WO2013111413A1

WO2013111413A1 - Phase-sensitive amplifier and method of designing same, bpsk signal phase noise suppressor using phase-sensitive amplifier, bpsk signal regenerator, qpsk signal demultiplexer, and qpsk signal regenerator

Info

Publication number: WO2013111413A1
Application number: PCT/JP2012/078474
Authority: WO
Inventors: 井上　崇; ミンイゴウ; 並木　周
Original assignee: 独立行政法人産業技術総合研究所
Priority date: 2012-01-24
Filing date: 2012-11-02
Publication date: 2013-08-01
Also published as: JP5979563B2; JPWO2013111413A1

Abstract

[Problem] To obtain a large gain-extinction ratio with a small nonlinear effect. [Solution] This phase-sensitive amplifier comprises: a pump beam emission means; a multiplexed beam emission means for multiplexing an inputted signal beam with the pump beam and emitting a multiplexed beam; a phase difference adjustment means for adjusting a relative phase difference between the signal beam and the pump beam; and a nonlinear medium which receives the relatively phase difference adjusted multiplexed beam and causes a parametric process. When a circle is drawn in a complex plane with the origin in the center, said circle having a radius which is a complex amplitude of an output signal beam of the phase-sensitive amplifier in which a target gain-extinction ratio is established to be 20dB or more, the intensity of the pump beam, and a nonlinear constant, a propagation length, and a distribution value of the nonlinear medium, are set such that the complex amplitude of the output signal beam when the phase of the input signal matches a quadrature component is contained in the circle, and the product of the nonlinear constant, the propagation length, and the intensity of the pump beam is less than 1.7rad.

Description

Phase sensitive optical amplifier and design method thereof, and BPSK signal phase noise suppressor, BPSK signal regenerator, QPSK signal demultiplexer and QPSK signal regenerator using the phase sensitive optical amplifier

The present invention relates to a phase-sensitive optical amplifier that can be used in an optical fiber communication system and the like, a design method thereof, a BPSK signal phase noise suppressor, a BPSK signal regenerator, and a QPSK signal demultiplexing using the phase-sensitive optical amplifier. And a QPSK signal regenerator.

In order to remove the phase noise generated in the phase-modulated signal light, a phase-sensitive optical amplifier (PSA) has been studied. In PSA, pump light and signal light are combined and incident on a nonlinear medium such as an optical fiber, and a parametric process generated there is used.
The parametric process is a four-wave mixing (Four-wave mixing) due to a nonlinear effect such as a Kerr effect generated when the pump light and the signal light combined and incident on the nonlinear medium propagate through the nonlinear medium. It is a process of exchanging energy through a phenomenon called mixing (FWM).
In the parametric process, idler light is generated from the pump light and the signal light. The phase of the idler light depends on the phase of the signal light and the pump light at the time of incidence. When the PSA is designed so that the frequencies of the idler light and the signal light are equal, the signal light that originally existed and the newly generated idler light interfere with each other. As a result, the gain obtained by the signal light depends on the relative phase difference between the pump light and the signal light when the nonlinear medium is incident, and the signal light is amplified or attenuated according to the phase state. Can be used for the signal processing.

There are several forms of PSA, but two continuous lights (Continuous Wave; CW) having different frequencies are used as the pump light, and the pump light and the center frequency are set to an average value of the frequencies of the two pump lights. A configuration in which the matched signal light is incident on a nonlinear medium such as an optical fiber and the parametric process generated there is often used (Non-Patent Documents 1 to 4). Here, only the PSA (Dual-Pump PSA; also referred to as DP-PSA) having this configuration is focused, and hereinafter simply referred to as PSA.

When the PSA is used, a certain component of the phase components of the signal light is amplified, while a component having a quadrature phase relationship with the component is attenuated. In order to describe this situation in detail, FIG. 1A shows four signal complex amplitudes whose phases are shifted by 90 degrees on the complex plane. The real axis indicated by Re indicates that when the signal light and the pump light are incident on the nonlinear medium, the amplification gain of the signal light after the PSA output is maximized. When the initial relative phase difference is selected, the phase of the signal light is set to be 0 or π.
That is, of the four signals shown in FIG. 1A, two signal components located on the real axis are components that maximize the amplification gain by the PSA. Such a phase component is hereinafter referred to as an “in-phase” component. On the other hand, the imaginary axis shown as Im in FIG. 1A means that the signal light is 90 degrees out of phase with the signal light in the case of “in-phase”, and two signals on this axis. The component is a component that is attenuated by the PSA. Hereinafter, this is referred to as an “orthogonal” component. An arbitrary phase component of the signal light can be decomposed into the in-phase component and the quadrature component, and the former obtains an amplification gain, while the latter attenuates. As an example, as a result of amplification of the in-phase component of the signal shown in FIG. 1B and attenuation of the quadrature component, a signal as shown in FIG. 1C is obtained as an output signal of the PSA.
In the case of binary phase shift keying (BPSK) modulation, “orthogonal” is obtained by adjusting the initial relative phase difference between the pump light and the signal light so that the phase of the modulation signal becomes an “in-phase” component in the PSA. Phase noise corresponding to the component can be suppressed.

FIG. 2 shows a typical configuration example of the PSA, and its operation will be described below.
When the input signal light 1 is input to the PSA 100, a part of the input signal light 1 is branched and input to the pump light generation means 10.
The pump light generating means 10 generates pump light composed of two continuous lights having different frequencies.
These pump lights are output with the light intensity adjusted by the first light intensity adjusting means 11. Further, the input signal light 1 is input to the signal light phase adjusting means 12, and the relative phase difference between the input signal light 1 and the pump light is adjusted and output. Since what value the relative phase difference is set changes depending on what PSA operation is performed, the phase adjustment signal 2 is input from the outside. However, in the PSA whose operation is specified in advance, The means for generating the phase adjustment signal 2 may be installed inside the PSA 100, or the phase adjustment signal 2 does not exist and the phase adjustment amount of the signal light phase adjustment means 12 is fixed to a certain value. The structure which is may be sufficient.
The pump light and input signal light 1 output in this way are combined by a combined light generating means 13 such as an optical coupler. The combined light is output after the light intensity is adjusted by the second light intensity adjusting means 14.
The combined light whose light intensity is adjusted is incident on a nonlinear medium 15 such as an optical fiber, where the parametric process occurs. At this time, as shown in FIGS. 1A to 1C, among the phase components of the input signal light 1, the in-phase component is amplified and the quadrature component is attenuated.
Finally, the pump light is removed from the signal output from the nonlinear medium 15 by the signal light extraction means 16 such as a band pass filter, and only the output signal light 3 is output.
Conventionally known PSA is an example in which the principle is confirmed with the configuration shown in FIG. 2 in mind, or an example in which the PSA is actually operated. In Non-Patent Document 2, the operating principle of PSA is experimentally confirmed, and in Non-Patent Documents 3 and 4, the PSA based on the configuration of FIG. 2 is generally used, and the effect of reducing phase noise of phase-modulated signal light is experimentally determined. It has been confirmed. Here, only an optical fiber is considered as the nonlinear medium 15.

An important index for operating the PSA is the ratio between the amplification gain of the in-phase component and the attenuation amount of the quadrature component of the phase components of the signal light, and this is the gain extinction ratio (Gain-Extension Ratio). GER). When the GER is large, the quadrature component with respect to the in-phase component becomes relatively small, so that the desired purpose of removing phase noise from the phase modulation signal can be achieved.
In the conventionally known technology, by designing the PSA so as to increase the amplification gain of the in-phase component as much as possible, the quadrature component becomes relatively small and consequently the GER is increased. A method has been adopted.
However, in the PSA, in order to increase the amplification gain of the in-phase component, it is necessary to extremely increase the degree of the parametric process such as extremely increasing the light intensity of the pump light.
Actually, according to Non-Patent Document 3 in which such a setting is made, the GER as large as 30 dB is achieved, but the light intensity of the pump light is as large as 32.5 dBm, and thus such a large light intensity. Has become a major obstacle to commercialization.

Incidentally, the nonlinear phase shift amount φNL can be used as an index indicating the amount of the parametric process in the fiber. φNL is given by the following equation: φNL = γP _p L Where γ and L are the nonlinear constant and effective length (propagation length) of the fiber for generating the parametric process, respectively, and P _p is the intensity when pump light is input to the fiber.
In the setting disclosed in Non-Patent Document 3, as the nonlinear medium, the nonlinear constant is γ = 1.1 [1 / W / m], the length is 5.64 m, the propagation loss is 1.4 dB / m, and a normal fiber. An optical fiber having a fusion loss of 1.5 dB at one end is used, and the effective length L for the non-linear effect is L = 2.60 m. The intensity of the pump light used to obtain the large GER of 30 dB is 32.5 dBm. As a result of considering the fusion loss, the intensity P _{p of} the light actually input to the optical fiber is P _p = 31 dBm. That is, since it is 1.26 W, the nonlinear phase shift amount φNL at this time is estimated as φNL = γP _p L = 3.6 rad. Similarly, the pump light intensity for obtaining the GER of 20 dB is 29.2 dBm, and as a result of considering the fusion loss, the light intensity P _p actually input to the fiber is P _p = 27.7 dBm. That is, since it is 0.59 W, the nonlinear phase shift amount φNL at this time is estimated as φNL = γP _p L = 1.7 rad.
In order to realize the same PSA operation while reducing the intensity P _{p of the} pump light, it is necessary to increase one or both of the nonlinear constant γ and the length L of the optical fiber, which increases the cost. It is a problem because it connects. That is, the large GER must be realized with the small nonlinear phase shift amount φNL.

This invention makes it a subject to solve the said various problems in the past and to achieve the following objectives. That is, the present invention uses a phase sensitive optical amplifier capable of obtaining a large gain extinction ratio with a small nonlinear effect and efficiently suppressing phase noise, a design method thereof, and the phase sensitive optical amplifier. It is an object of the present invention to provide a BPSK signal phase noise suppressor, a BPSK signal regenerator, a QPSK signal demultiplexer, and a QPSK signal regenerator.

Means for solving the problems are as follows. That is,
<1> Pump light generating means for generating pump light that is two continuous lights having different frequencies, signal light that is input as light whose center frequency matches an intermediate frequency of the two continuous lights, and the pump light A combined light generating means for generating a combined light, a phase difference adjusting means for adjusting a relative phase difference between the signal light and the pump light, and the combined light having the adjusted relative phase difference. A phase-sensitive optical amplifier having a non-linear medium for generating a parametric process, wherein a gain extinction ratio of the target phase-sensitive optical amplifier is determined to be 20 dB or more. The complex amplitude value of the output signal light when the phase of the input signal light coincides with the orthogonal component when a circle having a radius of the complex amplitude value is drawn on the complex plane with the origin as the center Is set such that the intensity of the pump light, the nonlinear constant, the propagation length, and the dispersion value of the nonlinear medium are within the circle, and the nonlinear constant, the propagation length, and the intensity of the pump light are set. And a phase-sensitive optical amplifier characterized by having a product of less than 1.7 rad.
<2> The phase sensitive optical amplifier according to <1>, wherein the nonlinear medium is an optical fiber having an anomalous dispersion value.
<3> The phase-sensitive light according to any one of <1> to <2>, wherein the nonlinear medium is a nonlinear optical fiber whose nonlinear constant γ satisfies the following formula: γ> 5 [1 / W / km] amplifier.
<4> The phase sensitive optical amplifier according to any one of <1> to <3>, wherein the nonlinear medium is a nonlinear optical fiber including quartz glass.
<5> The phase response according to any one of <1> to <4>, further including pump light intensity adjustment means for adjusting light intensity of pump light input to any one of the combined light generation means and the nonlinear medium. Type optical amplifier.
<6> Pump light generating means for generating pump light that is two continuous lights having different frequencies, signal light that is input as light whose center frequency matches an intermediate frequency of the two continuous lights, and the pump light Combined light generating means for generating combined light, phase difference adjusting means for adjusting the relative phase difference between the signal light and the pump light of the combined light, and the combined light whose relative phase difference has been adjusted. A phase-sensitive optical amplifier having a nonlinear medium that generates a parametric process by inputting wave light, and radiates a complex amplitude value of the output signal light of the phase-sensitive optical amplifier determined by a target gain extinction ratio. When the circle is drawn on the complex plane with the origin as the center, the complex amplitude value of the output signal light when the phase of the input signal light coincides with a quadrature component is included in the circle. In addition, A design method of a phase sensitive optical amplifier, wherein the intensity of the pump light and a nonlinear constant, a propagation length, and a dispersion value of the nonlinear medium are set.
<7> The phase sensitive optical amplifier according to any one of <1> to <5>, a phase adjustment signal generating unit that generates a phase adjustment signal and inputs the phase adjustment signal to the phase sensitive optical amplifier, An output signal light monitor that monitors the output signal light output from the phase sensitive optical amplifier and inputs a feedback signal to the phase adjustment signal generating means, and suppresses phase noise of the input BPSK signal light And outputting to the outside, a BPSK signal phase noise suppressor.
<8> The BPSK signal phase noise suppressor according to <7>, and an amplitude stabilizer that converges the amplitude of the output signal light output from the BPSK signal phase noise suppressor to a constant value, A BPSK signal regenerator that outputs BPSK signal light in which phase noise and amplitude noise of BPSK signal light input as signal light are suppressed to the outside.
<9> First BPSK signal phase noise suppressor and second BPSK signal phase noise suppressor configured by the BPSK signal phase noise suppressor according to <7>, and a QPSK signal input as signal light Input signal light branching means for splitting the light into two and outputting the branched light to the first BPSK signal phase noise suppressor and the second BPSK signal phase noise suppressor, one by one The QPSK signal light is separated into two BPSK signal lights output from the first BPSK signal phase noise suppressor and the second BPSK signal phase noise suppressor, and these are output. A characteristic QPSK signal demultiplexer.
<10> The first BPSK signal regenerator and the second BPSK signal regenerator configured by the BPSK signal regenerator described in <8> above, and the QPSK signal light input as signal light branched into two And an input signal light branching means for outputting the branched light to the first BPSK signal regenerator and the second BPSK signal regenerator one by one, and the QPSK signal light A QPSK signal demultiplexer characterized in that it is separated into two BPSK signal lights output from the first BPSK signal regenerator and the second BPSK signal regenerator and outputs them.
<11> The relative phase difference between the QPSK signal demultiplexer according to any one of <9> to <10> and two BPSK signals output from the QPSK signal demultiplexer is adjusted to 90 degrees. And BPSK signal multiplexing means for generating one output QPSK signal light, and outputting the output QPSK signal light, in which noise of the QPSK signal light input as signal light is suppressed, to the outside A characteristic QPSK signal regenerator.

According to the present invention, the phase-sensitive optical amplifier capable of solving the above-described problems in the prior art, obtaining a large gain extinction ratio with a small nonlinear effect, and efficiently suppressing phase noise, and its A design method, and a BPSK signal phase noise suppressor, a BPSK signal regenerator, a QPSK signal demultiplexer, and a QPSK signal regenerator using the phase sensitive optical amplifier can be provided.

It is a figure which shows four signal complex amplitudes which the phase shifted 90 degree | times from a complex plane. It is a figure which shows one example of input signal light. It is a figure which shows the output signal light obtained as a result of amplifying the in-phase component of input signal light, and attenuating a quadrature component. It is a figure which shows the basic composition of a phase sensitive type optical amplifier. It is the conceptual diagram which showed the frequency arrangement | positioning of input signal light and pump light. It is explanatory drawing which shows the structural example of PSA. It is a figure which shows the experimental system for confirming the principle of PSA operation | movement. It is a spectrum figure in case the relative phase of pump light and signal light is the same phase. It is a spectrum figure in case the relative phase of pump light and signal light is orthogonal. It is a figure which shows the primary idler light generate | occur | produced by the input pump light on the frequency axis, input signal light, the primary idler light generate | occur | produced with pump light-pump light FWM, and pump light-signal light FWM. It is a figure which shows the gain amount or attenuation amount of the signal light with respect to nonlinear phase shift amount (phi) NL. It is the figure which showed a mode that the complex amplitude of output signal light developed on a complex plane at the time of changing nonlinear phase shift amount (phi) NL from 0 to 1.4 rad. It is the figure which showed a mode that the complex amplitude of the signal beam | light developed when the dispersion value of a fiber was changed. It is a figure which shows the structural example of a BPSK signal phase noise suppressor and a BPSK signal regenerator. It is a figure which shows the structural example of a QPSK signal demultiplexer. It is a figure which shows the structural example of a QPSK signal regenerator.

(Phase sensitive optical amplifier)
The phase sensitive optical amplifier of the present invention will be described with reference to the drawings.
First, referring to FIG. 2 again, a basic configuration example of the phase sensitive optical amplifier of the present invention will be described.

<Pump light generating means>
When the input signal light 1 is input to the PSA 100 by signal light input means (not shown) (arbitrary light source, BPSK signal generation means, QPSK signal generation means, etc.), a part is branched and input to the pump light generation means 10. . An optical coupler (not shown) or the like is used for branching the input signal light 1.
The pump light generation means 10 generates continuous light having a single frequency synchronized with the input signal light 1 using, for example, a laser diode having an injection locking mechanism as a light source.
By optically modulating the continuous light at a certain frequency Δf, an optical frequency comb having a frequency interval of Δf is generated. Of these comb components, only two components whose frequency arrangement with the input signal light 1 is as shown in FIG. Thus, the pump light (comb 1 and comb 2) composed of two continuous lights having different frequencies can be obtained.
Further, due to the relationship between the input signal light 1 and the pump light, the center frequency of the input signal light 1 coincides with an intermediate frequency between the two continuous lights.

FIG. 3 is a conceptual diagram showing the frequency arrangement of the input signal light 1 and the pump light. In FIG. 3, Δf ′ indicates the frequency interval between one comb component of the pump light and the input signal light 1. ing.
Further, the pump light generating means used in the present invention is not particularly limited as long as it can generate pump light that is two continuous lights having different frequencies, and is not limited to the above configuration example. Further, the signal light input means is not particularly limited as long as it can input signal light having a center frequency that matches an intermediate frequency between the two continuous lights, and is not limited to the above configuration example.

<Combined light generation means>
Next, each pump light generated by the pump light generation means 10 and the input signal light 1 are combined by a combined light generation means 13 such as an optical coupler to be combined light.

<Signal light phase adjusting means>
The signal light phase adjusting means 12 adjusts the relative phase difference between the input signal light 1 and each pump light generated by the pump light generating means 10, and the input signal light 1 having the adjusted relative phase difference is combined with the input signal light 1. It outputs to the wave light generation means 13.
Of course, the adjustment of the relative phase difference may be performed either before or after the multiplexing. When adjusting after the multiplexing, for example, as shown in FIG. 4, the pump light generating means 20 and the light intensity adjusting means 21 are used. , 24, the combined light generating means 23, the signal light phase adjusting means 22, the nonlinear medium 25, and the signal light extracting means 26, the input signal light 1 combined by the combined light generating means 23 and two pumps Of the light, the signal light phase adjusting means 22 may be arranged so as to adjust the phase of the input signal light 1.
However, in the PSA 200 that adjusts the phase of the input signal light 1 after combining, the signal light phase adjusting means 22 independently adjusts the phase for each frequency component of the combined pump light and input signal light 1. It must be a means that can be controlled.
FIG. 4 is an explanatory diagram showing another configuration example of the PSA, and the PSA 200 is configured in the same manner as the PSA 100 except for the arrangement of the signal light phase adjusting means 22.

Also, what value the relative phase difference is set to varies depending on what kind of PSA operation is performed, and therefore the phase adjustment signal 2 is input from the outside. Thereby, the value of the relative phase difference can be appropriately set according to the purpose.

<Light intensity adjusting means>
In FIG. 2, the intensity of each pump light output from the pump light generating means 10 is adjusted by the light intensity adjusting means 11. Further, the light intensity of the input signal light 1 and each of the pump lights output from the signal light phase adjusting means 12 is adjusted by the light intensity adjusting means 14. These light intensity adjusting means 11 and 14 are used, for example, to amplify the intensity of light output from each means, and are constituted by an optical amplifier such as an erbium-doped optical fiber amplifier.

However, the light intensity adjusting means 11 and 14 are not necessarily required when the intensity of light output from each of the means is sufficient. Further, only the light intensity adjusting means 11 may be provided to adjust the intensity of the light of each pump light alone, and only the light intensity adjusting means 14 may be provided and output from the signal light phase adjusting means 12. The light intensity of the input signal light 1 and each pump light may be adjusted. Further, when an optical amplifier such as the erbium-doped optical fiber amplifier is used as the light intensity adjusting means 11 and 14, the light intensity may be adjusted by adjusting the amplification gain, but the amplification gain is a large value instead. And a means for adjusting the light intensity by arranging a variable optical attenuator (VOA) or the like downstream of the light intensity adjusting means 11, 14.

The input signal light 1 output from the light intensity adjusting means 14 and the combined light of the pump lights are incident on a nonlinear medium 15 such as an optical fiber, where the aforementioned parametric process occurs. At this time, as shown in FIGS. 1A to 1C, among the phase components of the input signal light 1, the in-phase component is amplified and the quadrature component is attenuated.

<Nonlinear media>
The nonlinear medium 15 is not particularly limited as long as the target GER is obtained, and examples thereof include an optical fiber. Among these, an optical fiber having an anomalous dispersion value is preferable. When the optical fiber having the anomalous dispersion value is used, the target GER can be achieved with an ideal design for practical use of the PSA.
The nonlinear medium 15 is not particularly limited, but is preferably a highly nonlinear optical fiber whose nonlinear constant γ satisfies the following equation, γ ≧ 5 [1 / W / Km]. When the nonlinear constant γ is less than 5, the design width for achieving the target GER is likely to be limited.
Although there is no restriction | limiting in particular as such a nonlinear medium 15, The highly nonlinear optical fiber containing quartz glass is preferable. For example, a highly nonlinear optical fiber based on quartz glass, which is doped with other materials (germanium, etc.) that increase the refractive index in the core at a high concentration, and the core is designed to have a smaller diameter than a normal fiber. preferable.

<Other means>
The pump light is removed from the signal output from the nonlinear medium 15 by signal light extraction means 16 such as a band pass filter, and only the output signal light 3 in which the gain of the input signal light 1 is amplified is output.
However, the signal light extraction means 16 is not necessarily arranged in the PSA, and may be provided outside the PSA 100, for example.
Further, the phase sensitive optical amplifier of the present invention can be constituted by appropriately adopting means other than the means shown in FIG. 2 as long as the effect is not hindered.

<Design principle>
The core of the technology is that the phase sensitive amplifier (PSA) has the pump light intensity, the nonlinear constant of the nonlinear medium, the propagation length, and the dispersion value set according to the design principle described below.

First, an experimental system performed to confirm the effectiveness of the design principle of the phase sensitive amplifier will be described. FIG. 5 shows an experimental system for confirming the principle of PSA operation.
The optical pulse generator (OPG) 302 modulates continuous light having a wavelength of 1,561 nm output from the wavelength tunable light source (TLS) 301 to generate an optical frequency comb having a frequency interval of 43 GHz.
Of these, the bandpass optical filter (OBPF) 303 removes components other than the three frequency comb components centered on the frequency corresponding to the wavelength of 1,561 nm. At the time of passing through the OBPF 303, the three frequency comb components are in phase, and the center frequency comb component is signal light, and the other two comb components are combined into pump light.
The frequency difference between the two CWs constituting the pump light is 86 GHz, which is approximately 0.7 nm when converted to a wavelength difference.

The light intensity is amplified to an arbitrary value by an erbium-doped optical fiber amplifier (EDFA) 304, and spontaneous emission light noise is removed by OBPF 305.
Using a variable band spectrum shaper (VBS) 306 capable of phase adjustment for each frequency component, in the PSA operation of the PSA 300, the phase of the signal light matches either the in-phase component or the quadrature component. The relative phase difference between the signal light and the pump light is adjusted.
The light intensity of the signal light and the pump light is again amplified by the EDFA 307 and noise is removed by the OBPF 308, and then input to the highly nonlinear fiber (HNLF) 309 having an anomalous dispersion value.

The length of the HNLF 309 is 600 m, the dispersion value is 0.482 ps / nm / km in the anomalous dispersion region, and the nonlinear constant is γ = 10 [1 / W / km]. The dispersion slope value is 0.03 ps / nm ² / km or less, and the propagation loss value is 1 dB / km or less.
The HNLF 309 used here is a non-perforated fiber in which quartz glass is used as a host glass and germanium is doped at a high concentration in the core. This type of fiber has much smaller propagation loss and connection loss than those using lead glass or bismuth as the material, or those with a perforated shape, and has excellent controllability of dispersion value and dispersion slope. Therefore, it is most suitable for PSA applications.
In addition, the nonlinear constant is a condition of γ ≧ 5 [1 / W / km], and it has a great effect on shortening the length and reducing the required incident intensity compared to transmission optical fibers such as SMF and DSF. To do.

The optical spectrum before and after the HNLF 309 is input is measured by an optical spectrum analyzer (OSA) 310 and 311 to evaluate the gain or attenuation of the signal light. Further, the intensity of output light is monitored by a power meter (PM) 312.
As an example, the input light intensity to the HNLF 309 is P _p = 21.8 dBm, and the relative phase difference between the pump light and the signal light is the same as that of the “in-phase” component or “quadrature” component of the PSA 300 FIG. 6 shows a spectrum measurement result when setting is performed. 6A shows a spectrum measurement result when the phase of the signal light matches the “in-phase” component, and FIG. 6B shows a spectrum measurement result when the phase of the signal light matches the “quadrature” component. Yes.

6A and 6B, it can be seen that a very large value of about 30 dB is obtained as the GER of the signal light. At this time, the nonlinear phase shift amount φNL is φNL = 0.9 rad. In Non-Patent Document 3, as described above, the nonlinear phase shift amount φNL for obtaining the GER of 30 dB is estimated to be φNL = 3.6 rad. When this value is compared with the value of the experimental system, the experiment It can be said that the system was able to realize a large GER with a considerably small φNL.

Hereinafter, the reason why the efficient PSA operation can be realized as described above will be clarified, and the optimum design method of the PSA will be clarified.

FIG. 7 shows the input pump light (ωp1 and ωp2), the input signal light (ωs), and the primary idler light (ωpp1 and ωpp2) generated by the pump light-pump light FWM resulting from the parametric process occurring in the fiber. The primary idler light (ωps1 and ωps2) generated by the pump light-signal light FWM is represented on the frequency axis.
Conventionally used PSA configurations focus only on parametric processes that occur between input light components indicated by the dotted square frame in FIG.
Here, this is called a “three-wave model”, and the existence of idler light components is not recognized. In the three-wave model, in order to efficiently generate the parametric process and obtain a large GER with respect to the input signal light, the pump light-pump light FWM and the pump light-signal light FWM are generated. Therefore, a configuration in which the primary idler light component does not grow is required.
This is because when the primary idler light component grows, the energy of the pump light is dissipated to those components or even higher order idler light components, and the parametric process grows before the signal light has sufficient amplification gain. Is saturated.
On the other hand, it is known that the gain of the idler light is remarkably increased when the fiber for generating the parametric process has an anomalous dispersion value. In order to suppress this and increase the GER of the signal light with the PSA of the three-wave model, Non-Patent Document 2 to Non-Patent Document 4 use a fiber having a relatively large normal dispersion value.
On the other hand, in the present invention, by actively growing the idler light component (see FIG. 7), the attenuation amount of the quadrature component out of the phase components of the signal light has never been considered so far. As a result, the large GER is achieved with the small nonlinear phase shift amount.

The high efficiency PSA operation obtained as shown in FIG. 6 using the experimental system shown in FIG. 5 is analyzed in consideration of the seven components shown in FIG. Here, this is referred to as a “7-wave model”.
The evolution equation for the light intensity P _i of each light wave component and the propagation distance z of the phase φ _i is given by the following simultaneous ordinary differential equations.

However, in the formula (2), the subscripts i, m, n, p, q, and o are the subscripts s, p1, p2, pp1, pp2, ps1, and ps2 of the seven waves shown in FIG. Any one of them, and θ _{i, m, n, p} are

In the equation (3), Δβ _{i, m, n, p} is

And β represents the propagation constant at the frequency of each component.
However, in the sum sign of the right side of the formula (1) and the right side of the formula (2), the subscripts other than i are summed. Among these, terms including p, m, and n are caused by non-degenerate FWM. Is what

Suppose that the sum of subscript combinations for which
The term including q and o is due to the degenerate FWM.

It is assumed that a sum is taken for combinations of subscripts that satisfy the above relationship.
In the equations (1) and (2), θ _{i, q, q, o} is given in the same manner as θ _{i, m, n, p} .

FIG. 8 shows the gain amount or attenuation amount of the signal light with respect to the nonlinear phase shift amount φNL (φNL = γPpL). The phase of the input signal light is expressed by the in-phase component or the quadrature component of the PSA 300. The ratio of the intensity of the signal light output to the initial value when matched with the phase is shown by changing the intensity P _p of the input pump light.
The conditions excluding the input pump light intensity P _p are the same as those for obtaining the result of FIG.
The horizontal axis in FIG. 8 indicates the nonlinear phase shift amount φNL (φNL = γP _p L), and the nonlinear constant and length of the fiber are γ = 10 [1 / W / km] and L, respectively. = 600 [m], and only the intensity P _p of the input pump light is changed. For the same value of φNL, it is considered that the same result can be obtained even if different values of γ, P _p , and L are used as combinations.

In FIG. 8, dots indicate experimental results, solid lines indicate calculation results obtained by solving the equations (1) and (2) in consideration of the seven-wave model, and dotted lines indicate the three-wave model. The calculation result which solved the said Formula (1) and the said Formula (2) in consideration of is shown. Further, when the vertical axis takes a positive value, it indicates that the signal light is amplified with respect to the initial value, and the phase of the input signal light is made to coincide with the phase of the in-phase component of the PSA. The results obtained are shown below. Similarly, when the vertical axis takes a negative value, it indicates that the signal light has attenuated with respect to the initial value, and the phase of the input signal light matches the phase of the orthogonal component of the PSA. The results obtained are shown below. Further, for one φNL = γP _p L, the difference between the result in the “in-phase” case and the result in the “quadrature” case means the GER at that φNL.

FIG. 8 shows that the maximum GER value of 30 dB is obtained when φNL = γP _p L = 0.9 [rad], that is, P _p = 0.15 [W] (21.8 dBm). Recognize. Further, the calculation result (solid line) based on the 7-wave model agrees better with the experimental result than the calculation result (dotted line) based on the 3-wave model. The difference between the calculation results of both models can be interpreted as follows.
In the three-wave model, since the idler light does not exist, the intensity of the pump light does not saturate, and the amplification gain in the case of the in-phase is relatively large, while the attenuation amount in the case of the quadrature is the case of the in-phase. Because of the relationship between the gain and the reciprocal (positive / negative inversion on the logarithmic axis), it cannot be dramatically large.
On the other hand, in the seven-wave model, the intensity of the pump light is reduced by the growth of the idler component, and the gain of the signal light is relatively small, but the energy of the signal light is the idler. As a result of shifting to the component, it is considered that the attenuation amount in the case of the orthogonality suddenly increases, and as a result, a large GER is obtained.

Next, when the 7-wave model is calculated using the equations (1) and (2) and the nonlinear phase shift amount φNL is changed from 0 to 1.4 rad, the output signal of the PSA FIG. 9 shows how the complex amplitude of light develops on the complex plane.
In FIG. 9, each point indicated by a square and a circle corresponds to the case of the in-phase (square) and the orthogonal (circle), respectively, and indicates a value obtained by changing φNL every 0.1 rad. However, unlike the conditions for obtaining the results shown in FIGS. 6 and 8, the dispersion value of the fiber is set to zero.

In both cases, the phase rotates around the vicinity of the origin, which is due to the self-phase modulation of the signal light itself and the mutual phase modulation from other components. In the orthogonal case, when φNL = 0.9 [rad], the amplitude of the signal light is closest to the origin, and the GER at this time is 32 dB, which is the maximum in the calculation result. From this, if the parameters of the PSA are determined so that the curve indicating the development of the complex amplitude of the signal light passes through the origin, the infinite GER can be obtained in principle at the parameters at the origin. It is predicted. The present invention provides an optimum design method of the PSA based on this prediction. Hereinafter, a design method for obtaining a large GER by optimizing the dispersion value of the fiber and the nonlinear phase shift amount φNL will be described.

FIG. 10 shows how the complex amplitude of the signal light develops when the dispersion value of the fiber is changed. Specifically, the phase of the input signal light is changed to the phase of the orthogonal component. , The state in which the complex amplitude of the output signal light develops with respect to φNL every 0.1 rad from 0 to 1.4 rad is calculated using the expressions (1) and (2). The result calculated by the 7-wave model is shown.
However, when the dispersion value of the fiber constituting the PSA is changed in four ways, and the square, circle, rhombus, and triangle points are -0.208 ps / nm / km (square), 0 ps, respectively. The results are shown for / nm / km (circle), 0.208 ps / nm / km (diamond), and 0.494 ps / nm / km (triangle).
In order to increase the dispersion effect, the wavelength difference of the pump light is set to 3.5 nm.

As shown in FIG. 10, the state of development of the complex amplitude of the output signal light can be understood from the nonlinear phase shift amount φNL and the dispersion value of the fiber. Now, if the dispersion value is set to 0.208 ps / nm / km (diamonds) in the anomalous dispersion region and the nonlinear phase shift amount φNL is set to 0.9 rad, the GER can be set to the maximum value of 42 dB. That is, by considering the seven-wave model that allows the idler light, the PSA can be designed to achieve a very large GER under a considerably small amount of the nonlinear phase shift.
If the required value of φNL can be reduced, the input light intensity can be reduced, the fiber length can be shortened, and further the nonlinear constant of the fiber can be reduced. Can be provided.
In particular, when the fiber having the anomalous dispersion value (dispersion value is greater than 0) that actively uses the idler light is adopted as the fiber, the intensity attenuation, self-phase modulation, and cross-phase modulation are used. A moderate anomalous dispersion effect is exerted on both of the phase shift amounts due to the above, and the complex amplitude can be developed so that the balance between the two is balanced and, as a result, approaches the origin most (the diamond points in FIG. 10). In other words, it is easier to obtain a large GER with a small amount of the nonlinear phase shift than those having a normal dispersion value or zero dispersion. However, since an excessive anomalous dispersion effect breaks the balance, it is difficult to obtain a large GER. A preferable upper limit value of the anomalous dispersion value can be about 0.4 ps / nm / km.

From the above, when the desired GER value is given, it is possible to design the setting parameters of the intensity of the pump light, the nonlinear constant of the nonlinear medium, the propagation length, and the dispersion value with a range.
In the result of FIG. 10, when the φNL is larger than 0.6 rad, the amplification gain of the output signal light when the phase of the input signal light is the same phase is substantially constant with respect to the φNL. Therefore, the GER in this case is determined by the attenuation amount of the output signal light when the phase of the input signal light is orthogonal.
When the desired GER is given, a circle having a radius of the amplitude of the output signal light corresponding to the desired GER value can be drawn with the origin at the center in FIG.
Therefore, based on the seven-wave model and using the dispersion value of the fiber and the nonlinear phase shift amount φNL (φNL = γP _p L) as parameters, the PSA operation is performed using the equations (1) and (2). When the complex amplitude of the output signal light at the time is calculated and the complex amplitude passes through the inside of the circle, the dispersion value and the nonlinear phase shift amount φNL at that time give the desired GER Obtained as a design parameter.
In addition, if the dispersion value and the nonlinear phase shift amount φNL are determined in this way, design parameters having a certain range can be obtained, which is advantageous when manufacturing the phase sensitive optical amplifier.
As a specific example, when the frequency difference between two frequency combs forming the pump light is 430 GHz, if the target GER value is set to 20 dB, −0.52 ps / nm / km to 1.04 ps / nm / It is found that there is at least one nonlinear phase shift amount φNL that satisfies the condition for the dispersion value in the range of km.

Here, an object of the phase sensitive optical amplifier is to achieve a large GER with a small nonlinear phase shift amount φNL.
Therefore, the GER value is at least 20 dB, preferably 25 dB or more, and more preferably 30 dB or more. Furthermore, the nonlinear phase shift amount φNL for achieving the GER is preferably less than 1.7 rad and less than 1 rad.

The output signal light when the phase of the input signal light coincides with a quadrature component when a circle having a radius of the amplitude value of the output signal light determined by the GER is drawn on a complex plane. The GER and the non-linear phase shift amount necessary for determining whether or not the complex amplitude value falls within the circle with respect to the non-linear phase shift amount within a certain range are as follows from the actual system of the PSA. Can be confirmed.
That is, the signal light whose phase is adjusted to match that of the in-phase component or the quadrature component of the PSA is input, the intensity of the output signal light is measured, and the ratio of these is taken to obtain the GER value. Get the value. Next, the nonlinear phase shift amount is calculated by measuring the nonlinear constant γ and length L of the optical fiber being used and the intensity P _p of the input pump light.

(Design method of phase sensitive optical amplifier)
The phase-sensitive optical amplifier design method of the present invention includes pump light generating means for generating pump light that is two continuous lights having different frequencies, and light whose center frequency matches the intermediate frequency between the two continuous lights. Combined light generating means for combining the input signal light and the pump light to generate combined light; and a phase difference adjusting means for adjusting a relative phase difference between the signal light of the combined light and the pump light; A phase-sensitive optical amplifier having a non-linear medium for generating a parametric process by inputting the combined light, the relative phase difference of which is adjusted, and being determined by a target gain extinction ratio When the circle having the radius of the complex amplitude value of the output signal light is drawn on the complex plane with the origin as the center, the phase of the input signal light when the phase of the signal light matches the orthogonal component Duplicate So that the amplitude value falls within the circle, the intensity of the pump light, the nonlinear constant of the nonlinear medium, and sets a propagation length and variance.

The matters described in the phase sensitive amplifier of the present invention can be applied to the pump light generating means, the combined light generating means, the phase difference adjusting means, and the nonlinear medium.
The phase sensitive amplifier of the present invention also describes details of a method for setting the intensity of the pump light in consideration of the complex amplitude value of the output signal light and the nonlinear constant, propagation length, and dispersion value of the nonlinear medium. The matters described as the design principle can be applied.
The method for designing the phase sensitive optical amplifier can be applied to any of the phase sensitive optical amplifiers having the basic configuration of the phase sensitive optical amplifier (see, for example, FIG. 2 and FIG. 4). Unlike the description in the amplifier, the target GER and the nonlinear phase shift amount set when the GER is determined are not limited. However, from the viewpoint of achieving a large GER with a small nonlinear phase shift amount φNL, The set value of GER is preferably 20 dB or more, more preferably 25 dB or more, and particularly preferably 30 dB or more. Further, the value of the nonlinear phase shift amount φNL is preferably less than 1.7 rad, and more preferably less than 1 rad.

(BPSK signal phase noise suppressor and BPSK signal regenerator)
By using the phase sensitive optical amplifier of the present invention, phase noise of a BPSK (binary phase shift keying) signal can be suppressed. A BPSK signal phase noise suppressor and a BPSK signal regenerator using the phase sensitive optical amplifier of the present invention will be described below.

FIG. 11 shows a configuration example of a BPSK signal phase noise suppressor and a BPSK signal regenerator according to the present invention.
The BPSK signal phase noise suppressor 30 includes a PSA 100, phase adjustment signal generation means 32, and a signal light monitor 33.
The input BPSK signal light 31 is input to the PSA 100 from the outside, and is also generated from the phase adjustment signal generating means 32 by the input BPSK signal light 31 and the pump light generating means 10 of the PSA 100 (see FIG. 2). A phase adjustment signal for adjusting a relative phase difference with each pump light is input.
As a result, when the output signal light is output from the PSA 100 and input to the signal light monitor (output signal light monitor) 33, the signal light monitor 33 monitors the output signal light and feeds it back to the phase adjustment signal generating means. Input the signal.
At this time, feedback control is performed so that the feedback signal is supplied to the PSA 100 as the phase adjustment signal that most amplifies the output signal light. That is, control is performed so that the phase of the input BPSK signal light 31 matches the phase of the in-phase component of the PSA 100.
As a result, the phase noise corresponding to the quadrature component of the PSA 100 is suppressed, and the desired output BPSK signal light 34 can be output from the BPSK signal phase noise suppressor 30 through the feedback-controlled PSA 100.

Since the output BPSK signal light 34 has noise in the amplitude direction, the BPSK signal regenerator 50 stabilizes it and outputs it.
That is, the BPSK signal regenerator 50 includes a BPSK signal phase noise suppressor 30 and an amplitude stabilizer 51 that converges the amplitude of the output BPSK signal light 34 to a constant value.
As the amplitude stabilizer 51, a known amplitude stabilizer using a parametric process generated in an optical fiber can be appropriately adopted and used.
In the BPSK signal regenerator 50, the output BPSK signal light 52 in which the noise in the amplitude direction is further suppressed is obtained by the amplitude stabilizer 51 with respect to the output BPSK signal light 34 in which the noise in the phase direction is suppressed.
Therefore, as a result, the noise of the input signal BPSK signal light 31 can be suppressed in both the amplitude direction and the phase direction.

(QPSK signal demultiplexer and QPSK signal regenerator)
Furthermore, by using the phase sensitive optical amplifier of the present invention, it is possible to demultiplex QPSK (quaternary phase shift keying) signal light into two BPSK signals as they are and to suppress phase noise. A QPSK signal demultiplexer and a QPSK signal regenerator using the phase sensitive optical amplifier of the present invention will be described below.

FIG. 12 shows a configuration example of the QPSK signal demultiplexer according to the present invention. This QPSK signal demultiplexer is configured as a QPSK signal demultiplexer that converts QPSK signal light into two BPSK signal lights.
The QPSK signal demultiplexer 70 includes an input signal light branching unit that branches the input QPSK signal light 71 into two parts, a first BPSK signal regenerator 50A, and a second BPSK signal regenerator 50B. The BPSK signal regenerator of the present invention is used for each of these BPSK signal regenerators. A 3 dB optical coupler or the like can be applied as the input signal light branching means.
When the input QPSK signal light 71 is input from the outside to the QPSK signal demultiplexer 70, the input QPSK signal light 71 is branched into two by the input signal light branching means (not shown), and the first split light is the first light. The signals are input to the BPSK signal regenerator 50A and the second BPSK signal regenerator 50B, respectively.
The input QPSK signal light 71 is obtained by combining the I channel and the Q channel as phase components. In the first BPSK signal regenerator 50A, the I channel of the input QPSK signal light is converted to the PSA 100 (see FIGS. 2 and 11). On the other hand, in the second BPSK signal regenerator 50A, the Q channel of the input QPSK signal light 71 is adjusted to match the in-phase component of the PSA 100.
As a result, each of the I channel and Q channel of the input QPSK signal light 71 is output BPSK signal light (first output BPSK signal light 52A and second output BPSK signal light 52B) in a state where noise is suppressed. Demultiplexed and output.

Note that, as a function of the QPSK signal demultiplexer, it is not always necessary to suppress noise in the amplitude direction as the output BPSK signal light. In the QPSK signal demultiplexer shown in FIG. Instead of the regenerator 50A and the second BPSK signal regenerator 50B, two BPSK signal phase noise suppressors 30 shown in FIG. 11 are prepared, and these are used as the first BPSK signal phase noise suppressor and the second BPSK signal. It may be configured as a phase noise suppressor.

Next, the QPSK signal regenerator of the present invention will be described with reference to FIG. FIG. 13 shows a configuration example of a QPSK signal regenerator.
The QPSK signal regenerator 90 includes a QPSK signal demultiplexer 70 and a BPSK signal multiplexing unit 91 shown in FIG.
The BPSK signal multiplexing means 91 multiplexes the two output BPSK signal lights output from the QPSK signal demultiplexer 70 so that the relative phase difference between them is 90 degrees. That is, the BPSK signal multiplexing unit 91 converts the two output BPSK signal lights whose noises are suppressed by the QPSK signal demultiplexer 70 from the first output BPSK signal light 52A whose relative phase difference is 90 degrees and the first output BPSK signal light 52A. 2 output BPSK signal light 52B.
As a result, an output QPSK signal light 92 in which noise is suppressed in both the amplitude direction and the phase direction with respect to the original input QPSK signal light 71 is obtained. This configuration is proposed in Non-Patent Document 5, but can be realized under more practical and highly efficient design parameters by using the phase sensitive optical amplifier of the present invention. .

In the QPSK signal regenerator 90 shown in FIG. 13, since the output QPSK signal light 92 in which noise is suppressed in both the amplitude direction and the phase direction is obtained, the first BPSK signal regenerator 50A and the second BPSK signal regenerator 90 are obtained. In place of the detector 50B, two BPSK signal phase noise suppressors 30 shown in FIG. 11 are prepared and arranged as a first BPSK signal phase noise suppressor and a second BPSK signal phase noise suppressor. Good.

DESCRIPTION OF SYMBOLS 1 Input signal light 2 Phase adjustment signal 3

Output signal light

10, 20 Pump light generation means 11, 21 Light intensity adjustment means 12, 22 Signal light phase adjustment means 13, 23 Combined light generation means 14, 24 Light intensity adjustment means 15 , 25

Non-linear medium

16, 26 Signal light extraction means 30 BPSK signal phase noise suppressor 31 Input BPSK signal light 32 Phase adjustment signal generation means 33 Signal light monitor 34, 52 Output BPSK signal light 50A First BPSK signal regenerator 50B Second BPSK signal regenerator 50 BPSK signal regenerator 51 Amplitude stabilizer 52A First output BPSK signal light 52B Second output BPSK signal light 70 PSK signal inverse multiplexer 71 input QPSK signal light 90 QPSK signal regenerator 91 BPSK signal combining means 92 output QPSK signal light 100, 200, 300 PSA
301 Variable wavelength light source (TLS)
302 Optical pulse generator (OPG)
303, 305, 308 Bandpass filter (OBPF)
304,307 Erbium-doped fiber amplifier (EDFA)
306 Variable band spectrum shaper (VBS)
309 Optical Nonlinear Fiber (HNLF)
310, 311 Optical spectrum analyzer (OSA)
312 Power meter (PM)

Claims

Pump light generating means for generating pump light that is two continuous lights having different frequencies;
A combined light generating means for generating a combined light by combining the pumping light with the signal light that is input as light having a center frequency matching an intermediate frequency between the two continuous lights;
A phase difference adjusting means for adjusting a relative phase difference between the signal light and the pump light;
A phase-sensitive optical amplifier comprising: a nonlinear medium that inputs the combined light with the adjusted relative phase difference and generates a parametric process;
A circle whose radius is the complex amplitude value of the output signal light of the phase-sensitive optical amplifier, which is determined with the gain extinction ratio of the target phase-sensitive optical amplifier being 20 dB or more, is drawn on the complex plane with the origin as the center. The intensity of the pump light and the nonlinear medium of the nonlinear medium so that the complex amplitude value of the output signal light when the phase of the input signal light coincides with a quadrature component is within the circle. A phase sensitive optical amplifier, wherein a constant, a propagation length, and a dispersion value are set, and a product of the nonlinear constant, the propagation length, and the intensity of the pump light is less than 1.7 rad.
2. The phase sensitive optical amplifier according to claim 1, wherein the nonlinear medium is an optical fiber having an anomalous dispersion value.
3. The phase sensitive optical amplifier according to claim 1, wherein the nonlinear medium is a nonlinear optical fiber whose nonlinear constant γ satisfies the following formula, γ> 5 [1 / W / km].
4. The phase sensitive optical amplifier according to claim 1, wherein the nonlinear medium is a nonlinear optical fiber containing quartz glass.
5. The phase sensitive optical amplifier according to claim 1, further comprising pump light intensity adjusting means for adjusting the light intensity of the pump light input to either the multiplexed light generating means or the nonlinear medium.
Pump light generating means for generating pump light that is two continuous lights having different frequencies;
A combined light generating means for generating a combined light by combining the pumping light with the signal light that is input as light having a center frequency matching an intermediate frequency between the two continuous lights;
A phase difference adjusting means for adjusting a relative phase difference between the signal light of the combined light and the pump light;
A phase-sensitive optical amplifier having a nonlinear medium that receives the combined light with the adjusted relative phase difference and generates a parametric process;
The signal light input when a circle having a radius of the complex amplitude value of the output signal light of the phase sensitive optical amplifier determined by the target gain extinction ratio is drawn on the complex plane with the origin as the center The intensity of the pump light, the nonlinear constant of the nonlinear medium, the propagation length, and the dispersion value are set so that the complex amplitude value of the output signal light when the phase of the output signal coincides with a quadrature component falls within the circle A method for designing a phase-sensitive optical amplifier.
A phase sensitive optical amplifier according to any one of claims 1 to 5;
A phase adjusting signal generating means for generating a phase adjusting signal and inputting it to the phase sensitive optical amplifier;
An output signal light monitor that monitors the output signal light output from the phase sensitive optical amplifier and inputs a feedback signal to the phase adjustment signal generating means;
A BPSK signal phase noise suppressor for suppressing phase noise of input BPSK signal light and outputting the same to the outside.
A BPSK signal phase noise suppressor according to claim 7;
An amplitude stabilizer that converges the amplitude of the output signal light output from the BPSK signal phase noise suppressor to a constant value;
A BPSK signal regenerator that outputs BPSK signal light in which phase noise and amplitude noise of BPSK signal light input as signal light are suppressed to the outside.
A first BPSK signal phase noise suppressor and a second BPSK signal phase noise suppressor, each comprising the BPSK signal phase noise suppressor according to claim 7;
QPSK signal light input as signal light is branched into two, and one of the branched lights is supplied to the first BPSK signal phase noise suppressor and the second BPSK signal phase noise suppressor. An input signal light branching means for outputting,
The QPSK signal is characterized by separating the QPSK signal light into two BPSK signal lights output from the first BPSK signal phase noise suppressor and the second BPSK signal phase noise suppressor and outputting them. Inverse multiplexer.
A first BPSK signal regenerator and a second BPSK signal regenerator, each comprising the BPSK signal regenerator according to claim 8;
An input signal for branching the QPSK signal light input as signal light into two and outputting the branched light to the first BPSK signal regenerator and the second BPSK signal regenerator one by one Optical branching means,
A QPSK signal demultiplexer, wherein the QPSK signal light is separated into two BPSK signal lights output from the first BPSK signal regenerator and the second BPSK signal regenerator, and these are output.
QPSK signal demultiplexer according to any of claims 9 to 10,
BPSK signal multiplexing means for adjusting and multiplexing the relative phase difference between the two BPSK signals output from the QPSK signal demultiplexer to 90 degrees and generating one output QPSK signal light;
A QPSK signal regenerator that outputs the output QPSK signal light, in which noise of the QPSK signal light input as signal light is suppressed, to the outside.