Optical signal processing device and optical transmission system

Abstract

This optical signal processing device comprises: an excitation light generation unit that generates excitation light for use in wavelength conversion; a first excitation light multiplexing unit that multiplexes the excitation light generated by the excitation light generation unit and an optical signal of a first wavelength; a first wavelength conversion unit that converts the optical signal of the first wavelength into an optical signal of a second wavelength by a nonlinear optical effect; an excitation light demultiplexing unit that, on the basis of the optical signal of the first wavelength and the excitation light multiplexed by the first excitation light multiplexing unit, demultiplexes the optical signal of the second wavelength and the excitation light; an optical signal processing unit that performs optical signal processing on the optical signal of the second wavelength; a second excitation light multiplexing unit that multiplexes the excitation light demultiplexed by the excitation light demultiplexing unit with respect to the optical signal of the second wavelength on which the optical signal processing has been performed by the optical signal processing unit; and a second wavelength conversion unit that converts the optical signal of the second wavelength into the optical signal of the first wavelength by the nonlinear optical effect on the basis of the optical signal of the second wavelength and the excitation light multiplexed by the second excitation light multiplexing unit.　

Description

Optical signal processing device and optical transmission system

[0001] The present invention relates to an optical signal processing device and an optical transmission system.

[0002] In recent years, communication traffic has been increasing exponentially with the launch of the 5th Generation Mobile Communication System and the widespread use of rich content such as high-resolution video. This has led to a demand for continuous increases in the communication capacity of optical transmission systems. In optical fiber transmission, the transmission capacity per optical fiber can be improved by widening the optical transmission band. Therefore, various studies are being conducted to realize ultra-wideband wavelength division multiplexing transmission.

[0003] The wavelength range with low transmission loss in optical fibers is divided into several optical transmission bands. Long-distance optical fiber communication networks primarily use the C-band or L-band, which has the lowest transmission loss among all optical transmission bands, from approximately 4 THz to 5 THz. This optical transmission band can utilize high-performance optical amplifier repeaters, such as erbium-doped fiber amplifiers (EDFAs).

[0004] In order to broaden the optical transmission band, in addition to the combined use of the C-band and L-band, there has been active research and development into ultra-wideband wavelength division multiplexing transmission systems that use new optical transmission bands such as the S-band and U-band. Such wideband transmission systems that use multiple optical transmission bands are called multiband transmission systems. Multiband transmission systems require the development of new transponders that support optical transmission bands that have not been used before.

[0005] In addition to optical fibers and optical transceivers, optical node devices (optical node units) are also used for the transmission paths of optical signals in long-distance optical transmission systems. Optical node devices can amplify optical signals as they are, and perform add / drop and routing of wavelength channels. Optical node devices that perform add / drop of wavelength channels are called ROADMs (Reconfigurable Optical Add-Drop Multiplexers). Optical node devices that switch wavelength paths for multi-directional routes are called optical cross connects (OXCs).

[0006] ROADMs and optical cross connects (OXCs) use wavelength selective switches (WSSs) to switch the wavelength channel routes. To convert the wavelength of a channel, an optical transceiver converts the optical signal into an electrical signal, receives the electrical signal, and then modulates it again to a new wavelength. In multiband transmission systems, the wavelength selective switch (WSS) must be adaptable to not only conventional optical transmission bands but also multiple new optical transmission bands. Furthermore, as the number of wavelength channels increases, the number of transponders required for wavelength conversion also increases, resulting in issues such as increased costs associated with devices such as power consumption and an increase in the scale of the optical transmission system.

[0007] Against this background, all-optical wavelength conversion technologies using nonlinear optical effects have recently attracted attention. For example, representative technologies under consideration include wavelength conversion using four-wave mixing (FWM), a third-order nonlinear optical effect, and wavelength conversion using differential frequency generation (DFG), a second-order nonlinear optical effect (see Patent Document 1). Wavelength conversion using cross-phase modulation and cross-gain modulation effects by semiconductor optical amplifiers is also being considered.

[0008] In particular, wavelength conversion using difference frequency generation, which is a second-order nonlinear optical effect, and wavelength conversion using difference frequency generation, which is a second-order nonlinear optical effect, are capable of wavelength conversion over a wide band. Methods using four-wave mixing and difference frequency generation are capable of simultaneously converting wavelength multiplexed signals from one optical transmission band to a different optical transmission band. By utilizing such wideband wavelength band conversion and configuring a wavelength multiplexed signal to be generated in a conventionally used optical transmission band (e.g., C-band) and then converted to another optical transmission band, multiband transmission can be realized without the need to prepare a new optical transceiver adapted to the new optical transmission band (see Non-Patent Document 1).

[0009] In optical node equipment, by simultaneously converting all channels to a conventional optical transmission band (e.g., C-band), optical amplifiers for existing optical transmission bands, such as wavelength selective switches (WSSs) and erbium-doped optical fiber amplifiers (EDFAs), can be used for channels in other optical transmission bands. This also enables low-latency, low-power wavelength conversion without the use of optical transceivers (i.e., optical-to-electrical conversion). For example, optical signals in the S-band or U-band are converted to the C-band by a wavelength converter, then pass through a wavelength selective switch (WSS) or optical amplifier for the C-band, and are then reconverted to the original transmission band by another wavelength converter.

[0010] In wavelength conversion using four-wave mixing, a third-order nonlinear optical effect, pump light is placed between the signal light and the wavelength-converted light. In wavelength conversion using difference frequency generation, a second-order nonlinear optical effect, pump light of a second harmonic, which has a frequency twice that of the frequency between the signal light and the wavelength-converted light, is used. It is also difficult to directly prepare high-power pump light of a second harmonic. Therefore, a configuration is used in which light having a frequency between the signal light and the wavelength-converted light is amplified by a high-power optical amplifier such as an erbium-doped optical fiber amplifier (EDFA), and then converted into a second harmonic using the second harmonic generation (SHG) process in a second-order nonlinear medium. Hereinafter, the pump light before being converted into a second harmonic is referred to as the "fundamental pump light."

[0011] In wavelength conversion using four-wave mixing, a third-order nonlinear optical effect, stimulated Brillouin scattering and phase modulation of the pump light can cause signal distortion and distortion of the conversion efficiency spectrum. To suppress stimulated Brillouin scattering, a method of modulating phase dither with the pump light is used, but the phase noise and frequency fluctuation of the pump light are transmitted to the wavelength-converted light, so the effect of phase dither on the signal becomes an issue.

[0012] In wavelength conversion using difference frequency generation (DFR), a second-order nonlinear optical effect, the influence of stimulated Brillouin scattering is small in principle, so phase dithering is generally not necessary. On the other hand, as with wavelength conversion using four-wave mixing (FWM), a third-order nonlinear optical effect, the phase noise and frequency fluctuation of the pump light are transmitted to the wavelength-converted light, so it is desirable that the linewidth and frequency noise of the pump light source be as small as possible.

[0013] Japanese Patent Application Laid-Open No. 2020-86031

[0014] T. Kato, H. Muranaka, Y. Tanaka, Y. Akiyama, T. Hoshida, S. Shimizu, T. Kobayashi, T. Kazama, T. Umeki, K. Watanabe, and Y. Miyamoto, “S+C+L-Band WDM Transmission Using 400-Gb / s Real-Time Transceivers Extended by PPLN-Based Wavelength Converter”, Proceeding of European Conference on Optical Communication (ECOC), We4D.4, September 2022M. Nakagawa, H. Kawahara, T. Seki, and T. Miyamura, “Highly Efficient Multi-Band Optical Networks with Wavelength-Selective Band Switching”, IEICE Trans. Commun., vol. E106-B, no. 5, pp. 416-426, May 2022.A. Arnould and A. Ghazisaeidi, “Equalization Enhanced Phase Noise in Coherent Receivers: DSP-Aware Analysis and Shaped Constellations”, J. Lightwave Technol., 37(20), 5282-5290 (2019).

[0015] In long-distance optical transmission networks, optical signals are transmitted through multiple optical node devices (optical node units). In optical node configurations that perform wavelength band conversion, optical signals undergo multiple wavelength band conversions before reaching the receiving end. Therefore, if a penalty occurs in signal quality when wavelength band conversion is performed, the penalty will accumulate multiple times. This can significantly impair the quality of the received signal.

[0016] The main cause of signal quality degradation in wavelength band converters is thought to be increased optical noise due to optical loss within the converter. To suppress this increase in optical noise, the conversion efficiency of the converter is important, but achieving high conversion efficiency requires a large pump light power. Furthermore, the phase noise of the pump light is transferred to the wavelength-converted light via the optical parametric process, which can result in a penalty that degrades signal quality. Therefore, it is desirable to use laser light with low phase noise (narrow linewidth) as the pump light.

[0017] Narrow-linewidth lasers generally have low output power, so to obtain high pump light power, the pump light must be amplified using an additional amplifier, such as an erbium-doped optical fiber amplifier, before being combined with the signal light and input to the nonlinear optical medium. In the optical signal processing via wavelength conversion described above, the wavelength-converted optical signal undergoes optical signal processing using a wavelength selective switch or optical amplifier, and then undergoes wavelength conversion again to reconvert it to the original band. Therefore, in such cases, wavelength converters are operated in pairs. Therefore, two pump light lasers and amplifiers are required per band. This results in problems such as increased system size and power consumption.

[0018] In view of the above circumstances, an object of the present invention is to provide a technique that can realize a configuration using a plurality of wavelength converters that is smaller in size and consumes less power than conventional configurations.

[0019] One aspect of the present invention is an optical signal processing device comprising: an excitation light generating unit that generates excitation light to be used for wavelength conversion; a first excitation light multiplexing unit that multiplexes the excitation light generated by the excitation light generating unit with an optical signal of a first wavelength; a first wavelength converting unit that converts the optical signal of the first wavelength into an optical signal of a second wavelength by a nonlinear optical effect based on the optical signal of the first wavelength and the excitation light multiplexed by the first excitation light multiplexing unit; an excitation light demultiplexing unit that demultiplexes the optical signal of the second wavelength from the excitation light; an optical signal processing unit that performs optical signal processing on the optical signal of the second wavelength; a second excitation light multiplexing unit that multiplexes the excitation light demultiplexed by the excitation light demultiplexing unit with the optical signal of the second wavelength that has been subjected to optical signal processing by the optical signal processing unit; and a second wavelength converting unit that converts the optical signal of the second wavelength into an optical signal of the first wavelength by a nonlinear optical effect based on the optical signal of the second wavelength and the excitation light multiplexed by the second excitation light multiplexing unit.

[0020] One aspect of the present invention is an optical transmission system comprising an optical signal transmitting device that transmits an optical signal, m (m is an integer greater than or equal to 1) optical node units that perform optical signal processing on the optical signal transmitted from the optical signal transmitting device, and an optical signal receiving device that receives the optical signal that has undergone optical signal processing by the m optical node units, wherein the m optical node units comprise one or more of the optical signal processing devices described above.

[0021] According to the present invention, in a configuration using a plurality of wavelength converters, it is possible to realize a configuration that is smaller in size and consumes less power than conventional configurations.

[0022] FIG. 1 is a basic configuration diagram of an optical signal processing device 1 according to a first embodiment. FIG. 2 is a detailed configuration diagram (part 1) of an example of an optical signal processing device when wavelength conversion using difference frequency generation, which is a second-order nonlinear optical effect, is assumed. FIG. 3 is a detailed configuration diagram (part 3) of an example of an optical signal processing device when wavelength conversion using difference frequency generation, which is a second-order nonlinear optical effect, is assumed. FIG. 1 is a detailed configuration diagram (part 1) of an example of an optical signal processing device according to a second embodiment. FIG. 2 is a detailed configuration diagram (part 2) of an example of an optical signal processing device according to the second embodiment. FIG. 3 is a detailed configuration diagram (part 3) of an example of an optical signal processing device according to the second embodiment. FIG. 4 is a diagram illustrating an example of a configuration of an optical transmission system according to a third embodiment. FIG. 5 is a diagram illustrating an example of a configuration of an optical transmission system according to a fourth embodiment.

[0023] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0024] (Summary) First, an overview of the present invention will be described. In the optical signal processing device of the present invention, the pumping light used in the input-side wavelength converter is reused in the output-side wavelength converter. This eliminates the need to prepare a pumping light laser or amplifier for the output-side wavelength converter, thereby reducing the operating costs of the optical signal processing device. Below, a specific configuration for realizing the above processing will be described.

[0025] 1 is a diagram showing the basic configuration of an optical signal processing device 1 according to a first embodiment. The optical signal processing device 1 includes a pump light generating unit 11, a first pump light multiplexing unit 12, a first wavelength converting unit 13, a pump light demultiplexing unit 14, an optical signal processing unit 15, a second pump light multiplexing unit 16, and a second wavelength converting unit 17. Note that FIG. 1 shows only the basic configuration required to obtain the effects of the present invention.

[0026] The pumping light generating unit 11 generates pumping light to be used for wavelength conversion and outputs the generated pumping light to the first pumping light multiplexing unit 12.

[0027] The first pumping light multiplexing unit 12 receives an optical signal transmitted from outside and the pumping light generated by the pumping light generating unit 11. The first pumping light multiplexing unit 12 multiplexes the input optical signal and the pumping light.

[0028] The first wavelength converter 13 receives the optical signal and the pump light multiplexed by the first pump light multiplexer 12, and converts the optical signal into light of a desired wavelength by a nonlinear optical effect using the input pump light. The first wavelength converter 13 outputs the wavelength-converted optical signal to the pump light demultiplexer 14 and the optical signal processor 15.

[0029] The pumping light demultiplexing unit 14 separates the wavelength-converted optical signal from the pumping light, and outputs the separated optical signal to the optical signal processing unit 15, and outputs the separated pumping light to the second pumping light multiplexing unit 16.

[0030] The optical signal processing unit 15 performs predetermined optical signal processing on the wavelength-converted optical signal. The optical signal processing here refers to wavelength add / drop of optical channels using a wavelength selective switch (WSS), routing, gain equalization, etc. The optical signal processing unit 15 outputs the optical signal that has undergone optical signal processing to the second pumping light multiplexer 16.

[0031] The second pumping light multiplexing section 16 multiplexes the optical signal that has been subjected to optical signal processing by the optical signal processing section 15 with the pumping light that has been separated by the pumping light demultiplexing section 14 .

[0032] The second wavelength converter 17 receives the optical signal and the pump light multiplexed by the second pump light multiplexer 16, and reconverts the input optical signal to the original wavelength band by a nonlinear optical effect. The second wavelength converter 17 outputs the optical signal reconverted to the original wavelength band.

[0033] In this way, optical signal processing is performed by the optical signal processing unit 15 arranged between the pair of wavelength conversion units (first wavelength conversion unit 13 and second wavelength conversion unit 17). Furthermore, in the optical signal processing device 1, the pump light used in the first wavelength conversion unit 13 is also reused in the second wavelength conversion unit 17. In other words, the first wavelength conversion unit 13 and the second wavelength conversion unit 17 perform wavelength conversion using the same pump light.

[0034] 2 is a detailed configuration diagram (part 1) of an example of an optical signal processing device assuming wavelength conversion using difference frequency generation, which is a second-order nonlinear optical effect. As shown in Fig. 2, the optical signal processing device 1a includes a polarization demultiplexing unit 101, a pump light generating unit 102, a pump light multiplexing unit 103, a nonlinear medium 104, a pump light demultiplexing unit 105, a pump light multiplexing unit 106, a nonlinear medium 107, a pump light demultiplexing unit 108, a polarization multiplexing unit 109, a wavelength conversion light extraction filter 110, an optical signal processing unit 111, a polarization demultiplexing unit 112, a pump light multiplexing unit 113, a nonlinear medium 114, a pump light demultiplexing unit 115, a pump light multiplexing unit 116, a nonlinear medium 117, a pump light demultiplexing unit 118, a polarization multiplexing unit 119, and a wavelength conversion light extraction filter 120.

[0035] The pump light generating section 102 corresponds to the pump light generating section 11 shown in FIG. 1. The polarization demultiplexing section 101, the pump light multiplexing section 103, and the pump light multiplexing section 106 correspond to the first pump light multiplexing section 12 shown in FIG. 1. The nonlinear medium 104 and the nonlinear medium 107 correspond to the first wavelength converting section 13 shown in FIG. 1. The pump light demultiplexing section 105 and the pump light demultiplexing section 108 correspond to the pump light demultiplexing section 14 shown in FIG. 1. The optical signal processing section 111 corresponds to the optical signal processing section 15 shown in FIG. 1. The polarization demultiplexing section 112, the pump light multiplexing section 113, and the pump light multiplexing section 116 correspond to the second pump light multiplexing section 16 shown in FIG. 1. The nonlinear medium 114 and the nonlinear medium 117 correspond to the second wavelength converting section 17 shown in FIG. 1.

[0036] In wavelength conversion using difference frequency generation, a second-order nonlinear optical effect, second-harmonic pump light, which has a frequency twice the center frequency of the gain band, is used. It is difficult to directly prepare high-power pump light for second-harmonic waves. Therefore, a configuration is used in which light with a frequency between the signal light and the wavelength-converted light is amplified by a high-output optical amplifier such as an erbium-doped optical fiber amplifier (EDFA), and then converted into a second harmonic by utilizing the second-harmonic generation (SHG) process in a second-order nonlinear medium. Because nonlinear optical effects are polarization-dependent, a polarization diversity configuration is used to achieve polarization independence.

[0037] An optical signal is input from the outside to the polarization demultiplexing unit 101. The polarization demultiplexing unit 101 demultiplexes the input optical signal into a first optical signal and a second optical signal which are orthogonal in polarization state. For example, the first optical signal is an X-polarized optical signal, and the second optical signal is a Y-polarized optical signal. The polarization demultiplexing unit 101 is, for example, a polarization beam splitter.

[0038] The pumping light generating unit 102 generates a plurality of pumping lights to be used for wavelength conversion. The pumping light generating unit 102 includes a pumping light source 150, a branching unit 151, an optical amplifier 152, a nonlinear medium 153, an optical amplifier 154, and a nonlinear medium 155. The pumping light source 150 outputs the pumping light to the branching unit 151. The branching unit 151 branches the pumping light output from the pumping light source 150 and outputs the branched light to the optical amplifier 152 and the optical amplifier 154.

[0039] The optical amplifier 152 amplifies the pumping light branched by the branching unit 151 and outputs the amplified pumping light to the nonlinear medium 153. The optical amplifier 152 is a high-output optical amplifier such as an erbium-doped optical fiber amplifier (EDFA). The pumping light amplified by the optical amplifier 152 is converted into a second harmonic by utilizing a second harmonic generation (SHG) process in the nonlinear medium 153.

[0040] The optical amplifier 154 amplifies the pumping light branched by the branching unit 151 and outputs the amplified pumping light to the nonlinear medium 155. The optical amplifier 154 is a high-output optical amplifier such as an erbium-doped optical fiber amplifier (EDFA). The pumping light amplified by the optical amplifier 154 is converted into a second harmonic by utilizing a second harmonic generation (SHG) process in the nonlinear medium 155.

[0041] The pumping light multiplexer 103 receives the first optical signal demultiplexed by the polarization demultiplexer 101 and the pumping light converted into a second harmonic by the nonlinear medium 153. The pumping light multiplexer 103 multiplexes the input first optical signal and the pumping light. The pumping light multiplexer 103 is, for example, a wavelength multiplexing filter made of a dielectric multilayer film or the like, or a dichroic mirror.

[0042] The first optical signal and the pumping light multiplexed by the pumping light multiplexer 103 are input to the nonlinear medium 104. The nonlinear medium 104 uses the input pumping light to perform all-optical wavelength conversion of the first optical signal by a nonlinear optical effect. Hereinafter, the first optical signal after wavelength conversion will be referred to as the converted first optical signal.

[0043] The pumping light and the converted first optical signal are input to the pumping light demultiplexing unit 105. The pumping light demultiplexing unit 105 demultiplexes the input pumping light and the converted first optical signal. The pumping light demultiplexed by the pumping light demultiplexing unit 105 is input to the pumping light multiplexing unit 113 via an optical transmission path. The optical transmission path is configured using a spatial optical system such as optical fiber or lenses. The converted first optical signal demultiplexed by the pumping light demultiplexing unit 105 is input to the polarization multiplexing unit 109 via the optical transmission path. The pumping light demultiplexing unit 105 is, for example, a wavelength multiplexing filter made of a dielectric multilayer film or a dichroic mirror.

[0044] The pumping light multiplexer 106 receives the second optical signal demultiplexed by the polarization demultiplexer 101 and the pumping light converted into a second harmonic by the nonlinear medium 155. The pumping light multiplexer 106 multiplexes the input second optical signal and the pumping light. The pumping light multiplexer 106 is, for example, a wavelength multiplexing filter made of a dielectric multilayer film or the like, or a dichroic mirror or the like.

[0045] The second optical signal and the pumping light multiplexed by the pumping light multiplexer 106 are input to the nonlinear medium 107. The nonlinear medium 107 uses the input pumping light to all-optically convert the wavelength of the second optical signal by a nonlinear optical effect. Hereinafter, the second optical signal after wavelength conversion will be referred to as the converted second optical signal.

[0046] The pumping light and the converted second optical signal are input to the pumping light demultiplexing unit 108. The pumping light demultiplexing unit 108 demultiplexes the input pumping light and the converted second optical signal. The pumping light demultiplexed by the pumping light demultiplexing unit 108 is input to the pumping light multiplexing unit 116 via an optical transmission path. The converted second optical signal demultiplexed by the pumping light demultiplexing unit 108 is input to the polarization multiplexing unit 109 via an optical transmission path. The pumping light demultiplexing unit 108 is, for example, a wavelength multiplexing filter made of a dielectric multilayer film or a dichroic mirror.

[0047] The polarization multiplexer 109 combines the converted first optical signal output from the pumping light demultiplexer 105 and the converted second optical signal output from the pumping light demultiplexer 108 in orthogonal polarization planes. The polarization multiplexer 109 outputs the combined optical signal to the wavelength conversion light extraction filter 110.

[0048] The wavelength conversion light extraction filter 110 receives the combined optical signal output from the polarization multiplexer 109. The light from the output ends of the nonlinear medium 104 and the nonlinear medium 107 contains both wavelength-converted light and an optical signal in the original wavelength band. Therefore, the wavelength conversion light extraction filter 110 attenuates the optical signal in the original wavelength band and extracts only the wavelength-converted light. The optical signal in the original wavelength band is the optical signal before wavelength conversion. The wavelength conversion light extraction filter 110 may be, for example, a wavelength multiplexing filter made of a dielectric multilayer film or a wavelength selective switch (WSS).

[0049] The optical signal processing unit 111 performs optical signal processing on the wavelength-converted light extracted by the wavelength conversion light extraction filter 110. The optical signal processing unit 111 outputs the wavelength-converted light after the optical signal processing to the polarization demultiplexing unit 112.

[0050] The polarization demultiplexing unit 112 receives the wavelength-converted light after optical signal processing output from the optical signal processing unit 111. The polarization demultiplexing unit 112 demultiplexes the input wavelength-converted light after optical signal processing into a third optical signal and a fourth optical signal which are orthogonal polarization states. For example, the third optical signal is an X-polarized optical signal, and the fourth optical signal is a Y-polarized optical signal. The polarization demultiplexing unit 112 is, for example, a polarization beam splitter.

[0051] The pumping light multiplexer 113 receives the third optical signal demultiplexed by the polarization demultiplexer 112 and the pumping light demultiplexed by the pumping light demultiplexer 105. The pumping light multiplexer 113 multiplexes the input third optical signal and the pumping light. The pumping light multiplexer 113 is, for example, a wavelength multiplexing filter made of a dielectric multilayer film or a dichroic mirror.

[0052] The third optical signal and pump light multiplexed by the pump light multiplexing unit 113 are input to the nonlinear medium 114. The nonlinear medium 114 uses the input pump light to all-optically convert the wavelength of the third optical signal by a nonlinear optical effect. Hereinafter, the third optical signal after wavelength conversion will be referred to as the converted third optical signal. Hereinafter, the pump light used to generate the nonlinear optical effect in the nonlinear medium 114 is the same as the pump light used to generate the nonlinear optical effect in the nonlinear medium 104. In this way, the optical signal processing device 1a of the present invention reuses the pump light on the input side and the output side.

[0053] The pumping light and the converted third optical signal are input to the pumping light demultiplexing unit 115. The pumping light demultiplexing unit 115 demultiplexes the input pumping light and the converted third optical signal. The converted third optical signal demultiplexed by the pumping light demultiplexing unit 115 is input to the polarization multiplexing unit 119 via an optical transmission path. The pumping light demultiplexing unit 115 is, for example, a wavelength multiplexing filter made of a dielectric multilayer film or a dichroic mirror.

[0054] The pumping light multiplexer 116 receives the fourth optical signal demultiplexed by the polarization demultiplexer 112 and the pumping light demultiplexed by the pumping light demultiplexer 108. The pumping light multiplexer 116 multiplexes the input fourth optical signal and the pumping light. The pumping light multiplexer 116 is, for example, a wavelength multiplexing filter made of a dielectric multilayer film or the like, or a dichroic mirror.

[0055] The nonlinear medium 117 receives the fourth optical signal and pump light multiplexed by the pump light multiplexing unit 116. The nonlinear medium 117 uses the input pump light to all-optically convert the wavelength of the fourth optical signal by a nonlinear optical effect. Hereinafter, the wavelength-converted fourth optical signal will be referred to as a converted fourth optical signal. Hereinafter, the pump light used to generate the nonlinear optical effect in the nonlinear medium 117 is the same as the pump light used to generate the nonlinear optical effect in the nonlinear medium 107. In this way, the optical signal processing device 1a of the present invention reuses the pump light on the input side and the output side.

[0056] The pumping light and the converted fourth optical signal are input to the pumping light demultiplexing unit 118. The pumping light demultiplexing unit 118 demultiplexes the input pumping light and the converted fourth optical signal. The converted fourth optical signal demultiplexed by the pumping light demultiplexing unit 118 is input to the polarization multiplexing unit 119 via an optical transmission path. The pumping light demultiplexing unit 118 is, for example, a wavelength multiplexing filter made of a dielectric multilayer film or a dichroic mirror.

[0057] The polarization multiplexer 119 combines the converted third optical signal output from the pump light demultiplexer 115 and the converted fourth optical signal output from the pump light demultiplexer 118 in orthogonal polarization planes. The polarization multiplexer 119 outputs the combined optical signal to the wavelength conversion light extraction filter 120.

[0058] The wavelength conversion light extraction filter 120 receives the combined optical signal output from the polarization multiplexer 119. The light from the output ends of the nonlinear medium 114 and the nonlinear medium 117 contains both the wavelength-converted light and the optical signal in the original wavelength band. Therefore, the wavelength conversion light extraction filter 120 attenuates the optical signal in the original wavelength band and extracts only the wavelength-converted light. The wavelength conversion light extraction filter 120 may be, for example, a wavelength multiplexing filter made of a dielectric multilayer film or a wavelength selective switch (WSS).

[0059] The optical signal processing device 1a configured as described above includes the pumping light generating unit 11 (pumping light generating unit 102 in FIG. 2) that generates pumping light to be used for wavelength conversion, the first pumping light multiplexing unit 12 (polarization demultiplexing unit 101, pumping light multiplexing unit 103, and pumping light multiplexing unit 106 in FIG. 2) that multiplexes the pumping light generated by the pumping light generating unit 11 with an optical signal of a first wavelength, the first wavelength converting unit 13 (nonlinear medium 104 and nonlinear medium 107 in FIG. 2) that converts the optical signal of the first wavelength into an optical signal of a second wavelength by a nonlinear optical effect based on the optical signal of the first wavelength and the pumping light multiplexed in the first pumping light multiplexing unit 12, and the pumping light demultiplexing unit 14 that demultiplexes the optical signal of the second wavelength from the pumping light. 4 (pumping light demultiplexing section 105 and pumping light demultiplexing section 108 in FIG. 2 ), an optical signal processing section 15 (optical signal processing section 111 in FIG. 2 ) that performs optical signal processing on the optical signal of the second wavelength, a second pumping light multiplexing section 16 (polarization demultiplexing section 112, pumping light multiplexing section 113, and pumping light multiplexing section 116 in FIG. 2 ) that multiplexes the pumping light demultiplexed in the pumping light demultiplexing section 14 with the optical signal of the second wavelength that has been subjected to optical signal processing by the optical signal processing section 15, and a second wavelength conversion section 17 (nonlinear medium 114 and nonlinear medium 117 in FIG. 2 ) that converts the optical signal of the second wavelength into an optical signal of the first wavelength by a nonlinear optical effect, based on the optical signal of the second wavelength and the pumping light multiplexed in the second pumping light multiplexing section 16.

[0060] In this way, the pump light used on the input side is also reused on the output side. This causes an optical parametric process to occur in the nonlinear medium 114 and the nonlinear medium 117. With this configuration, there is no need to prepare a new laser light source or optical amplifier for the pump light on the output side. This makes it possible to realize a configuration that is smaller in size and consumes less power than conventional configurations.

[0061] (Another Configuration Example 1 of the First Embodiment) Next, a configuration different from the configuration shown in Fig. 2 will be described in an optical signal processing device assuming wavelength conversion using difference frequency generation, which is a second-order nonlinear optical effect. If the output optical power of the pump light source 150 is sufficiently large for the conversion efficiency required by the nonlinear media 104 and 107, which are wavelength converters, an optical amplifier is not necessarily required. Therefore, a configuration in which an optical amplifier is not provided in the pump light generating unit 102b will be described here.

[0062] 3 is a detailed configuration diagram (part 2) of an example of an optical signal processing device assuming wavelength conversion using difference frequency generation, which is a second-order nonlinear optical effect. As shown in Fig. 3, the optical signal processing device 1b includes a polarization demultiplexing unit 101, a pump light generating unit 102b, a pump light multiplexing unit 103, a nonlinear medium 104, a pump light demultiplexing unit 105, a pump light multiplexing unit 106, a nonlinear medium 107, a pump light demultiplexing unit 108, a polarization multiplexing unit 109, a wavelength conversion light extraction filter 110, an optical signal processing unit 111, a polarization demultiplexing unit 112, a pump light multiplexing unit 113, a nonlinear medium 114, a pump light demultiplexing unit 115, a pump light multiplexing unit 116, a nonlinear medium 117, a pump light demultiplexing unit 118, a polarization multiplexing unit 119, and a wavelength conversion light extraction filter 120.

[0063] The pump light generating section 102b corresponds to the pump light generating section 11 shown in FIG. 1. The polarization demultiplexing section 101, the pump light multiplexing section 103, and the pump light multiplexing section 106 correspond to the first pump light multiplexing section 12 shown in FIG. 1. The nonlinear medium 104 and the nonlinear medium 107 correspond to the first wavelength converting section 13 shown in FIG. 1. The pump light demultiplexing section 105 and the pump light demultiplexing section 108 correspond to the pump light demultiplexing section 14 shown in FIG. 1. The optical signal processing section 111 corresponds to the optical signal processing section 15 shown in FIG. 1. The polarization demultiplexing section 112, the pump light multiplexing section 113, and the pump light multiplexing section 116 correspond to the second pump light multiplexing section 16 shown in FIG. 1. The nonlinear medium 114 and the nonlinear medium 117 correspond to the second wavelength converting section 17 shown in FIG. 1.

[0064] The optical signal processing device 1b differs in configuration from the optical signal processing device 1a in that it includes an excitation light generating unit 102b instead of the excitation light generating unit 102. The following description will focus on the differences from the optical signal processing device 1a.

[0065] The pumping light generating unit 102b includes a pumping light source 150, a branching unit 151, a nonlinear medium 153, and a nonlinear medium 155. In this manner, the pumping light generating unit 102b does not include the optical amplifier 152 and the optical amplifier 154.

[0066] 3, it is assumed that the output optical power of the pumping light source 150 is sufficiently large. The pumping light generated by the pumping light source 150 is split by a splitter 151 and input to nonlinear media 153 and 155. A laser light source with high optical power, such as that in this configuration, generally has a wide linewidth, so attention must be paid to deterioration of signal quality due to the transmission of phase noise to the wavelength-converted light.

[0067] The pumping light branched by the branching unit 151 is converted into a second harmonic by utilizing a second harmonic generation (SHG) process by a nonlinear medium 153. The pumping light branched by the branching unit 151 is converted into a second harmonic by utilizing a second harmonic generation (SHG) process by a nonlinear medium 155. The subsequent processing is the same as the processing described in FIG. 2.

[0068] (Another Configuration Example 2 of First Embodiment) Next, a configuration different from that shown in FIG. 2 will be described in an optical signal processing device assuming wavelength conversion using difference frequency generation, which is a second-order nonlinear optical effect.

[0069] 4 is a detailed configuration diagram (part 3) of an example of an optical signal processing device assuming wavelength conversion using difference frequency generation, which is a second-order nonlinear optical effect. As shown in Fig. 4, the optical signal processing device 1c includes a polarization demultiplexing unit 101, a pump light generating unit 102c, a pump light multiplexing unit 103, a nonlinear medium 104, a pump light demultiplexing unit 105, a pump light multiplexing unit 106, a nonlinear medium 107, a pump light demultiplexing unit 108, a polarization multiplexing unit 109, a wavelength conversion light extraction filter 110, an optical signal processing unit 111, a polarization demultiplexing unit 112, a pump light multiplexing unit 113, a nonlinear medium 114, a pump light demultiplexing unit 115, a pump light multiplexing unit 116, a nonlinear medium 117, a pump light demultiplexing unit 118, a polarization multiplexing unit 119, and a wavelength conversion light extraction filter 120.

[0070] The pump light generating section 102c corresponds to the pump light generating section 11 shown in Figure 1. The polarization demultiplexing section 101, the pump light multiplexing section 103, and the pump light multiplexing section 106 correspond to the first pump light multiplexing section 12 shown in Figure 1. The nonlinear medium 104 and the nonlinear medium 107 correspond to the first wavelength converting section 13 shown in Figure 1. The pump light demultiplexing section 105 and the pump light demultiplexing section 108 correspond to the pump light demultiplexing section 14 shown in Figure 1. The optical signal processing section 111 corresponds to the optical signal processing section 15 shown in Figure 1. The polarization demultiplexing section 112, the pump light multiplexing section 113, and the pump light multiplexing section 116 correspond to the second pump light multiplexing section 16 shown in Figure 1. The nonlinear medium 114 and the nonlinear medium 117 correspond to the second wavelength converting section 17 shown in Figure 1.

[0071] The optical signal processing device 1c differs in configuration from the optical signal processing device 1a in that it includes an excitation light generating unit 102c instead of the excitation light generating unit 102. The following description will focus on the differences from the optical signal processing device 1a.

[0072] The pumping light generating unit 102c includes a pumping light source 150 and a branching unit 151. As such, the pumping light generating unit 102c does not include the optical amplifier 152, the nonlinear medium 153, the optical amplifier 154, or the nonlinear medium 155. That is, in the pumping light generating unit 102c, the pumping light output from the pumping light source 150 is branched by the branching unit 151 and input to the pumping light multiplexing unit 103 and the pumping light multiplexing unit 106, respectively. The pumping light multiplexing unit 103 receives the first optical signal branched by the polarization branching unit 101 and the pumping light output from the pumping light generating unit 102c (the pumping light branched by the branching unit 151). The pumping light multiplexing unit 103 multiplexes the input first optical signal and the pumping light. The pump light multiplexer 106 receives the second optical signal demultiplexed by the polarization demultiplexer 101 and the pump light output from the pump light generator 102c (pump light branched by the brancher 151). The pump light multiplexer 106 multiplexes the input second optical signal and the pump light. This configuration is applicable when high-power laser light in the second harmonic band can be directly prepared as the pump light source 150, and when wavelength conversion is performed using an optical parametric process that uses a third-order nonlinear medium. This configuration makes it possible to realize a simpler configuration that is smaller in size and consumes less power than conventional configurations.

[0073] Second Embodiment In a second embodiment, a configuration including a delay adjustment unit will be described.

[0074] The phase noise of the pump light is transmitted to the wavelength-converted light via the optical parametric process, which can result in a penalty to the signal quality. Therefore, in the past, it was necessary to use a laser light source with a small phase noise and a narrow linewidth as the pump light. On the other hand, in the configuration shown in the first embodiment, the pump light used in the wavelength converter on the input side (e.g., the nonlinear medium 104 and the nonlinear medium 107) is reused in the wavelength converter on the output side (e.g., the nonlinear medium 114 and the nonlinear medium 117). Therefore, the phase noise transmitted to the wavelength-converted light is correlated.

[0075] The correlation of phase noise depends on the optical path length difference between the pump light and the optical signal after they are separated by the pump light demultiplexers 105 and 108 and before they are recombined by the pump light combiners 113 and 116. By adjusting the delay difference so that this optical path length difference becomes zero, the phase noises transmitted to the optical signals in the pump light demultiplexers 105 and 108 and the pump light combiners 113 and 116 are in a phase conjugate relationship, and are added together and canceled out in the pump light combiners 113 and 116. In this way, the phase noise penalty can be reduced in the configuration of the first embodiment, in which the wide-linewidth, high-optical-power laser light source shown in FIGS. 3 and 4 is used as pump light without passing through an optical amplifier. In the second embodiment, a configuration that can achieve this effect will be described.

[0076] 5 is a detailed configuration diagram (part 1) of an example of an optical signal processing device according to the second embodiment. As shown in Fig. 5, the optical signal processing device 1d includes a polarization demultiplexing unit 101, a pump light generating unit 102, a pump light multiplexing unit 103, a nonlinear medium 104, a pump light demultiplexing unit 105, a pump light multiplexing unit 106, a nonlinear medium 107, a pump light demultiplexing unit 108, a polarization multiplexing unit 109, a wavelength conversion light extraction filter 110, an optical signal processing unit 111, a polarization demultiplexing unit 112, a pump light multiplexing unit 113, a nonlinear medium 114, a pump light demultiplexing unit 115, a pump light multiplexing unit 116, a nonlinear medium 117, a pump light demultiplexing unit 118, a polarization multiplexing unit 119, a wavelength conversion light extraction filter 120, a first delay adjustment unit 121, and a second delay adjustment unit 122.

[0077] The optical signal processing device 1d differs in configuration from the optical signal processing device 1a in that it additionally includes a first delay adjustment unit 121 and a second delay adjustment unit 122. The following description will focus on the differences from the optical signal processing device 1a.

[0078] In the optical signal processing device 1d, a delay adjustment unit is arranged in each of the optical transmission line directly connecting the pump light demultiplexing unit 105 and the pump light multiplexing unit 113 and the optical transmission line directly connecting the pump light demultiplexing unit 108 and the pump light multiplexing unit 116.

[0079] The first delay adjustment unit 121 is disposed in an optical transmission path directly connecting the pump light demultiplexing unit 105 and the pump light multiplexing unit 113. That is, the first delay adjustment unit 121 is disposed between the pump light demultiplexing unit 105 and the pump light multiplexing unit 113. The first delay adjustment unit 121 adjusts the optical path length, through which the pump light passes, from the pump light demultiplexing unit 105 to the pump light multiplexing unit 113 so that it matches the optical path length from the pump light demultiplexing unit 105 to the pump light multiplexing unit 113 via the polarization multiplexing unit 109, the wavelength conversion light extraction filter 110, the optical signal processing unit 111, and the polarization demultiplexing unit 112. For example, the first delay adjustment unit 121 performs the adjustment by imparting a significant loss to the light (e.g., the pump light) passing through it.

[0080] The delay amount is controlled by using an optical fiber of an appropriate length so that each communication path has an appropriate optical path length. However, the control method is not limited to this, and the delay amount may be controlled by using, for example, a variable optical fiber stretcher using a piezoelectric element or the like, or a variable delay line using a spatial optical system or the like.

[0081] The delay adjustment is performed by directly measuring the optical path length of each communication path and １ = τ ２ However, the adjustment method is not limited to this, and for example, a method may be used in which the phase noise spectrum of the optical signal wavelength-converted by the second wavelength conversion unit 17 (e.g., the nonlinear medium 114 and the nonlinear medium 117) is measured and the phase noise spectrum is adjusted to match the phase noise spectrum of the optical signal before wavelength conversion (i.e., the optical signal input to the first wavelength conversion unit 13). The phase noise spectrum can be measured by a method using a self-delayed heterodyne interferometer, for example.

[0082] The second delay adjustment unit 122 is disposed in an optical transmission path directly connecting the pump light demultiplexing unit 108 and the pump light multiplexing unit 116. That is, the second delay adjustment unit 122 is disposed between the pump light demultiplexing unit 108 and the pump light multiplexing unit 116. The second delay adjustment unit 122 adjusts the optical path length, through which the pump light passes, from the pump light demultiplexing unit 108 to the pump light multiplexing unit 116 so that it matches the optical path length from the pump light demultiplexing unit 108 to the pump light multiplexing unit 116 via the polarization multiplexing unit 109, the wavelength conversion light extraction filter 110, the optical signal processing unit 111, and the polarization demultiplexing unit 112. For example, the second delay adjustment unit 122 performs the adjustment by imparting a significant loss to the light (e.g., the pump light) passing through it.

[0083] The optical signal processing device 1d configured as described above can achieve the same effects as those of the first embodiment. Furthermore, the optical signal processing device 1d includes delay adjustment units (first delay adjustment unit 121 and second delay adjustment unit 122) that adjust the optical path length between the path through which the pump light propagates and the path through which the optical signal propagates. More specifically, the optical signal processing device 1d includes delay adjustment units (first delay adjustment unit 121 and second delay adjustment unit 122) that adjust the optical path length of the path through which the pump light propagates to match the optical path length of the path through which the optical signal propagates. This allows phase noise derived from the pump light that is transmitted to the wavelength-converted light to be canceled.

[0084] The pump light generating unit 102 of the optical signal processing device 1d shown in Figure 5 may be configured similarly to the pump light generating unit 102b of the optical signal processing device 1b or the pump light generating unit 102c of the optical signal processing device 1c in the first embodiment.

[0085] (Another Configuration Example 1 of the Second Embodiment) When delay adjustment is performed on the path along which the pump light propagates as shown in FIG. 5 , the pump light weakens when used in the nonlinear medium 114 and the nonlinear medium 117 due to optical loss in the delay adjustment units (first delay adjustment unit 121 and second delay adjustment unit 122). The reduction in pump light can induce gain saturation due to pump depletion, resulting in a penalty to the signal. Therefore, the pump light needs to be reused while maintaining as high an optical power as possible. Therefore, FIG. 6 describes a configuration for solving this problem.

[0086] 6 is a detailed configuration diagram (part 2) of an example of an optical signal processing device according to the second embodiment. As shown in Fig. 6, the optical signal processing device 1e includes a polarization demultiplexing unit 101, a pump light generating unit 102, a pump light multiplexing unit 103, a nonlinear medium 104, a pump light demultiplexing unit 105, a pump light multiplexing unit 106, a nonlinear medium 107, a pump light demultiplexing unit 108, a polarization multiplexing unit 109, a wavelength conversion light extraction filter 110, an optical signal processing unit 111, a polarization demultiplexing unit 112, a pump light multiplexing unit 113, a nonlinear medium 114, a pump light demultiplexing unit 115, a pump light multiplexing unit 116, a nonlinear medium 117, a pump light demultiplexing unit 118, a polarization multiplexing unit 119, a wavelength conversion light extraction filter 120, a first delay adjustment unit 121, and a second delay adjustment unit 122.

[0087] The optical signal processing device 1e differs from the optical signal processing device 1d in the locations of the first delay adjustment unit 121 and the second delay adjustment unit 122. Specifically, the optical signal processing device 1e performs delay adjustment not in the path along which the pump light propagates, but in the path along which the optical signal propagates. Therefore, in the optical signal processing device 1e, a delay adjustment unit is provided in each of the optical transmission path connecting the polarization demultiplexing unit 112 and the pump light multiplexing unit 113, and the optical transmission path directly connecting the polarization demultiplexing unit 112 and the pump light multiplexing unit 116.

[0088] In the optical signal processing device 1e configured as described above, the path along which the pump light propagates is configured to be longer than the path along which the optical signal propagates. A method for making the path along which the pump light propagates longer than the path along which the optical signal propagates is to make the length of the optical fiber used in the path along which the pump light propagates longer than the length of the optical fiber used in the path along which the optical signal propagates. As a result, the path directly connecting the pump light demultiplexing unit 105 and the pump light multiplexing unit 113 is longer than the path from the pump light demultiplexing unit 108 via the polarization multiplexing unit 109, the wavelength conversion light extraction filter 110, the optical signal processing unit 111, the polarization demultiplexing unit 112, and the first delay adjustment unit 121 to the pump light multiplexing unit 113. Similarly, the path directly connecting the pump light demultiplexing unit 108 and the pump light multiplexing unit 116 is longer than the path from the pump light demultiplexing unit 108 to the pump light multiplexing unit 116 via the polarization multiplexing unit 109, the wavelength conversion light extraction filter 110, the optical signal processing unit 111, the polarization demultiplexing unit 112, and the second delay adjustment unit 122.

[0089] The first delay adjustment unit 121 is disposed in an optical transmission path connecting the polarization demultiplexing unit 112 and the pump light multiplexing unit 113. That is, the first delay adjustment unit 121 is disposed between the polarization demultiplexing unit 112 and the pump light multiplexing unit 113. The first delay adjustment unit 121 adjusts the optical path length from the pump light demultiplexing unit 105 via the polarization demultiplexing unit 109, the wavelength conversion light extraction filter 110, the optical signal processing unit 111, the polarization demultiplexing unit 112, and the first delay adjustment unit 121 to the pump light multiplexing unit 113 so that it matches the optical path length from the pump light demultiplexing unit 105 to the pump light multiplexing unit 113 through which the pump light passes. For example, the first delay adjustment unit 121 performs the adjustment by imparting a significant loss to the passing light (e.g., an optical signal). Note that the means for controlling the delay amount and adjusting the delay have been described above and will not be described here.

[0090] The second delay adjustment unit 122 is disposed in an optical transmission path connecting the polarization demultiplexing unit 112 and the pump light multiplexing unit 116. That is, the second delay adjustment unit 122 is disposed between the polarization demultiplexing unit 112 and the pump light multiplexing unit 116. The second delay adjustment unit 122 adjusts the optical path length from the pump light demultiplexing unit 108 via the polarization demultiplexing unit 109, the wavelength conversion light extraction filter 110, the optical signal processing unit 111, the polarization demultiplexing unit 112, and the second delay adjustment unit 122 to the pump light multiplexing unit 116 so that it matches the optical path length from the pump light demultiplexing unit 108 to the pump light multiplexing unit 116, through which the pump light passes. For example, the second delay adjustment unit 122 performs the adjustment by imparting a significant loss to the light (e.g., an optical signal) passing through.

[0091] The optical signal processing device 1e configured as described above can achieve the same effects as those of the first embodiment. Furthermore, the optical signal processing device 1e includes delay adjustment units (first delay adjustment unit 121 and second delay adjustment unit 122) that adjust the optical path length between the path through which the pump light propagates and the path through which the optical signal propagates. More specifically, the optical signal processing device 1e includes delay adjustment units (first delay adjustment unit 121 and second delay adjustment unit 122) that adjust the optical path length of the path through which the optical signal propagates so that it matches the optical path length of the path through which the pump light propagates. This allows phase noise derived from the pump light that is transmitted to the wavelength-converted light to be canceled.

[0092] The pump light generating unit 102 of the optical signal processing device 1e shown in FIG. 6 may be configured similarly to the pump light generating unit 102b of the optical signal processing device 1b or the pump light generating unit 102c of the optical signal processing device 1c in the first embodiment.

[0093] (Another Configuration Example 2 of the Second Embodiment) Within the wavelength converter, each polarization component of the optical signal is independently processed by an optical parametric process. Meanwhile, polarization rotation occurs randomly in the wavelength conversion light extraction filter 110 and the optical signal processing unit 111 subsequent to the polarization multiplexing unit 109. Therefore, the polarization components (TM component, TE component) demultiplexed by the polarization demultiplexing unit 112 do not necessarily match the TM component and TE component within the input-side wavelength converter (e.g., the nonlinear medium 104 and the nonlinear medium 107), resulting in an optical field in which both components are mixed at an arbitrary ratio. If there is an optical path length difference between the pump light used for wavelength conversion of each polarization component within the input-side wavelength converter (e.g., the nonlinear medium 104 and the nonlinear medium 107), the output of the input-side wavelength converter (e.g., the nonlinear medium 104 and the nonlinear medium 107) will have phase noise derived from the pump light that depends on the polarization state. Therefore, as described above, it is not possible to cancel the phase noise for all electric field components of the optical signal even if the delay adjustment is performed in either the path along which the pump light propagates or the path along which the optical signal propagates by the first delay adjustment unit 121 and the second delay adjustment unit 122. Therefore, a configuration for solving this problem will be described with reference to FIG.

[0094] 7 is a detailed configuration diagram (part 3) of an example of an optical signal processing device according to the second embodiment. As shown in Fig. 7, the optical signal processing device 1f includes a polarization demultiplexing unit 101, a pump light generating unit 102f, a pump light multiplexing unit 103, a nonlinear medium 104, a pump light demultiplexing unit 105, a pump light multiplexing unit 106, a nonlinear medium 107, a pump light demultiplexing unit 108, a polarization demultiplexing unit 109, a wavelength conversion light extraction filter 110, an optical signal processing unit 111, a polarization demultiplexing unit 112, a pump light multiplexing unit 113, a nonlinear medium 114, a pump light demultiplexing unit 115, a pump light multiplexing unit 116, a nonlinear medium 117, a pump light demultiplexing unit 118, a polarization demultiplexing unit 119, a wavelength conversion light extraction filter 120, a first delay adjustment unit 121, and a second delay adjustment unit 122.

[0095] Note that Figure 7 shows an example of application to a configuration in which delay adjustment is performed in an optical transmission path through which excitation light propagates, such as the optical signal processing device 1d shown in Figure 5, but the configuration shown in Figure 7 can also be applied to a configuration in which delay adjustment is performed in an optical transmission path through which an optical signal propagates, such as the optical signal processing device 1e shown in Figure 6.

[0096] The pump light generating section 102f corresponds to the pump light generating section 11 shown in Figure 1. The polarization demultiplexing section 101, the pump light multiplexing section 103, and the pump light multiplexing section 106 correspond to the first pump light multiplexing section 12 shown in Figure 1. The nonlinear medium 104 and the nonlinear medium 107 correspond to the first wavelength converting section 13 shown in Figure 1. The pump light demultiplexing section 105 and the pump light demultiplexing section 108 correspond to the pump light demultiplexing section 14 shown in Figure 1. The optical signal processing section 111 corresponds to the optical signal processing section 15 shown in Figure 1. The polarization demultiplexing section 112, the pump light multiplexing section 113, and the pump light multiplexing section 116 correspond to the second pump light multiplexing section 16 shown in Figure 1. The nonlinear medium 114 and the nonlinear medium 117 correspond to the second wavelength converting section 17 shown in Figure 1.

[0097] The optical signal processing device 1f differs in configuration from the optical signal processing device 1e in that it includes a pumping light generating unit 102f instead of the pumping light generating unit 102. The following description will focus on the differences from the optical signal processing device 1e. The pumping light generating unit 102f includes a pumping light source 150, a branching unit 151, an optical amplifier 152, a nonlinear medium 153, an optical amplifier 154, a nonlinear medium 155, and a third delay adjustment unit 124.

[0098] In the optical signal processing device 1 f , a third delay adjustment unit 124 is disposed in the optical transmission line connecting the branching unit 151 and the optical amplifier 154 .

[0099] The third delay adjusting section 124 adjusts the optical path length from the branching section 151 to the pumping light multiplexing section 106 so that it matches the optical path length from the branching section 151 to the pumping light multiplexing section 103 .

[0100] In this way, in the optical signal processing device 1f, the third delay adjustment unit 124 adjusts the optical path length from the branching unit 151 to the pump light multiplexing unit 103 in the pump light generating unit 102f so that it is equal to the optical path length from the branching unit 151 to the pump light multiplexing unit 106. As a result, the input-side wavelength converter (nonlinear medium 104 and nonlinear medium 107) generates wavelength-converted light having phase noise derived from the pump light that is independent of the polarization state. In this way, even if polarization rotation occurs between the input-side wavelength converter (nonlinear medium 104 and nonlinear medium 107) and the output-side wavelength converter (nonlinear medium 114 and nonlinear medium 117), the first delay adjustment unit 121 and the third delay adjustment unit 124 can perform delay adjustment that cancels out the phase noise for all optical field components.

[0101] Third Embodiment In a third embodiment, a system configuration including the optical signal processing device shown in the first or second embodiment will be described.

[0102] 8 is a diagram showing an example of the configuration of an optical transmission system S according to the third embodiment. The optical transmission system S includes an optical signal transmitting device 200, an optical transmission path 250, an optical node unit 300, and an optical signal receiving device 400. The optical transmission system S is a system that performs multiband transmission. M (M is an integer equal to or greater than 1) combinations of the optical transmission path 250 and the optical node unit 300 are arranged between the optical signal transmitting device 200 and the optical signal receiving device 400.

[0103] The optical signal transmission device 200 transmits optical signals in various wavelength bands (for example, wavelength multiplexed signals). The optical transmission path 250 connects the optical signal transmission device 200 and the optical node unit 300. The optical signal transmitted from the optical signal transmission device 200 is input to the optical node unit 300 via the optical transmission path 250.

[0104] The optical node unit 300 performs optical signal processing on the input optical signal. Wavelength-multiplexed signals of various communication wavelength bands pass through the optical node unit 300 in multiband transmission. Therefore, the optical node unit 300 needs to be equipped with optical signal processing devices 1 corresponding to the number of communication wavelength bands to be used.

[0105] The optical node unit 300 includes a wavelength multiplexing / demultiplexing unit 310, multiple optical signal processing devices 1a, an optical signal processing unit 320, and a wavelength multiplexing / demultiplexing unit 330. Although Fig. 8 shows a configuration in which three communication wavelength bands are used as the optical node unit 300, it is sufficient that the optical node unit 300 processes multiple communication wavelength bands. Furthermore, although Fig. 8 shows the optical signal processing device 1a as an example, the optical node unit 300 may include any of the other optical signal processing devices 1b, 1c, 1d, 1e, and 1f described above.

[0106] The wavelength multiplexing / demultiplexing unit 310 demultiplexes the wavelength-multiplexed signal transmitted from the optical signal transmission device 200 into signals of each wavelength. The wavelength multiplexing / demultiplexing unit 310 is connected to the optical signal processing device 1a or the optical signal processing unit 320 according to the communication wavelength band to be processed.

[0107] The optical signal processing unit 320 processes optical signals in a conventional communication wavelength band (for example, C-band) that does not require wavelength conversion.

[0108] The optical signal processing device 1a processes optical signals in a communication wavelength band that require wavelength conversion.

[0109] The wavelength multiplexer / demultiplexer 330 multiplexes the optical signals output from the optical signal processor 320 and the optical signal processing device 1a.

[0110] The optical signal receiving device 400 receives the optical signal multiplexed by the wavelength multiplexing / demultiplexing section 330 .

[0111] In addition, when channels are routed using a wavelength selective switch or the like in the optical signal processing device 1a or the optical signal processing unit 320, it is possible to move channels between bands by inserting them into an optical signal processing unit that processes different band components (see, for example, non-patent document 2).

[0112] (Fourth Embodiment) When the phase noise cancellation by the configuration of the first embodiment is not performed, or when routing to a different band as in the third embodiment is performed, and the phase noise of the pump light is transmitted to the output optical signal, degradation of signal quality occurs. Therefore, when designing an optical transmission system, it is necessary to take such degradation of signal quality into consideration and ensure a margin of the signal-to-noise ratio (SNR) or select the linewidth of the pump light.

[0113] The impact of pump light phase noise on signal quality can be thought of as two types of distortion: phase distortion and distortion called equalization-enhanced phase noise (EEPN). Equalization-enhanced phase noise is the effect of phase noise being converted into timing jitter by applying chromatic dispersion compensation to the received signal in digital signal processing. Phase distortion can be effectively compensated for in the carrier phase recovery block in the digital signal processing of a digital coherent receiver.

[0114] On the other hand, it is not easy to compensate for the effect of timing jitter due to equalization emphasis phase noise using digital signal processing. The effect of phase noise from the receiver local oscillator in a digital coherent receiver on signal quality as equalization emphasis phase noise is well known, and can be regarded as additive-white Gaussian noise (AWGN) expressed by the variance shown in the following equation (1) (see, for example, Non-Patent Document 3).

[0115]

[0116] In equation (1), c represents the speed of light, and D ｔｏｔａｌ represents the total amount of chromatic dispersion added to the received optical signal in the transmission path, B represents the symbol rate of the received signal, and f ｒ represents the frequency of the received signal, and Δν ＬＯ represents the linewidth of the local oscillator.

[0117] 9 is a diagram showing an example of the configuration of an optical transmission system Sa according to the fourth embodiment. The optical transmission system Sa is a transmission system that transmits optical signals by amplification and repeating of M spans using the optical signal processing device 1a shown in the first embodiment. When the above formula (1) is applied to the phase noise transmitted by the wavelength converter in this system, the following formula (2) can be derived as the sum of additive Gaussian noise generated by the influence of equalization-emphasized phase noise from the phase noise added by each optical signal processing device 1a.

[0118]

[0119] In formula (2), Dｍ represents the amount of chromatic dispersion of the optical signal at the time of input to the m-th (m is an integer equal to or greater than 1) optical signal processing device 1a, and Δν ｐ represents the linewidth of the pump light. The reason why the coefficients are different between equations (1) and (2) is that when a second-order nonlinear process is used, second harmonic generation (SHG) occurs, and when a third-order nonlinear process is used, the phase noise of the pump light component transmitted to the wavelength-converted light is effectively doubled due to the degenerate four-wave mixing process of the pump light. Therefore, when designing a transmission system, a margin secured as a penalty for the phase noise transmitted from the pump light in the wavelength conversion unit is set as σ ２ ａｄｄ In this case, the line width of the excitation light is Δν ｐ It turns out that it needs to be.

[0120]

[0121] According to the optical transmission system Sa of the fourth embodiment configured as described above, by selecting a laser light source with a narrow linewidth that satisfies the above formula (3), it is possible to reduce the phase noise transmitted from the excitation light and obtain a high-quality received signal.

[0122] A part of the configuration of the optical signal processing devices 1, 1a, 1b, 1c, 1d, 1e, and 1f in the above-described embodiments may be realized by a computer. In this case, a program for realizing this function may be recorded on a computer-readable recording medium, and the program recorded on the recording medium may be read into and executed by a computer system. Note that the term "computer system" here includes hardware such as an OS (Operating System) and peripheral devices.

[0123] Furthermore, "computer-readable recording media" refers to portable media such as flexible disks, optical magnetic disks, ROMs (Read Only Memory), and CD-ROMs, as well as storage devices such as hard disks built into computer systems. Furthermore, "computer-readable recording media" may also include devices that dynamically store programs for a short period of time, such as communication lines used when transmitting programs over networks like the Internet or communication lines like telephone lines, or devices that store programs for a fixed period of time, such as volatile memory within the computer systems that serve as servers or clients. Furthermore, the programs may be designed to realize some of the aforementioned functions, or may be capable of realizing the aforementioned functions in combination with programs already stored in the computer system, or may be realized using programmable logic devices such as FPGAs (Field Programmable Gate Arrays).

[0124] Although an embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention.

[0125] The present invention can be applied to an optical signal processing device that performs wavelength conversion by utilizing a nonlinear optical effect.

[0126] DESCRIPTION OF SYMBOLS 1, 1a, 1b, 1c, 1d, 1e, 1f... Optical signal processing device, 101, 112... Polarization demultiplexing unit, 102, 102b, 102c, 102f... Pump light generation unit, 103, 106, 113, 116... Pump light multiplexing unit, 104, 107, 114, 117, 153, 155... Nonlinear medium, 105, 108, 115, 118... Pump light demultiplexing unit, 109, 119... Polarization multiplexing unit, 110, 120... Wavelength conversion light extraction filter, 111... Optical signal processing unit, 121... First delay adjustment unit, 122... Second delay adjustment unit, 124... Third delay adjustment unit, 150... Pump light source, 151... Branching unit, 152, 154... Optical amplifier 200...optical signal transmitting device, 250...optical transmission line, 300...optical node unit, 310, 330...wavelength multiplexing / demultiplexing unit, 320...optical signal processing unit, 400...optical signal receiving device

Claims

1. An optical signal processing device comprising: a pumping light generation unit that generates pumping light to be used for wavelength conversion; a first pumping light multiplexing unit that multiplexes the pumping light generated by the pumping light generation unit with an optical signal of a first wavelength; a first wavelength conversion unit that converts the optical signal of the first wavelength into an optical signal of a second wavelength by a nonlinear optical effect based on the optical signal of the first wavelength and the pumping light multiplexed by the first pumping light multiplexing unit; a pumping light demultiplexing unit that demultiplexes the optical signal of the second wavelength from the pumping light; an optical signal processing unit that performs optical signal processing on the optical signal of the second wavelength; a second pumping light multiplexing unit that multiplexes the pumping light demultiplexed by the pumping light demultiplexing unit with the optical signal of the second wavelength that has been subjected to optical signal processing by the optical signal processing unit; and a second wavelength conversion unit that converts the optical signal of the second wavelength into an optical signal of the first wavelength by a nonlinear optical effect based on the optical signal of the second wavelength and the pumping light multiplexed by the second pumping light multiplexing unit.

2. The optical signal processing device according to claim 1, further comprising a delay adjustment unit that adjusts the delay so that the optical path length of the pumping light demultiplexed by the pumping light demultiplexing unit until it is multiplexed in the second pumping light multiplexing unit matches the optical path length of the optical signal of the second wavelength demultiplexed by the pumping light demultiplexing unit until it is multiplexed in the second pumping light multiplexing unit, or adjusts the delay so that the optical path length of the optical signal of the second wavelength demultiplexed by the pumping light demultiplexing unit until it is multiplexed in the second pumping light multiplexing unit matches the optical path length of the pumping light demultiplexed by the pumping light demultiplexing unit until it is multiplexed in the second pumping light multiplexing unit.

3. The optical signal processing device according to claim 2, wherein the pumping light generating unit further comprises: a branching unit that branches the pumping light output from a single light source; and an internal delay adjusting unit that adjusts the delay so that the optical path length of a first path connecting the branching unit and the first pumping light multiplexing unit is equal to the optical path length of a second path connecting the branching unit and the first pumping light multiplexing unit.

4. An optical signal processing device according to any one of claims 1 to 3, wherein the pumping light generating unit outputs first pumping light and second pumping light generated in response to branching pumping light output from a single light source to the first pumping light multiplexing unit, and the first pumping light multiplexing unit demultiplexes the optical signal of the first wavelength into a first optical signal and a second optical signal having different polarization states, multiplexes the first optical signal with the first pumping light, and multiplexes the second optical signal with the second pumping light.

5. The optical signal processing device according to claim 4, wherein the pump light generating unit generates the first pump light and the second pump light by converting the branched pump light into second harmonics using a second harmonic generation process by a nonlinear medium.

6. An optical signal processing device according to claim 5, wherein the pumping light generating unit generates the first pumping light and the second pumping light by amplifying the branched pumping light with an optical amplifier and then converting it into a second harmonic by utilizing a second harmonic generation process caused by the nonlinear medium.

7. An optical transmission system comprising: an optical signal transmitting device that transmits optical signals; m (m is an integer of 1 or greater) optical node units that perform optical signal processing on the optical signals transmitted from said optical signal transmitting device; and an optical signal receiving device that receives the optical signals that have been optically processed by said m optical node units, wherein said m optical node units comprise one or more optical signal processing devices according to claim 1.

8. The optical transmission system according to claim 7, wherein the Lorentz linewidth of the pump light used for wavelength conversion by the one or more optical signal processing devices is a value that satisfies a condition expressed using pi, the speed of light, the accumulated chromatic dispersion up to the mth optical node unit, the symbol rate, and the frequency of the received signal, relative to the allowable amount of additional noise power value generated in addition to noise derived from spontaneous emission light out of the total noise power generated in the m optical node units.

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