JP2019004253A - Optical amplification device and optical transmission system employing the same - Google Patents

Abstract

To provide an optical transmission system to which a phase sensitive optical amplifier (PSA) is applied, capable of preventing signal quality from being deteriorated by phase fluctuation with dispersion in an optical fiber even for a signal that is transmitted not through a dispersion compensation fiber but through a single-mode fiber (SMF).SOLUTION: In an optical transmission system 400, at the side of a transmitter 401, pre-compensation is performed for applying wavelength dispersion reverse to wavelength dispersion that occurs within a transmission line, to a modulation signal and a modulation light to which the dispersion pre-compensation has been applied, is transmitted to the transmission line, thereby reducing or cancelling deterioration of signal quality caused by wavelength dispersion that occurs within the transmission line. The optical transmission system is configured by combining a signal light modulated by a modulation signal which is obtained by performing the dispersion pre-compensation on a binary phase shift keying (BPSK) signal with a degeneration type PSA or combining a signal light group modulated by a modulation signal which is obtained by performing the dispersion pre-compensation on a quadrature phase shift keying (QPSK) signal with a non-degeneration type PSA.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an optical amplifying device used in an optical communication system and an optical measurement system, and an optical transmission system using the same.

  In a conventional optical transmission system, in order to regenerate a signal attenuated by propagating through an optical fiber, an identification regenerative optical repeater that converts an optical signal into an electrical signal and regenerates the optical signal after identifying the digital signal was used. . In the identification reproduction optical repeater, there are problems such as a limitation in response speed of an electronic component for optical-electrical conversion and an increase in power consumption. Therefore, fiber laser amplifiers and semiconductor laser amplifiers that amplify signal light as it is by entering pump light into an optical fiber doped with rare earth elements have appeared. These laser amplifiers have no function of shaping a deteriorated signal light waveform. Conversely, spontaneously emitted light that is unavoidably and randomly generated is mixed in completely irrespective of the signal component, and the S / N of the signal light decreases by at least 3 dB before and after amplification. The S / N reduction increases the transmission code error rate at the time of digital signal transmission and reduces the transmission quality.

  As means for overcoming the limitations of laser amplifiers, phase sensitive amplifiers (PSAs) have been studied. The PSA has a function of shaping a deteriorated signal light waveform or phase signal due to the influence of dispersion of the transmission fiber. Spontaneous emission light having a quadrature phase irrelevant to the signal can be suppressed, and in-phase spontaneous emission light can be minimized. Therefore, in principle, the S / N of the signal light can be kept the same before and after amplification.

  FIG. 1 is a diagram showing a basic configuration of a conventional PSA. As shown in FIG. 1, the PSA 100 includes a phase sensitive light amplification unit 101, a pumping light source 102, a pumping light phase control unit 103, a first light branching unit 104-1, and a second light branching using optical parametric amplification. Unit 104-2. As shown in FIG. 1, the signal light 110 input to the PSA 100 is branched into two by the optical branching unit 104-1, and one enters the phase sensitive light amplification unit 101 and the other enters the excitation light source 102. . The phase of the excitation light 111 emitted from the excitation light source 102 is adjusted via the excitation light phase control unit 103 and is incident on the phase sensitive light amplification unit 101. The phase sensitive light amplifying unit 101 outputs an output signal light 112 based on the input signal light 110 and the excitation light 111.

  The phase sensitive light amplifying unit 101 amplifies the signal light 110 when the phase of the signal light 110 and the phase of the excitation light 111 coincide with each other, and attenuates the signal light 110 when the phase of the both is 90 degrees. Have. If the phase between the pumping light 111 and the signal light 110 is matched so that the amplification gain is maximized using this characteristic, the spontaneous emission light having the quadrature phase with the signal light 110 is not generated, and the in-phase component is also generated. Does not generate excessive spontaneous emission light beyond the noise of signal light. For this reason, the signal light 110 can be amplified without deteriorating the S / N ratio.

  In order to achieve phase synchronization between the signal light 110 and the pump light 111, the pump light phase control unit 103 is synchronized with the phase of the signal light 110 branched by the first light branching unit 104-1. Control the phase of. The pumping light phase control unit 103 detects a part of the output signal light 112 branched by the second optical branching unit 104-2 with a narrow-band detector so that the amplification gain of the output signal light 112 is maximized. The phase of the excitation light 111 is controlled.

Nonlinear optical media that perform the parametric amplification described above include second-order nonlinear optical materials typified by periodically poled LiNbO ₃ (PPLN) waveguides and _third- order nonlinear optical materials typified by quartz glass fibers.

  FIG. 2 is a diagram showing a configuration of a conventional PSA using a PPLN waveguide (see Non-Patent Document 1). 2 includes an erbium-doped fiber laser amplifier (EDFA) 201, a first second-order nonlinear optical element 202, a second second-order nonlinear optical element 204, a first optical branching unit 203-1, and A second optical branching unit 203-2, a phase modulator 205, an optical fiber stretcher 206, a polarization maintaining fiber 207, a photodetector 208, and a phase locked loop (PLL) circuit 209 are provided. The first second-order nonlinear optical element 202 includes a first spatial optical system 211, a first PPLN waveguide 212, a second spatial optical system 213, and a first dichroic mirror 214. The second second-order nonlinear optical element 204 has the same configuration and will not be described in detail.

  The signal light 250 incident on the PSA 200 in FIG. 2 is branched by the optical branching unit 203-1, and one is incident on the second second-order nonlinear optical element 204. The other of the branched lights is incident on the EDFA 201 after being phase-controlled as excitation fundamental wave light 251 via the phase modulator 205 and the optical fiber expander 206. The EDFA 201 sufficiently amplifies the incident excitation fundamental wave light 251 and enters the first second-order nonlinear optical element 202. With the EDFA 201, sufficient power can be obtained from the weak excitation fundamental wave light 251 to obtain a nonlinear optical effect. In the first second-order nonlinear optical element 202, second harmonic wave (hereinafter referred to as SH light) 252 is generated from the incident excitation fundamental wave light 251. The generated SH light 252 enters the second second-order nonlinear optical element 204 through the polarization maintaining fiber 207. The second second-order nonlinear optical element 204 performs phase-sensitive optical amplification by performing degenerate parametric amplification with the incident signal light 250 and SH light 252, and outputs the output signal light 253.

In PSA, in order to amplify only light in phase with signal light, it is necessary that the phase of the signal light and the phase of the excitation light coincide with each other or be shifted by π radians as described above. That is, when using the second-order nonlinear optical effect, the phase phi _2Omegaesu of the excitation light is a wavelength corresponding to the SH light, and the phase phi _.omega.s of signal light required to satisfy the following equation (1) Become. Here, n is an integer.
_{Δφ = 1/2 (φ 2ωs} -φ ωs) = nπ formula (1)

  FIG. 3 is a diagram showing the relationship between the phase difference Δφ between the input signal light and the pumping light and the gain in the PSA using the second-order nonlinear optical effect of the prior art. It can be seen that the gain (dB) on the vertical axis is maximum when the phase difference Δφ on the horizontal axis is −π, 0, or π.

  In order to synchronize the phase between the signal light 250 and the excitation fundamental light 251, first, the phase modulator 205 performs phase modulation on the excitation fundamental light 251 with a weak pilot signal, and a part of the output signal light 253 is branched. Detection is performed by the detector 208. The pilot signal component is minimized when the phase difference Δφ shown in FIG. 3 is minimized and phase synchronization is established. Therefore, feedback is performed to the optical fiber expander 206 using the PLL circuit 209 so that the pilot signal is minimized, that is, the amplified output signal is maximized. The phase of the excitation fundamental light 251 can be controlled by the optical fiber stretcher 206 to achieve phase synchronization between the signal light 250 and the excitation fundamental light 251.

  As shown in FIG. 3, the phase sensitive optical amplifier using the above-described degenerate parametric process has a characteristic of attenuating orthogonal phase components. Therefore, an intensity modulation signal (OOK) used in normal optical communication, an intensity modulation / direct detection (IMDD) method using binary phase modulation, binary phase modulation (BPSK), or a difference It can be used only for amplification of modulated signals such as dynamic phase shift keying (DPSK). Further, only the signal light of one wavelength can be amplified by the phase sensitive light. In order to widely apply the phase sensitive optical amplifier to the optical communication technology, it is necessary to cope with various optical signals such as a multi-level modulation format and a wavelength multiplexed signal. As an example of this correspondence, Non-Patent Document 3 reports a phase-sensitive optical amplifier that can relay and amplify a plurality of wavelengths at once by using a configuration based on non-degenerate parametric amplification and corresponding to an arbitrary modulation format. .

T. Umeki, O. Tadanaga, A. Takada and M. Asobe, "Phase sensitive degenerate parametric amplification using directly-bonded PPLN ridge waveguides," Optics Express, 2011, Vol.19, No.7, p.6326-6332 Takeshi Umeki, Masaki Asobe, and Hirokazu Takenouchi, “In-line phase sensitive amplifier based on PPLN waveguides,” Optics Express, May 2013, Vol. 21, No. 10, p.12077-12084 M. Asobe, T. Umeki, H. Takenouchi, and Y. Miyamoto, “In-line phase-sensitive amplifier for QPSK signal using multiple QPM LiNbO3 waveguide,” In Proceedings of the Opto Electronics and Communications Conference, OECC, 2013, PDP paper PD2-3 Masaki Asobe, Takeshi Umeki, Kouji Enbutsu, Osamu Tadanaga, and Hirokazu Takenouchi, "Phase squeezing and dispersion tolerance of phase sensitive amplifier using periodically poled LiNbO3 waveguide," J. Opt. Soc. Am. B 31, 3164-3169 2014 D. McGhan, C. Laperle, A. Savchenko, C. Li, G. Mak, and M. O'Sullivan, "5120 km RZ-DPSK Transmission over G652 Fiber at 10Gb / s with No Optical Dispersion Compensation," in Optical Fiber Communication Conference and Exposition and The National Fiber Optic Engineers Conference, Technical Digest (CD) (Optical Society of America, 2005, paper PDP27 Koji Enbutsu, Takeshi Umeki, Osamu Tadanaga, Masaki Asobe, Hirokazu Takenouchi, "PPLN-Based Low-Noise In-Line Phase Sensitive Amplifier with Highly Sensitive Carrier-Recovery System," IEICE Transactions on Communications, vol. E99.B 2016 No 8 pp. 1727-1733

  However, the conventional phase-sensitive optical amplifier has the following problems. As shown in FIG. 3, in the phase sensitive optical amplifier, the gain changes depending on the phase relationship between the signal and the pumping light. For this reason, it has amplification characteristics that are very sensitive to signal phase fluctuations. When a phase sensitive optical amplifier is used as a relay amplifier, if the phase fluctuation depending on the frequency component of the signal light is large due to the influence of dispersion in the optical fiber, the signal quality after phase sensitive optical amplification will be deteriorated (non- Patent Document 4). Since the frequency spectrum spread of the signal light differs depending on the signal modulation rate, the tolerance to dispersion also differs. For example, it has been pointed out that the signal quality after phase-sensitive optical amplification is degraded by adding about 40 ps / nm cumulative dispersion to signal light modulated at a symbol rate of 40 GHz. If the dispersion value of a commonly used single mode fiber (SMF) is 18 ps / nm · km for 1.5 μm band light, the accumulated dispersion value of 40 ps / nm corresponds to a length of about 2.2 km. Considering that one span of the transmission fiber usually has a length of about 80 km, the phase sensitive optical amplifier cannot amplify the signal light transmitted through the SMF.

  As a transmission fiber when using a phase sensitive optical amplifier, a technique for optically suppressing dispersion in a transmission line using a dispersion compensating fiber has been taken (Non-Patent Document 2 and Non-Patent Document 3). By using the dispersion compensating fiber, the dispersion value in the used wavelength band can be suppressed to several ps / nm, and low-noise amplification can be realized without deterioration of signal quality even through the phase sensitive optical amplifier. However, it is not practical to use a dispersion compensating fiber for all the transmission fibers for arranging the phase sensitive optical amplifiers, which involves a major renewal of existing optical communication equipment.

  The present invention has been made in view of the above-described problems of the prior art, and an object thereof is to provide a configuration in which a phase sensitive optical amplifier can be applied to a signal after transmitting an SMF.

  In order to achieve the above object, the present invention provides a transmitter that generates a modulated signal light and an optical device connected to the transmitter via an optical fiber transmission line. An optical transmission system comprising an amplifying device, wherein the transmitter includes a digital signal generator for generating digital signal data to which pre-dispersion compensation according to chromatic dispersion occurring in the optical fiber transmission line is added, and a signal An optical modulation unit for generating the data-modulated signal light by changing at least the optical phase of the carrier light based on the digital signal data with respect to the carrier light from the optical light source, A pumping light generating unit that generates first pumping light based on the signal light transmitted through the optical fiber transmission line, and a parametric process based on the first pumping light from the pumping light generating unit. A phase-sensitive optical amplifier that generates second pump light to be used and performs degenerate parametric amplification on the signal light; and means for synchronizing the phase of the signal light and the phase of the second pump light This is an optical transmission system. This optical transmission system corresponds to the optical transmission system of the first embodiment.

  Invention of Claim 2 is the optical transmission system of Claim 1, Comprising: The said excitation light production | generation part is a said 1st second order nonlinear optical element which produces | generates 2nd harmonic light from the said signal light, The said 1st Including a second second-order nonlinear optical element that generates difference frequency light of second harmonic light and local oscillation light, and a semiconductor laser that generates the first excitation light from the difference frequency light by injection locking, The sensitive light amplification unit includes a third second-order nonlinear optical element that generates the second excitation light that is a sum frequency light of the local oscillation light and the first excitation light from the first excitation light, and And a fourth second-order nonlinear optical element that performs degenerate parametric amplification with the second excitation light.

  The invention according to claim 3 is an optical transmission system comprising a transmitter that generates a modulated signal light group and an optical amplifying device connected to the transmitter via an optical fiber transmission line, The transmitter is a digital signal generator for generating two sets of digital signal data having a phase conjugate relationship, which is digital signal data to which pre-dispersion compensation according to chromatic dispersion occurring in the optical fiber transmission line is added An idler light generation unit that generates idler light having a phase conjugate relationship with the carrier light from carrier light and local oscillation light from the signal light source, and two sets of digital signal data having the phase conjugate relationship. Based on one, based on the other of the two sets of digital signal data in a phase conjugate relationship with the first optical modulation unit that generates the modulated signal light by changing the optical phase and optical intensity of the carrier light. A second optical modulation unit that generates a modulated idler light by changing the optical phase and light intensity of the idler light, and the modulated signal light, the modulated idler light, and the local oscillation light are sent together, The optical amplifying device includes: a first second-order nonlinear optical element that generates excitation light based on the local oscillation light transmitted through the optical fiber transmission line; and the modulated signal light and the modulation light based on the excitation light. An optical transmission comprising: a second second-order nonlinear optical element that performs non-degenerate parametric amplification on the modulated idler light; and means for synchronizing the phase of the modulated signal light and the phase of the excitation light. System. This optical transmission system corresponds to the optical transmission system of the second embodiment.

  The invention according to claim 4 is the optical transmission system according to claim 3, wherein the transmitter includes a third second-order nonlinear optical element that generates second harmonic light from the local oscillation light, and It further includes a fourth second-order nonlinear optical element that generates the idler light that is the difference frequency light between the second harmonic light and the carrier light.

  The invention according to claim 5 is signal light generated in a transmitter by a modulation signal to which pre-dispersion compensation according to chromatic dispersion generated in an optical fiber transmission line is added, and transmitted through the optical fiber transmission line An optical amplifying device for photosensitively amplifying the signal light, wherein a pumping light generating unit that generates first pumping light based on the signal light transmitted through the optical fiber transmission line, and a pumping light generating unit Generating a second pumping light used in a parametric process on the basis of the first pumping light and performing degenerate parametric amplification on the signal light, a phase of the signal light, And a means for synchronizing the phase of the second pumping light. This optical amplification device corresponds to the optical amplification device of the first embodiment.

  The invention according to claim 6 is a group of signal lights generated in a transmitter by a modulation signal to which pre-dispersion compensation according to chromatic dispersion occurring in an optical fiber transmission line is added, and is transmitted through the optical fiber transmission line An optical amplifying apparatus for photo-amplifying the signal light group, wherein the signal light group is a carrier light from a signal light source based on one of two sets of digital signal data having a phase conjugate relationship. Based on the modulated signal light modulated by changing the optical phase and the light intensity of the light and the other of the two sets of digital signal data in the phase conjugate relationship, the carrier light and the local oscillation light are generated. The idler modulated light modulated by changing the optical phase and the light intensity of the idler light having a phase conjugate relationship with the modulated signal light and the idler modulated light and transmitted locally. The optical amplification device includes a first second-order nonlinear optical element that generates excitation light based on the local oscillation light transmitted through the optical fiber transmission line, and the modulation based on the excitation light. A second-order nonlinear optical element that performs non-degenerate parametric amplification on the signal light and the idler-modulated light; and means for synchronizing the phase of the modulated light signal and the phase of the pumping light. This is an optical amplifying device. This optical amplification device corresponds to the optical amplification device of the second embodiment.

  According to the present invention, it is possible to realize phase-sensitive optical amplification with low noise without characteristic deterioration due to dispersion even for a signal after transmission of SMF.

FIG. 1 is a diagram showing a basic configuration of a conventional PSA. FIG. 2 is a diagram showing the configuration of a conventional PSA using a PPLN waveguide. FIG. 3 is a diagram showing the relationship between the phase difference between PSA input signal light pumping light and gain. FIG. 4 is a diagram illustrating a configuration of the optical transmission system according to the first embodiment of the present invention. FIG. 5 is a diagram illustrating a PSA configuration of the optical transmission system according to the first embodiment. FIG. 6 is a diagram for explaining the relationship on the wavelength axis of each signal of the relay type PSA. FIG. 7 is a diagram illustrating a spectrum of signal light amplified by the relay type PSA. FIG. 8 is a diagram illustrating a signal light constellation of each part of the optical transmission system. FIG. 9 is a diagram illustrating the configuration of the optical transmission system according to the second embodiment of the present invention. FIG. 10 is a diagram illustrating a configuration of a transmitter of the optical transmission system according to the second embodiment.

  In the optical transmission system of the present invention, pre-dispersion compensation is performed on the transmitter side to give a chromatic dispersion opposite to the chromatic dispersion generated in the transmission path for the modulation signal applied to the modulator. By transmitting the pre-dispersion-compensated modulated light to the transmission line, it is possible to reduce or cancel signal quality degradation caused by chromatic dispersion in the transmission line. An optical transmission system is disclosed in which signal light modulated with a modulated signal obtained by performing pre-dispersion compensation on a BPSK signal and a degenerate PSA are combined. Also disclosed is an optical transmission system in which signal light modulated by a modulated signal obtained by performing pre-dispersion compensation on a QPSK signal and a non-degenerate PSA are combined. According to the present invention, it is possible to realize low-noise phase-sensitive optical amplification without characteristic deterioration due to dispersion even for a signal after SMF transmission, which has been impossible until now. In addition to enabling low-noise optical amplification, it is possible to compensate the phase noise received by the optical signal in the transmission path as it is, and to improve the SNR that is essential for large-capacity optical transmission. . Hereinafter, embodiments of an optical transmission system and an optical amplifying apparatus according to the present invention will be described in detail with reference to the drawings.

[Embodiment 1]
FIG. 4 is a diagram illustrating a configuration of the optical transmission system according to the first embodiment of the present invention. In the optical amplifying device and the optical transmission system according to the present invention, a configuration of a PSA using a PPLN waveguide is shown. The optical transmission system according to the present embodiment can compensate for the dispersion of the transmission path in advance by pre-digital signal processing, thereby enabling phase-sensitive optical amplification with low noise even for an optical signal after transmission through an optical fiber. Embodiment 1 in FIG. 4 shows a configuration in which signal amplification after fiber transmission is realized using pre-dispersion compensation in a degenerate PSA that amplifies only the in-phase component of pump light. The degenerate PSA can amplify an intensity modulation signal or a signal in which only the in-phase component is modulated. In the present embodiment, a configuration example for amplifying signal light subjected to binary phase modulation (BPSK) will be described.

  The optical transmission system 400 of FIG. 4 roughly includes a transmitter 401 that transmits signal light that has been pre-dispersed by digital signal processing, an optical fiber 430, a polarization compensator 440, and a PSA 500. Although details will be described later along with the operation, the transmitter 401 includes a signal light source 409, a digital signal generation unit 402, digital-analog converters (DACs) 405 and 406, drive amplifiers 407 and 408, and an IQ that is a light modulation unit. A modulator (IQM) 410 and an EDFA 420 are provided. In the optical transmission system of the present embodiment, the transmitter 401 generates a BPSK signal with pre-dispersion compensation.

  FIG. 5 is a diagram illustrating a configuration of a relay PSA in the optical transmission system according to the first embodiment. 5 is roughly divided into a pump light generation unit 530 and a phase sensitive light amplification unit 540 that perform a method of extracting a carrier phase from a BPSK signal. Each of the excitation light generation unit 530 and the phase sensitive light amplification unit 540 is configured using two PPLN waveguide modules. In the excitation light generation unit 530, the first PPLN waveguide module 504 is used for second harmonic (SH light) generation (SHG) to be excitation light, and the second PPLN waveguide module 505 is , Used for difference frequency generation. The first PPLN waveguide module 504 includes both input and output spatial optical systems, a PPLN waveguide, and an output-side dichroic mirror. The second PPLN waveguide module 505 includes both input and output spatial optical systems, a PPLN waveguide, and both input and output dichroic mirrors. In the phase sensitive optical amplifying unit 540, the third PPLN waveguide module 516 is used for generation of SH light serving as excitation light, and the fourth PPLN waveguide module 517 is used for parametric amplification (OPA). It is done. The configuration of each PPLN waveguide module is the same as that of the excitation light generator.

  Here, a method for manufacturing the PPLN waveguide used in the PSA 500 in FIG. 5 is exemplified below. First, a periodic electrode having a period of about 17 μm was formed on LiNbO 3 to which Zn was added. Next, a polarization inversion grating corresponding to the above electrode pattern was formed in Zn: LiNbO3 by an electric field application method. Next, the Zn: LiNbO3 substrate having this periodically poled structure was directly bonded onto the LiTaO3 serving as the cladding, and heat treatment was performed at 500 ° C. to firmly bond both substrates. Next, the core layer was thinned to about 5 μm by polishing, and a ridge type optical waveguide was formed using a dry etching process. The temperature of this waveguide can be adjusted by a Peltier element. The length of the waveguide was 50 mm. The second-order nonlinear optical element having the PPLN waveguide formed as described above has a module configuration capable of inputting and outputting light using a 1.5 μm band polarization maintaining fiber. In this embodiment, Zn-added LiNbO3 was used, but other nonlinear materials such as KNbO3, LiTaO3, LiNbxTa1-xO3 (0 ≦ x ≦ 1) or KTiOPO4, or Mg, Zn, Sc, In You may use the material which contains at least 1 type chosen from the group which consists of as an additive.

  With reference to FIG. 4 again, the operation of the transmitter 401 that transmits the signal light subjected to the pre-dispersion compensation in the optical transmission system 400 will be further described. In the transmitter 401 of FIG. 4, the digital signal generation unit 402 performs an operation that gives a shift opposite to the shift of the optical phase caused by the dispersion received in the optical fiber transmission line, and applies the modulation signal based on the transmission data. Add compensation. That is, the digital signal generation unit 402, the first data signal 404 subjected to pre-dispersion compensation, and the second data signal 403 are output. These data signals were input to the first DAC 406 and the second DAC 405, converted into analog signals, and further amplified to a required level by the first drive amplifier 408 and the second drive amplifier 407. As a result, the two modulated signals I and Q input to the IQ modulator 410 are signals that have been subjected to pre-compensation for chromatic dispersion. The carrier light from the signal light source 409 is modulated in intensity and phase by the above-mentioned modulation signals I and Q in the IQ modulator 410, and a BPSK signal having a symbol rate of 10 GHz subjected to pre-dispersion compensation is output.

  The distortion given by the digital signal generation unit 402 is given so as to be canceled by receiving signal distortion due to dispersion accumulated in the signal light after being transmitted through the optical fiber 430 at the subsequent stage. In order to compensate for the level drop in the IQ modulator 410, the signal light was amplified using the EDFA 420 and then input to the 80 km optical fiber 430. The optical fiber 430 has a dispersion characteristic of 16.7 ps / nm / km, and the total dispersion value after transmission of 80 km is 1336.0 ps. As shown in the signal light constellations 421 and 422 before and after the optical fiber 430 in FIG. 4, the distortion of the signal light is compensated by propagating through the optical fiber 430. By transmitting the optical fiber 430 of 80 km and receiving signal distortion due to dispersion accumulated in the signal light, ideal BPSK signal light can be obtained. In the pre-dispersion compensation process, compensation can be performed in consideration of the slope of dispersion. For this reason, it is possible to perform dispersion compensation with higher accuracy than a conventional optical compensation means for a predetermined wavelength, and it is possible to obtain signal light free from distortion due to dispersion caused by optical fiber transmission. . In this way, by compensating the accumulated dispersion value of the signal light input to the PSA, it is possible to perform phase-sensitive optical amplification with low noise even for the signal light transmitted through the optical fiber. The signal light transmitted through the optical fiber 430 is compensated for polarization in the optical fiber by the polarization compensator 440, and then the signal light 501 is input to the PSA 500. Next, the operation of the PSA 500 will be described with reference to FIG.

  Referring to FIG. 5, in the PSA 500, a part of the input signal light 501 is branched by the optical coupler 502 and is incident on the excitation light generation unit 530. When a degenerate PSA is used as a relay amplifier in optical transmission, an average phase is extracted from the modulated signal light, and the pumping light generation unit 530 generates pumping light synchronized with the carrier phase of the signal. There is a need to. In the following description, the operation of the PSA 500 will be described with reference to the relationship on the wavelength axis of the light of each part of the relay type PSA 500 in FIG.

  6A to 6D are diagrams for explaining the relationship on the wavelength axis of each signal in the relay type PSA 500 of FIG. 6A and 6B conceptually show the relative positional relationship of each signal on the wavelength axis with the horizontal axis as the wavelength. It should be noted that light having a higher frequency is shown as light having a shorter wavelength in FIG. 6 because the horizontal axis is the wavelength axis in each diagram of FIG. Therefore, the higher the frequency of light, the closer to the short wavelength side on the left side of the horizontal axis in FIG.

  Returning again to FIG. 5, in the pumping light generation unit 530, after the branched signal light 501 is amplified by the EDFA 503, the second light having a half wavelength with respect to the wavelength of the signal light is amplified by the first PPLN waveguide module 504. Harmonic light (SH light) is generated. On the other hand, in the excitation light generation unit 530, the excitation light (Lo1) 551 generated by the local oscillation light source 507 and the SH light from the first PPLN waveguide module 504 described above are input to the second PPLN module 505. . In the second PPLN module 505, difference frequency light (Lo2) between the excitation light (Lo1) and the SH light is generated.

  From the signal light, the excitation light (Lo1), and the difference frequency light (Lo2) output from the second PPLN waveguide module 505, only the difference frequency light (Lo2) is extracted by the band pass filter 506. After passing through the optical circulator 513, the difference frequency light (Lo2) is input to the semiconductor laser 512 via, for example, an arrayed waveguide grating (AWG) type wavelength multiplexer / demultiplexer 511. The semiconductor laser 512 generates second excitation light having the same phase and the same wavelength as the difference frequency light (Lo2) by light injection locking. Since the light intensity of the second pumping light is determined by the output of the semiconductor laser 512, the weak difference frequency light (Lo2) of about several tens μW from the second PPLN waveguide module 505 is used, and the second pumping light has a light intensity of several tens of mW or more. 2 excitation light (Lo2) can be obtained. The pumping light (Lo1) branched by the optical coupler 508 from the local oscillation light source 507 is incident on the multiplexing side port of the wavelength multiplexing / demultiplexing unit 511 from the demultiplexing side port of the wavelength multiplexing / demultiplexing unit 511, and the semiconductor laser 510 The pumping light output 552 is output from the circulator 513 in combination with the second pumping light (Lo2) that has been injection-synchronized from the circulator.

  Here, referring to FIG. 6A, the excitation light (Lo1) p1 is shown on the short wavelength side on the wavelength axis with respect to the signal light s. Since the signal light s is modulated, the spectrum is broadened. Referring to FIG. 6B, difference frequency light (Lo2) p2 is shown on the opposite side of the excitation light (Lo1) p1 with respect to the signal light s on the wavelength axis. Intensity noise is removed from the difference frequency light (Lo2) p2 by injection locking (injection lock) to the semiconductor laser 512.

The following expression is satisfied among the phase φs of the signal light s, the phase φ _{p1 of} the pumping light (Lo1) p1, and the phase φ _p2 of the difference frequency light (Lo2) p2 in the relay type PSA of FIG.
_{2φs - φ p1 - φ p2 =} 0 equation (2)

Therefore, the phase φ _p2 of the difference frequency light (Lo2) p2 is expressed by using the phase φs of the signal light s and the phase φ _p1 of the excitation light (Lo1) p1 as shown in the following equation.
φ _p2 = 2φs − φ _p1 formula (3)

  As can be seen from the equations (2) and (3), the phase φs of the signal light s can be doubled by generating SH light from the signal light s in the first PPLN waveguide module 504. . Usually, since signal light is modulated by information data to be transmitted, it is difficult to extract a carrier wave phase. However, binary phase modulation can be removed by doubling the phase φs of the signal light s as in the excitation light generation unit 530 of FIG. Further, as shown in FIG. 6B, the intensity noise of the second excitation light (Lo2) p2, which is the difference frequency light between the SH light and the excitation light (Lo1), is removed by injection locking. In the PSA 500 of FIG. 5, the second pumping light (Lo2) 552 having a pure S / N ratio and retaining the phase information of the carrier wave of the signal light 501 is obtained.

The pumping light (Lo1) 551 from the local oscillation light source 507 and the second pumping light (Lo2) 552 injection-locked are amplified by the EDFA 514 in the phase sensitive light amplifying unit 540. Further, unnecessary ASE light is removed using the BPF 515, and then input to the third PPLN waveguide module 516. In the third PPLN waveguide module 516, as shown in FIG. 6C, the excitation having the sum frequency (SF: Sum Frequency) of the excitation light (Lo1) p1 and the second excitation light (Lo2) p2. An optical SF is generated. At this time, the following expression is satisfied among the phase φ _p1 of the pumping light (Lo1) p1, the phase φ _{p2 of} the second pumping light (Lo2) p2, and the phase φ _SF of the sum frequency pumping light SF.
φ _SF = φ _p1 + φ _p2
= 2φs Equation (4)

The sum frequency excitation light 553 from the third PPLN waveguide module 516 in FIG. 5 is incident on the fourth PPLN waveguide module 517. In the fourth PPLN waveguide module 517, parametric amplification of the signal light 501 via the optical coupler 502 and the sum frequency excitation light 553 is performed. For phase-sensitive optical amplification, as shown in FIG. 6D, the following equation must be satisfied between the phase φs of the signal light s and the phase φ _SF of the sum frequency light SF.
_{ΔΦ = φ SF - 2φs = nπ} (n is an integer) (5)

  That is, the gain is maximized when the phase difference ΔΦ between the input signal light and the sum frequency pump light is −π, 0, or π. In order to synchronize the phase between the signal light and each excitation light, the phase modulation is applied to the excitation light 551 by a weak signal using the phase modulator 509. Part of the output light that has passed through the fourth PPLN waveguide module 517 is branched by the optical coupler 518. A change in the light intensity of the branched light is detected by the optical detector 519, and feedback is applied to the optical fiber stretcher 521 using the PLL circuit 520 so that the phase is synchronized between the excitation light 551 and the signal light 501. By the above-described phase synchronization, the relay type PSA 500 of FIG. 5 can be stably operated. Therefore, the loop including the optical coupler 518, the PLL circuit 520, and the optical fiber expander 521 constitutes a means for synchronizing the phase of the signal light and the phase of the second pumping light.

  As an example of the wavelength of each signal, the signal light s is 1535.8 nm, the pumping light p1 (Lo1) is 1534.25 nm, the difference frequency p2 (Lo2) is 1537.4 nm, and the sum frequency SF is 767.9 nm.

  In the optical transmission system 400 of FIG. 4, in order to confirm the optical amplification characteristics of the PSA 500, the signal optical frequency spectrum before and after amplification and the modulation constellation were confirmed under different conditions of pre-dispersion compensation.

  FIG. 7 is a diagram illustrating the frequency spectrum of the signal light amplified by the phase sensitive optical amplifier according to the first embodiment. In any of (a) to (c) of FIG. 7, three types of spectra are superimposed and displayed, one being an input (Input) of PSA 500 and an output of two PSA 500 (position of arrow C in FIG. 4). The PSA indicates a normal operation state (PSA amp) and the PSA indicates an attenuation state (PSA deamp). The attenuation state (PSA deamp) of the PSA is obtained by making the phase of the input signal light 501 to the PSA 500 and the sum frequency excitation light 553 orthogonal (shift by π / 2). For reference, FIG. 7A shows a spectrum when a BPSK signal “without pre-dispersion compensation” is input to the PSA 500 without being transmitted through the optical fiber 430. That is, the spectrum (Input) of the BPSK signal not subjected to pre-dispersion compensation (without distortion) at the position indicated by the arrow A in FIG. 4 and the spectrum in an ideal state in which the PSA is not affected by transmission line dispersion (PSA amp, PSA). deamp) is shown.

  FIG. 7B shows a spectrum when a “no pre-dispersion compensation” BPSK signal is input to the PSA after 80 km optical fiber transmission. That is, the input spectrum (Input) is at the position indicated by the arrow B in FIG. FIG. 7C shows a spectrum when a “predispersion-compensated” BPSK signal is input to the PSA after 80 km optical fiber transmission.

  As shown in FIG. 7B, a signal without pre-dispersion compensation is out of phase for each frequency component due to the influence of dispersion of the optical fiber, so that the phase sensitivity synchronized with each frequency component is obtained. Characteristics are not obtained. In particular, the spectrum in the attenuation region sensitive to the phase error is deteriorated, and the distortion in the adjacent channel band is increased. On the other hand, as shown in FIG. 7C, when a signal with pre-dispersion compensation is used, no spectral degradation is observed in the phase-sensitive optical amplification / attenuation operation, and FIG. A spectrum equivalent to the input signal in the ideal state and the signal light optically amplified in the ideal state was obtained.

  FIG. 8 is a diagram illustrating a constellation of signal light amplified by the phase sensitive optical amplifier according to the first embodiment. In order to confirm the signal quality after phase-sensitive light amplification, constellation diagrams of signal light before and after amplification were obtained. For reference, FIG. 8A shows a constellation in the PSA output of a BPSK signal that is “no pre-dispersion compensation” and is not subjected to optical fiber transmission. FIG. 8B shows a constellation at the PSA output after transmitting the BPSK signal “without pre-dispersion compensation” to the optical fiber of 80 km. FIG. 8 (c) shows the constellation at the PSA output after 80km fiber transmission of the “predispersion compensated” BPSK signal.

  In FIGS. 7A, 7B, and 7C, the Q values are 17.6 dB, 6.9 dB, and 17.3 dB, respectively. Here, the Q value in the BPSK signal is defined by the difference between the standard deviation and the average amplitude of the amplitudes “1” and “0” of the binary signal. For a signal without pre-dispersion compensation, the Q value of the signal light has deteriorated due to the phase-sensitive optical amplification of the signal light affected by the dispersion in the optical fiber. On the other hand, by using pre-dispersion compensation, phase-sensitive optical amplification without Q-value degradation can be realized even when a single mode fiber is transmitted and affected by fiber dispersion.

  In the PSA 500 of the present embodiment, the light injection locking is used for the phase locking between the signal light 501 and the local oscillation light 551, but other methods may be used. For example, phase synchronization may be performed by feeding back high-speed electrical signal feedback typified by a Costas loop to the local oscillation light source 507.

  In the optical transmission system of the first embodiment described above, the phase error caused by the dispersion of the optical fiber transmission line is compensated in advance at the stage of the transmitter 401 digital signal generation unit. This makes it possible to realize phase-sensitive optical amplification without characteristic deterioration due to dispersion even for signal light transmitted through an optical fiber having dispersion. The optical transmission system of the present invention makes it possible to apply a PSA that can be applied only to a transmission line constituted by a dispersion-compensated fiber in the prior art to a signal after ordinary SMF transmission. The application area of PSA, which is a key for improving the SNR necessary for large-capacity optical transmission, can be greatly expanded.

[Embodiment 2]
Hereinafter, an optical amplifying apparatus and an optical transmission system according to Embodiment 2 of the present invention will be described. The optical transmission system of the first embodiment has a configuration in which a degenerate PSA is used for a BPSK modulated signal. The optical transmission system according to the first embodiment has no problem in application to a system that sufficiently satisfies the transmission capacity even when a modulation method such as a BPSK modulation signal is used. However, in a system that requires larger capacity transmission, it is difficult to apply a degenerate PSA that has a limitation on the modulation format and the number of wavelengths that can be amplified. The optical transmission system of this embodiment can support signals of any modulation format such as a quadrature amplitude modulation (QAM) signal including a data modulation component in the quadrature phase component, and amplifies a plurality of wavelengths collectively. A possible non-degenerate PSA configuration is presented. In the present embodiment in which pre-dispersion compensation is applied to a modulation signal including a data modulation component also in a quadrature phase component, a four-phase QAM quadrature phase shift keying (QPSK) signal is taken as an example. explain.

  FIG. 9 is a diagram illustrating the configuration of the optical transmission system according to the second embodiment of the present invention. The optical transmission system 900 according to this embodiment preliminarily compensates for the dispersion of the transmission path with respect to the modulated signal by digital signal processing in the transmitter 1000, thereby reducing low noise even for the optical signal after the optical fiber transmission. Enables phase-sensitive optical amplification. The optical transmission system 900 of FIG. 9 includes a transmitter 1000 that transmits signal light, idler light, and a pilot signal, an optical fiber (single mode fiber: SMF) 910, a polarization compensator 920, and pump light using the pilot signal. It consists of non-degenerate PSA 930 to be generated.

  FIG. 10 is a diagram illustrating a detailed configuration of the transmitter 1000 of the optical transmission system according to the second embodiment. Hereinafter, the configuration and operation of the transmitter will be described with reference to FIG. 10, and the configuration and operation of the non-degenerate PSA 930 will be described with reference to FIG. 10 roughly includes a signal light source 1001, a local oscillation light source 1003, EDFAs 1005 and 1022, PPLN waveguide modules 1002 and 1007, optical couplers 1004, 1021, and 1023, and a bandpass filter (BPF). ) 1006 and a wavelength selective optical switch (WSS: Wavelength Selective Switch) 1020. In order to generate a pre-dispersion compensated modulation signal, digital signal generation units 1010 and 1011, DACs 1012 to 1015, drive amplifiers 1016 to 1019, and IQ modulators 1008 and 1009 are further provided.

  In the transmitter 1000, idler light that is paired with the signal light 1030 is generated by a difference frequency generation (DFG) process using a PPLN waveguide. The DFG process is operated by the first PPLN waveguide module 1007 for generating SH light serving as excitation light and the second PPLN waveguide module 1002 for generating idler light. The configuration of the PPLN waveguide module and the method for manufacturing the PPLN waveguide in the module are the same as those in the first embodiment.

  The excitation light (Lo1) from the local oscillation light source 1003 generates SH light 1038 in the first PPLN waveguide module 1007 via the optical coupler 1004, the EDFA 1005, and the BPF 1006. The signal light carrier 1030 from the SH light 1038 and the signal light source 1001 generates idler light corresponding to the difference frequency between the SH light 1038 and the signal light carrier 1030 in the second PPLN waveguide module 1002. Therefore, the output light 1031 from the second PPLN waveguide module 1002 includes a signal light carrier wave and idler light. Here, the frequency of the signal light and the frequency of the idler light have a symmetric positional relationship with respect to the frequency of the local oscillation light on the frequency axis. Furthermore, the carrier wave of the signal light and the idler light have a phase conjugate relationship.

  Based on the transmission data, the first digital signal generation unit 1010 and the second digital signal generation unit 1011 perform an operation that gives a shift opposite to the shift of the optical phase caused by dispersion received in the optical fiber transmission line. Compensation is applied to the modulation signal. The first data signal 1034 and the second data signal 1035 from the first digital signal generation unit 1010 generate a modulation signal for the signal light. Similarly, the third data signal 1036 and the fourth data signal 1037 from the second digital signal generation unit 1011 generate a modulation signal for idler light. Data signals 1034 to 1037 were input to DACs 1012 to 1015 and converted into analog signals, respectively, and further amplified to required levels by drive amplifiers 1016 to 1019. The two modulation signals I and Q input to the first IQ modulator 1008, which is an optical modulation unit, are modulation signals for the signal light subjected to pre-compensation for chromatic dispersion. Similarly, the two modulation signals I and Q input to the second IQ modulator 1009, which is an optical modulation unit, are modulation signals for idler light subjected to pre-compensation for chromatic dispersion. Distortion due to pre-dispersion compensation given by the digital signal generation units 1010 and 1011 is canceled by receiving signal distortion due to dispersion accumulated in the signal light and idler light after transmission through the optical fiber 910 at the subsequent stage. In addition, the first data signal 1034 and the second data signal 1035, and the third data signal 1036 and the fourth data signal 1037 are data signals having a phase conjugate relationship with each other.

  The signal light and idler light from the second PPLN waveguide module 1002 are demultiplexed by the WSS 1020 and the intensity and phase are modulated by IQ modulators 1008 and 1009, respectively. That is, the IQ modulator 1008 outputs QPSK modulated signal light with a symbol rate of 10 GHz subjected to pre-dispersion compensation, and the IQ modulator 1009 outputs QPSK with a symbol rate of 10 GHz subjected to pre-dispersion compensation. Modulated idler light is output. The QPSK signals from the two IQ modulators 1008 and 1009 are multiplexed by an optical multiplexer / demultiplexer (optical coupler) 1021. As described above, the modulation signals to the two IQ modulators 1008 and 1009 are signals having a phase conjugate relationship with each other. Further, signal light and idler light as carrier waves to be modulated are also in phase conjugate relation. That is, the modulated signal light and idler light from the IQ modulators 1008 and 1009 have a phase conjugate relationship between the modulated data and the optical phase of the carrier wave.

  In order to compensate for the level drop in the IQ modulator, the combined modulation signal is amplified using the EDFA 1022. Thereafter, the excitation light demultiplexed by the optical coupler 1004 was combined with the signal light and idler light by the optical coupler 102 and input to the 80 km optical fiber 910 in FIG. The transmission fiber and its dispersion characteristics are the same as in the first embodiment. When phase-sensitive light amplification is performed, excitation light having information on the reference phase of the signal light and idler light to be amplified is required. In the optical transmission system of this embodiment, the pumping light 1032 output from the local oscillation light source 1033 that is the reference phase of the signal light and idler light is used as a pilot tone that is transmitted together with the signal light and idler light.

  Referring to FIG. 9 again, the relay type PSA 930 is roughly composed of a wavelength multiplexer / demultiplexer 931, a fourth optical multiplexer / demultiplexer, BPFs 933, 938, 942, a circulator 934, and a local oscillation light source (semiconductor laser) 935. A phase modulator 936, an EDFA 937, PPLN waveguide modules 939 and 940, a photodetector 943, a PLL circuit 944, and an optical fiber expander 945 using PZT. Similarly to the transmitter 1000 in the relay type PSA 930, the phase-sensitive optical amplification process is performed by the third PPLN waveguide module 939 for generating SH light (SHG) as excitation light and the fourth PPLN guide for OPA. It operates by the waveguide module 940. The configuration of each PPLN waveguide module and the method of manufacturing the PPLN waveguide in the module are the same as those in the first embodiment.

  The signal light group transmitted through the optical fiber 910 including the signal light, the idler light, and the pilot tone is compensated for polarization fluctuation in the optical fiber by the polarization compensator 920. In the PSA 930, only the pilot tone in the signal light group 951 is demultiplexed by the wavelength multiplexer / demultiplexer 931, and the signal light and idler light are input to the fourth PPLN waveguide module 940. In the pilot tone, unnecessary ASE light components were removed by BPF 933, and then light injection synchronization was performed on second local oscillation light source 935 via optical circulator 934. The local oscillation light having the same wavelength and the same phase information as the pilot tone was generated by the light injection locking. The local oscillation light source 935 can be realized by a semiconductor laser, for example.

  The optical circulator 934 takes out the output synchronized with the injection from the local oscillation light source 935, and the local oscillation light 953 is amplified to 3 W by the EDFA 937. Further, the spontaneous emission light of the EDFA was removed by the BPF 938 and then incident on the third PPLN waveguide module 939. The SH light excitation light 954 was generated by the SHG operation in the PPLN waveguide in the third PPLN waveguide module 939. An excitation light 954 having an intensity of 1 W was obtained by the local oscillation light of 3 W. This excitation light 954 is incident on the fourth PPLN waveguide module 940. In the PPLN waveguide in the fourth PPLN waveguide module 940, a non-degenerate parametric process is caused for the signal light and the idler light.

  The signal light and idler light are synchronized with the reference phase of the excitation light 1038 in the transmitter 1000. For this reason, even in the relay type PSA 930, by synchronizing the pumping light 954 with the reference phase of the transmitter 1000, it is possible to realize collective phase sensitive optical amplification at all wavelengths. In order to synchronize the phase of the pump light and the signal light in the PSA 930, the phase modulator 936 is used to phase modulate the local oscillation light with a weak signal. Part of the output light 955 that has passed through the fourth PPLN module 940 was branched by the optical coupler 941. Only the wavelength of the signal light of the output light 955 is cut out by the BPF 942, and the change in light intensity is detected by the photodetector 943. Using the PLL circuit 944, feedback was applied to the optical fiber expander 945 so that the phase of the pumping light and the phase of the signal light were synchronized. Here, only the signal light in the output light 955 is cut out in order to synchronize the phase. However, even if the idler light of the output light 955 is cut out and fed back to the optical fiber expander 945, the phase sensitive light is similarly obtained. Amplification is possible.

  In the optical transmission system 900 of this embodiment, optical injection locking is used for phase synchronization between the pilot tone transmitted from the transmitter 1000 and the local oscillation light 953 of the PSA 930. As another method, for example, phase synchronization may be performed by feeding back high-speed electric signal feedback typified by a Costas loop to the local oscillation light source 935.

  Also in the above-described optical transmission system of the present embodiment, the phase error caused by the dispersion of the optical fiber transmission line is compensated in advance at the stage of the digital signal generation units 1010 and 1011 of the transmitter 1000. This makes it possible to realize phase-sensitive optical amplification without characteristic deterioration due to dispersion even for signal light transmitted through an optical fiber having dispersion. The optical transmission system of the present invention makes it possible to apply a PSA that can be applied only to a transmission line constituted by a dispersion-compensated fiber in the prior art to a signal after ordinary SMF transmission. A PSA applicable to a modulation format such as a QAM signal including a quadrature phase component and a data modulation component and capable of collectively amplifying a plurality of wavelengths can expand the application area of the PSA necessary for large-capacity optical transmission.

  The present invention can be used in an optical transmission system. In particular, it can be used for a relay type optical amplifier.

100, 200, 500, 930 Phase sensitive optical amplifier (PSA)
102 Excitation light source 103 Excitation light phase control unit 201, 420, 503, 514, 937, 1005, 1022 EDFA
202, 204, 504, 505, 516, 517, 939, 940, 1002, 1007 PPLN waveguide module 203-1, 203-2, 502, 508, 518, 941, 1004, 1021, 1023 Optical coupler (optical branching unit) )
205, 936 Phase modulator 206, 207, 521, 945 Optical fiber stretcher 209, 420, 520, 944 PLL circuit 400, 900 Optical transmission system 401, 1000 Transmitter 402, 1010, 1011 Digital signal generator 405, 406, 1012 to 1015 Digital-to-analog converter (DAC)
409, 1001 Signal light source 410, 1008, 1009 IQ modulator (IQM)
430, 910 Optical fiber 440, 920 Dispersion and polarization compensator 506, 515, 933, 938, 942, 1006 BPF
507, 1003 Local oscillation light source 512, 935 Semiconductor laser (local oscillation light source)
513, 934 Optical circulator 530 Excitation light generation unit 540 Phase sensitive optical amplification unit 931 Wavelength multiplexer / demultiplexer 1020 Wavelength selective optical switch

Claims (6)

A transmitter for generating modulated signal light;
An optical transmission system comprising: an optical amplification device connected to the transmitter via an optical fiber transmission line;
The transmitter is
A digital signal generator for generating digital signal data to which pre-dispersion compensation is added according to chromatic dispersion generated in the optical fiber transmission line;
An optical modulation unit for generating the data-modulated signal light by changing at least the optical phase of the carrier light based on the digital signal data with respect to the carrier light from the signal light source;
The optical amplification device includes:
A pumping light generating unit that generates first pumping light based on the signal light transmitted through the optical fiber transmission line;
A phase-sensitive light amplifying unit that generates second pumping light used in a parametric process based on the first pumping light from the pumping light generation unit and performs degenerate parametric amplification on the signal light;
An optical transmission system comprising: means for synchronizing the phase of the signal light and the phase of the second pumping light. The excitation light generator is
A first second-order nonlinear optical element that generates second harmonic light from the signal light;
A second second-order nonlinear optical element that generates a difference frequency light of the second harmonic light and the local oscillation light;
A semiconductor laser that generates the first pumping light from the difference frequency light by injection locking,
The phase sensitive light amplification unit is
A third second-order nonlinear optical element that generates, from the first excitation light, the second excitation light that is a sum frequency light of the local oscillation light and the first excitation light;
The optical transmission system according to claim 1, further comprising: a fourth second-order nonlinear optical element that performs degenerate parametric amplification with the second pumping light. A transmitter for generating a modulated signal light group;
An optical transmission system comprising: an optical amplification device connected to the transmitter via an optical fiber transmission line;
The transmitter is
Digital signal data to which pre-dispersion compensation is added according to chromatic dispersion generated in the optical fiber transmission line, and two sets of digital signal data having a phase conjugate relationship;
An idler light generator that generates idler light in a phase conjugate relationship with the carrier light from the carrier light and local oscillation light from the signal light source;
A first optical modulation unit that generates a modulated signal light by changing an optical phase and an optical intensity of the carrier light based on one of the two sets of digital signal data having a phase conjugate relationship;
A second light modulation unit that generates modulated idler light by changing the optical phase and light intensity of the idler light based on the other of the two sets of digital signal data in the phase conjugate relationship, and
The modulated signal light, the modulated idler light and the local oscillation light are sent together,
The optical amplification device includes:
A first second-order nonlinear optical element that generates excitation light based on the local oscillation light transmitted through the optical fiber transmission line;
A second-order nonlinear optical element that performs non-degenerate parametric amplification on the modulated signal light and the modulated idler light based on the excitation light;
An optical transmission system comprising: means for synchronizing the phase of the modulated signal light and the phase of the pumping light. The transmitter is
A third second-order nonlinear optical element that generates second harmonic light from the local oscillation light;
The optical transmission system according to claim 3, further comprising: a fourth second-order nonlinear optical element that generates the idler light that is the difference frequency light between the second harmonic light and the carrier light. Signal light generated in a transmitter by a modulated signal to which pre-dispersion compensation corresponding to chromatic dispersion generated in an optical fiber transmission line is added, and light that amplifies the signal light transmitted through the optical fiber transmission line. An amplifying device,
A pumping light generator that generates first pumping light based on the signal light transmitted through the optical fiber transmission line;
A phase-sensitive light amplifying unit that generates second pumping light used in a parametric process based on the first pumping light from the pumping light generation unit and performs degenerate parametric amplification on the signal light;
An optical amplifying apparatus comprising: means for synchronizing the phase of the signal light and the phase of the second pumping light. A signal light group generated in a transmitter by a modulated signal to which pre-dispersion compensation according to chromatic dispersion generated in an optical fiber transmission line is added, and the signal light group transmitted through the optical fiber transmission line is light-sensitive amplified. An optical amplifying device,
The signal light group is
A modulated signal light modulated by changing the optical phase and light intensity of the carrier light from the signal light source based on one of the two sets of digital signal data having a phase conjugate relationship;
Based on the other of the two sets of digital signal data in the phase conjugate relationship, the optical phase and the light are generated from the carrier light and the local oscillation light, and the idler light in the phase conjugate relationship with the carrier light Idler-modulated light modulated with varying intensity,
Including the local oscillation light transmitted together with the modulated signal light and the idler modulated light;
The optical amplification device includes:
A first second-order nonlinear optical element that generates pumping light based on the local oscillation light transmitted through the optical fiber transmission line;
A second-order nonlinear optical element that performs non-degenerate parametric amplification on the modulated signal light and the idler modulated light based on the excitation light;
An optical amplifying apparatus comprising: means for synchronizing the phase of the modulated optical signal and the phase of the pumping light.

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