Wavelength converter and wavelength conversion method

Abstract

To provide a wavelength converter and a wavelength conversion method for converting the wavelength of an optical signal while maintaining signal quality with a simple configuration.SOLUTION: The reception means demultiplexes a quadrature-phase-modulated optical signal having a first wavelength into first and second optical signals, causes the first optical signal to interfere with first local oscillation light, causes the second optical signal to interfere with second local oscillation light whose phase is shifted so as to be a quadrature phase with respect to the first local oscillation light, and outputs an in-phase analog signal and a quadrature-phase analog signal. The analog compensation means performs analog compensation on the in-phase analog signal and the quadrature-phase analog signal. The transmission means modulates the first transmission light and the second transmission light of the second wavelength into a first in-phase optical signal and a first quadrature-phase optical signal based on the in-phase analog signal and the quadrature-phase analog signal after the analog compensation, multiplexes the first in-phase optical signal and the first quadrature-phase optical signal of which the phase is shifted so as to cancel a deviation amount of the phase shift given to the second local light, and outputs an optical signal of the second wavelength subjected to quadrature phase modulation.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a wavelength converter and a wavelength conversion method. [Background technology]

[0002] Wavelength converters that convert an optical signal of a certain wavelength into an optical signal of another wavelength are known as devices used in optical networks. For example, as shown in Patent Document 1, wavelength converters that convert the wavelength of a quadrature-phase modulated optical signal containing an I (in-phase) phase and a Q (quadrature) phase that are orthogonal to each other are widely used.

[0003] This wavelength converter converts the received optical signal into an analog signal by coherent detection. Then, it outputs an optical signal of another wavelength by modulating light of a different wavelength from the received optical signal based on the converted analog signal. In coherent detection, the received signal is split into two. One of the split optical signals is then interfered with local light to generate an I-phase optical signal. The other split optical signal is then interfered with local light whose phase is shifted by 90° to generate a Q-phase optical signal. Then, it is possible to obtain I-phase and Q-phase analog signals by opto-electrically converting the I-phase and Q-phase optical signals. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2024-036713 Summary of the Invention [Problem to be solved by the invention]

[0005] In a typical wavelength converter, a Q-phase optical signal is obtained by interfering a local light beam, which has been phase-shifted by 90° using a phase shifter, with a received optical signal. However, it is difficult to achieve a phase shift of exactly 90° using a phase shifter. For example, due to manufacturing errors in the phase shifter, the phase shift that the phase shifter imparts to the local light beam deviates from 90°. Furthermore, while phase shifters are expected to be used within a certain wavelength range, it is difficult to design them so that the phase shift is 90° over the entire wavelength range. This results in an imbalance between the I-phase analog signal and the Q-phase analog signal. The imbalance between the I-phase and Q-phase leads to degradation in the quality of the optical signal after wavelength conversion. [Means for solving the problem]

[0006] A wavelength converter according to the present disclosure includes a receiving means for receiving a quadrature-phase modulated optical signal of a first wavelength, splitting the received optical signal into first and second optical signals, causing the first optical signal to interfere with a first local oscillator light of the first wavelength, and causing the second optical signal to interfere with a second local oscillator light of the first wavelength that has been phase-shifted to be in quadrature with the first local oscillator light, thereby outputting an in-phase analog signal and a quadrature analog signal that indicate the coherent detection results of the first and second optical signals; and an analog compensating means for analog-compensating the in-phase analog signal and the quadrature analog signal. and transmitting means for modulating first and second transmission lights of a second wavelength different from the first wavelength into a first in-phase optical signal and a first quadrature-phase optical signal, respectively, based on the analog-compensated in-phase analog signal and the quadrature-phase analog signal, shifting the phase of the first quadrature-phase optical signal so as to cancel the deviation included in the phase shift given to the second local light in the receiving means, multiplexing the first in-phase optical signal and the phase-shifted first quadrature-phase optical signal, and outputting a quadrature-phase modulated optical signal of the second wavelength.

[0007] A wavelength conversion method according to the present disclosure includes receiving a quadrature-phase modulated optical signal of a first wavelength, splitting the received optical signal into first and second optical signals, interfering the first optical signal with a first local optical signal of the first wavelength, and interfering the second optical signal with a second local optical signal of the first wavelength that has been phase-shifted to be in quadrature with respect to the first local optical signal, thereby outputting an in-phase analog signal and a quadrature-phase analog signal that indicate coherent detection results of the first and second optical signals, performing analog compensation on the in-phase analog signal and the quadrature-phase analog signal, modulating first and second transmission lights of a second wavelength different from the first wavelength into a first in-phase optical signal and a first quadrature-phase optical signal, respectively, based on the analog-compensated in-phase analog signal and the quadrature-phase analog signal, shifting the phase of the first quadrature-phase optical signal so as to cancel an amount of deviation included in the phase shift applied to the second local optical signal, and combining the first in-phase optical signal with the phase-shifted first quadrature-phase optical signal, thereby outputting a quadrature-phase modulated optical signal of the second wavelength. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to realize a wavelength converter and a wavelength conversion method that convert the wavelength of an optical signal while maintaining signal quality with a simple configuration. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram illustrating a configuration of a wavelength converter according to an embodiment. [Figure 2] FIG. 2 is a diagram illustrating a configuration of a wavelength converter according to an embodiment in more detail. [Figure 3] FIG. 1 is a diagram illustrating a configuration of a wavelength converter according to an embodiment. [Figure 4] 10 is a flowchart illustrating an operation of a wavelength converter according to an embodiment. [Figure 5] FIG. 1 is a diagram illustrating a configuration of a wavelength converter according to an embodiment. [Figure 6] 10 is a flowchart illustrating an operation of a wavelength converter according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Embodiment 1 A wavelength converter according to a first embodiment will be described. The wavelength converter is configured to convert an input optical signal into an optical signal of another wavelength and output the converted optical signal. FIG. 1 is a diagram schematically illustrating the configuration of a wavelength converter according to one embodiment. The wavelength converter 100 includes a receiving unit 10, a transmitting unit 20, and an analog compensation unit 30. The receiving unit 10 is configured as a so-called receiving front end of the wavelength converter 100. The transmitting unit 20 is configured as a so-called transmitting front end of the wavelength converter 100.

[0011] A more detailed description will be given of the configuration of wavelength converter 100. Fig. 2 is a diagram showing in more detail the configuration of a wavelength converter according to one embodiment.

[0012] A quadrature-phase modulated optical signal IN with a wavelength λ1 is input to the receiving unit 10. Hereinafter, the wavelength λ1 will also be referred to as the first wavelength. The receiving unit 10 coherently detects the optical signal IN to output an I-phase analog signal SI, which is an in-phase (I-phase) analog signal, and a Q-phase analog signal SQ, which is a quadrature-phase (Q-phase) analog signal. As shown in FIG. 2, the receiving unit 10 includes a light source 11, a phase shifter 12, optical couplers 13 and 14, opto-electric converters 15 and 16, and optical couplers C11 and C12. The phase shifter 12, the optical couplers 13 and 14, and the optical couplers C11 and C12 form a so-called 90-degree hybrid. The optical couplers C11 and C12 will also be referred to as first and second optical demultiplexing units or optical demultiplexing means.

[0013] Optical signal IN is split into optical signals IN1 and IN2 by optical coupler C11. Optical signals IN1 and IN2 are guided to optical couplers 13 and 14, respectively. Hereinafter, optical signals IN1 and IN2 are also referred to as first and second optical signals, respectively.

[0014] The light source 11 is configured as, for example, a wavelength-tunable laser light source, and outputs a local light LO with a wavelength λ1. The local light LO is split into local light LO1 and local light LO2 by an optical coupler C12. The local light LO1 and local light LO2 are respectively guided to an optical coupler 13 and a phase shifter 12. Hereinafter, the local light LO1 and local light LO2 are also referred to as a first and second local light, respectively. The light source 11 is also referred to as a first light source.

[0015] The optical coupler 13 is configured as a two-input, two-output optical coupler. An optical signal IN1 is input to one input port of the optical coupler 13, and a local optical signal LO1 is input to the other input port. The optical coupler 13 outputs an I-phase optical signal I1, obtained by interfering the optical signal IN1 with the local optical signal LO1, to the opto-electric converter 15 via two output ports. Hereinafter, the I-phase optical signal I1 will also be referred to as a second in-phase optical signal. The optical coupler 13 will also be referred to as a first multiplexing / demultiplexing means.

[0016] The phase shifter 12 is configured to impart a phase shift of π / 2 to the local light LO2. Note that the phase shift of π / 2 that the phase shifter 12 imparts to the local light LO2 is a design value, and the phase shift that the phase shifter 12 actually imparts to the local light LO2 is π / 2 plus a deviation due to the error, due to manufacturing errors, etc. Furthermore, due to dispersion of the phase shifter, the deviation amount of the phase shift may differ depending on the value of the wavelength λ1. Therefore, here, the actual phase shift that the phase shifter 12 imparts to the local light LO2 is expressed as φ1=π / 2+φ err The phase-shifted local light LO2 is output to the optical coupler 14. The phase shifter 12 is also referred to as a first phase shifter.

[0017] The optical coupler 14 is configured as a two-input, two-output optical coupler. An optical signal IN2 is input to one input port of the optical coupler 14, and a local optical signal LO2 phase-shifted by the phase shifter 12 is input to the other input port. The optical coupler 14 outputs a Q-phase optical signal Q1 obtained by interfering the optical signal IN2 with the phase-shifted local optical signal LO2 to the opto-electric converter 16 via two output ports. Hereinafter, the Q-phase optical signal Q1 will also be referred to as a second quadrature-phase optical signal. The optical coupler 14 will also be referred to as a second multiplexing / demultiplexing means.

[0018] The photoelectric converter 15 is configured as a balanced detector in which two photodiodes (hereinafter referred to as PDs) are cascade-connected. Here, the PD on the upper side of the drawing is the + side, and the PD on the lower side of the drawing is the - side. One PD of the photoelectric converter 15 receives the I-phase optical signal I1 output from one output port of the optical coupler 13. The other PD of the photoelectric converter 15 receives the I-phase optical signal I1 output from the other output port of the optical coupler 13. The photoelectric converter 15 then converts the current signal output from the node between the two PDs into an I-phase analog signal SI using, for example, a transimpedance amplifier. The photoelectric converter 15 is also referred to as a first photoelectric converter.

[0019] Like the photoelectric converter 15, the photoelectric converter 16 is configured as a balanced detector in which two PDs are cascade-connected. Here, the PD on the upper side of the drawing is the positive side, and the PD on the lower side of the drawing is the negative side. One PD of the photoelectric converter 16 receives a Q-phase optical signal Q1 output from one output port of the optical coupler 14. The other PD of the photoelectric converter 16 receives a Q-phase optical signal Q1 output from the other output port of the optical coupler 14. The photoelectric converter 16 then converts the current signal output from the node between the two PDs into a Q-phase analog signal SQ using, for example, a transimpedance amplifier. The photoelectric converter 16 is also referred to as a second photoelectric converter.

[0020] The analog compensation unit 30 has analog compensators 31 and 32. The analog compensators 31 and 32 perform appropriate compensation processing on the I-phase analog signal SI and the Q-phase analog signal SQ, respectively. The analog compensators 31 and 32 then output the compensated I-phase analog signal SI and the Q-phase analog signal SQ, respectively, to the transmission unit 20. The I-phase analog signal SI is a differential analog signal and may be composed of two analog signals, an I-phase analog signal SI+ and an I-phase analog signal SI-. The Q-phase analog signal SQ is a differential analog signal and may be composed of two analog signals, a Q-phase analog signal SQ+ and a Q-phase analog signal SQ-. When the I-phase analog signal SI and the Q-phase analog signal SQ are differential analog signals, the analog compensators 31 and 32 may be composed of + and - analog compensators, respectively. The analog compensators 31 and 32 may also be compensators that input differential analog signals and output differential analog signals.

[0021] The transmitter 20 modulates light with wavelength λ2 based on the I-phase analog signal SI and the Q-phase analog signal SQ, thereby outputting a quadrature-phase modulated optical signal OUT. Hereinafter, wavelength λ2 will also be referred to as the second wavelength. The transmitter 20 includes a light source 21, a phase shifter 22, Mach-Zehnder modulators (hereinafter referred to as MZ modulators) 23 and 24, drivers 25 and 26, and optical couplers C21 and C22. The optical coupler C21 will also be referred to as a third optical demultiplexing unit or optical demultiplexing means. The optical coupler C22 will also be referred to as an optical multiplexing unit or optical multiplexing means. The drivers 25 and 26 will also be referred to as first and second drivers, respectively.

[0022] The light source 21 is configured as, for example, a wavelength-tunable laser light source, and outputs transmission light L of wavelength λ2. The transmission light L is split into transmission light L1 and transmission light L2 by an optical coupler C21. The transmission light L1 and transmission light L2 are guided to MZ modulators 23 and 24, respectively. Hereinafter, the transmission light L1 and transmission light L2 are also referred to as first and second transmission light, respectively. The light source 21 is also referred to as the second light source.

[0023] The MZ modulator 23 branches the transmission light L1 into two arms. Electrodes 27 are provided on the two arms. An I-phase modulation signal MI, output by the driver 25 based on the I-phase analog signal SI received from the analog compensator 31, is applied to the electrode 27. The transmission light L1 is modulated in accordance with the I-phase modulation signal MI, and an I-phase optical signal I2 is output from the MZ modulator 23. Although the electrode 27 is shown as a single electrode in the figure for the sake of simplicity, this is not restrictive. Therefore, the MZ modulator 23 may be configured as various common MZ modulators, such as one in which an electrode is provided on each of the two arms and a different modulation signal or bias voltage is applied to each. The I-phase optical signal I2 is also referred to as a first in-phase optical signal. The MZ modulator 23 is also referred to as a first modulator.

[0024] The MZ modulator 24 branches the input transmission light L2 into two arms. Electrodes 28 are provided on the two arms. A Q-phase modulation signal MQ, output by the driver 26 based on the Q-phase analog signal SQ received from the analog compensator 32, is applied to the electrode 28. The transmission light L2 is modulated in accordance with the Q-phase modulation signal MQ, and a Q-phase optical signal Q2 is output from the MZ modulator 24. Although the electrode 28 is shown as a single electrode in the figure for simplification, this is for simplicity's sake. Therefore, the MZ modulator 24 may be configured as various general MZ modulators, such as one in which an electrode is provided on each of the two arms and a different modulation signal or bias voltage is applied to each. Hereinafter, the Q-phase optical signal Q2 will also be referred to as a first quadrature-phase optical signal. The MZ modulator 24 will also be referred to as a second modulator.

[0025] The phase shifter 22 shifts the Q-phase optical signal Q2 by φ2=π / 2+φ MOD where φ MOD is the compensation amount of phase shift intentionally given to the Q-phase optical signal Q2 in order to remove the complex conjugate component contained in the Q-phase optical signal Q2, which will be described later. In this configuration, φ is set to π so that φ1 + φ2 = π. MOD is set, that is, π / 2+φ err (λ1)+π / 2+φ MOD = π, so φMOD =-φ err (λ1) so that φ MOD is set. The phase shifter 22 is also called a second phase shifter.

[0026] The I-phase optical signal I2 and the Q-phase optical signal Q2 phase-shifted by the phase shifter 22 are multiplexed by the optical coupler C22. The multiplexed optical signal is output as a quadrature-phase modulated optical signal OUT with wavelength λ2.

[0027] As described above, the wavelength converter 100 can convert a quadrature-phase modulated optical signal IN having a wavelength λ1 into an optical signal OUT having a wavelength λ2 that is different from the quadrature-phase modulated wavelength λ1.

[0028] Next, a description will be given of the operation of the wavelength converter 100. First, a process in which the receiver 10 receives the optical signal IN and outputs the I-phase analog signal SI and the Q-phase analog signal SQ will be considered.

[0029] Here, the electric field strength of the optical signal IN is E IN (t)e jω 1 t The electric field strength of the local light LO is E LO e jω 1 t where t represents time, j represents an imaginary unit, and ω1 represents the frequency of the optical signal IN and the local oscillator LO. That is, if c represents the speed of light, then ω1=2πc / λ1. At this time, the electric field intensity E of the I-phase optical signal I1 received by the PD on the positive side of the photoelectric converter 15 is I+ is expressed by the following formula:

number

number

[0030] The electric field strength E of the Q-phase optical signal Q1 received by the PD on the positive side of the photoelectric converter 16 is Q+ is expressed by the following formula:

number

number

[0031] At this time, the intensity I of the I-phase analog signal SI is expressed by the following formula.

number

number

[0032] Under the above assumptions, the intensity of the optical signal OUT output by the transmitter 20 will be considered. First, to facilitate understanding of the problem solved by the wavelength converter 100, an example will be described in which the phase shift that the transmitter 20 imparts to the Q-phase optical signal Q2 is simply π / 2, as in a typical wavelength converter. In this case, the electric field intensity E of the optical signal OUT is OUT is expressed by the following equation: where ω2 is the frequency of the transmitted light L with wavelength λ2 and the optical signal OUT. That is, ω2=2πc / λ2.

number

number

[0033] The first term on the right side of equation [8] is the phase shift deviation amount φerr The constant determined by (λ1) is the electric field strength E of the optical signal IN. IN (t), compensation by general digital signal processing is possible, for example, in a downstream coherent receiver that finally receives the optical signal OUT and converts it into a digital signal. However, the second term on the right side of equation [8] is a constant determined by the amount of phase shift deviation in the phase shifter 12, which is the electric field strength E of the optical signal IN. IN Complex conjugate E of (t) IN (t) * Therefore, the complex conjugate component of the second term on the right side interferes with the signal component of the first term on the right side, degrading the signal quality of the optical signal OUT.

[0034] Therefore, in the wavelength converter 100, as described above, the phase shift φ1=π / 2+φ that the phase shifter 12 gives to the local light LO2 is err (λ1) and the phase shift φ2=π / 2+φ that the phase shifter 22 imparts to the Q-phase optical signal Q2 MOD φ so that the sum of MOD This cancels out the complex conjugate component of the second term on the right side of equation [8]. This will be explained in detail below.

[0035] The phase shifter 22 intentionally applies a compensation amount φ to the Q-phase optical signal Q2. MOD π / 2+φ MOD When a phase shift of E is applied, the electric field strength of the optical signal OUT OUT is expressed by the following formula:

number

number

[0036] In order to cancel the complex conjugate component of the second term on the right side of equation

[10] , in the wavelength converter 100, the phase shift φ1=π / 2+φ that the phase shifter 12 gives to the local light LO2 is err(λ1) and the phase shift φ2=π / 2+φ that the phase shifter 22 imparts to the Q-phase optical signal Q2 MOD The compensation amount φ is set so that the sum of MOD Therefore, the compensation amount φ MOD is the deviation amount φ err It has the same absolute value as (λ1) but with the sign reversed.

number

[11] . MOD This compensation amount φ MOD By setting the phase shifter 22, the second term on the right side of the equation

[10] can be set to 0. Therefore, the electric field intensity E OUT is as follows:

number

[0037] As a result, wavelength converter 100 can remove the complex conjugate component that may be included in optical signal OUT, as indicated by the second term on the right side of equation

[10] , and prevent degradation of the signal quality of optical signal OUT.

[0038] As described above, wavelength converter 100 can convert an optical signal IN with wavelength λ1 into an optical signal OUT with wavelength λ2 without degrading the quality by removing the influence of the complex conjugate component.

[0039] It is also possible to replace the analog compensator 30 in the wavelength converter 100 with a digital signal processor and eliminate the imbalance between the I and Q phases using digital signal processing. However, in this case, the power consumption of the digital signal processor is greater than that of the analog compensator 30, making it difficult to meet the low power consumption required of wavelength converters. Furthermore, digital signal processing results in greater signal delay than analog signal processing. Therefore, it is difficult to meet the increasing demand for faster wavelength conversion processing.

[0040] In contrast, the wavelength converter 100 can eliminate the imbalance between the I phase and the Q phase without performing digital signal processing. This has the advantage that the wavelength converter 100 can achieve lower power consumption and shorter delays than when digital signal processing is performed.

[0041] Embodiment 2 A wavelength converter according to a second embodiment will now be described. Fig. 3 is a diagram schematically illustrating the configuration of a wavelength converter according to one embodiment. Wavelength converter 200 has a configuration in which wavelength converter 100 is further provided with a storage unit 41 and a control unit 42.

[0042] Wavelength converter 200 is configured to be able to externally specify the wavelength λ1 of the input optical signal IN and the wavelength λ2 of the output optical signal OUT. For example, by externally issuing a command INS to wavelength converter 200, the wavelength λ1 of the input optical signal IN and the wavelength λ2 of the output optical signal OUT can be specified.

[0043] The storage unit 41 stores a compensation amount φ included in the phase shift that the phase shifter 22 applies to the Q-phase optical signal Q2 in accordance with the wavelength λ1 of the local light LO and the wavelength λ2 of the transmitted light L. MOD The storage unit 41 may also store setting information for the receiving unit 10, the transmitting unit 20, and the analog compensation unit 30.

[0044] The control unit 42 calculates the compensation amount φ corresponding to the wavelengths λ1 and λ2 specified by the received command INS. MOD is read from the storage unit 41. Then, the read compensation amount φ MOD is set in the phase shifter 22.

[0045] Next, a description will be given of the operation of wavelength converter 200. Fig. 4 is a flowchart of the operation of a wavelength converter according to one embodiment.

[0046] Step S11 The control unit 42 reads the initial setting information of the receiving unit 10, the transmitting unit 20, and the analog compensation unit 30 from the storage unit 41. Then, the control unit 42 performs initial setting of the receiving unit 10, the transmitting unit 20, and the analog compensation unit 30 based on the initial setting information.

[0047] The settings of the receiving unit 10 may include, for example, setting the gain of a transimpedance that converts a current signal indicating the detection result of an optical signal into a voltage signal in the receiving unit 19. The settings of the transmitting unit 20 may include, for example, setting the bias of an MZ modulator, the gain of a driver, etc. The settings of the analog compensating unit 30 may include setting frequency compensation and skew adjustment for the I and Q phases.

[0048] Step S12 After the initial setting, a command INS is given to the control unit 42 by, for example, a user of the wavelength converter 200 .

[0049] Step S13 The control unit 42 sets the wavelength λ1 specified by the received command INS to the light source 11, and sets the wavelength λ2 to the light source 21.

[0050] Step S14 The control unit 42 calculates the compensation amount φ corresponding to the wavelengths λ1 and λ2 specified by the received command INS. MOD is read from the storage unit 41. Then, the control unit 42 calculates the read compensation amount φ MOD is set in the phase shifter 22.

[0051] In addition, when the control unit 42 updates the settings of the receiving unit 10, the transmitting unit 20, and the analog compensation unit 30 in accordance with the wavelength settings of the light sources 11 and 12, it may read the necessary setting information from the memory unit 41 as appropriate and update the settings of the receiving unit 10, the transmitting unit 20, and the analog compensation unit 30.

[0052] As described above, wavelength converter 200 can set an appropriate phase shift in phase shifter 22 according to the wavelength λ1 of input optical signal IN and the wavelength λ2 of output optical signal OUT. This makes it possible to effectively cancel the complex conjugate component in optical signal OUT even when the wavelength λ1 of optical signal IN and the wavelength λ2 of optical signal OUT are changed.

[0053] Embodiment 3 A wavelength converter according to a third embodiment will now be described. Fig. 5 is a diagram schematically illustrating the configuration of a wavelength converter according to one embodiment. Wavelength converter 300 has a configuration in which a processing unit 50 is further provided in wavelength converter 200.

[0054] The processing unit 50 has analog-to-digital converters (hereinafter referred to as ADCs) 51 and 52 and a signal processing unit 53. The ADCs 51 and 52 convert the I-phase analog signal SI and the Q-phase analog signal SQ output by the receiving unit 10 into digital signals DI and DQ, respectively. The signal processing unit 53 calculates a phase shift compensation amount φ to be set in the phase shifter 22 based on the digital signals DI and DQ. MOD Calculate.

[0055] Next, a description will be given of the operation of wavelength converter 300. Fig. 6 is a flowchart showing the operation of a wavelength converter according to one embodiment.

[0056] Step S21 The signal processing unit 53 calculates the imbalance between the I phase and the Q phase based on the digital signals DI and DQ.

[0057] Step S22 The signal processing unit 53 calculates a phase shift compensation amount φ to be set in the phase shifter 22 that is appropriate for eliminating the calculated imbalance between the I phase and the Q phase. MOD In order to eliminate the imbalance between the I phase and the Q phase, the signal processing unit 53 calculates the phase shift compensation amount φ MOD Alternatively, the setting information of the receiving unit 10, the transmitting unit 20, and the analog compensation unit 30 may be calculated.

[0058] Step S23 The signal processing unit 53 calculates the calculated phase shift compensation amount φ MOD to the storage unit 41. Note that the signal processing unit 53 writes the phase shift compensation amount φ MOD Alternatively, the calculated setting information of the receiving unit 10, the transmitting unit 20 and the analog compensating unit 30 may be written to the storage unit 41.

[0059] Step S24 The control unit 42 calculates the phase shift compensation amount φ written in the storage unit 41 by the signal processing unit 53. MOD Then, the control unit 42 reads the read phase shift compensation amount φ MOD in the phase shifter 22. The control unit 42 may read the setting information of the receiving unit 10, the transmitting unit 20, and the analog compensating unit 30 that the signal processing unit 53 has written to the storage unit 41, and update the settings of the receiving unit 10, the transmitting unit 20, and the analog compensating unit 30.

[0060] This allows the wavelength converter 300 to perform feedback control to set each component so as to eliminate the imbalance between the I and Q phases based on the observed imbalance, thereby enabling the wavelength converter 300 to more efficiently maintain the quality of the wavelength-converted optical signal OUT.

[0061] Other embodiments Although the present disclosure has been described above with reference to the embodiments, the present disclosure is not limited to the above-described embodiments. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present disclosure within the scope of the present disclosure. Furthermore, each embodiment can be combined with other embodiments as appropriate.

[0062] In the above-described embodiments, a wavelength converter that converts the wavelength of a quadrature-phase modulated optical signal has been described. However, the wavelength converters according to the above-described embodiments can also be applied to optical signals of other modulation methods. For example, in the case of DP-QPSK (Dual Polarization-Quadrature Phase Shift Keying), it is also possible to similarly wavelength-convert the QPSK signals of each polarization component after polarization separation. That is, even for optical signals modulated by combining quadrature phase modulation with other modulation methods, wavelength conversion can be performed by the wavelength converters according to the above-described embodiments by converting the target optical signal into a quadrature-phase modulated optical signal using a demultiplexing means or the like.

[0063] Each drawing is merely an example for describing one or more embodiments. Each drawing may relate not only to one particular embodiment, but also to one or more other embodiments. As will be understood by those skilled in the art, various features or steps described with reference to any one drawing can be combined with features or steps shown in one or more other drawings to create, for example, an embodiment not explicitly shown or described. Not all features or steps shown in any one drawing are necessary to describe an exemplary embodiment, and some features or steps may be omitted. The order of steps described in any drawing may be changed as appropriate.

[0064] A part or all of the above-described embodiments can be described as, but not limited to, the following supplementary notes.

[0065] (Supplementary Note 1) A receiving means for receiving a quadrature-phase modulated optical signal of a first wavelength, separating the received optical signal into first and second optical signals, interfering the first optical signal with a first local oscillator light of the first wavelength, and interfering the second optical signal with a second local oscillator light of the first wavelength whose phase is shifted to be in quadrature with respect to the first local oscillator light, thereby outputting an in-phase analog signal and a quadrature analog signal indicative of a coherent detection result of the first and second optical signals; and an analog compensation means for analog-compensating the in-phase analog signal and the quadrature analog signal. and transmitting means for modulating first and second transmission lights of a second wavelength different from the first wavelength into a first in-phase optical signal and a first quadrature-phase optical signal, respectively, based on the in-phase analog signal and the quadrature-phase analog signal that have been analog-compensated, shifting the phase of the first quadrature-phase optical signal so as to cancel an amount of deviation included in a phase shift given to the second local light in the receiving means, and multiplexing the first in-phase optical signal and the phase-shifted first quadrature-phase optical signal to output a quadrature-phase modulated optical signal of the second wavelength.

[0066] (Supplementary Note 2) The receiving means comprises a first light source that outputs light of the first wavelength, first optical demultiplexing means that demultiplexes the optical signal of the first wavelength into the first and second optical signals, second optical demultiplexing means that demultiplexes the light of the first wavelength into the first and second local oscillator lights, a first phase shifter that shifts the phase of the second local oscillator light so that the second local oscillator light is in quadrature phase with the first local oscillator light, multiplexing and demultiplexing means that outputs a second in-phase optical signal by interfering the first optical signal with the first local oscillator light and outputs a second quadrature-phase optical signal by interfering the second optical signal with the second local oscillator light whose phase has been shifted by the first phase shifter, and opto-electrical conversion means that converts the second in-phase optical signal and the second quadrature-phase optical signal into the in-phase analog signal and the quadrature-phase analog signal, respectively. The transmitting means comprises a light source that outputs light of the second wavelength, into the first and second transmission lights; first and second drivers that output an in-phase modulated signal and a quadrature-phase modulated signal based on the analog-compensated in-phase analog signal and the quadrature-phase analog signal; a first modulator that modulates the first transmission light in accordance with the in-phase modulated signal to output the first in-phase optical signal; a second modulator that modulates the second transmission light in accordance with the quadrature-phase modulated signal to output the first quadrature-phase optical signal; a second phase shifter that shifts the phase of the first quadrature-phase optical signal so as to cancel an amount of deviation included in a phase shift applied to the second local light by the first phase shifter; and optical multiplexing means that multiplexes the first in-phase optical signal and the first quadrature-phase optical signal whose phase has been shifted by the second phase shifter, and outputs the quadrature-phase modulated optical signal of the second wavelength.

[0067] (Supplementary Note 3) The wavelength converter according to Supplementary Note 2, wherein the second phase shifter shifts the phase of the first quadrature phase optical signal so that the sum of the phase shift that the first phase shifter imparts to the second local oscillator light and the phase shift that the second phase shifter imparts to the first quadrature phase optical signal is π.

[0068] (Supplementary Note 4) The wavelength converter according to Supplementary Note 3, wherein the phase shift imparted by the first phase shifter to the second local light is a value obtained by adding a deviation amount to π / 2, and the phase shift imparted by the second phase shifter to the first quadrature phase optical signal is a value obtained by adding a compensation amount to π / 2, and the compensation amount has an opposite sign to and the same magnitude as the deviation amount.

[0069] (Supplementary Note 5) The wavelength converter according to Supplementary Note 4, further comprising: a memory means for storing information indicating the compensation amount according to the first wavelength and the second wavelength; and a control means for reading the information indicating the compensation amount from the memory means according to the first wavelength and the second wavelength, and setting the compensation amount in the second phase shifter based on the read information.

[0070] (Appendix 6) The wavelength converter according to appendix 5, wherein the control means receives a command specifying the first wavelength and the second wavelength, and reads out the information indicating the compensation amount from the storage means according to the first wavelength and the second wavelength specified by the received command.

[0071] (Supplementary Note 7) The wavelength converter according to Supplementary Note 5 or 6, further comprising a processing means for calculating an imbalance between the in-phase analog signal and the quadrature-phase analog signal, and calculating the compensation amount to be set to eliminate the effect of the calculated imbalance, wherein the control means sets the compensation amount calculated by the processing means in the second phase shifter.

[0072] (Supplementary Note 8) The multiplexing / demultiplexing means comprises: a first multiplexing / demultiplexing means for demultiplexing the second in-phase optical signal obtained by interfering the first optical signal with the first local light, into two signals, and outputting the demultiplexed signals; and a second multiplexing / demultiplexing means for demultiplexing the second quadrature-phase optical signal obtained by interfering the second optical signal with the second local light, the phase of which has been shifted by the first phase shifter, into two signals, and outputting the demultiplexed signals; and the photoelectric conversion means comprises: a first photoelectric converter configured as a balanced detector for receiving the two branched second in-phase optical signal and converting it into the in-phase analog signal; and a second photoelectric converter configured as a balanced detector for receiving the two branched second quadrature-phase optical signal and converting it into the quadrature-phase analog signal. 8. The wavelength converter according to claim 2, wherein the wavelength converter is a wavelength converter having a wavelength of 100 nm or less.

[0073] (Supplementary Note 9) A wavelength conversion method comprising: receiving a quadrature-phase modulated optical signal of a first wavelength; separating the received optical signal into first and second optical signals; interfering the first optical signal with a first local optical signal of the first wavelength; interfering the second optical signal with a second local optical signal of the first wavelength, the second optical signal being phase-shifted to be in quadrature with respect to the first local optical signal, thereby outputting an in-phase analog signal and a quadrature-phase analog signal indicating coherent detection results of the first and second optical signals; performing analog compensation on the in-phase analog signal and the quadrature-phase analog signal; modulating first and second transmission lights of a second wavelength different from the first wavelength into a first in-phase optical signal and a first quadrature-phase optical signal, respectively, based on the analog-compensated in-phase analog signal and the quadrature-phase analog signal; shifting the phase of the first quadrature-phase optical signal so as to cancel an amount of deviation included in the phase shift applied to the second local optical signal; [Explanation of symbols]

[0074] 10 Receiving unit 11, 21 Light source 12, 22 Phase Shifter 13, 14, C11, C12, C21, C22 Optical Couplers 15, 16 Photoelectric conversion unit 20 Transmitter 23, 24 MZ Modulator 25, 26 Driver 27, 28 electrodes 30 Analog compensation section 31, 32 Analog Compensator 41 Storage section 42 Control Unit 50 Processing section 51, 52 ADC 53 Signal Processing Unit 100, 200, 300 wavelength converter I1, I2 I-phase optical signal L, L1, L2 transmitting light LO, LO1, LO2 local light MI I-phase modulation signal MQ Q-phase modulation signal Q1, Q2 Q phase optical signal SI I-phase analog signal SQ Q-phase analog signal

Claims

1. receiving means for receiving a quadrature-phase modulated optical signal of a first wavelength, separating the received optical signal into first and second optical signals, interfering the first optical signal with a first local oscillator light of the first wavelength, and interfering the second optical signal with a second local oscillator light of the first wavelength whose phase is shifted to be in quadrature with respect to the first local oscillator light, thereby outputting an in-phase analog signal and a quadrature-phase analog signal indicative of the results of coherent detection of the first and second optical signals; an analog compensation means for analog-compensating the in-phase analog signal and the quadrature-phase analog signal; a transmitting means for modulating first and second transmission lights of a second wavelength different from the first wavelength into a first in-phase optical signal and a first quadrature-phase optical signal, respectively, based on the analog-compensated in-phase analog signal and the quadrature-phase analog signal, shifting the phase of the first quadrature-phase optical signal so as to cancel an amount of deviation included in the phase shift given to the second local light in the receiving means, and multiplexing the first in-phase optical signal and the phase-shifted first quadrature-phase optical signal to output a quadrature-phase modulated optical signal of the second wavelength. Wavelength converter.

2. The receiving means a first light source that outputs light of the first wavelength; a first optical demultiplexing means for demultiplexing the optical signal of the first wavelength into the first and second optical signals; a second optical demultiplexing means for demultiplexing the light having the first wavelength into the first and second local oscillator lights; a first phase shifter that shifts the phase of the second local oscillator light so that the second local oscillator light is in quadrature with respect to the first local oscillator light; a multiplexing / demultiplexing means for outputting a second in-phase optical signal by causing interference between the first optical signal and the first local light, and for outputting a second quadrature-phase optical signal by causing interference between the second optical signal and the second local light whose phase has been shifted by the first phase shifter; opto-electrical conversion means for converting the second in-phase optical signal and the second quadrature-phase optical signal into the in-phase analog signal and the quadrature-phase analog signal, respectively; The transmitting means a light source that outputs light of a second wavelength; a third optical demultiplexing means for demultiplexing the light of the second wavelength into the first and second transmission lights; first and second drivers for outputting an in-phase modulated signal and a quadrature modulated signal based on the analog-compensated in-phase analog signal and the quadrature analog signal; a first modulator that modulates the first transmission light in accordance with the in-phase modulation signal and outputs the first in-phase optical signal; a second modulator that modulates the second transmission light in accordance with the quadrature phase modulation signal to output the first quadrature phase optical signal; a second phase shifter that shifts the phase of the first quadrature phase optical signal so as to cancel a deviation included in a phase shift that the first phase shifter has given to the second local light; an optical multiplexing means for multiplexing the first in-phase optical signal and the first quadrature-phase optical signal whose phase has been shifted by the second phase shifter, and outputting the quadrature-phase modulated optical signal of the second wavelength, 2. The wavelength converter of claim 1.

3. the second phase shifter shifts the phase of the first quadrature phase optical signal so that the sum of the phase shift imparted by the first phase shifter to the second local light and the phase shift imparted by the second phase shifter to the first quadrature phase optical signal is π; 3. The wavelength converter according to claim 2.

4. the phase shift that the first phase shifter imparts to the second local light is a value obtained by adding a shift amount to π / 2, the phase shift that the second phase shifter imparts to the first quadrature-phase optical signal is a value obtained by adding a compensation amount to π / 2; The compensation amount has an opposite sign to the deviation amount and a value of the same magnitude.

4. The wavelength converter according to claim 3.

5. a storage means for storing information indicating the compensation amount corresponding to the first wavelength and the second wavelength; a control unit that reads the information indicating the compensation amount from the storage unit in accordance with the first wavelength and the second wavelength, and sets the compensation amount in the second phase shifter based on the read information.

5. The wavelength converter according to claim 4.

6. the control means receives a command specifying the first wavelength and the second wavelength, and reads out the information indicating the compensation amount from the storage means in accordance with the first wavelength and the second wavelength specified by the received command.

6. The wavelength converter according to claim 5.

7. further comprising processing means for calculating an imbalance between the in-phase analog signal and the quadrature-phase analog signal, and calculating the compensation amount to be set in order to eliminate the effect of the calculated imbalance; the control means sets the compensation amount calculated by the processing means in the second phase shifter.

7. The wavelength converter according to claim 5 or 6.

8. The multiplexing / demultiplexing means a first multiplexing / demultiplexing means for demultiplexing the second in-phase optical signal obtained by interfering the first optical signal with the first local light into two signals and outputting the two signals; a second multiplexing / demultiplexing means for demultiplexing the second quadrature phase optical signal obtained by interfering the second optical signal with the second local light whose phase has been shifted by the first phase shifter, into two signals and outputting the two signals; The photoelectric conversion means a first photoelectric converter configured as a balanced detector that receives the second in-phase optical signal split into two and converts it into the in-phase analog signal; a second photoelectric converter configured as a balanced detector that receives the second quadrature-phase optical signal split into two and converts it into the quadrature-phase analog signal; 7. A wavelength converter according to claim 2.

9. receiving a quadrature-phase modulated optical signal at a first wavelength; demultiplexing the received optical signal into first and second optical signals; causing the first optical signal to interfere with a first local optical signal of the first wavelength, and causing the second optical signal to interfere with a second local optical signal of the first wavelength that has been phase-shifted to be in quadrature with the first local optical signal, thereby outputting an in-phase analog signal and a quadrature-phase analog signal that indicate coherent detection results of the first and second optical signals; analog-compensating the in-phase analog signal and the quadrature-phase analog signal; modulating first and second transmission lights having a second wavelength different from the first wavelength into a first in-phase optical signal and a first quadrature-phase optical signal, respectively, based on the analog-compensated in-phase analog signal and the quadrature-phase analog signal; shifting the phase of the first quadrature phase optical signal so as to cancel a deviation included in the phase shift given to the second local light; multiplexing the first in-phase optical signal and the phase-shifted first quadrature-phase optical signal to output a quadrature-phase modulated optical signal of the second wavelength; Wavelength conversion method.

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