator at an input end and / or an output end of the optical amplifier. To do.

  The invention according to claim 9 is the optical amplifier according to any one of claims 1 to 8, wherein the 1480 nm band semiconductor laser in the optical amplifier generates a laser beam having a wavelength range of 1465 to 1485 nm. It is characterized by making it.

  The invention described in claim 10 is a broadband composite optical amplifier, comprising the optical amplifier according to any one of claims 1 to 9 as a first optical amplifier, and according to any one of claims 1 to 9. In the described optical amplifier, an erbium-doped fiber amplifier configured by using an erbium-doped fiber that amplifies L-band signal light as an amplification medium instead of the tellurite glass fiber is further provided as a second optical amplifier. The first optical amplifier further comprising: a band multiplexer that multiplexes input signal light of different bands; and a band splitter that demultiplexes and outputs the signal light of different bands after amplification; The second optical amplifier is connected in parallel between the band multiplexer and the band demultiplexer.

  The invention according to claim 11 is the broadband optical amplifier according to claim 10, wherein the erbium-doped fiber in the second optical amplifier is a phosphorus-doped erbium-doped fiber.

  As described above, the conventional U-band optical amplifier has a complicated structure in which pumping laser light is input to an erbium-doped fiber to generate 1530-1570 nm light that is pumping light to a quartz fiber as an amplification medium. An excitation system configuration is used. According to the present invention, an optical amplifier has an advantage that a U-band optical amplifier having a simple optical amplifier configuration can be realized by directly using laser light generated by a 1480 nm band semiconductor laser as excitation light of a tellurite glass fiber. .

1 is a block diagram illustrating a configuration example of an optical amplifier according to a first embodiment of the present invention. It is a figure which shows the spectrum of the laser beam generate | occur | produced by an example of a 1480 nm band semiconductor laser in FIG. It is a figure which shows the gain spectrum at the time of using the 1480 nm band semiconductor laser of FIG. 2 as an excitation light source. It is a figure which shows the spectrum of the laser beam generate | occur | produced by another example of the 1480 nm band semiconductor laser in FIG. It is a figure which shows the gain spectrum at the time of using the 1480 nm band semiconductor laser of FIG. 4 as an excitation light source. It is a block diagram which shows the structural example of the optical amplifier by the 2nd Embodiment of this invention. It is a figure which shows the gain spectrum at the time of using the optical amplifier in FIG. It is a block diagram which shows the structural example of the optical amplifier by the 3rd Embodiment of this invention. It is a figure which shows the gain spectrum at the time of using the optical amplifier in FIG. It is a figure which shows the structure of the optical amplifier which is a comparative example with respect to the 3rd Embodiment of this invention. It is a figure which shows the gain spectrum at the time of using the optical amplifier in FIG. It is a figure which shows the gain spectrum at the time of using the optical amplifier by the 4th Embodiment of this invention. It is a figure which shows the loss spectrum of a transmission fiber.

  The conventional U-band optical amplifier uses a complicated excitation system configuration as described in Non-Patent Documents 1 to 3. First, specific pump laser light is generated, and the generated pump laser light is input to an erbium-doped fiber. From this erbium-doped fiber, 1530 to 1570 nm light is generated and used as excitation light to the quartz fiber that is an amplification medium.

  The optical amplifier of the present invention uses a tellurite glass fiber as an amplifying medium, and the laser light generated by a 1480 nm band semiconductor laser is directly used as the excitation light of the tellurite glass fiber, thus providing a simple amplifier configuration.

As the tellurite glass fiber, glass mainly composed of tellurium oxide (TeO ² ) (tellurium oxide in a molar ratio of 50% or more) can be used, and the relative refractive index difference (Δn) is 3.7. %, And the cutoff wavelength is 1.3 μm. Such a fiber is characterized in that Raman amplification can be performed with a short fiber length because Δn is as large as 3.7%.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(First embodiment)
FIG. 1 is a diagram illustrating a configuration example of an optical amplifier according to a first embodiment of the present invention. The optical amplifier 100 includes an optical isolator 101 that propagates input signal light in one direction, an optical fiber (tellite glass fiber) 102 that serves as an amplification medium, and a multiplexer 104 that combines signal light and pumping light. A gain equalization filter 105 that equalizes the amplified signal light and an optical isolator 106 that propagates and outputs the gain equalized signal light in one direction are sequentially connected. A 1480 nm band semiconductor laser 103 serving as an excitation light source for generating excitation light to the tellurite glass fiber 102 is connected to the multiplexer 104.

  In FIG. 1, input signal light is input to a tellurite glass fiber 102 through an optical isolator 101. Excitation light from the excitation light source 103 is input to the tellurite glass fiber 102 via the multiplexer 104. In the tellurite glass fiber 102, U-band signal light is amplified by the excitation light. The amplified signal light is input to the subsequent gain equalization filter 105 via the multiplexer 104. The gain-equalized signal light is output through the optical isolator 106.

  FIG. 2 shows a spectrum of laser light generated by an example of the 1480 nm band semiconductor laser in FIG. This laser is a Fabry-Perot laser, and laser light oscillates over a wavelength range of 1464 to 1482 nm. Specifically, 80% or more of the total laser output light power oscillates in the wavelength range of 1465 to 1474 nm, and most of them oscillate in the vicinity of 1470 nm.

  The excitation light shown in FIG. 2 is directly input to the tellurite glass fiber via the multiplexer, and the U-band signal light is amplified. The resulting gain spectrum is shown in FIG. Here, the length of the tellurite glass fiber is 150 m, the pumping light power is 900 mW, and the input signal light power is −30 dBm. That is, the gain of FIG. 3 is a non-saturation gain, and is almost equal to the gain spectrum when the DWDW signal is amplified. This gain is a gain after gain equalization by the gain equalization filter. The gain of the tellurite glass fiber itself has wavelength dependence, and the wavelength dependence can be reduced by filtering with a gain equalization filter. As shown in FIG. 3, an optical amplifier having a 3-dB amplification band of 36 nm with a peak gain of 18 dB and a wavelength range of 1622.5-1658.6 nm can be realized.

  FIG. 4 shows a spectrum of laser light generated by another example of the 1480 nm band semiconductor laser in FIG. This laser has most of the oscillation laser light power at 1470-1480 nm.

  FIG. 5 shows a gain spectrum when the 1480 nm band semiconductor laser of FIG. 4 is used as an excitation light source. Here, the length of the tellurite glass fiber is 150 m, and the excitation light power and the input signal light power are 900 mW and −30 dBm, respectively. When FIG. 5 is compared with FIG. 3, when the tellurite glass fiber is excited with laser light in the vicinity of 1477 nm, the gain spectrum shifts to a longer wavelength than when excited with excitation light of 1465 to 1474 nm, but the shape of the gain spectrum is It is almost the same. As shown in FIG. 5, an optical amplifier having a 3-dB amplification band of 36 nm with a peak gain of 18 dB and a wavelength range of 1630.3-1666.3 nm can be realized.

  As described above, according to this embodiment, a simple optical amplifier is obtained by using a tellurite glass fiber as an amplifying medium and directly using laser light generated by a 1480 nm band semiconductor laser as excitation light of the tellurite glass fiber. A U-band optical amplifier having a configuration can be realized.

  In this embodiment, the backward excitation light source 103 is used, but a forward excitation light source can also be used. When the forward pumping light source is used, the configuration of the optical amplifier is similar to that of the optical amplifier 100, but a tellurite glass fiber as an amplification medium is arranged at the subsequent stage of the multiplexer. In such a configuration, the input signal light is input to the multiplexer through the optical isolator, combined with the excitation light from the forward pumping light source by the multiplexer, and the combined light is used as an amplification medium. Amplification is performed with a tellurite glass fiber. Then, the amplified signal light output from the tellurite glass fiber is gain-equalized by a subsequent gain equalization filter and output through an output optical isolator.

  In the present embodiment, bidirectional excitation can be performed using both the front excitation light source and the rear excitation light source. In the case of bidirectional pumping, the optical amplifier is an optical amplifier 100 using a backward pumping light source, and a forward multiplexer that combines forward pumping light and signal light is an optical isolator 101 and a tellurite glass fiber 102. A forward pumping light source inserted between them and generating forward pumping light can be configured to be connected to the forward multiplexer. In such a configuration, the input signal light is input to the forward multiplexer through the optical isolator. Then, it is combined with the forward pumping light from the forward pumping light source by the forward multiplexer, and is input to one end of the tellurite glass fiber as the amplification medium. On the other hand, the backward pumping light from the backward pumping light source is input to the other end of the tellurite glass fiber serving as an amplification medium via the rear multiplexer. In the tellurite glass fiber, U-band signal light is amplified by forward pumping light and backward pumping light. The amplified signal light is input to the subsequent gain equalization filter via the rear multiplexer. The gain-equalized signal light is output through an optical isolator.

  As described above, the bidirectionally pumped optical amplifier combines forward pumping and backward pumping by arranging a tellurite glass fiber as a common amplification medium between the front multiplexer and the rear multiplexer. It is configured. In such a configuration, a gain equalizing filter that does not block the excitation light can be inserted into the tellurite glass fiber between the front multiplexer and the rear multiplexer. This gain equalization filter can perform gain equalization for amplification in a common amplification medium.

  Note that a 1480 nm band semiconductor laser generally refers to a laser that oscillates at a wavelength of 1460 to 1490 nm (for example, the data sheets described in Non-Patent Documents 4 and 5). In the U band optical amplifier, a 1465 to 1480 nm laser beam is used. It is preferred to excite the tellurite glass fiber.

(Second Embodiment)
FIG. 6 is a diagram illustrating a configuration example of an optical amplifier according to the second embodiment of the present invention. This optical amplifier 200 includes an optical isolator 201 that propagates input signal light in one direction, optical fibers (tellite glass fibers) 202 and 206 that are amplification media, and multiplexing that combines signal light and pumping light. The devices 204 and 208, the gain equalization filter 205 for gain equalizing the amplified signal light, and the optical isolator 209 for propagating the signal light in one direction and outputting it are connected in sequence. Further, 1480 nm band semiconductor lasers 203 and 207 serving as excitation light sources for generating excitation light to the tellurite glass fibers 202 and 206 are connected to the multiplexers 204 and 208, respectively.

  This optical amplifier 200 has a two-stage amplification configuration. The first-stage amplification unit includes a tellurite glass fiber 202, a 1480 nm band semiconductor laser 203, and a multiplexer 204. The second stage amplification unit includes a tellurite glass fiber 206, a 1480 nm band semiconductor laser 207, and a multiplexer 208. The two amplification units use two tellurite glass fibers, and each tellurite glass fiber amplifies a signal. After the signal light is amplified by the first-stage tellurite glass fiber, the signal light is passed through the gain equalization filter 205, and the signal light is further amplified by the second-stage tellurite glass fiber and output.

  Since the optical amplifier according to the first embodiment has a loss medium at the output end, it is not suitable for high output. In the optical amplifier according to the present embodiment, a high-power optical amplifier can be realized by using a two-stage amplification configuration as shown in FIG.

  FIG. 7 shows a gain spectrum when the optical amplifier of FIG. 6 is used. Here, the excitation light power is 900 mW for each tellurite glass fiber, and the input signal light power is −30 dBm. Compared with FIGS. 3 and 5, a gain as high as 3 dB is obtained.

  As described above, according to the present embodiment, a high-output U-band optical amplifier can be realized by further including the second-stage amplification unit in the optical amplifier according to the first embodiment.

  In the present embodiment, a two-stage amplification configuration is shown, but an amplification unit having three or more stages may be provided.

(Third embodiment)
FIG. 8 is a diagram illustrating a configuration example of an optical amplifier according to the third embodiment of the present invention. The optical amplifier 300 includes a band multiplexer 310 that multiplexes signal lights in different bands, a tellurite fiber Raman amplifier 300a that can amplify U-band signal light, and a band splitter 311 that demultiplexes signal lights in different bands. Are connected sequentially. Further, an erbium-doped fiber amplifier 300b capable of amplifying the L-band signal light is connected in parallel with the tellurite fiber Raman amplifier 300a between the band multiplexer 310 and the band demultiplexer 311. The tellurite fiber Raman amplifier 300a has the same configuration as the optical amplifier 200 disclosed in the second embodiment, and uses a tellurite glass fiber as an amplification medium. The erbium-doped fiber amplifier 300b is similar in configuration to the optical amplifier 200, but uses an erbium-doped fiber as an amplification medium, and uses a forward pumping light source instead of a backward pumping light source in the first stage amplification unit. . Both the tellurite fiber Raman amplifier 300a and the erbium-doped fiber amplifier 300b use a 1480 nm band semiconductor laser as an excitation light source.

  FIG. 9 shows a gain spectrum when the optical amplifier of FIG. 8 is used. Here, the length of the tellurite glass fiber is 150 m, the pump light power is 900 mW, the erbium-doped fiber length is 35 m, and the pump light power is 300 mW. The input signal light power is -30 dBm. As shown in FIG. 9, the tellurite fiber Raman amplifier obtained a 36-nm 3-dB band with a wavelength range of 1622.5-1658.6 nm in the U band, while the erbium-doped fiber amplifier has a wavelength range in the L band. 43.7 nm 3-dB was obtained with a 1564.5-1608.2 nm. As an entire optical amplifier, an amplification band of about 80 nm is obtained from the L band to the U band.

  In this embodiment, the erbium-doped fiber amplifier 300b has a structure in which a first-stage amplification unit that is forward pumping and a second-stage amplification unit that is backward pumping are combined via a gain equalization filter 305b. . If the gain equalization filter 305b does not block the forward pumping light and the backward pumping light, the erbium-doped fiber amplifier 300b may be regarded as one bidirectional pumping structure.

  Like the optical amplifier of this embodiment, an optical amplifier having a configuration in which a tellurite fiber Raman amplifier and an erbium-doped fiber amplifier are connected in parallel is compared with an optical amplifier in which a tellurite fiber Raman amplifier and an erbium-doped fiber amplifier are connected in series. Thus, it is effective for U-band amplification.

(Comparative example)
FIG. 10 is a diagram showing a comparative example for the optical amplifier according to the third embodiment of the present invention. The optical amplifier 400 has a configuration of an optical amplifier in which a tellurite fiber Raman amplifier 400a that can amplify U-band signal light and an erbium-doped fiber amplifier 400b that can amplify L-band signal light are connected in series via an optical isolator 410. is there. The tellurite fiber Raman amplifier 400a is the same as the tellurite fiber Raman amplifier 300a of FIG. 8 except that there is no isolator on the output side. The erbium-doped fiber amplifier 400b is the same as the erbium-doped fiber amplifier 300b of FIG. 8 except that there is no input-side isolator.

  FIG. 11 shows a gain spectrum when the optical amplifier of FIG. 10 is used. Here, the length of the tellurite glass fiber is 150 m, the pump light power is 900 mW, the erbium-doped fiber length is 35 m, and the pump light power is 300 mW. The input signal light power is -30 dBm. As is apparent from FIG. 11, in the cascade connection type optical amplifier of the tellurite fiber Raman amplifier and the erbium-doped fiber amplifier, the gain is greatly reduced at a wavelength longer than 1626 nm, and is not suitable for U-band signal light amplification. Recognize.

  As described above, according to the third embodiment, an optical amplifier effective for simultaneous amplification of the L band and the U band is realized by connecting the tellurite fiber Raman amplifier and the erbium-doped fiber amplifier in parallel. be able to.

(Fourth embodiment)
The configuration of the optical amplifier disclosed in the present embodiment is the same as the configuration of the optical amplifier 300 according to the third embodiment, except that the erbium-doped fibers 302b and 306b in the optical amplifier are phosphorus-doped erbium-doped fibers. Features.

  The phosphorus-doped erbium-doped fiber amplifier that uses a phosphorus-doped erbium-doped fiber as an amplification medium has a larger amplification band than the erbium-doped fiber amplifier disclosed in the third embodiment, and in particular has an amplification band from 1610 nm to a long wave as a long wavelength band. . By combining the phosphorus-doped erbium-doped fiber amplifier and the tellurite fiber Raman amplifier, the amplification band is further expanded.

  FIG. 12 shows a gain spectrum when the optical amplifier of this embodiment is used. Here, the length of the tellurite glass fiber is 150 m, the pump light power is 900 mW, the erbium-doped fiber length is 35 m, and the pump light power is 300 mW. The input signal light power is -30 dBm. As shown in FIG. 12, the tellurite fiber Raman amplifier obtained a 36-nm 3-dB band with a wavelength range of 1622.5-1658.6 nm in the U-band, while the erbium-doped fiber amplifier has a wavelength range in the L-band. Yielded 3-dB of 62.398.4 nm with a 1554.3-1617.6 nm. As an entire optical amplifier, an amplification band of 100 nm is obtained from the L band to the U band.

  As described above, according to the fourth embodiment, in the optical amplifier according to the third embodiment, the erbium-doped fiber uses a phosphorus-doped erbium-doped fiber, so that the amplification band is further expanded. And an optical amplifier effective for simultaneous amplification in the U band.

100, 200, 300, 400 Optical amplifier 101, 106, 201, 209, 301a, 309b, 401a, 409b, 410 Isolator 102, 202, 206, 302a, 306a, 402a, 406a Tellurite glass fiber 103, 203, 207, 303a, 307a, 303b, 307b, 403a, 407a, 403b, 407b 1480 nm band semiconductor laser 104, 204, 208, 304a, 308a, 304b, 308b, 404a, 408a, 404b, 408b Multiplexer 105, 205, 305a, 305b 405a, 405b Gain equalization filter 310 Band multiplexer 311 Band splitter 302b, 306b, 402b, 406b Erbium-doped fiber 300a, 400a Tellurite fiber Raman Amplifier 300b, 400b Erbium-doped fiber amplifier

Claims (11)

Tellurite glass fiber that amplifies U band signal light;
A 1480 nm band semiconductor laser that directly generates excitation light for exciting the tellurite glass fiber;
An optical amplifier comprising: a multiplexer that combines the pumping light generated by the 1480 nm band semiconductor laser and the U band signal light and inputs the combined light to the tellurite glass fiber. The amplification unit is
The 1480 nm band semiconductor laser is a backward pumping light source, a tellurite glass fiber is disposed in front of the multiplexer, the U band signal light is input to the tellurite glass fiber, and the amplified signal light is 2. The optical amplifier according to claim 1, wherein the optical amplifier is output through a multiplexer. The amplification unit is
The 1480 nm band semiconductor laser is a forward pumping light source, a tellurite glass fiber is disposed at the rear stage of the multiplexer, the U band signal light is input to the multiplexer, and the amplified signal light is transmitted to the tellurium. 2. The optical amplifier according to claim 1, wherein the optical amplifier is output from a light glass fiber. The amplification unit is bi-directional excitation,
The two 1480 nm band semiconductor lasers used as a front excitation light source and a rear excitation light source;
The two multiplexers, which are a front multiplexer to which the front pumping light source is connected and a rear multiplexer to which the rear pumping light source is connected;
The tellurite glass fiber disposed between the front multiplexer and the rear multiplexer, and
The U-band signal light is input to the front multiplexer, amplified by the tellurite glass fiber with the forward pumping light from the front multiplexer and the backward pumping light from the rear multiplexer, and after amplification The optical amplifier according to claim 1, wherein the signal light is output from the rear multiplexer.   The tellurite glass fiber in the amplification unit is inserted with a gain equalizing filter that does not block the forward pumping light and the backward pumping light, and the gain equalizing filter is used for amplification in the tellurite glass fiber. The optical amplifier according to claim 4, wherein gain equalization is performed.   6. The optical amplifier according to claim 1, comprising a plurality of the amplification units, wherein each amplification unit is connected in a column.   2. The gain equalization filter for gain equalizing signal light amplified by the amplification unit is further provided at a stage subsequent to at least one amplification unit of the one or a plurality of amplification units. The optical amplifier according to any one of 1 to 6.   The optical amplifier according to claim 1, further comprising an optical isolator at an input end and / or an output end of the optical amplifier.   The optical amplifier according to claim 1, wherein the 1480 nm band semiconductor laser in the optical amplifier generates laser light having a wavelength range of 1465 to 1485 nm. The optical amplifier according to any one of claims 1 to 9 is provided as a first optical amplifier,
10. An optical amplifier according to claim 1, wherein an erbium-doped fiber that amplifies L-band signal light is used as an amplifying medium instead of a tellurite glass fiber. As a second optical amplifier,
A band multiplexer that multiplexes the input signal lights of different bands, and a band splitter that demultiplexes and outputs the signal lights of different bands after amplification;
The wideband composite optical amplifier, wherein the first optical amplifier and the second optical amplifier are connected in parallel between the band multiplexer and the band demultiplexer.   11. The broadband composite optical amplifier according to claim 10, wherein the erbium-doped fiber in the second optical amplifier is a phosphorus-doped erbium-doped fiber.

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