Optical transmission system, phase conjugate converter and phase sensitive amplifier

Abstract

This optical transmission system comprises: a phase conjugate conversion device (200) that performs optical parametric amplification in a first optical parametric amplification unit (238) and in a second optical parametric amplification unit (244), monitors electric power of a first polarized component and a second polarized component of first pilot light, controls the phase of higher harmonic wave excitation light by means of phase shifters (218, 224) so as to maximize the optical power of first pilot light to thereby synchronize the phase of the higher harmonic wave and the first pilot light, and controls a phase shifter (264) disposed in at least one path so as to maximize interference waveforms of respective components of second pilot light, which is different from the first pilot light in terms of the wavelength or the optical power and which has passed through from a pilot light source (270) in a reverse direction, to thereby match the optical length of the path of the first optical parametric amplification unit (238) and the path of the second optical parametric amplification unit (244); and a phase sensitive amplification device (400) for performing phase sensitive amplification on idler light and on an optical signal included in an optical transmission signal through optical parametric amplification using the excitation light controlled by using the first pilot light included in the optical transmission signal.

Description

[Technical Field]

[0001] The present invention relates to an optical transmission system, a phase conjugate converter, and a phase sensitive amplifier. [Background technology]

[0002] With the recent launch of fifth-generation mobile communication systems and the spread of rich content such as high-resolution video, communication traffic has been increasing exponentially, requiring continuous increases in the capacity of optical fiber networks. In optical fiber communications, optical amplifiers are used to amplify optical signals that have been attenuated by fiber transmission, while retaining their optical power, in order to relay signals and improve receiving sensitivity.

[0003] Conventional optical amplifiers, such as erbium-doped fiber amplifiers (EDFAs), which use erbium-doped optical fiber as the amplification medium, are classified as phase-insensitive amplifiers (PIAs). Phase-insensitive amplifiers are known to suffer from excessive degradation of the signal-to-noise ratio, equivalent to a noise figure of 3 dB or more, due to the inclusion of noise from amplified spontaneous emission (ASE).

[0004] Among the various noise factors in optical fiber transmission, ASE noise degrades the optical signal-to-noise ratio (OSNR), limiting transmission capacity and distance. This is one of the essential factors. To ensure a high OSNR, the transmission power of the optical signal must be strong relative to the noise. However, as the energy density in the optical fiber increases, waveform distortion due to nonlinear optical effects in the optical fiber becomes apparent, which in turn causes degradation of signal quality. Therefore, reducing ASE noise and compensating for nonlinear distortion in optical amplifiers is important for further increasing the distance and capacity of optical fiber transmission.

[0005] As a means to overcome the theoretical noise limit of conventional phase-insensitive amplifiers, phase-sensitive amplifiers (PSAs) using optical parametric amplification (OPAs) are being investigated. It is a nonlinear optical process that amplifies an optical signal by inputting an optical signal with an appropriate wavelength relationship and high-power pump light into a medium with linear characteristics.

[0006] There are two types of nonlinear media: those that utilize second-order nonlinearity and those that utilize third-order nonlinearity, with lithium niobate and dispersion-shifted optical fiber being representative examples. Signal amplification by optical parametric amplification generates idler light, which is the phase conjugate light of the optical signal. By utilizing this idler light, optical parametric amplification can perform a variety of optical signal processing, one of which is phase-sensitive amplification.

[0007] In a phase-sensitive amplifier, one of the orthogonal phase components of the ASE is suppressed by superimposing the generated phase conjugate light and the original input optical signal within the same band. This achieves ultra-low noise amplification below the theoretical noise limit of conventional phase-insensitive amplifiers. In addition, it also has the effect of compensating for phase distortion caused by nonlinear optical effects, etc.

[0008] One configuration of a phase-sensitive amplifier is the degenerate PSA, which places the optical signal to be amplified at a degenerate frequency that is the center of the amplification band of the optical parametric amplifier. In a degenerate PSA, the interaction between the optical signal and pump light in the nonlinear medium generates idler light at the same degenerate frequency as the optical signal, and the superposition of these generates a phase-sensitive band effect. The generated idler light has a phase derived from the relative phase difference between the optical signal and pump light, and when the optical signal and idler light are orthogonal to each other, one of the phase components is suppressed, achieving low-noise amplification. Therefore, a phase-locked loop (PLL: Phase-Locking Loop) is required to appropriately control the phase of the optical signal and pump light. become.

[0009] However, in the degenerate PSA, when amplifying wavelength division multiplexing (WDM) signals, multiple devices must be used to amplify them in parallel, and when amplifying signals such as QAM (Quadrature Amplitude Modulation) signals, the real and imaginary axes on the complex plane must be separated. The inability to amplify signals with signal distributions on both sides is a problem. Therefore, in order to phase-sensitively amplify WDM signals and QAM signals, research and development is being conducted on non-degenerate PSA (ND-PSA), which allocates signals to frequencies shifted from the degenerate frequencies of the phase-sensitive amplifier (see, for example, Non-Patent Document 1).

[0010] In non-degenerate PSA, the optical signal and idler light are generated in advance on the transmitting side at frequencies symmetrical to the degenerate frequency, and are co-propagated through the transmission path. In the optical parametric amplification process in a nonlinear medium, phase-sensitive amplification is achieved through the interaction between three light waves, each with a different frequency: the optical signal, the idler light, and the pump light. When the three light waves are in the appropriate frequency arrangement, phase-conjugated light of the idler light is generated at the same frequency as the optical signal during the optical parametric amplification process. The phase-conjugated light of the optical signal is generated at the frequency of the idler light.

[0011] At this time, when the optical signal and the converted idler light are superimposed in phase, constructive interference generates a gain difference with the ASE noise component, resulting in low-noise amplification. In order for the optical signal and idler light to be superimposed in phase, the pump light must be synchronized with the average frequency and average phase (carrier component) between the optical signal and the idler light. By generating and transmitting idler light in the same amount as the wavelength-multiplexed optical signal, the non-degenerate PSA can perform batch phase-sensitive amplification of WDM signals.

[0012] Focusing only on the bandwidth of the optical signal, the phase-conjugated light of the input idler light, i.e., light with the same complex amplitude distribution as the original optical signal, is superimposed in phase, so the phase information is maintained even after amplification, making it possible to amplify any form of modulated signal. Idler light generated in advance on the transmitting side is generally generated optically by modulating the optical signal as in normal optical transmission, and then optically generating it using optical parametric amplification with only the optical signal as input. A device that generates idler light, which is the phase conjugate light of an optical signal using such optical parametric amplification, is called an optical phase conjugator (OPC). [Prior art documents] [Non-patent literature]

[0013] [Non-Patent Document 1] Z. Tong, C. Lundstrom, PA Andrekson, CJ McKinstrie, DJ Blessing, E. Tipsuwannakul, BJ Puttnam, H. Toda, and L. Gruner-Nielsen, “Towards ultrasensitive optical links enabled by low-noise phase-sensitive amplifiers”, Nat. Photonics, vol. 5, no. 7, pp. 430-436, July 2011. [Patent documents]

[0014] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-218173 [Patent Document 2] Japanese Patent Application Publication No. 2018-205595 Summary of the Invention [Problem to be solved by the invention]

[0015] Optical parametric amplification, a nonlinear optical effect, generally has polarization dependence. Therefore, when amplifying a polarization-division multiplexed (PDM) signal, In this case, a polarization diversity configuration is used that handles orthogonal polarization components independently (see, for example, Patent Document 1). This applies not only to phase-sensitive amplifiers but also to optical phase conjugate converters that generate idler light.

[0016] In a polarization diversity configuration, a polarization beam splitter is used to split the input light into two orthogonal polarization components, and each component is amplified by optical parametric amplification and then combined again by a polarization beam combiner. Here, to perform phase-sensitive amplification, the relative phases between the optical signal, idler light, and pump light must be properly synchronized for each polarization component so that the optical signal and the converted idler light undergo constructive interference.

[0017] Because random polarization rotation occurs within the optical fiber, which serves as the transmission path, the polarization state input to the phase-sensitive amplifier is random. The components (X-polarized and Y-polarized components) split by the polarization beam splitter in the phase-sensitive amplifier do not necessarily match the X-polarized and Y-polarized components in the optical phase conjugate converter, but are mixed together. In an optical phase conjugate converter using a conventional polarization diversity OPA, the X-polarized and Y-polarized components generate idler lights using different pump lights. There is uncorrelated phase rotation between these pump lights due to factors such as phase drift in the optical fiber, and the signal-idler pair after polarization combining has carrier components that are uncorrelated between the orthogonal polarizations.

[0018] If there are signal-idler pairs with multiple carrier components among the X-polarized and Y-polarized components split by the phase-sensitive amplifier, the frequency and phase to which the pump light should be synchronized cannot be uniquely determined, making it impossible to perform optimal phase-sensitive amplification for all input optical field components in any input polarization state. Therefore, to achieve polarization-independent operation of a phase-sensitive amplifier, the signal-idler pairs to be amplified must have the same carrier component for all polarization components. However, due to the effects of the phase drift mentioned above, this is difficult to achieve with a typical polarization diversity configuration.

[0019] To solve this problem, an optical transmitter configuration has been proposed that uses multiple phase-locked loops to generate a signal-idler pair with a polarization-independent carrier component (see, for example, Patent Document 2). In the configuration described in Patent Document 2, continuous light split from a pump light source is used as pilot light and multiplexed with continuous light before modulating the optical signal. The pilot light is optically modulated in the same way as the optical signal, and then passes through a nonlinear medium to generate idler light. At this time, idler light is generated by optical parametric amplification, and the pilot light, which is located at a degenerate wavelength, is overlapped with its own idler light and is thus degenerately phase-sensitively amplified.

[0020] The condition under which the degenerate phase-sensitive amplification of the pilot light achieves maximum amplification gain is when the phase of the pump light and the phase of the pilot light are identical. Therefore, by synchronizing the phase of the pump light using a phase-locked loop so that the power of the amplified pilot light is maximized, the relative phase between the pump light and the optical signal can be fixed. Therefore, the phase of the idler light generated by the interaction between the pump light and the optical signal is also fixed. By performing the above-mentioned processing on each of the orthogonal polarization components and combining them using a polarization beam combiner, a polarization division multiplexed signal-idler pair is obtained. At this time, because each polarization component travels a separate path, phase drift causes random phase differences between the orthogonal polarizations.

[0021] To make this phase difference zero, the degenerate phase-sensitively amplified pilot light is separated, the 45-degree linearly polarized component is extracted, and the power is monitored to obtain the interference pattern between the components that have passed through each path. To ensure that this interference pattern is always maximized, a separate phase-locked loop is controlled to synchronize the optical lengths of each path within the polarization diversity OPA, achieving phase-aligned multiplexing. Through the above process, a polarization division multiplexed signal-idler pair is generated, which has a polarization-independent carrier component.

[0022] However, this configuration has the problem of interference between the operation of each PLL because three PLLs are operated with one pilot light. For example, the PLL that synchronizes the phase between polarizations operates on the assumption that the PLL in the degenerate phase-sensitive amplifier section is operating. Therefore, it is directly affected by fluctuations in the PLL in the degenerate phase-sensitive amplifier section, and once control fails, it can become difficult to restore normal operation. Because pilot lights of the same wavelength are used, components of the pilot light that are multiplexed within the system can flow into the monitor section of each PLL, causing instability in operation.

[0023] In view of the above circumstances, an object of the present invention is to provide a technique that can realize stable polarization independence in an optical transmission system using phase sensitive amplification. [Means for solving the problem]

[0024] One aspect of the present invention is a laser diode including: a first branching unit that branches excitation light; and a laser diode for receiving the excitation light branched by the first branching unit. On the other hand a multiplexing section that multiplexes a first pilot light propagating in a first direction based on the first pilot light and an optical signal transmitted from an optical transmitter; and a multiplexing section that multiplexes the pumping light branched by the first branching section. On the other hand a second branching section for branching the pumping light; and a plurality of phase-controlling sections for controlling the phases of the branched pumping light. phase shift a part; and phase shifta splitter that splits the first pilot light and the optical signal combined by the combiner into two orthogonal polarization components; a first optical parametric amplifier that performs optical parametric amplification based on the first polarization component of the first pilot light and the first polarization component of the optical signal split by the splitter and the harmonics converted by the plurality of harmonic generators; a second optical parametric amplifier that performs optical parametric amplification based on the second polarization component of the first pilot light and the second polarization component of the optical signal split by the splitter and the harmonics converted by the plurality of harmonic generators; and a multiplexer that combines the first polarization component of the first pilot light and the first polarization component of the optical signal amplified by the first optical parametric amplifier and the second polarization component of the first pilot light amplified by the second optical parametric amplifier and the second polarization component of the optical signal to generate an optical transmission signal. a combiner for combining the first and second pilot lights, a first monitor for monitoring the power of a first polarization component of the first pilot light amplified by the first optical parametric amplifier, a second monitor for monitoring the power of a second polarization component of the first pilot light amplified by the second optical parametric amplifier, a first controller for controlling the phase of pump light input to the plurality of harmonic generators so that the optical power of the first pilot light amplified by the first and second optical parametric amplifiers is maximized, based on the monitoring results of the first monitor and the second monitor, thereby synchronizing the phase of the harmonics and the first pilot light, a second pilot light source for outputting second pilot light having at least a wavelength or optical power different from that of the first pilot light, and a circulator for propagating the second pilot light output from the second pilot light source in a second direction opposite to the first direction, and outputting the optical transmission signal output from the combiner to the outside. propagating in the second direction, and The second pilot light is arranged in at least one of the paths so that the interference waveform of each component of the second pilot light that has passed through it is maximized. Phase shiftera second control unit that controls the optical lengths of the paths of the first optical parametric amplifier unit and the second optical parametric amplifier unit to match each other; and an optical transmission unit that transmits the optical transmission signal output from the phase conjugation device; A phase sensitive amplifier to which the optical transmission signal transmitted through the optical transmission section is input, by optical parametric amplification using pump light controlled by using first pilot light included in the optical transmission signal, entered The optical transmission system includes a phase sensitive amplifier that performs phase sensitive amplification of the optical signal and idler light included in the optical transmission signal.

[0025] One aspect of the present invention is a laser diode including: a first branching unit that branches excitation light; and a laser diode for receiving the excitation light branched by the first branching unit. On the other hand a multiplexing section that multiplexes a first pilot light propagating in a first direction based on the first pilot light and an optical signal transmitted from an optical transmitter; and a multiplexing section that multiplexes the pumping light branched by the first branching section. On the other hand a second branching section for branching the pumping light; and a plurality of phase-controlling sections for controlling the phases of the branched pumping light. phase shift a part; and phase shifta splitter that splits the first pilot light and the optical signal combined by the combiner into two orthogonal polarization components; a first optical parametric amplifier that performs optical parametric amplification based on the first polarization component of the first pilot light and the first polarization component of the optical signal split by the splitter and the harmonics converted by the plurality of harmonic generators; a second optical parametric amplifier that performs optical parametric amplification based on the second polarization component of the first pilot light and the second polarization component of the optical signal split by the splitter and the harmonics converted by the plurality of harmonic generators; and a multiplexer that combines the first polarization component of the first pilot light and the first polarization component of the optical signal amplified by the first optical parametric amplifier and the second polarization component of the first pilot light amplified by the second optical parametric amplifier and the second polarization component of the optical signal to generate an optical transmission signal. a combiner for combining the first and second pilot lights, a first monitor for monitoring the power of a first polarization component of the first pilot light amplified by the first optical parametric amplifier, a second monitor for monitoring the power of a second polarization component of the first pilot light amplified by the second optical parametric amplifier, a first controller for controlling the phase of pump light input to the plurality of harmonic generators so that the optical power of the first pilot light amplified by the first and second optical parametric amplifiers is maximized, based on the monitoring results of the first monitor and the second monitor, thereby synchronizing the phase of the harmonics and the first pilot light, a second pilot light source for outputting second pilot light having at least a wavelength or optical power different from that of the first pilot light, and a circulator for propagating the second pilot light output from the second pilot light source in a second direction opposite to the first direction, and outputting the optical transmission signal output from the combiner to the outside. propagated in the second direction; the first optical parametric amplifier section and the second optical parametric amplifier section, Through The second pilot light is arranged in at least one of the paths so that the interference waveform of each component of the second pilot light passing through the second pilot light is maximized. Phase shifterand a second control unit that controls the first optical parametric amplifier unit and the second optical parametric amplifier unit to match the optical lengths of the paths of the first optical parametric amplifier unit and the second optical parametric amplifier unit.

[0026] One aspect of the present invention is a pumping light source that outputs pumping light for optical parametric amplification by performing optical injection locking on a pumping light source using first pilot light included in an optical transmission signal transmitted from a phase conjugate conversion device that performs optical parametric amplification; a third branching unit that branches the pumping light output from the pumping light source; and a plurality of branching units that phase-control the branched pumping light. phase shift a part; and phase shifta plurality of harmonic generation units for converting the pump light phase-controlled by each of the harmonic generation units into harmonics; a division unit for dividing an optical signal included in the optical transmission signal into two orthogonal polarization components; a third optical parametric amplification unit for performing optical parametric amplification based on a first polarization component of the optical signal divided by the division unit and the harmonics converted by the plurality of harmonic generation units; a fourth optical parametric amplification unit for performing optical parametric amplification based on a second polarization component of the optical signal divided by the division unit and the harmonics converted by the plurality of harmonic generation units; a combination unit for combining the first polarization component of the optical signal amplified by the third optical parametric amplification unit and the second polarization component of the optical signal amplified by the fourth optical parametric amplification unit; a third monitor unit that monitors the power of a first polarization component of the optical signal amplified by the fourth optical parametric amplifier unit; a fourth monitor unit that monitors the power of a second polarization component of the optical signal amplified by the fourth optical parametric amplifier unit; a third control unit that synchronizes the phases of the harmonics and the optical signal by controlling the phase of pump light input to the plurality of harmonic generators based on the monitoring results of the third monitor unit and the fourth monitor unit so that the optical powers of the optical signals amplified by the third optical parametric amplifier unit and the fourth optical parametric amplifier unit are maximized, respectively; a third pilot light source that outputs third pilot light having a wavelength or optical power different from at least the first pilot light; and a circulator that propagates the third pilot light output from the third pilot light source in a second direction that is opposite to the first direction. propagated in the second direction; the third optical parametric amplifier section and the fourth optical parametric amplifier section, Through The third pilot light is arranged in at least one of the paths so that the interference waveform of each component of the third pilot light passing through the path is maximized. Phase shifter and a fourth control unit that controls the third optical parametric amplifier unit and the fourth optical parametric amplifier unit to match the optical lengths of the paths of the third optical parametric amplifier unit and the fourth optical parametric amplifier unit. [Effects of the Invention]

[0027] According to the present invention, it is possible to realize stable polarization independence in an optical transmission system using phase sensitive amplification. [Brief explanation of the drawings]

[0028] [Figure 1] 1 is a diagram illustrating an example of the configuration of an optical transmission system according to a first embodiment. [Figure 2] 1 is a diagram showing a specific configuration of a phase conjugate converter and a phase sensitive amplifier according to a first embodiment. [Figure 3] FIG. 10 is a diagram illustrating an example of the configuration of an optical transmission system according to a second embodiment. [Figure 4] FIG. 10 is a diagram showing a specific configuration of a phase conjugate converter and a phase sensitive amplifier according to the second embodiment. [Figure 5] FIG. 10 is a diagram showing a specific configuration of a phase conjugate converter and a phase sensitive amplifier according to a modification of the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0029] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. (First embodiment) 1 is a diagram showing an example of the configuration of an optical transmission system 10 according to the first embodiment. The optical transmission system 10 includes an optical transmitter 100, a phase conjugation device 200, a transmission line 300, a phase sensitive amplifier 400, and an optical receiver 500. The optical transmission system 10 is assumed to employ repeaterless transmission using a phase sensitive amplifier as a preamplifier. Here, repeaterless transmission refers to a transmission method that does not use optical repeaters.

[0030] The optical transmitter 100 transmits an optical signal. The optical signal transmitted by the optical transmitter 100 may be a polarization division multiplexed signal.

[0031] The phase conjugate converter 200 receives the optical signal transmitted from the optical transmitter 100 as input and performs optical parametric amplification based on the input optical signal. The optical parametric amplification generates idler light, which is the phase conjugate light of the optical signal. The phase conjugate converter 200 outputs an optical transmission signal to the transmission path 300, which includes the optical signal, the idler light, and pilot light used for optical injection locking in the phase sensitive amplifier 400.

[0032] The transmission line 300 connects the optical phase conjugator 200 and the phase sensitive amplifier 400. The transmission line 300 is, for example, an optical fiber or free space. The optical transmission signal output from the optical phase conjugator 200 is transmitted through the transmission line 300.

[0033] The phase sensitive amplifier 400 receives an optical transmission signal transmitted via the transmission line 300 as an input, and performs phase sensitive amplification based on the input optical transmission signal.

[0034] The optical receiver 500 receives the optical transmission signal amplified by the phase sensitive amplifier 400 .

[0035] 2 is a diagram showing a specific configuration of a phase conjugate converter 200 and a phase sensitive amplifier 400 according to the first embodiment. In the following description, a configuration example of the phase conjugate converter 200 and the phase sensitive amplifier 400 in the case where a second-order nonlinear medium is used as the optical parametric amplification medium will be shown.

[0036] (Configuration of optical phase conjugator 200) The optical phase conjugator 200 includes a WDM coupler 202, an excitation light source 204, multiplexers / branchers 206, 216, 252, and 258, a variable optical attenuator (VOA) 208, polarization controllers (PCs) 210, 230, and 268, circulators 212 and 266, a first phase modulator 214, and phase shift250, a second phase modulator 256, a PBC 262, and a pilot light source 270.

[0037] The WDM coupler 202 multiplexes or demultiplexes the input optical signals. For example, the WDM coupler 202 receives a first pilot light and an optical signal transmitted from the optical transmitter 100. The WDM coupler 202 multiplexes the input first pilot light and the optical signal to generate a multiplexed signal. Here, the first pilot light is a continuous light generated based on pump light output from a pump light source 204 (denoted as "Pump" in FIG. 2).

[0038] More specifically, the first pilot light is generated in the following order. First, the pump light output from the pump light source 204 is branched by the multiplexer / brancher 206. The part of the pump light branched by the multiplexer / brancher 206 has its optical power adjusted by the VOA 208. Then, the pump light after the optical power adjustment is input to the polarization controller 210 (denoted as "PC" in FIG. 2), and the polarization controller 210 extracts a 45-degree linearly polarized component of the pump light. The 45-degree linearly polarized component of the pump light extracted by the polarization controller 210 is the first pilot light. The first pilot light is used as pilot light propagating in the forward direction. Here, the forward direction refers to the direction from the direction where the optical transmitter 100 is connected to the direction where the transmission line 300 is connected.

[0039] The pumping light source 204 outputs pumping light. For example, the pumping light source 204 outputs continuous light with a degenerate wavelength around 1.5 μm as the pumping light.

[0040] The multiplexer / branch 206 is provided between the pump light source 204 and the first phase modulator 214 (denoted as "PM1" in FIG. 2). The multiplexer / branch 206 branches and outputs the pump light output from the pump light source 204. The multiplexer / branch 206 outputs the branched pump light to the VOA 208 and the first phase modulator 214. The multiplexer / branch 206 is an example of a first branching section.

[0041] The VOA 208 is provided between the multiplexer / splitter 206 and the polarization controller 210. The pump light split by the multiplexer / splitter 206 is input to the VOA 208. The VOA 208 adjusts the power (optical power) of the input pump light. The VOA 208 is a variable optical attenuator.

[0042] The polarization controller 210 is provided between the WDM coupler 202 and the VOA 208. The polarization controller 210 receives pump light whose power (optical power) has been adjusted by the VOA 208. The polarization controller 210 extracts a 45-degree linearly polarized component of the pump light from the input pump light whose power (optical power) has been adjusted. That is, the polarization controller 210 extracts a first pilot light.

[0043] The circulator 212 has a first port, a second port, and a third port. The first port of the circulator 212 is connected to the WDM coupler 202. The second port of the circulator 212 is connected to the PBS 234. The third port of the circulator 212 is connected to the polarization controller 230. An optical signal input to the first port is output from the second port. An optical signal input to the second port is output from the third port. An optical signal input to the third port is output from the first port.

[0044] For example, the multiplexed signal generated by the WDM coupler 202 is input to a first port of the circulator 212. The multiplexed signal input to the first port of the circulator 212 is output from a second port.

[0045] The pump light branched by the multiplexer / brancher 206 is input to the first phase modulator 214. The first phase modulator 214 phase-modulates the input pump light. For example, the first phase modulator 214 phase-modulates the input pump light with a dither signal.

[0046] The combiner / divider 216 divides and outputs the pump light phase-modulated by the first phase modulator 214. The combiner / divider 216 divides and outputs the divided phase-modulated pump light. phase shift The splitter 216 outputs the signal to the splitters 218 and 224. The splitter 216 is an example of a second splitting section.

[0047] phase shift The phase-modulated pump light split by the splitter 216 is input to the splitters 218 and 224 . phase shift The modulators 218 and 224 control the phase of the input phase-modulated pump light. phase shift The device used may be a phase modulator or a piezo-driven fiber stretcher. phase shift The phases controlled in the detectors 218 and 224 are determined based on the first pilot light.

[0048] The optical amplifiers 220 and 226 include: phase shift The pump light whose phase has been controlled is input by the amplifiers 218 and 224. The optical amplifiers 220 and 226 amplify the optical power of the input pump light whose phase has been controlled.

[0049] The BPFs 222 and 228 receive pumping light whose optical power has been amplified by the optical amplifiers 220 and 226. The BPFs 222 and 228 transmit the pumping light whose optical power has been amplified and remove unwanted noise components. Here, the unwanted noise components include, for example, ASE noise generated in the optical amplifiers 220 and 226. In this way, the BPFs 222 and 228 are set to transmit the frequency band of the pumping light and to attenuate other frequency bands.

[0050] The pump light transmitted through the BPF 222 is input to the second-order nonlinear optical medium 248. The second-order nonlinear optical medium 248 converts the input pump light using second-order high-frequency generation to generate second-order high-frequency pump light. The second-order nonlinear optical medium 248 outputs the generated second-order high-frequency pump light to the pump light filter 242. In this way, the second-order nonlinear optical medium 248 is a second-order nonlinear optical medium for second-order high-frequency generation. The second-order nonlinear optical medium 248 is an example of a harmonic generation section.

[0051] The pump light transmitted through the BPF 228 is input to the second-order nonlinear optical medium 250. The second-order nonlinear optical medium 250 converts the input pump light using second-harmonic generation (SHG) to generate second-order high-frequency pump light. The medium 250 outputs the generated second-order high-frequency excitation light to the excitation light filter 236. In this way, the second-order nonlinear optical medium 250 is a second-order nonlinear optical medium for generating second-order high-frequency waves. The second-order nonlinear optical medium 250 is an example of a harmonic generating section.

[0052] When the optical parametric amplification medium is a second-order nonlinear medium as in this embodiment, the pump light must be a second harmonic having a frequency twice the central wavelength (degenerate wavelength) of the phase-matching characteristic of the optical parametric amplification medium. To generate idler light without excessive degradation of the noise figure, it is necessary to perform optical parametric amplification with a relatively high amplification gain using strong pump light.

[0053] However, it is difficult to generate a strong second harmonic (wavelength of about 750 nm) for near-infrared light with a wavelength of about 1.5 μm, which is generally used in optical fiber communications. Therefore, a configuration is used in which a pump light source 204 that outputs continuous light with a degenerate wavelength of about 1.5 μm is used, and the continuous light is amplified by an optical amplifier such as an EDFA (e.g., optical amplifiers 220, 226), and then converted using second harmonic generation to obtain a strong second harmonic pump light.

[0054] As described above, in the configuration of this embodiment, the pump light output from a single pump light source 204 is split by the multiplexer / splitter 216 to generate pump light for two polarization components. The optical path length from the split to the optical parametric amplification medium is sufficiently shorter than the coherence length of the pump light, making frequency noise between the two pump lights negligible. For the PLL operation to synchronize the relative phase of each pump light with the first pilot light, an optical modulator such as a phase modulator must be used to modulate the pump light with a dither signal. This modulator may be located before the pump light is split, or a separate modulator may be used after the split. In the example shown in FIG. 2, the first phase modulator 214 phase-modulates the dither signal onto the pump light before the pump light is split.

[0055] The polarization controller 230 is provided between the circulator 212 and the BPF 232. The polarization controller 230 receives the second pilot light output from the pilot light source 270. The second pilot light is used as pilot light propagating in the reverse direction. Here, the reverse direction refers to the direction opposite to the propagation direction of the first pilot light, for example, the direction from the direction in which the transmission line 300 is connected to the direction in which the optical transmitter 100 is connected. The polarization controller 230 extracts a 45-degree linearly polarized light component from the input second pilot light.

[0056] The pilot light source 270 outputs a second pilot light. A light source different from that for the pump light is used for the second pilot light. The second pilot light has at least a wavelength or optical power different from that of the first pilot light to avoid interference with the reflected component of the first pilot light. That is, the second pilot light has a wavelength or optical power different from that of the first pilot light, or both a wavelength and optical power different from those of the first pilot light.

[0057] By making the wavelengths of the first pilot light and the second pilot light different, the desired pilot component and the unwanted reflected component can be effectively separated by the BPFs 232 and 254 arranged in the monitor units of the pilot lights. The influence of interference can also be reduced by making the power of the second pilot light sufficiently larger than that of the first pilot light.

[0058] The second pilot light uses a light source different from the pump light and is incoherent, so even if the reflected component propagates forward in the amplification medium, it is not amplified by the degenerate phase-sensitive amplification. Therefore, the monitor section of the first pilot light (for example, the "Monitor" at the output of BPF 254) Even if the second pilot light flows into the optical fiber, the observed time fluctuation is largely due to the degenerate phase-sensitive amplification of the first pilot light, and the second pilot light only biases the monitored value, so its effect on control is small.

[0059] On the other hand, when the reflected light of the first pilot light that has been subjected to degenerate phase sensitive amplification flows into the monitor section of the second pilot light (for example, the “Monitor” of the output destination of the BPF 232), the second pilot light Therefore, by increasing the input optical power so that the second pilot light is sufficiently stronger than the reflected light of the first pilot light and enters the monitor unit, the influence of interference between the two pilots can be reduced, enabling the desired control to be performed stably.

[0060] The 45-degree linearly polarized light component extracted by the polarization controller 230 is input to the BPF 232. The BPF 232 transmits the input 45-degree linearly polarized light component and removes unnecessary noise components.

[0061] The PBS 234 splits the multiplexed signal output from the second port of the circulator 212 into two orthogonal polarization components. For example, the PBS 234 splits the multiplexed signal into an X polarization component (first polarization component) and a Y polarization component (second polarization component). The multiplexed signal includes an optical signal and a first pilot light. Therefore, the PBS 234 splits each of the optical signal and the first pilot light into an X polarization component and a Y polarization component. The PBS 234 outputs the X polarization component of the optical signal and the X polarization component of the first pilot light to the pumping light filter 236, and outputs the Y polarization component of the optical signal and the Y polarization component of the first pilot light to the pumping light filter 242. The PBS 234 is an example of a splitting unit.

[0062] The excitation light filter 236 is, for example, a dichroic filter. The X-polarized component of the optical signal, the X-polarized component of the first pilot light, and the second-order high-frequency excitation light output from the second-order nonlinear optical medium 250 are input to the excitation light filter 236. The excitation light filter 236 multiplexes the input X-polarized component of the optical signal, the X-polarized component of the first pilot light, and the second-order high-frequency excitation light.

[0063] The second-order nonlinear optical medium 238 performs optical parametric amplification using the X-polarized component of the optical signal and the X-polarized component of the first pilot light combined by the pumping light filter 236, and the second-order high-frequency pumping light. As a result, the X-polarized component of the optical signal and the X-polarized component of the first pilot light are amplified, and idler light, which is phase conjugate light of the X-polarized component of the optical signal and the X-polarized component of the first pilot light, is generated. The second-order nonlinear optical medium 238 is a second-order nonlinear optical medium for optical parametric amplification. The second-order nonlinear optical medium 238 is an example of a first optical parametric amplifier.

[0064] The pumping light filter 240 is, for example, a dichroic filter. The pumping light filter 240 receives the X-polarized component of the amplified optical signal output from the second-order nonlinear optical medium 238, the X-polarized component of the amplified first pilot light, the idler light, and the secondary high-frequency pumping light. The pumping light filter 240 separates the X-polarized component of the amplified optical signal input from the second-order nonlinear optical medium 238, the X-polarized component of the amplified first pilot light, the idler light, and the secondary high-frequency pumping light from the secondary high-frequency pumping light. Specifically, the pumping light filter 240 reflects the secondary high-frequency pumping light and transmits the X-polarized component of the amplified optical signal, the X-polarized component of the amplified first pilot light, and the idler light.

[0065] The excitation light filter 242 is, for example, a dichroic filter. The Y-polarized component of the optical signal and the Y-polarized component of the first pilot light, and the secondary high-frequency excitation light output from the second-order nonlinear optical medium 248 are input to the excitation light filter 242. The excitation light filter 242 multiplexes the input Y-polarized component of the optical signal and the Y-polarized component of the first pilot light with the secondary high-frequency excitation light.

[0066] The second-order nonlinear optical medium 244 performs optical parametric amplification using the Y-polarized component of the optical signal and the Y-polarized component of the first pilot light combined by the pumping light filter 242, and the second-order high-frequency pumping light. As a result, the Y-polarized component of the optical signal and the Y-polarized component of the first pilot light are amplified, and idler light, which is phase conjugate light of the Y-polarized component of the optical signal and the Y-polarized component of the first pilot light, is generated. The second-order nonlinear optical medium 244 is a second-order nonlinear optical medium for optical parametric amplification. The second-order nonlinear optical medium 244 is an example of a second optical parametric amplifier.

[0067] The pumping light filter 246 is, for example, a dichroic filter. The pumping light filter 246 receives the Y-polarized component of the amplified optical signal and the Y-polarized component of the amplified first pilot light output from the second-order nonlinear optical medium 244, the idler light, and the secondary high-frequency pumping light. The pumping light filter 246 separates the Y-polarized component of the amplified optical signal and the Y-polarized component of the amplified first pilot light input from the second-order nonlinear optical medium 244, the idler light, and the secondary high-frequency pumping light from the input secondary high-frequency pumping light. Specifically, the pumping light filter 246 reflects the secondary high-frequency pumping light and transmits the Y-polarized component of the amplified optical signal and the Y-polarized component of the amplified first pilot light, and the idler light.

[0068] The multiplexer / splitter 252 splits and outputs the X-polarized component of the amplified optical signal, the X-polarized component of the amplified first pilot light, and the idler light that have passed through the pumping light filter 240. The multiplexer / splitter 252 outputs the split X-polarized component of the amplified optical signal, the X-polarized component of the amplified first pilot light, and the idler light to the BPF 254 and the second phase modulator 256 (denoted as "PM2" in FIG. 2).

[0069] BPF 254 transmits the X-polarized component of the first pilot light among the X-polarized component of the amplified optical signal branched by branching / combining device 252, the X-polarized component of the amplified first pilot light, and the idler light. In this way, BPF 254 is set to transmit the frequency band of the X-polarized component of the first pilot light and to attenuate other frequency bands. The X-polarized component of the first pilot light transmitted by BPF 254 is input to a monitor unit (first monitor unit).

[0070] The second phase modulator 256 receives the X-polarized component of the amplified optical signal, the X-polarized component of the amplified first pilot light, and the idler light that have been branched by the branching / multiplexing device 252. The second phase modulator 256 phase-modulates the X-polarized component of the amplified optical signal, the X-polarized component of the amplified first pilot light, and the idler light that have been input. For example, the second phase modulator 256 phase-modulates a dither signal onto the X-polarized component of the amplified optical signal, the X-polarized component of the amplified first pilot light, and the idler light that have been input.

[0071] The multiplexer / splitter 258 splits and outputs the Y-polarized component of the amplified optical signal, the Y-polarized component of the amplified first pilot light, and the idler light that have passed through the pumping light filter 246. The multiplexer / splitter 258 splits and outputs the Y-polarized component of the amplified optical signal, the Y-polarized component of the amplified first pilot light, and the idler light through the BPF 260 and phase shift The signal is output to the image processing device 264.

[0072] BPF 260 transmits the Y polarization component of the first pilot light among the Y polarization component of the amplified optical signal branched by multiplexer / brancher 258, the Y polarization component of the amplified first pilot light, and the idler light. In this way, BPF 260 is set to transmit the frequency band of the Y polarization component of the first pilot light and to attenuate other frequency bands. The Y polarization component of the first pilot light transmitted by BPF 260 is input to a monitor unit (second monitor unit).

[0073] phase shift The amplifier 264 controls the phases of the Y-polarized component of the input amplified optical signal, the Y-polarized component of the amplified first pilot light, and the idler light. phase shift The phase controlled in the amplifier 264 is determined based on the second pilot light.

[0074] The PBC 262 receives the X-polarized component of the phase-modulated optical signal output from the second phase modulator 256, the X-polarized component of the first pilot light, and the idler light, phase shift The Y-polarized component of the optical signal whose phase has been controlled by the amplifier 264, the Y-polarized component of the first pilot light, and the idler light are multiplexed to generate an optical transmission signal.

[0075] The circulator 266 has a first port, a second port, and a third port. The first port of the circulator 266 is connected to the PBC 262. The second port of the circulator 266 is connected to the transmission line 300. The third port of the circulator 266 is connected to the polarization controller 268. An optical signal input to the first port is output from the second port. An optical signal input to the second port is output from the third port. An optical signal input to the third port is output from the first port.

[0076] For example, the optical transmission signal generated by the PBC 262 is input to a first port of the circulator 266, and the input optical transmission signal is output to the transmission line 300 from a third port.

[0077] The polarization controller 268 receives the second pilot light output from the pilot light source 270. The polarization controller 268 extracts a 45-degree linearly polarized light component from the input second pilot light.

[0078] (Configuration of phase sensitive amplifier 400) The phase sensitive amplifier 400 includes a WDM coupler 402, optical amplifiers 404, 422, and 428, BPFs 406, 424, 430, 452, and 456, a polarization controller 408, a VOA 410, a circulator 412, a pumping light source 414, a third phase modulator 416, and multiplexers / branchers 418, 450, and 454. phase shift The optical filter 430 includes filters 420 and 426, a PBS 432, pumping light filters 434, 438, 440, and 444, second-order nonlinear optical media 436, 442, 446, and 448, and a PBC 458.

[0079] The optical transmission signal transmitted through the transmission path 300 is input to the WDM coupler 402. The WDM coupler 402 demultiplexes the input optical transmission signal. For example, the WDM coupler 402 outputs the first pilot light included in the optical transmission signal to the optical amplifier 404, and outputs the optical signal and idler light to the PBS 432.

[0080] The optical amplifier 404 amplifies the optical power of the first pilot light demultiplexed by the WDM coupler 402 .

[0081] The first pilot light, the optical power of which has been amplified by the optical amplifier 404, is input to the BPF 406. The BPF 406 transmits the input first pilot light, the optical power of which has been amplified, and removes unnecessary noise components. In this way, the BPF 406 is set to transmit the frequency band of the first pilot light and to attenuate other frequency bands.

[0082] The first pilot light that has passed through the BPF 406 is input to the polarization controller 408. The polarization controller 408 adjusts the polarization state of the input first pilot light so that it becomes TM polarization.

[0083] The first pilot light adjusted to TM polarization by the polarization controller 408 is input to the VOA 410. The VOA 410 adjusts the power (optical power) of the input first pilot light. The VOA 410 is a variable optical attenuator.

[0084] The circulator 412 has a first port, a second port, and a third port. The first port of the circulator 412 is connected to the pump light source 414. The second port of the circulator 412 is connected to the third phase modulator 416 (denoted as "PM3" in FIG. 2). The third port of the circulator 412 is connected to the polarization controller 408. An optical signal input to the first port is output from the second port. An optical signal input to the second port is output from the third port. An optical signal input to the third port is output from the first port.

[0085] For example, the first pilot light whose power (optical power) has been adjusted by the VOA 410 is input to the third port of the circulator 412. The first pilot light input to the third port of the circulator 412 is output from the first port.

[0086] The first pilot light output from the first port of the circulator 412 is input to the pumping light source 414. The pumping light source 414 is optically injection locked by the input first pilot light, so that the pumping light source 414 outputs pumping light synchronized with the first pilot light.

[0087] The pump light output by the pump light source 414 is input to the third phase modulator 416 via the circulator 412. The third phase modulator 416 phase-modulates the input pump light. For example, the third phase modulator 416 phase-modulates the input pump light with a dither signal.

[0088] The combiner / divider 418 divides and outputs the pump light phase-modulated by the third phase modulator 416. The combiner / divider 418 divides and outputs the divided phase-modulated pump light. phase shift The splitter 418 outputs the output signal to the splitters 420 and 426. The splitter 418 is an example of a third splitting section.

[0089] phase shift The phase-modulated pump light split by the splitter 418 is input to the splitters 420 and 426 . phase shift The modulators 420 and 426 control the phase of the input phase-modulated pump light. phase shift The phases controlled in the converters 420 and 426 are determined based on the optical signal or the idler light.

[0090] The optical amplifiers 422 and 428 include: phase shift The pump light whose phase has been controlled is input by the amplifiers 420 and 426. The optical amplifiers 422 and 428 amplify the optical power of the input pump light whose phase has been controlled.

[0091] The pumping light whose optical power has been amplified by the optical amplifiers 422, 428 is input to the BPFs 424, 430. The BPFs 424, 430 transmit the input pumping light whose optical power has been amplified and remove unnecessary noise components. In this way, the BPFs 424, 430 are set to transmit the frequency band of the pumping light and attenuate other frequency bands.

[0092] The pump light transmitted through the BPF 424 is input to the second-order nonlinear optical medium 446. The second-order nonlinear optical medium 446 converts the input pump light using second-order high-frequency generation to generate second-order high-frequency pump light. The second-order nonlinear optical medium 446 outputs the generated second-order high-frequency pump light to the pump light filter 440. In this way, the second-order nonlinear optical medium 446 is a second-order nonlinear optical medium for second-order high-frequency generation. The second-order nonlinear optical medium 446 is an example of a harmonic generation section.

[0093] The pump light transmitted through the BPF 430 is input to the second-order nonlinear optical medium 448. The second-order nonlinear optical medium 448 converts the input pump light using second-order high-frequency generation to generate second-order high-frequency pump light. The second-order nonlinear optical medium 448 outputs the generated second-order high-frequency pump light to the pump light filter 434. In this way, the second-order nonlinear optical medium 448 is a second-order nonlinear optical medium for second-order high-frequency generation. The second-order nonlinear optical medium 448 is an example of a harmonic generation section.

[0094] The PBS 432 splits each of the optical signal and idler light branched by the WDM coupler 402 into two orthogonal polarization components. For example, the PBS 432 splits each of the optical signal and idler light into an X polarization component and a Y polarization component. The PBS 432 outputs the X polarization component of the optical signal and the X polarization component of the idler light to the pumping light filter 434, and outputs the Y polarization component of the optical signal and the Y polarization component of the idler light to the pumping light filter 440. The PBS 432 is an example of a splitting unit.

[0095] The excitation light filter 434 is, for example, a dichroic filter. The X-polarized component of the optical signal and the X-polarized component of the idler light, and the second-order high-frequency excitation light output from the second-order nonlinear optical medium 448 are input to the excitation light filter 434. The excitation light filter 434 combines the X-polarized component of the input optical signal and the X-polarized component of the idler light with the second-order high-frequency excitation light.

[0096] The second-order nonlinear optical medium 436 receives the X-polarized component of the optical signal combined by the pumping light filter 434, the X-polarized component of the idler light, and the second-order high-frequency pumping light. The second-order nonlinear optical medium 436 performs optical parametric amplification using the X-polarized component of the input optical signal and the second-order high-frequency pumping light. This amplifies the X-polarized component of the optical signal, and generates idler light, which is a phase conjugate light of the X-polarized component of the optical signal. Furthermore, the X-polarized component of the idler light is also phase-sensitively amplified with the same amplification gain and low noise as the optical signal. The second-order nonlinear optical medium 436 is a second-order nonlinear optical medium for optical parametric amplification. The second-order nonlinear optical medium 436 is an example of a third optical parametric amplifier unit.

[0097] The pumping light filter 438 is, for example, a dichroic filter. The pumping light filter 438 receives the X-polarized component of the amplified optical signal output from the second-order nonlinear optical medium 436, the X-polarized component of the idler light, and the second-order high-frequency pumping light. The pumping light filter 438 separates the X-polarized component of the amplified optical signal, the X-polarized component of the idler light, and the second-order high-frequency pumping light in the second-order high-frequency pumping light. Specifically, the pumping light filter 438 reflects the second-order high-frequency pumping light and transmits the X-polarized component of the amplified optical signal and the X-polarized component of the idler light.

[0098] The excitation light filter 440 is, for example, a dichroic filter. The Y-polarized component of the optical signal and the Y-polarized component of the idler light, and the second-order high-frequency excitation light output from the second-order nonlinear optical medium 446 are input to the excitation light filter 440. The excitation light filter 440 combines the input Y-polarized component of the optical signal and the Y-polarized component of the idler light with the second-order high-frequency excitation light.

[0099] The second-order nonlinear optical medium 442 receives the Y-polarized component of the optical signal combined by the pumping light filter 440, the Y-polarized component of the idler light, and the second-order high-frequency pumping light. The second-order nonlinear optical medium 442 performs optical parametric amplification using the input Y-polarized component of the optical signal and the second-order high-frequency pumping light. This amplifies the Y-polarized component of the optical signal, and generates idler light, which is a phase conjugate light of the Y-polarized component of the optical signal. Furthermore, the Y-polarized component of the idler light is also phase-sensitively amplified with the same amplification gain and low noise as the optical signal. The second-order nonlinear optical medium 442 is a second-order nonlinear optical medium for optical parametric amplification. The second-order nonlinear optical medium 442 is an example of a fourth optical parametric amplifier unit.

[0100] The pumping light filter 444 is, for example, a dichroic filter. The pumping light filter 444 receives the Y-polarized component of the amplified optical signal output from the second-order nonlinear optical medium 442, the Y-polarized component of the idler light, and the second-order high-frequency pumping light. The pumping light filter 444 separates the Y-polarized component of the amplified optical signal, the Y-polarized component of the idler light, and the second-order high-frequency pumping light in the second-order high-frequency pumping light. Specifically, the pumping light filter 444 reflects the second-order high-frequency pumping light and transmits the Y-polarized component of the amplified optical signal and the Y-polarized component of the idler light.

[0101] The multiplexer / splitter 450 splits and outputs the X-polarized component of the optical signal that has passed through the pumping light filter 438 and the X-polarized component of the idler light. The multiplexer / splitter 450 outputs the split X-polarized component of the optical signal and the X-polarized component of the idler light to the BPF 452 and the PBC 458.

[0102] BPF 452 transmits the X-polarized component of the optical signal or the X-polarized component of the idler light branched by multiplexer / branch 450. In this way, BPF 452 is set to transmit the frequency band of the X-polarized component of the optical signal or the X-polarized component of the idler light, and to attenuate other frequency bands. The X-polarized component of the optical signal or the X-polarized component of the idler light branched by BPF 452 is input to a monitor unit (third monitor unit).

[0103] The multiplexer / splitter 454 splits and outputs the Y-polarized component of the optical signal and the Y-polarized component of the idler light that have passed through the pumping light filter 444. The multiplexer / splitter 454 outputs the split Y-polarized component of the optical signal and the Y-polarized component of the idler light to the BPF 456 and the PBC 458.

[0104] BPF 456 transmits the Y-polarized component of the optical signal or the Y-polarized component of the idler light branched by branching / combining device 454. In this way, BPF 456 is set to transmit the frequency band of the Y-polarized component of the optical signal or the Y-polarized component of the idler light and to attenuate other frequency bands. The Y-polarized component of the optical signal or the Y-polarized component of the idler light branched by BPF 456 is input to a monitor unit (fourth monitor unit).

[0105] The PBC 458 multiplexes the X-polarized component of the optical signal and the X-polarized component of the idler light branched by the multiplexer / branch 450 with the Y-polarized component of the optical signal and the Y-polarized component of the idler light branched by the multiplexer / branch 454 .

[0106] (Operation in the first embodiment) Next, an example of the operation of the optical phase conjugate converter 200 and the phase sensitive amplifier 400 in the first embodiment will be described. The optical phase conjugate converter 200 multiplexes the optical signal transmitted from the optical transmitter 100 with pump light output from a pump light source 204 using a WDM coupler 202. Specifically, the pump light output from the pump light source 204 is split by a multiplexer / splitter 206 and its optical power is adjusted by a VOA 208, after which the 45-degree linearly polarized pump light is extracted by a polarization controller 210. Then, the optical phase conjugate converter 200 multiplexes the 45-degree linearly polarized pump light (first pilot light) extracted by the polarization controller 210 with the optical signal transmitted from the optical transmitter 100 using the WDM coupler 202 to generate a multiplexed signal.

[0107] Next, the multiplexed signal generated by the WDM coupler 202 is split into two orthogonal polarization components by the PBS 234 via the circulator 212. For example, the multiplexed signal is split into an X polarization component and a Y polarization component by the PBS 234. Each polarization component of the multiplexed signal split into two polarization components by the PBS 234 is optically parametrically amplified by a different nonlinear medium (e.g., second-order nonlinear optical media 238 and 244).

[0108] The process leading up to optical parametric amplification will be described in more detail. The pump light split by the splitter 216 is divided into two parts, one for controlling the phase, and the other for controlling the phase. phase shift The pump light is phase-controlled by amplifiers 218 and 224. Thereafter, the pump light is amplified by optical amplifiers 220 and 226, and then passes through BPFs 222 and 228 to remove unwanted noise components generated in the optical amplifiers 220 and 226. The pump light that has passed through the BPFs 222 and 228 is converted into second-order high-frequency pump light by second-order nonlinear optical media 248 and 250.

[0109] The pumping light filter 236 receives the second-order high-frequency pumping light generated by the second-order nonlinear optical medium 250 and the X-polarized component of the multiplexed signal split by the PBS 234. The pumping light filter 236 combines the second-order high-frequency pumping light generated by the second-order nonlinear optical medium 250 with the X-polarized component of the multiplexed signal. The optical signal combined with the second-order high-frequency pumping light and the X-polarized component of the multiplexed signal is input to the second-order nonlinear optical medium 238.

[0110] Similarly, the second-order high-frequency excitation light generated by the second-order nonlinear optical medium 248 and the Y-polarized component of the multiplexed signal split by the PBS 234 are input to the excitation light filter 242. The excitation light filter 242 multiplexes the second-order high-frequency excitation light generated by the second-order nonlinear optical medium 248 with the Y-polarized component of the multiplexed signal. The optical signal obtained by multiplexing the second-order high-frequency excitation light and the Y-polarized component of the multiplexed signal is input to the second-order nonlinear optical medium 244.

[0111] The optical signals input to the second-order nonlinear optical media 238 and 244 are amplified by optical parametric amplification, generating idler light. At this time, the first pilot light is subjected to degenerate phase-sensitive amplification by overlapping with idler light generated at the same wavelength as itself. The phase of the idler light has a phase corresponding to the relative phase difference between the second-order high-frequency pump light and the first pilot light. Therefore, the degenerate phase-sensitively amplified first pilot light, which becomes interference light with the idler light, experiences temporal fluctuations in optical power due to the phase drift of the second-order high-frequency pump light and its own phase. When the phase of the second-order high-frequency pump light (phase at the degenerate wavelength) and the phase of the first pilot light coincide, the overlap with the idler light results in constructive interference, and the amplification gain, i.e., the optical power after amplification, is maximized.

[0112] The optical signal amplified by the second-order nonlinear optical medium 238 and the generated idler light are separated from the pump light by the pump light filter 240, and then branched by the combiner / branch 252. Of the optical signal and idler light branched by the combiner / branch 252, only the first pilot light is extracted by the BPF 254. Thereafter, an error signal generated by monitoring the optical power of the first pilot light by the monitor unit is used to constantly maximize the optical power of the amplified first pilot light. phase shift By controlling the amplifiers 218 and 224 by a PLL (first control unit), the phases of the pump light and the first pilot light can be synchronized. phase shift The PLL that controls the filters 218 and 224 is connected to a monitor unit that is connected to the BPF 254, or to a monitor unit to which the optical signal output from the combiner / splitter 258 is input.

[0113] Of the two polarization components of the multiplexed signal split by the PBS 234, one (for example, the X polarization component of the multiplexed signal) passes through a second phase modulator 256 to modulate a dither signal, and the other (for example, the Y polarization component of the multiplexed signal) passes through a second phase modulator 256 to modulate a dither signal. phase shift The two polarization components are then passed through a PBC 262. Here, the dither signal uses a different frequency from that used for pump light synchronization to avoid interference.

[0114] The second pilot light output from the pilot light source 270 is extracted by the polarization controller 268 as a continuous light with 45-degree linear polarization, similar to the first pilot light. The extracted second pilot light as a continuous light with 45-degree linear polarization is then input to the third port of the circulator 266 and output from the first port. The second pilot light is separated from the optical signal by the circulator 212. The polarization controller 230 then extracts the 45-degree linearly polarized component of the second pilot light. The BPF 232 transmits the 45-degree linearly polarized component of the second pilot light extracted by the polarization controller 230. The optical power of the second pilot light transmitted through the BPF 232 is then observed by a monitor unit, thereby obtaining an interference waveform between the components that have passed through the two paths. The two paths here refer to paths equipped with second-order nonlinear optical media 238 and 244 that perform optical parametric amplification.

[0115] The error signal obtained from this interference waveform is used to phase shift By controlling the second pilot light 264 by a PLL (second control unit), the optical lengths (amount of phase rotation) between the two paths can be synchronized. Specifically, the second pilot light is used, and the second pilot light 264 is arranged in the path of at least one of the nonlinear media so that the interference waveform of each component of the second pilot light that has passed through each nonlinear medium from the rear is maximized. phase shift By controlling the amplifier 264 by a PLL, the optical lengths (amounts of phase rotation) of the paths of the nonlinear media are made to match. phase shift The PLL that controls the phase conjugate converter 264 is connected to a monitor unit that is connected to the BPF 232, for example. Through the above processing, a signal-idler pair having a carrier component that is independent of polarization can be obtained. If the amplification gain of the phase conjugate converter 200 is insufficient for transmission, additional optical amplification using an EDFA or the like may be performed in the subsequent stage of the phase conjugate converter 200.

[0116] After the above-described processing by the phase conjugate converter 200, the light including the optical signal, idler light, and first pilot light propagates through the transmission line 300 and is input to the phase sensitive amplifier 400. In the phase sensitive amplifier 400, the WDM coupler 402 separates the first pilot light from the input light. The separated first pilot light is output to the optical amplifier 404, and the optical signal and idler light are output to the PBS 432. The first pilot light is amplified by the optical amplifier 404, and after unnecessary noise components generated in the optical amplifier 404 are removed by the BPF 406, the first pilot light is input to the polarization controller 408. The first pilot light is adjusted to TM polarization by the polarization controller 408, and after power adjustment by the VOA 410, it is injected into the pump light source 414 for phase sensitive amplification.

[0117] By optical injection locking, the pump light source 414 is synchronized with the first pilot light. At this time, if the first pilot light does not have sufficient optical power for optical injection locking, it may be amplified after being separated by the WDM coupler 402 using an optical amplifier such as an EDFA. If amplified, unnecessary ASE light generated in the optical amplifier needs to be cut using the BPF 406. Note that if the first pilot light has sufficient optical power for optical injection locking, the phase sensitive amplifier 400 does not need to include the optical amplifier 404 and the BPF 406.

[0118] The synchronized pump light is passed through the third phase modulator 416, the combiner / demultiplexer 418, the optical fiber 419, the optical fiber 420, and the optical fiber 422 in the same manner as the pump light of the optical phase conjugator 200 (for example, the pump light output from the pump light source 204). phase shift The light is converted into second-order high-frequency excitation light via transducers 420 and 426, optical amplifiers 422 and 428, BPFs 424 and 430, and second-order nonlinear optical media 446 and 448.

[0119] The PBS 432 splits each of the optical signal and the idler light separated by the WDM coupler 402 into two polarization components. The PBS 432 outputs the X polarization component of the optical signal and the X polarization component of the idler light to the pumping light filter 434, and outputs the Y polarization component of the optical signal and the Y polarization component of the idler light to the pumping light filter 440.

[0120] The pumping light filter 434 receives the second-order high-frequency pumping light generated by the second-order nonlinear optical medium 448, and the X-polarized component of the optical signal and the X-polarized component of the idler light split by the PBS 432. The pumping light filter 434 combines the second-order high-frequency pumping light generated by the second-order nonlinear optical medium 448 with the X-polarized component of the optical signal and the X-polarized component of the idler light. The combined optical signal of the second-order high-frequency pumping light, the X-polarized component of the optical signal, and the X-polarized component of the idler light is input to the second-order nonlinear optical medium 436.

[0121] Similarly, the pumping light filter 440 receives the second-order high-frequency pumping light generated by the second-order nonlinear optical medium 446, and the Y-polarized component of the optical signal and the Y-polarized component of the idler light split by the PBS 432. The pumping light filter 440 multiplexes the second-order high-frequency pumping light generated by the second-order nonlinear optical medium 446, and the Y-polarized component of the optical signal and the Y-polarized component of the idler light. The optical signal obtained by multiplexing the second-order high-frequency pumping light, the Y-polarized component of the optical signal, and the Y-polarized component of the idler light is input to the second-order nonlinear optical medium 442.

[0122] The optical signals input to the second-order nonlinear optical media 436 and 442 are amplified by optical parametric amplification while generating idler light. Because the pump light is synchronized with the average frequency of the signal-idler pair by synchronization with the first pilot light, the idler light, which has been converted to the signal band by the interaction between the pump light and the idler light, is coherently combined with the optical signal, and the optical signal is phase-sensitively amplified. The same applies to the idler light.

[0123] At this time, the optical signal and pump light are multiplexed via different paths, so even if the optical injection locking is performed, a random relative phase difference occurs due to phase drift. The random fluctuation in the relative phase difference causes the amplification gain of the optical signal and idler light to fluctuate randomly. A portion of the optical power of the optical signal or idler light is monitored, and the fluctuation in the amplification gain is adjusted to maximize the phase shift By controlling the amplifiers 420 and 426 by a PLL (third control unit), phase sensitive amplification is performed with maximum gain for the optical signal and idler light, thereby realizing low noise amplification. phase shift The PLLs controlling the amplifiers 420 and 426 are connected to a monitor connected to the BPF 452 or to the BPF 456, for example.

[0124] At this time, due to processing by the optical phase conjugate converter, the signal-idler pair has a constant carrier component regardless of the polarization state, and no matter what polarization plane it is divided into by the PBS432, phase-sensitive amplification can be achieved with maximum amplification gain for all input electric field components without signal distortion.

[0125] In the example of this embodiment, a configuration in which second-harmonic generation and optical parametric amplification are performed using different second-order nonlinear optical media has been described. On the other hand, in optical parametric amplification using a third-order nonlinear medium, the pump light is arranged at a degenerate frequency and is input together with the optical signal. The same applies to a configuration in which second-harmonic generation for pump light conversion and optical parametric amplification are performed simultaneously in a single second-order nonlinear medium. In such an optical parametric amplification configuration, an interferometer or the like is required to separate the pump light and pilot light arranged at the same frequency after amplification (see Reference 1).

[0126] (Reference 1: W. Imajuku and A. Takada, “Gain Characteristics of Coherent Optical Amplifiers Using a Mach-Zehnder Interferometer with Kerr Media”, IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 35, NO. 11, NOVEMBER 1999, 1657-1665.)

[0127] According to the optical transmission system 10 configured as described above, in the phase conjugate converter 200 that generates the idler light, the phases of the phase conjugate converter 200 and the pump light are stably synchronized using the first pilot light propagating in the forward direction and the second pilot light propagating in the backward direction, respectively, thereby making it possible to realize a stable polarization-independent optical transmission system using the phase sensitive amplifier 400.

[0128] (Second embodiment) 3 is a diagram showing an example of the configuration of an optical transmission system 10a according to the second embodiment. The optical transmission system 10a includes an optical transmitter 100, a phase conjugation device 200, a plurality of transmission lines 300-1 to 300-N (N is an integer equal to or greater than 2), a plurality of phase sensitive amplifiers 400a-1 to 400a-N, and an optical receiver 500. In the optical transmission system 10a, it is assumed that the phase sensitive amplifier 400a is used as an amplifying repeater. The optical transmission system 10a according to the second embodiment is a system that transmits signals while amplifying them at regular intervals using an optical amplifier before the optical power of the signal is reduced to the point where it becomes unreceivable due to loss in the transmission line 300.

[0129] Fig. 4 is a diagram showing specific configurations of a phase conjugate converter 200 and phase sensitive amplifiers 400a-n (1≦n≦N) in the second embodiment. Fig. 4 shows a configuration example of the phase conjugate converter 200 and phase sensitive amplifiers 400a-n when a second-order nonlinear medium is used as an optical parametric amplification medium. In the second embodiment, the configuration of the phase conjugate converter 200 is the same as in the first embodiment, so a description thereof will be omitted.

[0130] When the phase sensitive amplifier 400a-n is used as an amplifying repeater, it is necessary to compensate for the relative phase difference between the orthogonal polarization components due to the phase drift of the phase sensitive amplifier 400a-n, and transmit the signal to the next-stage phase sensitive amplifier 400a-n while maintaining the polarization independence of the carrier component of the signal-idler pair. Therefore, the same processing as that of the phase conjugate converter 200 must also be performed in the phase sensitive amplifier 400a-n. Here, the specific configuration of the phase sensitive amplifier 400a is as follows:

[0131] (Configuration of Phase Sensitive Amplifiers 400a-n) The phase sensitive amplifiers 400a-n include optical amplifiers 404, 422, and 428, BPFs 406, 424, 430, 452, 456, 466, and 468, polarization controllers 408, 464, and 476, a VOA 410, circulators 412, 462, and 474, a pumping light source 414, a third phase modulator 416, and multiplexers / branchers 418, 450, 454, and 460. phase shift The phase sensitive amplifier 400 includes filters 420, 426, and 472, a PBS 432, pump light filters 434, 438, 440, and 444, second-order nonlinear optical media 436, 442, 446, and 448, a PBC 458, a fourth phase modulator 470, and a pilot light source 478. The following describes the configuration that differs from the phase sensitive amplifier 400.

[0132] The optical transmission signal transmitted through the transmission path 300 is input to the multiplexer / branch 460. For example, a first pilot light, an optical signal, and an idler light are input to the multiplexer / branch 460. The multiplexer / branch 460 branches and outputs the input first pilot light, optical signal, and idler light. The multiplexer / branch 460 outputs the branched first pilot light, optical signal, and idler light to the circulator 462 and the BPF 468.

[0133] The circulator 462 has a first port, a second port, and a third port. The first port of the circulator 462 is connected to the multiplexer / splitter 460. The second port of the circulator 462 is connected to the PBS 432. The third port of the circulator 462 is connected to the polarization controller 464. An optical signal input to the first port is output from the second port. An optical signal input to the second port is output from the third port. An optical signal input to the third port is output from the first port.

[0134] The polarization controller 464 is provided between the circulator 462 and the BPF 466. The third pilot light is input to the polarization controller 464. The polarization controller 464 extracts a 45-degree linearly polarized light component from the input third pilot light.

[0135] The light extracted by the polarization controller 464 is input to the BPF 466. The BPF 466 transmits the input light and removes unnecessary noise components.

[0136] The first pilot light, the optical signal, and the idler light branched by the branching / combining device 460 are input to the BPF 468. The BPF 468 transmits the first pilot light among the input first pilot light, the optical signal, and the idler light. In this way, the BPF 468 is set to transmit the frequency band of the first pilot light and to attenuate other frequency bands.

[0137] The fourth phase modulator 470 (denoted as "PM4" in FIG. 2) is provided between the multiplexer / splitter 450 and the PBC 458. The fourth phase modulator 470 phase-modulates the X-polarized component of the first pilot light and the X-polarized component of the idler light split by the multiplexer / splitter 450. For example, the first phase modulator 214 phase-modulates a dither signal onto the X-polarized component of the input first pilot light and the X-polarized component of the idler light.

[0138] phase shift The divider 472 is provided between the branch / combiner 454 and the PBC 458 . phase shift The amplifier 472 controls the phase of the Y-polarized component of the input first pilot light and the Y-polarized component of the idler light.

[0139] The circulator 474 has a first port, a second port, and a third port. The first port of the circulator 474 is connected to the PBC 458. The second port of the circulator 474 is connected to the transmission line 300-(n+1). The third port of the circulator 474 is connected to the polarization controller 476. An optical signal input to the first port is output from the second port. An optical signal input to the second port is output from the third port. An optical signal input to the third port is output from the first port.

[0140] The polarization controller 476 receives the third pilot light output from the pilot light source 478. The polarization controller 476 extracts a 45-degree linearly polarized light component from the input third pilot light.

[0141] The pilot light source 478 outputs a third pilot light. The third pilot light is different from the first pilot light in at least wavelength or optical power to avoid interference with the reflected component of the first pilot light. That is, the third pilot light is different from the first pilot light in wavelength or optical power, or both in wavelength and optical power.

[0142] The third pilot light output from the pilot light source 478 is extracted by the polarization controller 476 as continuous light with 45-degree linear polarization. The extracted third pilot light is then input to the third port of the circulator 474 and output from the first port. The third pilot light is separated from the optical signal by the circulator 462. The polarization controller 464 then extracts the 45-degree linearly polarized component of the third pilot light. The BPF 466 transmits the 45-degree linearly polarized component of the third pilot light extracted by the polarization controller 464. The optical power of the third pilot light transmitted through the BPF 466 is then observed by a monitor unit, thereby obtaining an interference waveform between the components that have passed through the two paths. The two paths here are paths equipped with second-order nonlinear optical media 436 and 442 that perform optical parametric amplification.

[0143] The error signal obtained from this interference waveform is used to phase shift By controlling the third pilot light from the third pilot light source 472 by a PLL (fourth control unit), the optical lengths (amount of phase rotation) between the two paths can be synchronized. Specifically, the third pilot light is used, and the third pilot light is arranged in the path of at least one of the nonlinear media so that the interference waveform of each component of the third pilot light passing through each nonlinear medium from the rear is maximized. phase shift By controlling the amplifier 472 by a PLL, the optical lengths (amounts of phase rotation) of the paths of the nonlinear media are made to match. phase shift The PLL that controls the amplifier 472 is connected to, for example, a monitor unit that is connected to the BPF 466. Through the above processing, a signal-idler pair having a carrier component that is independent of polarization can be obtained.

[0144] (Operation in the second embodiment) Next, an example of the operation of the phase conjugate converter 200 and the phase sensitive amplifier 400a according to the second embodiment will be described. In the phase sensitive amplifier 400a, an optical transmission signal is split by a splitter / multiplexer 460 arranged before a circulator 462, and only the first pilot light component is extracted by a BPF 468 and injected into a pump light source 414, as in the first embodiment, to perform optical injection locking. The component heading toward the optical parametric amplification medium (e.g., second-order nonlinear optical media 436, 442) passes through a configuration similar to that of the phase conjugate converter 200. At this time, the BPFs 452 and 456, which monitor the gain of the phase sensitive amplifier to perform relative phase locking of the pump light, may extract any component from the optical signal, the idler light, or the pilot light.

[0145] As with the optical phase conjugator 200, one of the amplified polarization components is phase shiftOne side passes through a fourth phase modulator 470 for modulating a dither signal. As in the optical phase conjugate converter 200, a pilot light beam with a wavelength different from the first pilot light beam is inserted from the rear using a circulator 474, and is separated on the input side using a circulator 462. The separated pilot light beam is extracted by a BPF 12, and then the 45-degree polarization plane is extracted to obtain an interference waveform of the components that have passed through each path of the PSA section. In order to maximize the intensity of this interference waveform, phase shift By controlling the amplifier 472 with a PLL, the phase drift between the two paths of the PSA section is compensated.

[0146] According to the optical transmission system 10a configured as above, a polarization-independent carrier component is maintained even in the output of the PSA unit, and polarization-independent operation can be realized in the PSA unit at the next stage.

[0147] (Modification of the second embodiment) The phase sensitive amplifier 400a in the second embodiment may be modified as shown in Fig. 5. Fig. 5 is a diagram showing specific configurations of a phase conjugate converter 200 and phase sensitive amplifiers 400b-n in a modification of the second embodiment. Fig. 5 shows a configuration example of the phase conjugate converter 200 and phase sensitive amplifiers 400b-n when a second-order nonlinear medium is used as the optical parametric amplification medium. In the modification of the second embodiment, the configuration of the phase conjugate converter 200 is the same as in the second embodiment, so a description thereof will be omitted.

[0148] (Configuration of phase sensitive amplifier 400b-n) The phase sensitive amplifiers 400b-n include WDM couplers 402 and 482, optical amplifiers 404, 422, and 428, BPFs 406, 424, 430, 452, 456, and 466, polarization controllers 408, 464, and 476, VOAs 410, circulators 412, 462, and 474, a pumping light source 414, a third phase modulator 416, and multiplexers / branchers 418, 450, 454, and 480. phase shiftThe phase sensitive amplifier 400 includes filters 420, 426, and 472, a PBS 432, pump light filters 434, 438, 440, and 444, second-order nonlinear optical media 436, 442, 446, and 448, a PBC 458, and a pilot light source 478. The following describes the configuration that differs from the phase sensitive amplifier 400a.

[0149] In the phase sensitive amplifier 400b-n, similarly to the phase sensitive amplifier 400 in the first embodiment, a first pilot light is demultiplexed from an optical signal transmitted via a transmission line 300 by a WDM coupler 402. Then, in the phase sensitive amplifier 400b-n, similarly to the other embodiments, optical injection locking is performed using the first pilot light.

[0150] 5, a first port of the circulator 412 is connected to a splitter / multiplexer 480. In FIG. 5, a third port of the circulator 474 is connected to a WDM coupler 482.

[0151] The coupler / splitter 480 receives the pumping light output from the pumping light source 414. The coupler / splitter 480 splits the input pumping light and outputs the split pumping light. The coupler / splitter 480 outputs the split pumping light to the circulator 412 and the WDM coupler 482.

[0152] The WDM coupler 482 multiplexes the signal output from the third port of the circulator 474 (a signal obtained by multiplexing the X-polarized component of the first pilot light and the X-polarized component of the idler light, and the Y-polarized component of the first pilot light and the Y-polarized component of the idler light) with the pump light branched by the multiplexer / branch 480. The WDM coupler 482 outputs the multiplexed signal to the transmission path 300.

[0153] The phase-sensitive amplifier 400b configured as described above can inject pilot light into the pump light source with a high signal-to-noise ratio, and can synchronize the frequency of the pump light source more stably. Since the first pilot light does not pass through the OPA medium, it is necessary to add the pilot light for the PSA unit in the next stage after phase-sensitive amplification by branching the pump light using the WDM coupler 3.

[0154] 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. [Industrial Applicability]

[0155] The present invention can be applied to an optical transmission system using phase-sensitive amplification. [Explanation of symbols]

[0156] 10, 10a...Optical transmission system, 100...Optical transmitter, 200...Phase conjugation device, 300...Transmission line, 400, 400a, 400b...Phase-sensitive amplifier, 500...Optical receiver, 202, 402, 482...WDM coupler, 204, 414...Pumping light source, 206, 216, 252, 258, 418, 450, 454, 460, 480...Multiplexer / splitter, 208, 410...VOA, 210, 230, 268, 408, 464, 476...Polarization controller, 212, 266, 412, 462, 474...Circulator, 214...First phase modulator, 218, 224, 264, 420, 426, 472... phase shift 220, 226, 404, 422, 428...Optical amplifiers, 222, 228, 232, 254, 260, 406, 424, 430, 452, 456, 466, 468...BPFs, 234, 432...PBSs, 236, 240, 242, 246, 434, 438, 440, 444...Pumping light filters, 238, 244, 248, 250, 436, 442, 446, 448...Second-order nonlinear optical media, 256...Second-order phase modulators, 262, 458...PBCs, 270, 478...Pilot light sources, 416...Third-order phase modulators, 470...Fourth-order phase modulators

Claims

1. a first branching section that branches pumping light; a multiplexing section that multiplexes a first pilot light propagating in a first direction, which is generated based on one of the pumping lights branched by the first branching section, with an optical signal transmitted from an optical transmitter; a second branching section that branches the other of the pumping lights branched by the first branching section; a plurality of phase shifting sections that phase-control each of the branched pumping lights; a plurality of harmonic generating sections that convert the pumping lights phase-controlled by each of the plurality of phase shifting sections into harmonics; a splitter that splits the first pilot light into two polarization components; a first optical parametric amplifier that performs optical parametric amplification based on the first polarization component of the first pilot light and the first polarization component of the optical signal split by the splitter and the harmonics converted by the multiple harmonic generators; a second optical parametric amplifier that performs optical parametric amplification based on the second polarization component of the first pilot light and the second polarization component of the optical signal split by the splitter and the harmonics converted by the multiple harmonic generators; a combiner that generates an optical transmission signal by combining the first polarization component of the first pilot light amplified by the first optical parametric amplifier and the first polarization component of the optical signal, and the second polarization component of the first pilot light amplified by the second optical parametric amplifier and the second polarization component of the optical signal; a first monitor that monitors the power of the first polarization component of the first pilot light amplified by the first optical parametric amplifier; a second monitor that monitors the power of the second polarization component of the first pilot light amplified by the second optical parametric amplifier; a first control unit that synchronizes the phases of the harmonics and the first pilot light by controlling the phase of the pump light input to the plurality of harmonic generation units so that the optical power of the first pilot light amplified by the first optical parametric amplifier unit and the second optical parametric amplifier unit is maximized based on the result of the synchronization; a second pilot light source that outputs second pilot light that is different from at least the first pilot light in wavelength or optical power; and a second optical parametric amplifier that propagates the second pilot light output from the second pilot light source in a second direction that is opposite to the first direction;a phase conjugate conversion device comprising: a circulator that outputs the optical transmission signal output from the combining unit to the outside; and a second control unit that controls a phase shift unit that is arranged in at least one of the paths so that an interference waveform of each component of the second pilot light that is propagated in the second direction and passed through each of the first optical parametric amplifier unit and the second optical parametric amplifier unit is maximized, thereby making the optical lengths of the paths of the first optical parametric amplifier unit and the second optical parametric amplifier unit equal to each other; an optical transmission section that transmits the optical transmission signal output from the optical phase conjugation device; a phase-sensitive amplifier to which the optical transmission signal transmitted through the optical transmission section is input, the phase-sensitive amplifier performing phase-sensitive amplification of the optical signal and idler light included in the input optical transmission signal by optical parametric amplification using pump light controlled using first pilot light included in the input optical transmission signal; An optical transmission system comprising:

2. The phase sensitive amplifier device comprises: a pumping light source that outputs pumping light for optical parametric amplification by performing optical injection locking on the pumping light source using the first pilot light included in the optical transmission signal; a third branching unit that branches the excitation light output from the excitation light source; a plurality of phase shifters for controlling the phases of the split pumping lights, respectively; a plurality of harmonic generating units for converting the excitation light phase-controlled by each of the plurality of phase shifting units into a harmonic; a splitter that splits the optical signal included in the optical transmission signal into two orthogonal polarization components; a third optical parametric amplifier that performs optical parametric amplification based on the first polarization component of the optical signal split by the splitter and the harmonics converted by the plurality of harmonic generators; a fourth optical parametric amplifier that performs optical parametric amplification based on the second polarization component of the optical signal split by the splitter and the harmonics converted by the plurality of harmonic generators; a combiner that combines the first polarization component of the optical signal amplified by the third optical parametric amplifier and the second polarization component of the optical signal amplified by the fourth optical parametric amplifier; a third monitor unit that monitors the power of the first polarization component of the optical signal amplified by the third optical parametric amplifier unit; a fourth monitor unit that monitors the power of the second polarization component of the optical signal amplified by the fourth optical parametric amplifier unit; a third control unit that synchronizes the phases of the harmonics and the optical signal by controlling the phases of the pump light input to the plurality of harmonic generating units so that the optical powers of the optical signals amplified by the third optical parametric amplifier unit and the fourth optical parametric amplifier unit are maximized, based on the monitoring results of the third monitor unit and the fourth monitor unit; a third pilot light source that outputs third pilot light having a wavelength or optical power different from that of the first pilot light; a circulator that propagates the third pilot light output from the third pilot light source in a second direction that is opposite to the first direction; a fourth control unit that controls a phase shift unit disposed in at least one of the paths so that an interference waveform of each component of the third pilot light propagated in the second direction and passed through each of the third optical parametric amplifier unit and the fourth optical parametric amplifier unit is maximized, thereby matching the optical lengths of the paths of the third optical parametric amplifier unit and the fourth optical parametric amplifier unit; The optical transmission system according to claim 1 , comprising:

3. The phase sensitive amplifier device comprises: a fourth branching unit that branches the optical transmission signal output from the optical phase conjugation device; a filter that extracts the first pilot light from the optical transmission signal branched by the fourth branching unit; Equipped with the pumping light source outputs pumping light for optical parametric amplification by optical injection locking the first pilot light extracted by the filter into the pumping light source.

3. The optical transmission system according to claim 2.

4. The phase sensitive amplifier device comprises: a demultiplexing unit that demultiplexes the first pilot light from the optical transmission signal output from the optical phase conjugation device; a fifth branching unit that branches the pumping light output from the pumping light source at a stage before the third branching unit; a second combining unit that combines the first polarization component of the optical signal and the second polarization component of the optical signal combined by the combining unit with the pump light branched by the fifth branching unit; Further provided with 3. The optical transmission system according to claim 2.

5. a first branching unit that branches the excitation light; a multiplexing unit that multiplexes first pilot light propagating in a first direction, the first pilot light being generated based on one of the pumping lights branched by the first branching unit, with an optical signal transmitted from an optical transmitter; a second branching unit that branches the other of the excitation lights branched by the first branching unit; a plurality of phase shifters for controlling the phases of the split pumping lights, respectively; a plurality of harmonic generating units for converting the excitation light phase-controlled by each of the plurality of phase shifting units into a harmonic; a splitter that splits the first pilot light and the optical signal multiplexed by the multiplexer into two orthogonal polarization components; a first optical parametric amplifier that performs optical parametric amplification based on the first polarization component of the first pilot light and the first polarization component of the optical signal split by the splitter, and the harmonics converted by the plurality of harmonic generators; a second optical parametric amplifier that performs optical parametric amplification based on the second polarization component of the first pilot light and the second polarization component of the optical signal split by the splitter, and the harmonics converted by the plurality of harmonic generators; a combiner that generates an optical transmission signal by combining a first polarization component of the first pilot light and a first polarization component of the optical signal amplified by the first optical parametric amplifier, and a second polarization component of the first pilot light and a second polarization component of the optical signal amplified by the second optical parametric amplifier; a first monitor that monitors the power of a first polarization component of the first pilot light amplified by the first optical parametric amplifier; a second monitor that monitors the power of the second polarization component of the first pilot light amplified by the second optical parametric amplifier; a first control unit that synchronizes the phases of the harmonics and the first pilot light by controlling the phases of pump light input to the plurality of harmonic generating units so that the optical powers of the first pilot light amplified by the first optical parametric amplifier unit and the second optical parametric amplifier unit are maximized, based on the monitoring results of the first monitor unit and the second monitor unit; a second pilot light source that outputs second pilot light having a wavelength or optical power different from that of the first pilot light; a circulator that propagates the second pilot light output from the second pilot light source in a second direction opposite to the first direction, and outputs the optical transmission signal output from the combiner to an outside; a second control unit that controls a phase shift unit disposed in at least one of the paths so that an interference waveform of each component of the second pilot light propagated in the second direction and passed through each of the first optical parametric amplifier unit and the second optical parametric amplifier unit is maximized, thereby matching the optical lengths of the paths of the first optical parametric amplifier unit and the second optical parametric amplifier unit; A phase conjugate conversion device comprising:

6. a pumping light source that outputs pumping light for optical parametric amplification by performing optical injection locking on the pumping light source using first pilot light included in an optical transmission signal transmitted from a phase conjugate conversion device that performs optical parametric amplification; a third branching unit that branches the excitation light output from the excitation light source; a plurality of phase shifters for controlling the phases of the split pumping lights, respectively; a plurality of harmonic generating units for converting the excitation light phase-controlled by each of the plurality of phase shifting units into a harmonic; a splitter that splits an optical signal included in the optical transmission signal into two orthogonal polarization components; a third optical parametric amplifier that performs optical parametric amplification based on the first polarization component of the optical signal split by the splitter and the harmonics converted by the plurality of harmonic generators; a fourth optical parametric amplifier that performs optical parametric amplification based on the second polarization component of the optical signal split by the splitter and the harmonics converted by the plurality of harmonic generators; a combiner that combines the first polarization component of the optical signal amplified by the third optical parametric amplifier and the second polarization component of the optical signal amplified by the fourth optical parametric amplifier; a third monitor unit that monitors the power of the first polarization component of the optical signal amplified by the third optical parametric amplifier unit; a fourth monitor unit that monitors the power of the second polarization component of the optical signal amplified by the fourth optical parametric amplifier unit; a third control unit that synchronizes the phases of the harmonics and the optical signal by controlling the phases of the pump light input to the plurality of harmonic generating units so that the optical powers of the optical signals amplified by the third optical parametric amplifier unit and the fourth optical parametric amplifier unit are maximized, based on the monitoring results of the third monitor unit and the fourth monitor unit; a third pilot light source that outputs third pilot light having a wavelength or optical power different from that of the first pilot light; a circulator that propagates the third pilot light output from the third pilot light source in a second direction that is opposite to the first direction; a fourth control unit that controls a phase shift unit disposed in at least one of the paths so that an interference waveform of each component of the third pilot light propagated in the second direction and passed through each of the third optical parametric amplifier unit and the fourth optical parametric amplifier unit is maximized, thereby matching the optical lengths of the paths of the third optical parametric amplifier unit and the fourth optical parametric amplifier unit; A phase sensitive amplifier comprising:

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