Optical amplifier

Abstract

To eliminate the need for a filter for removing idler light.SOLUTION: An optical amplifier includes: means for multiplexing linearly polarized wavelength multiplexed signal light containing a plurality of pieces of signal light and circularly polarized pump light to generate first multiplexed light; means for performing polarization-separating the first multiplexed light into second multiplexed light of first polarization and third multiplexed light of second polarization orthogonal to the first polarization; means for converting the third multiplexed light of the second polarization into the first polarization to output fourth multiplexed light; means for performing optical parametric amplification on the wavelength multiplexed signal light contained in the second multiplexed light by pump light contained in the second multiplexed light to output fifth multiplexed light, and performing optical parametric amplification on the wavelength multiplexed signal light contained in the fourth multiplexed light by pump light contained in the fourth multiplexed light to output sixth multiplexed light; and means for performing processing of outputting the wavelength multiplexed signal light on the basis of the fifth multiplexed light and the sixth multiplexed light.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to optical amplifiers. [Background technology]

[0002] An optical amplifier that uses a second-order, third-order, or other nonlinear optical effect is called an optical parametric amplifier. Compared to an optical amplifier that uses an ion-doped optical fiber, such as an EDFA, an optical parametric amplifier is capable of amplifying signals over an extremely wide bandwidth. Non-Patent Document 1 discloses a configuration in which an optical parametric amplifier amplifies wavelength-multiplexed signal light containing multiple wavelength-multiplexed signal light.

[0003] An optical parametric amplifier has a nonlinear medium, such as a waveguide on a semiconductor device or an optical fiber, in which signal light is amplified by pump light. The pump light is usually unmodulated continuous light. During the amplification process using the pump light, the pump light is attenuated and idler light is generated. The idler light is generated on the opposite side of the frequency axis from the signal light, with the pump light at the center, and its bandwidth corresponds to the bandwidth of the signal light. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] T. Kobayashi,et al.,"103-ch.132-Gbaud PS-QAM Signal Inline-amplified Transmission with 14.1-THz Bandwidth Lumped PPLN-based OPAs over 400-km G.652.D SMF".,2023 Optical Fiber Communications Conference and Exhibition (OFC),San Diego,CA,USA,2023,pp.1-3 Summary of the Invention [Problem to be solved by the invention]

[0005] For example, when a wavelength-multiplexed signal light containing multiple signal lights is amplified by an optical parametric amplifier, it is necessary to prevent the idler light from interfering with the signal light. In other words, it is necessary to determine the frequency allocation of multiple signal lights and pump light so that the interfering light does not overlap with the signal light. Furthermore, since the idler light is an unwanted signal, the optical amplifier must remove the idler light. In Non-Patent Document 1, the unwanted idler light is removed by a filter.

[0006] The present disclosure provides a technique that enables the use of a frequency arrangement in which the idler light overlaps with the signal light, or a technique that eliminates the need for a filter that removes the idler light. [Means for solving the problem]

[0007] According to one aspect of the present disclosure, an optical amplifier includes a multiplexing unit that multiplexes linearly polarized wavelength-multiplexed signal light including a plurality of signal lights with circularly polarized pump light to generate a first multiplexed light; a first polarization splitting unit that polarization-splits the first multiplexed light into a second multiplexed light of a first polarization and a third multiplexed light of a second polarization orthogonal to the first polarization; a first polarization conversion unit that converts the third multiplexed light of the second polarization into the first polarization to output a fourth multiplexed light of the first polarization; and a second polarization conversion unit that converts the third multiplexed light of the second polarization into the first polarization by converting the pump light contained in the second multiplexed light into a fourth multiplexed light of the first polarization. The optical fiber communication system includes a first amplifying means for optically parametrically amplifying wavelength-multiplexed signal light to output a fifth multiplexed light including idler light generated by the optical parametric amplification, and for optically parametrically amplifying the wavelength-multiplexed signal light included in the fourth multiplexed light using the pump light included in the fourth multiplexed light to output a sixth multiplexed light including idler light generated by the optical parametric amplification, and a processing means for performing processing to output the wavelength-multiplexed signal light based on the fifth multiplexed light and the sixth multiplexed light. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to use a frequency arrangement in which the idler light overlaps with the signal light, or to eliminate the need for a filter to remove the idler light. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of an optical amplifier. [Figure 2] 1A and 1B are diagrams showing examples of wavelength-multiplexed signal light, multiplexed light, and multiplexed light that has passed through a nonlinear medium. [Figure 3] FIG. 1 is a diagram showing an example of the configuration of an optical amplifier. [Figure 4] FIG. 1 is a diagram showing an example of the configuration of an optical amplifier. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, the embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the invention as claimed, and not all combinations of features described in the embodiments are necessarily essential to the invention. Two or more features among the multiple features described in the embodiments may be arbitrarily combined. Furthermore, the same reference numerals are used for the same or similar components, and redundant explanations will be omitted.

[0011] First Embodiment FIG. 1 is a schematic diagram of an optical amplifier according to this embodiment. A light source 10 generates linearly polarized pump light and outputs it to a quarter-wave plate 11. The quarter-wave plate 11 converts the linearly polarized pump light to circular polarization and outputs the circularly polarized pump light to a splitter 13. A polarization control unit 12 adjusts the polarization plane of the input wavelength-multiplexed signal light and outputs the polarization-adjusted wavelength-multiplexed signal light to the splitter 13. The polarization control unit 12 adjusts the polarization of the wavelength-multiplexed signal light so that the polarization-adjusted wavelength-multiplexed signal light is at a 45-degree angle with respect to both the X polarization and the Y polarization orthogonal to the X polarization. The splitter 13 splits the input circularly polarized pump light into two and outputs them from ports #1 and #2. The splitter 13 also splits the input linearly polarized wavelength-multiplexed signal light into two and outputs them from ports #1 and #2. Therefore, multiplexed light obtained by multiplexing linearly polarized wavelength-multiplexed signal light and circularly polarized pump light is output from ports #1 and #2. In this embodiment, only multiplexed light #1 output from port #1 is used.

[0012] Polarization beam splitter 14 outputs the X-polarized component of input multiplexed light #1 as X-polarized multiplexed light #2 to nonlinear medium 17. Polarization beam splitter 14 also outputs the Y-polarized component of input multiplexed light #1 as Y-polarized multiplexed light #3 to polarization rotation unit 15. Polarization rotation unit 15 rotates the polarization plane of input Y-polarized multiplexed light #3 by 90 degrees and outputs X-polarized multiplexed light #4 to nonlinear medium 16.

[0013] If the amplitude of the linearly polarized pump light input to the quarter-wave plate 11 is P, the Jones vector of the circularly polarized pump light output from the quarter-wave plate 11 is (1 / √2)(P, jP). Furthermore, if the amplitude of the linearly polarized wavelength-multiplexed signal light input to the polarization control unit 12 is S, the Jones vector of the linearly polarized wavelength-multiplexed signal light output from the polarization control unit 12 is (1 / √2)(S, S). Therefore, the Jones vector of the multiplexed light output from one of the two ports #1 and #2 by the splitter 13 is (1 / 2)(S+P, S+jP), and the Jones vector of the multiplexed light output from the other port is (1 / 2)(S, S-jP). In the following, the explanation will be given assuming that multiplexed light #1 expressed as (1 / 2)(S+P, S+jP) is output to port #1.

[0014] In this case, the Jones vector of the X-polarized multiplexed light #2 output by the PBS 14 is (1 / 2)(S+P,0), and the Jones vector of the Y-polarized multiplexed light #3 output by the PBS 14 is (1 / 2)(0,S+jP). Therefore, the Jones vector of the X-polarized multiplexed light #4 output by the polarization rotation unit 15 is (1 / 2)(S+jP,0).

[0015] FIG. 2A shows a wavelength-multiplexed signal light used to explain this embodiment. In the example of FIG. 2A, the wavelength-multiplexed signal light includes six signal lights S1 to S6 whose center frequencies are equally spaced on the frequency axis. In this example, the signal lights S1 to S6 have the same bandwidth. FIG. 2B also shows the multiplexed light #1 output by the splitter 13. The arrow between the signal lights S3 and S4 in FIG. 2B indicates the pump light. As mentioned above, the pump light included in the multiplexed light #1 output by the splitter 13 is circularly polarized, and the polarization-multiplexed signal light included in the multiplexed light #1 output by the splitter 13 is linearly polarized. Furthermore, FIG. 2B also shows the X-polarized multiplexed light #2 output by the PBS 14 and the X-polarized multiplexed light #4 output by the polarization rotation unit 15. As is clear from the above explanation of Jones vectors, the phase of the pump light contained in the X-polarized multiplexed light #2 is shifted by π / 2 with respect to the phase of the pump light contained in the X-polarized multiplexed light #4.

[0016] In this embodiment, the frequency (wavelength) of the pump light is set to satisfy the following condition. Condition 1: The frequency must be outside the band of each signal light. Condition 2: At least one signal light must exist on both the lower and higher frequency sides of the pump light. In FIG. 2B, three signal lights exist on the lower and higher frequency sides of the pump light, respectively, so condition 2 is satisfied.

[0017] 2B, the frequency distance between signal light S3 and signal light S4 and the pump light is equal, the frequency distance between signal light S2 and signal light S5 and the pump light is equal, and the frequency distance between signal light S1 and signal light S6 and the pump light is equal. In the following description, two signal lights having the same frequency distance from the pump light are referred to as a "signal light pair." According to FIG. 2B, signal light S1 and signal light S6 form one signal light pair, signal light S2 and signal light S5 form one signal light pair, and signal light S3 and signal light S4 form one signal light pair.

[0018] The wavelength-multiplexed signal light contained in the X-polarized multiplexed light #2 is amplified by the pump light contained in the multiplexed light #2 while propagating through the nonlinear medium 17. At the same time, idler light is generated and the pump light is attenuated. Similarly, the wavelength-multiplexed signal light contained in the X-polarized multiplexed light #4 is amplified by the pump light contained in the multiplexed light #4 while propagating through the nonlinear medium 16. At the same time, idler light is generated and the pump light is attenuated. In this way, the nonlinear medium 16 and the nonlinear medium 17 function as amplification media that amplify the wavelength-multiplexed signal light with the pump light.

[0019] Here, the electric field component of the pump light is E p and the electric field component of the signal light is E s Then, the electric field component of the idler light, E i is expressed by the following formula: E i ∝E p E p E s* In addition, E s * is E s In other words, the difference between the center frequency of the idler light and the frequency of the pump light corresponds to the difference between the center frequency of the signal light and the frequency of the pump light, and the electric field component of the idler light is the complex conjugate of the electric field component E s Here, when the pump light included in the X-polarized multiplexed light #2 is used as a reference, the phase of the pump light included in the X-polarized multiplexed light #4 is shifted by π / 2. As is clear from the above equation, the electric field component E of the idler light i Since is proportional to the square of the pump light, the phase difference between the electric field component of the idler light output by the nonlinear medium 17 and the electric field component of the idler light output by the nonlinear medium 16 is π. In other words, the electric field component of the idler light output by the nonlinear medium 16 is expressed as E i Then, the electric field component of the idler light output from the nonlinear medium 17 is (-E i ) becomes.

[0020] Therefore, the multiplexed light #5 including the wavelength-multiplexed signal light and the idler light output from the nonlinear medium 16 is as shown in FIG. 2(C), and the multiplexed light #6 including the wavelength-multiplexed signal light and the idler light output from the linear medium 17 is as shown in FIG. 2(D). In FIGS. 2(C) and 2(D), the upper side of the frequency axis indicates the wavelength-multiplexed signal light, and the lower side of the frequency axis indicates the wavelength-multiplexed idler light (wavelength-multiplexed idler light). Although FIGS. 2(C) and 2(D) show the wavelength-multiplexed signal light and the wavelength-multiplexed idler light separately, in reality, multiplexed light obtained by combining the wavelength-multiplexed signal light and the wavelength-multiplexed idler light is output from the nonlinear medium 16 and 17. In reality, the pump light attenuated by optical parametric amplification is also output from the nonlinear medium 16 and 17, but since there is no problem if the pump light remains, the pump light is omitted from FIGS. 2(C) and 2(D).

[0021] As shown in Figures 2(C) and 2(D), each of the signal lights S1 to S6 is combined with an idler light based on the other signal light of the signal light pair. For example, signal light S1 and signal light S6 are a signal light pair, but signal light S1 is combined with the idler light of signal light S6, and signal light S6 is combined with the idler light of signal light S1. As mentioned above, the idler light corresponds to the complex conjugate of the original signal light, so in Figures 2(C) and 2(D), the idler light of signal light Sn (n is an integer from 1 to 6) is referred to as Sn * As described above, the phase difference between the electric field component of the idler light output from the nonlinear medium 16 and the electric field component of the idler light output from the nonlinear medium 17 is π, so the idler light of the signal light Sn output from the nonlinear medium 16 is expressed as (-Sn * ), and the idler light of the signal light Sn output from the nonlinear medium 17 is (+Sn * )

[0022] The multiplexed light #5 and the multiplexed light #6 output from the nonlinear media 16 and 17 are output to the processing unit 30. The processing unit 30 multiplexes the multiplexed light #5 and the multiplexed light #6 output from the nonlinear media 16 and 17. As is clear from Figures 2(C) and 2(D), by multiplexing the multiplexed light #5 output from the nonlinear medium 16 and the multiplexed light #6 output from the nonlinear medium 17, the idler light is cancelled out, and wavelength-multiplexed signal light including signal light S1 to signal light S6 is output.

[0023] If the characteristics of the nonlinear medium 16 and the nonlinear medium 17 are different, the idler light may not be canceled out even when the multiplexed light #5 output from the nonlinear medium 16 and the multiplexed light #6 output from the nonlinear medium 17 are multiplexed, and the idler light may remain. However, if the nonlinear medium 16 and the nonlinear medium 17 are configured as waveguides on a semiconductor device, the characteristics of the nonlinear medium 16 and the nonlinear medium 17 can be made similar, and the level of the remaining idler light can be suppressed. Furthermore, in the processing unit 30, instead of simply multiplexing the multiplexed light #5 output from the nonlinear medium 16 and the multiplexed light #6 output from the nonlinear medium 17, optical MIMO processing can be applied to the two multiplexed lights #5 and #6. Optical MIMO processing can be realized, for example, using a two-stage Mach-Zehnder interferometer. Optical MIMO processing makes it possible to output wavelength-multiplexed signal light with suppressed residual idler light.

[0024] The above configuration makes it possible to use a frequency arrangement in which the idler light overlaps with the signal light.

[0025] In the above explanation, it has been explained that the combined light #1 expressed as (1 / 2)(S+P, S+jP) is output to port #1 of splitter 13, but even if the combined light #1 expressed as (1 / 2)(SP, S-jP) is output to port #1 of splitter 13, as is clear from the above explanation, the output of processing unit 30 will be wavelength-multiplexed signal light in which the idler light has been cancelled out.

[0026] In FIG. 2B, the number of signal lights on the lower frequency side of the pump light and the number of signal lights on the higher frequency side are both three. However, the number of signal lights on the lower frequency side of the pump light and the number of signal lights on the higher frequency side may be different. For example, if the pump light is placed between signal light S1 and signal light S2, there will be one signal light pair consisting of S1 and S2. In this case, in the multiplexed light that has passed through the nonlinear medium, only signal light S1 and signal light S2 overlap with the idler light. Signal lights S3 to S6 do not overlap with idler light based on other signal lights, and idler light based on signal lights S3 to S6 does not overlap with other signal lights. Even in this case, the idler light can be canceled out by multiplexing multiplexed light #5 output from nonlinear medium 16 with multiplexed light #6 output from nonlinear medium 17.

[0027] 2A, the bandwidths of the signal lights are the same and the center frequencies of the signal lights are equally spaced on the frequency axis. However, as long as the above conditions 1 and 2 are satisfied, the bandwidths of the signal lights may be different and the center frequencies of the signal lights do not need to be equally spaced on the frequency axis. This is because, due to condition 2, the idler light may overlap with the signal light. Therefore, in the above explanation, two signal lights that are equidistant from the pump light on the frequency axis are considered to be a signal light pair. However, more generally, two signal lights whose idler lights overlap each other are considered to be a signal light pair.

[0028] Furthermore, for example, when all signal lights are arranged on the high-frequency side or the low-frequency side of the pump light, that is, when condition 2 is not applied, all idler lights do not overlap with the signal lights. However, even in this case, the idler lights can be canceled out by multiplexing the multiplexed light #5 output from the nonlinear medium 16 and the multiplexed light #6 output from the nonlinear medium 17. In other words, there is no need to provide a filter for removing idler lights in the optical amplifier. Therefore, this embodiment has the advantage that a filter for removing idler lights is not required even when only condition 1 is applied.

[0029] Furthermore, in this embodiment, the splitter 13 splits the pump light into two and outputs them from ports #1 and #2, and splits the wavelength-multiplexed signal light into two and outputs them from ports #1 and #2, thereby outputting multiplexed light including the wavelength-multiplexed signal light and the pump light from each of ports #1 and #2. Here, if the power splitting ratio of the splitter 13 is α (0<α<1), the power of the pump light input to the splitter 13 is PP, and the power of the wavelength-multiplexed signal light input to the splitter 13 is PS, the power of the pump light included in the multiplexed light #1 output from port #1 is (1-α)×PP, and the power of the wavelength-multiplexed signal light included in the multiplexed light #1 is α×PS. Furthermore, the power of the pump light included in the multiplexed light output from port #2 is α×PP, and the power of the wavelength-multiplexed signal light included in the multiplexed light output from port #2 is (1-α)×PS.

[0030] In this manner, in this embodiment, (1-α) times the power of the input wavelength-multiplexed signal light is discarded and only α times the power is used. Since it is important in an optical amplifier to suppress the loss of power of the input wavelength-multiplexed signal light, α is set to 0.5 or more. In other words, splitter 13 is configured so that the power of the wavelength-multiplexed signal light contained in multiplexed light #1 output from port #1 used for subsequent amplification is equal to or greater than the power of the wavelength-multiplexed signal light contained in multiplexed light output from port #2 not used for subsequent amplification.

[0031] In this case, the power of the pump light contained in the multiplexed light #1 output from port #1 will be equal to or less than the power of the pump light contained in the multiplexed light output from port #2, meaning that more than half of the power of the pump light generated by light source 10 will not be used for amplification. However, since the pump light is generated within the optical amplifier, this does not pose a problem as long as light source 10 is configured so that the power of the pump light contained in multiplexed light #1 is at a level necessary for amplification.

[0032] Second Embodiment Next, the second embodiment will be described, focusing on the differences from the first embodiment. Fig. 3 is a configuration diagram of an optical amplifier according to this embodiment. The optical amplifier of this embodiment is provided with wavelength demultiplexers 18 and 19, receivers 20 and 21, and a MIMO processor 22 instead of the processor 30 of the first embodiment. The multiplexed light #5 and multiplexed light #6 output from the nonlinear media 16 and 17 are the same as those in the first embodiment, so a repeated description will be omitted.

[0033] The multiplexed light #5 and multiplexed light #6 output from the nonlinear media 16 and 17 are output to wavelength demultiplexers 18 and 19, respectively. The wavelength demultiplexers 18 and 19 demultiplex each signal light pair into a single wavelength and output a multiplexed light obtained by combining one of the two signal lights in the signal light pair with the idler light of the other signal light. Using the examples of FIGS. 2C and 2D, the wavelength demultiplexers 18 and 19 output, for example, a multiplexed light obtained by combining the idler light of signal light S1 and the idler light of signal light S6, a multiplexed light obtained by combining the idler light of signal light S2 and the idler light of signal light S5, and a multiplexed light obtained by combining the idler light of signal light S3 and the idler light of signal light S4. Note that instead of a multiplexed light obtained by combining the idler light of signal light S1 and the idler light of signal light S6, a configuration may be adopted in which multiplexed light obtained by combining the idler light of signal light S6 and the idler light of signal light S1 is output. The same applies to the other signal light pairs.

[0034] 2(C) and 2(D), three multiplexed lights corresponding to the three signal light pairs are output from the wavelength demultiplexers 18 and 19. Since the processing for each of the three multiplexed lights corresponding to the three signal light pairs is similar, the following describes the processing for the multiplexed light output from the wavelength demultiplexers 18 and 19, in which the idler light of signal light S1 and signal light S6 are multiplexed.

[0035] The receiving unit 20 coherently receives combined light obtained by combining signal light S1 and idler light of signal light S6 of the signal light shown in Fig. 2(C). That is, the receiving unit 20 has a light source that generates local light, combines the local light and combined light, and performs photoelectric conversion to output an electrical signal corresponding to the combined light obtained by combining signal light S1 and idler light of signal light S6. The receiving unit 21 also coherently receives combined light obtained by combining signal light S1 and idler light of signal light S6 of the signal light shown in Fig. 2(D), and outputs an electrical signal corresponding to the combined light obtained by combining signal light S1 and idler light of signal light S6. Note that the light source that generates the local light used by the receiving unit 20 for coherent reception and the light source that generates the local light used by the receiving unit 21 for coherent reception can be the same.

[0036] The electrical signals output by the receiving units 20 and 21 correspond to the sum of the complex conjugates of the electric field component of the signal light S1 and the electric field component of the signal light S6, respectively. However, the signs of the complex conjugates of the electric field component of the signal light S6 included in the electrical signal output by the receiving units 20 and the electrical signal output by the receiving units 21 are different from each other. The MIMO processing unit 22 performs MIMO processing in the electrical domain on the electrical signals from the receiving units 20 and 21, thereby outputting an electrical signal corresponding to the electric field component of the signal light S1 and an electrical signal corresponding to the electric field component of the signal light S6. Note that what is determined in the MIMO processing is the electrical signal corresponding to the complex conjugate of the electric field component of the signal light S6, and the MIMO processing unit 80 is configured to output an electrical signal corresponding to the complex conjugate of this electrical signal.

[0037] Similar processing is performed for the other two frequency pairs, resulting in six electrical signals corresponding to the signal lights S1 to S6 being obtained inside the optical amplifier. The optical amplifier then converts the six electrical signals into the signal lights S1 to S6 and outputs a wavelength-multiplexed signal light including the signal lights S1 to S6.

[0038] The above configuration makes it possible to use a frequency arrangement in which the idler light overlaps with the signal light, and also makes it possible to eliminate the need for a filter to remove the idler light.

[0039] As in the first embodiment, the number of signal lights on the lower frequency side of the pump light and the number of signal lights on the higher frequency side do not need to be the same. For example, if the pump light is placed between the signal light S1 and the signal light S2, there will be one signal light pair consisting of S1 and S2. In this case, the wavelength demultiplexers 18 and 19 extract and coherently receive the combined light of the signal light S1 and the idler light of the signal light S2, or the combined light of the signal light S2 and the idler light of the signal light S1, and then perform MIMO processing to generate electrical signals corresponding to the signal light S1 and the signal light S2. Furthermore, since the signal lights S3 to S6 do not overlap with the idler light, electrical signals corresponding to the signal lights S3 to S6 can be generated without performing MIMO processing. In this case, the wavelength demultiplexers 18 and 19 perform wavelength demultiplexing on a signal light basis for signal lights that are not part of a signal light pair.

[0040] In this embodiment, the two signal lights of the signal light pair do not need to have the same band. In addition, in this embodiment, the frequency distance between the center frequency of one signal light of the signal light pair and the pump light is equal to the frequency distance between the center frequency of the other signal light of the signal light pair and the pump light, but as long as one signal light of the signal light pair and the idler light of the other signal light of the signal light pair overlap, the frequency distance between the center frequencies of the two signal lights of the signal light pair and the pump light does not need to be equal.

[0041] Third Embodiment Next, the third embodiment will be described, focusing on the differences from the first embodiment. In the first embodiment, the multiplexed light #7 output from the splitter 13 to port #2 is discarded. In this embodiment, the multiplexed light #7 output from the splitter 13 to port #2 is also used. That is, as shown in FIG. 4, a PBS 140, a polarization rotation unit 150, a nonlinear medium 160, and a nonlinear medium 170 are provided to process the multiplexed light #7 output from the splitter 13 to port #2. The processing performed by the PBS 140, the polarization rotation unit 150, the nonlinear medium 160, and the nonlinear medium 170 is the same as the processing performed by the PBS 14, the polarization rotation unit 15, the nonlinear medium 16, and the nonlinear medium 17. The processing unit 300 cancels out the idle light by multiplexing the multiplexed light from the nonlinear medium 16, the nonlinear medium 17, the nonlinear medium 160, and the nonlinear medium 170, and outputs the wavelength-multiplexed signal light. Note that the processing unit 300 may be configured to extract wavelength-multiplexed signal light by applying MIMO processing in the optical domain to the multiplexed light output by the nonlinear medium 16 and the multiplexed light output by the nonlinear medium 17, extract wavelength-multiplexed signal light by applying MIMO processing in the optical domain to the multiplexed light output by the nonlinear medium 160 and the multiplexed light output by the nonlinear medium 170, and then multiplex the two wavelength-multiplexed signal light. Furthermore, as described in the second embodiment, it is also possible to perform coherent reception after wavelength separation and apply MIMO processing in the electrical domain.

[0042] The above configuration makes it possible to use a frequency arrangement in which the idler light overlaps with the signal light, and also makes it possible to eliminate the need for a filter to remove the idler light.

[0043] This configuration eliminates the need for a filter to remove idler light, making it possible to contribute to Goal 9 of the United Nations' Sustainable Development Goals (SDGs), which is to "Build resilient infrastructure, promote sustainable industrialization and foster innovation."

[0044] The invention is not limited to the above-described embodiment, and various modifications and variations are possible within the scope of the gist of the invention. [Explanation of symbols]

[0045] 13: Splitter, 14: PBS, 15: Polarization rotation unit, 16, 17: Nonlinear medium, 30: Processing unit

Claims

1. a multiplexing means for multiplexing a linearly polarized wavelength-multiplexed signal light including a plurality of signal lights with a circularly polarized pump light to generate a first multiplexed light; a first polarization splitting means for splitting the first multiplexed light into a second multiplexed light of a first polarization and a third multiplexed light of a second polarization orthogonal to the first polarization; a first polarization conversion means for converting the third multiplexed light of the second polarization into the first polarization, and outputting a fourth multiplexed light of the first polarization; a first amplifying means for optically parametrically amplifying the wavelength-multiplexed signal light included in the second multiplexed light using the pump light included in the second multiplexed light, thereby outputting a fifth multiplexed light including idler light generated by the optical parametric amplification, and for optically parametrically amplifying the wavelength-multiplexed signal light included in the fourth multiplexed light using the pump light included in the fourth multiplexed light, thereby outputting a sixth multiplexed light including idler light generated by the optical parametric amplification; a processing unit for performing processing to output the wavelength-multiplexed signal light based on the fifth multiplexed light and the sixth multiplexed light; An optical amplifier comprising:

2. 2. The optical amplifier according to claim 1, wherein at least one of said plurality of signal lights is at a lower frequency side than said pump light, and at least one of said plurality of signal lights is at a higher frequency side than said pump light.

3. 2. The optical amplifier according to claim 1, wherein said processing means generates said wavelength-multiplexed signal light by multiplexing said fifth multiplexed light and said sixth multiplexed light.

4. 2. The optical amplifier according to claim 1, wherein said processing means generates said wavelength-multiplexed signal light by performing MIMO processing on said fifth multiplexed light and said sixth multiplexed light in the optical domain.

5. The processing means a first wavelength separating means for separating the fifth multiplexed light into wavelengths and outputting light of a first band including a first signal light of the plurality of signal lights and a first idler light generated based on a second signal light of the plurality of signal lights; a second wavelength separating means for separating the sixth multiplexed light into wavelengths and outputting light of the first band; a first receiving means for coherently receiving the light output from the first wavelength separating means and outputting a first electrical signal; a second receiving means for coherently receiving the light output from the second wavelength separating means and outputting a second electrical signal; 3. The optical amplifier according to claim 2, further comprising: a MIMO processing means for performing MIMO processing on the first electrical signal and the second electrical signal in an electrical domain, thereby outputting an electrical signal corresponding to the first signal light and an electrical signal corresponding to the second signal light.

6. 2. The optical amplifier according to claim 1, wherein the wavelength-multiplexed signal light included in the first multiplexed light has a polarization that differs by 45 degrees from each of the first polarization and the second polarization.

7. 7. The optical amplifier according to claim 1, wherein the multiplexing means is a splitter that splits the wavelength-multiplexed signal light into two and outputs them from a first port and a second port, and splits the pump light into two and outputs them from the first port and the second port, thereby outputting the first multiplexed light from the first port.

8. the multiplexing means outputs a seventh multiplexed light including the wavelength-multiplexed signal light and the pump light from the second port; 8. The optical amplifier according to claim 7, wherein the power of the wavelength-multiplexed signal light included in the first multiplexed light output from the first port is equal to or greater than the power of the wavelength-multiplexed signal light included in the seventh multiplexed light output from the second port.

9. second polarization splitting means for splitting the seventh multiplexed light into an eighth multiplexed light of the first polarization and a ninth multiplexed light of the second polarization; a second polarization conversion means for converting the ninth multiplexed light of the second polarization into the first polarization, thereby outputting the tenth multiplexed light of the first polarization; a second amplifying means for optically parametrically amplifying the wavelength-multiplexed signal light included in the eighth multiplexed light using the pump light included in the eighth multiplexed light, thereby outputting an eleventh multiplexed light including idler light generated by the optical parametric amplification, and for optically parametrically amplifying the wavelength-multiplexed signal light included in the tenth multiplexed light using the pump light included in the tenth multiplexed light, thereby outputting a twelfth multiplexed light including idler light generated by the optical parametric amplification; Furthermore, 9. The optical amplifier according to claim 8, wherein the processing means performs processing to output the wavelength-multiplexed signal light based on the fifth multiplexed light, the sixth multiplexed light, the eleventh multiplexed light, and the twelfth multiplexed light.

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