WO2018143428A1 - Optical transceiver and modulation control method - Google Patents

Optical transceiver and modulation control method Download PDF

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Publication number
WO2018143428A1
WO2018143428A1 PCT/JP2018/003651 JP2018003651W WO2018143428A1 WO 2018143428 A1 WO2018143428 A1 WO 2018143428A1 JP 2018003651 W JP2018003651 W JP 2018003651W WO 2018143428 A1 WO2018143428 A1 WO 2018143428A1
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Prior art keywords
bias voltage
optical
mode
phase
offset value
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PCT/JP2018/003651
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French (fr)
Japanese (ja)
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伸吾 窪木
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日本電気株式会社
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Publication of WO2018143428A1 publication Critical patent/WO2018143428A1/en

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    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/03—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect
    • G02F1/035—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect in an optical waveguide structure
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/07—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems
    • H04B10/075—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an in-service signal
    • H04B10/077—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an in-service signal using a supervisory or additional signal
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/07—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems
    • H04B10/075—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an in-service signal
    • H04B10/079—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an in-service signal using measurements of the data signal
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/50—Transmitters
    • H04B10/516—Details of coding or modulation

Definitions

  • the present invention relates to modulation of an optical signal, and more particularly to a technique for correcting an optimum operating point of an optical modulator.
  • the optical signal is generated by phase-modulating the light output from an ILTA (Integrable Tunable Laser Assembly), which is a light source, with a Mach-Zehnder type LN modulator using an LN (Lithium Niobate: LiNbO 3 ) crystal. Generated.
  • ILTA Integrable Tunable Laser Assembly
  • LN Lithium Niobate: LiNbO 3
  • the optical modulator in the digital coherent system is controlled by applying a bias for controlling the three components in-phase component I (In-Phase), quadrature component Q (Quadrature) and phase component Ph (Phase). Is performed so that is output.
  • Is in-phase component
  • Q quadrature component
  • Ph phase component Ph
  • Is performed so that is output.
  • a phenomenon in which the Q-phase component slightly deviates from the optimum value also occurs due to the influence of the I-phase component in the optical modulator.
  • Such deviations are often resolved by manually offsetting the bias from the convergence point.
  • the optimum bias of the I-phase component, the Q-phase component, and the Ph component varies due to deterioration over time, it is necessary to optimize the amount of offset according to the variation of the optimum bias.
  • Patent Document 1 relates to an optical transmitter including an MZ type optical modulator having a function of correcting a deviation from an optimum bias.
  • the optical modulator disclosed in Patent Document 1 changes the bias voltage applied to the optical modulator and measures the output light while sweeping the operating point of the optical modulator to determine the optimum bias compensation amount.
  • Patent Document 2 and Patent Document 3 disclose techniques related to optimization of the bias voltage of the optical modulator of the optical transmitter similar to Patent Document 1.
  • Patent Document 1, Patent Document 2 and Patent Document 3 are not sufficient in the following points.
  • Patent Document 1, Patent Document 2 and Patent Document 3 the bias voltage of the Mach-Zehnder optical modulator is optimized. Regarding the influence of the I-phase component, the Q-phase component and the Ph component on each other, Not considered. For this reason, in Patent Document 1, Patent Document 2, and Patent Document 3, the I-phase component, the Q-phase component, and the Ph component affect each other, which may cause the operating point of the optical modulator to deviate from the optimum value. Therefore, the techniques of Patent Document 1, Patent Document 2 and Patent Document 3 are techniques for optimizing the bias voltage applied to the optical modulator with high accuracy when the characteristic variation of the optical modulator occurs. Not enough.
  • the present invention suppresses the influence of the interaction of each component when the characteristic variation of the optical modulator occurs, and optimizes the bias voltage applied to the optical modulator with high accuracy. It is an object of the present invention to provide an optical transceiver that can be used and a control method thereof.
  • the optical transceiver of the present invention includes optical modulation means, control means, and optimization means.
  • the light modulation means demultiplexes the input light into light of an I (In-Phase) phase component and a Q (Quadrature) phase component, and applies a bias voltage to each of the demultiplexed light to perform modulation.
  • the control unit controls the bias voltage applied in the light modulation unit for each component to be modulated.
  • the optimization means optimizes the bias voltage in the first mode and the second mode.
  • the first mode is a mode for setting a first bias voltage in which the bias voltage is optimized based on the optical signal output from the light modulation means.
  • the second mode is a mode for optimizing the bias voltage by adjusting the offset amount from the first bias voltage for each component to be modulated based on the quality of the optical signal. Further, the control unit controls application of the bias voltage in the light modulation unit based on the second bias voltage obtained by correcting the first bias voltage set by the optimization unit based on the offset value.
  • the modulation control method of the present invention demultiplexes input light into I-phase component and Q-phase component light.
  • modulation is performed by applying a bias voltage controlled for each component to be modulated to each of the demultiplexed light.
  • the modulation control method of the present invention outputs an optical signal obtained by combining modulated I-phase components and Q-phase components.
  • the bias voltage is optimized by the first mode and the second mode.
  • the first mode is a mode for setting a first bias voltage in which the bias voltage is optimized based on the optical signal output from the light modulation means.
  • the second mode is a mode in which the bias voltage is optimized by adjusting the offset value from the first bias voltage for each component to be modulated based on the quality of the optical signal.
  • the modulation control method of the present invention controls the application of the bias voltage based on the second bias voltage obtained by correcting the first bias voltage based on the offset value.
  • the present invention it is possible to optimize the bias voltage to be applied to the optical modulator with high accuracy while suppressing the influence of the interaction of each component even if characteristic variation or the like occurs.
  • FIG. 1 shows an outline of the configuration of the optical transceiver of this embodiment.
  • the optical transceiver of this embodiment includes an optical modulation unit 1, a control unit 2, and an optimization unit 3.
  • the light modulation means 1 is a means for demultiplexing the input light into light of an I (In-Phase) phase component and a Q (Quadrature) phase component, and a bias voltage is applied to each of the demultiplexed light to modulate it.
  • the control unit 2 controls the bias voltage applied in the light modulation unit 1 for each component to be modulated.
  • the optimization unit 3 optimizes the bias voltage in the first mode and the second mode.
  • the first mode is a mode in which a first bias voltage is set by optimizing the bias voltage based on the optical signal output from the light modulation unit 1.
  • the second mode is a mode in which the bias voltage is optimized by adjusting the offset value from the first bias voltage for each component to be modulated based on the quality of the optical signal.
  • the control unit 2 controls the application of the bias voltage in the light modulation unit 1 based on the second bias voltage obtained by correcting the first bias voltage set by the optimization unit 3 based on the offset value.
  • the optical transceiver according to the present embodiment optimizes the bias voltage in two stages: the first mode in which the optimization unit 3 sets the first bias voltage and the second mode in which the offset value of the first bias voltage is set. It has become.
  • the control unit 2 controls the bias voltage applied to each component in the optical modulation unit 1 based on the bias voltage optimized by the optimization unit 3 in two stages.
  • the optical transceiver of this embodiment can optimize the bias voltage even when there is an interaction with each component by optimizing the offset value for each component in the second mode.
  • the optical transceiver according to the present embodiment can optimize the bias voltage applied to the optical modulator with high accuracy while suppressing the influence of the interaction of each component even if characteristic variation or the like occurs.
  • FIG. 2 shows an outline of the configuration of the optical transceiver 10 of the present embodiment.
  • the optical transceiver 10 of the present embodiment includes a light source unit 11, an optical modulation unit 12, a control unit 13, a storage unit 14, an optical reception unit 15, and a signal processing unit 16.
  • the optical transceiver 10 generates a function of an optical transmitter that generates and outputs an optical signal to be transmitted via a transmission path based on an external signal input from the outside, and receives the function via the transmission path. It has a function as an optical receiver that decodes an optical signal and outputs it as an external signal.
  • the optical transceiver 10 of this embodiment is an optical transceiver compatible with a digital coherent optical communication system. That is, the optical transceiver 10 according to the present embodiment uses the optical modulation unit 12 based on the data encoded by the signal processing unit 16 based on the external signal, and the Q phase that is the quadrature phase component of the I phase and the I phase. The light is modulated and output.
  • the optical receiver 15 performs coherent detection of an optical signal received as an optical reception signal via a transmission path
  • the signal processing unit 16 performs signal processing such as decoding. Is output as an external signal.
  • the light source unit 11 has a function as a light source that outputs light of a carrier wave when transmitting an optical signal.
  • the light source unit 11 of the present embodiment is configured as an ITLA (Integrable Tunable Laser Assembly).
  • the light source unit 11 outputs continuity (CW: Continuous Wave).
  • the light output from the light source unit 11 is input to the light modulation unit 12.
  • the optical modulation unit 12 is an optical modulator that performs phase modulation on the CW light input from the light source unit 11 and generates an optical signal based on the control of the control unit 13.
  • a Mach-Zehnder type LN (Lithium Niobate: LiNbO 3 ) modulator is used for the light modulator 12 of the present embodiment.
  • the light modulator 12 may be replaced with another modulator using the electro-optic effect instead of the LN modulator.
  • FIG. 3 schematically shows the configuration of the optical modulator of the present embodiment.
  • the optical modulator includes two modulation units, an I-Ch modulation unit and a Q-Ch modulation unit, for the light branched into two optical paths.
  • the optical modulator is a control in which a control signal based on code data encoded for transmission on a transmission path in each modulation unit is input as an I-Ch modulation signal and a Q-Ch modulation signal, respectively. It has a terminal.
  • the optical modulator also includes a bias application terminal to which a control signal for applying a bias voltage in each modulator is input as an I-Ch bias voltage signal and a Q-Ch bias voltage signal.
  • the phase adjustment unit that adjusts the phase difference between the I-phase and Q-phase signals includes a bias application terminal to which a Ph-Ch bias voltage signal is input as a control signal for controlling the bias voltage.
  • the optical modulator modulates the input light in a state where a bias voltage is applied based on each control signal, and multiplexes and outputs so that the I-phase component and the Q-phase component are orthogonal.
  • the light modulation unit 12 of the present embodiment corresponds to the light modulation unit 1 of the first embodiment.
  • the control unit 13 has a function of controlling the modulation of the output light from the light source unit 11 in the light modulation unit 12 and a function of optimizing the bias voltage applied to the light modulation unit 12.
  • FIG. 4 shows the configuration of the control unit 13 of the present embodiment. As shown in FIG. 4, the control unit 13 of this embodiment includes an optimization processing unit 21 and a modulator control unit 22.
  • the optimization processing unit 21 has a function of optimizing the bias voltage applied to the light modulation unit 12.
  • the optimization processing unit 21 determines the optimum value of the bias voltage to be applied to the I-phase and Q-phase modulation units and the phase modulation unit based on the waveform of the electrical signal input from the signal processing unit 16 and the reception quality of the signal. Set.
  • the optimization processing unit 21 sets the optimum value of each bias voltage in two stages: A mode for optimizing the signal waveform and B mode for minimizing the signal BER (Bit Error Ratio). In other words, when the A mode is the first mode and the B mode is the second mode, the optimization processing unit 21 optimizes the reference value of the bias voltage in the first mode, and then performs the second mode. Optimize the offset value.
  • the optimization processing unit 21 In the optimization in the A mode, the optimization processing unit 21 superimposes a low-frequency test signal on the optical signal in the optical modulation unit 12 via the modulator control unit 22. In the A mode, the optimization processing unit 21 sweeps each bias voltage, determines the I-phase and Q-phase signal waveforms and the bias voltage at which the phase difference between the I-phase and the Q-phase is in an ideal state. The bias voltage when it is determined to be a typical state is used as a reference value for the bias voltage of each component. The optimization processing unit 21 acquires the waveform of the low-frequency signal output from the light modulation unit 12 as an electrical signal via the light receiving unit 15 and the signal processing unit 16.
  • the optimization processing unit 21 applies the bias voltage obtained by adding the offset value to the reference value of the bias voltage set in the A mode in the optical modulation unit 12 while changing the offset value. .
  • the optimization processing unit 21 changes the offset value for each component, and monitors the change in the BER when the offset value is changed.
  • the optimization processing unit 21 sets an offset value that minimizes the BER for each component as an offset value in the I-phase and Q-phase modulation units and the phase modulation unit.
  • the optimization processing unit 21 writes data necessary for arithmetic processing for setting the reference value and offset value of the bias voltage and the set reference value and offset data of the bias voltage in the storage unit 14. In addition, the optimization processing unit 21 reads data necessary for arithmetic processing and control of the light modulation unit 12 from the storage unit 14.
  • the optimization processing unit 21 is configured by, for example, a CPU (Central Processing Unit) that performs arithmetic processing.
  • the optimization processing unit 21 of the present embodiment corresponds to the optimization unit 3 of the first embodiment.
  • the modulator control unit 22 is a control circuit that controls the light modulation unit 12 based on the processing result of the optimization processing unit 21.
  • the modulator control unit 22 outputs to the optical modulation unit 12 a bias voltage signal that controls application of a bias voltage in the I-Ch modulation unit, Q-ch modulation unit, and phase modulation unit of the optical modulation unit 12. Further, the modulator control unit 22 outputs a control signal for performing modulation in the I-Ch modulation unit and the Q-ch modulation unit of the optical modulation unit 12 to the optical modulation unit 12.
  • the modulator control unit 22 controls the optical modulation unit 12 so that modulation based on code data input from the signal processing unit 16 is performed.
  • the modulator controller 22 controls the optical modulator 12 so that a low-frequency test signal is superimposed on the optical signal based on the control of the optimization processor 21. Control.
  • the modulator control unit 22 of the present embodiment corresponds to the control unit 2 of the first embodiment.
  • the storage unit 14 has a function of storing each data necessary for controlling the light modulation unit 12 and optimizing the bias voltage.
  • the storage unit 14 stores and reads data based on the control of the control unit 13.
  • the storage unit 14 is configured by a nonvolatile semiconductor memory element capable of writing and reading data, such as a flash memory.
  • the optical receiver 15 has a function of receiving an optical signal, converting it into an electrical signal, and outputting it to the signal processor 16.
  • the optical receiver 15 receives an optical signal transmitted from an optical transmission device facing through the transmission path.
  • the optical signal transmitted from the optical transceiver 10 is input to the optical receiver 15 after being folded back by a relay device or the like.
  • the optical receiver 15 has a function of performing coherent detection of an optical reception signal, and includes a local light source and a light receiving element for the optical reception signal.
  • the signal processor 16 has a function of processing a signal input from the optical receiver 15 and an external signal input from the outside.
  • FIG. 5 shows the configuration of the signal processing unit 16 of the present embodiment. As shown in FIG. 5, the signal processing unit 16 of this embodiment includes a reception signal processing unit 31, a transmission signal processing unit 32, and a BER measurement unit 33.
  • the received signal processing unit 31 separates the test signal for optimizing the bias voltage received by the optical receiving unit 15 into an I-phase component signal and a Q-phase component signal, and outputs them to the control unit 13.
  • the reception signal processing unit 31 performs processing such as decoding of the optical reception signal received by the optical reception unit 15 and converts it into a signal to be output to the outside.
  • the reception signal processing unit 31 outputs a signal converted into a signal to be output to the outside as an external signal.
  • the transmission signal processing unit 32 converts an external signal input from the outside into code data for transmission through the transmission path, and outputs the code data to the control unit 13.
  • the BER measuring unit 33 monitors the signal processing performed by the received signal processing unit 31 and calculates the BER of the optical signal input from the optical receiving unit 15.
  • the BER measurement unit 33 outputs the calculated BER value to the control unit 13 based on a request from the control unit 13.
  • the BER measurement unit 33 calculates the BER of each of the I-phase signal and the Q-phase signal and the BER of the Ph component. For example, the BER measurement unit 33 calculates the BER of the Ph component indicating the phase difference between the I phase and the Q phase by comparing the phase component of the detected signal with a predetermined reference to determine the presence or absence of an error.
  • the signal processing unit 16 is configured by, for example, a DSP (Digital Signal Processor).
  • the reception signal processing unit 31, the transmission signal processing unit 32, and the BER measurement unit 33 may be formed as circuit patterns on the same substrate, or may be formed as circuit patterns on different substrates. . Further, the signal processing of the signal processing unit 16 may be executed by a program executed using a CPU or a semiconductor memory element.
  • FIG. 6 shows a main flow when the bias voltage is optimized.
  • FIG. 7 shows an operation flow when performing optimization in the A mode.
  • FIG. 8 shows an operation flow when performing optimization in the B mode.
  • FIG. 9 shows an operation flow when an optimum offset value is set by feedback control in the B mode processing.
  • the optical transceiver 10 When the optical transceiver 10 starts operation, the optical transceiver 10 performs the operation of optimizing the bias voltage shown in FIG.
  • the control unit 13 When the operation for optimizing the bias voltage is started, the control unit 13 performs the control in the A mode and optimizes the bias voltage applied in the optical modulation unit 12 (step 111).
  • the operation shown in FIG. 7 is executed.
  • the control unit 13 controls the optical modulation unit 12 to superimpose a low-frequency test signal on the optical signal to be output.
  • the control unit 13 sweeps the value of the bias voltage applied to the light modulation unit 12 and performs optimization control of the bias voltage based on the waveform change of the low frequency test signal input via the signal processing unit 16. (Step 121). For example, the control unit 13 sets the voltage at which the amplitude of the low-frequency test signal is minimum as the optimum value of the bias voltage.
  • the low-frequency signal superimposed on the optical signal by the optical modulator 12 is turned back by a relay device or the like and input to the optical receiver 15.
  • the communication management system transmits the optical signal from its own device by using a relay device having a function of returning the optical signal to the path toward the optical signal transmission source based on the control.
  • the received optical signal can be received by the optical receiver 15.
  • the optical signal received by the optical receiver 15 is converted into an electrical signal and input to the signal processor 16.
  • the low frequency signal input to the signal processing unit 16 is processed by the signal processing unit 16 and input to the control unit 13.
  • the control unit 13 determines whether the applied bias voltage is optimal based on the fluctuation of the waveform data.
  • control unit 13 continues the operation of optimizing the bias voltage in the A mode.
  • Step 122 If it is determined that the bias voltage is optimal (Yes in Step 122), the control unit 13 stores the value of the bias voltage determined to be optimal in the storage unit 14 (Step 123). When the bias voltage value determined to be optimal is stored in the storage unit 14, the control unit 13 stores the initial value of the offset value of the bias voltage in the storage unit 14 (step 124). The initial value of the offset value is set as 0.
  • control unit 13 ends the control of optimizing the bias voltage in the A mode in step 111 in FIG. 6, and controls the optimization of the bias voltage in the B mode in step 112. To start.
  • the operation shown in FIG. 8 is executed.
  • the control unit 13 reads the value of BER from the signal processing unit 16 (step 131).
  • the signal processing unit 16 measures the BER of the signal received via the optical receiving unit 15.
  • the control unit 13 compares the BER value with a preset reference value.
  • the reference value of BER is set as a value sufficient as the reception quality of the optical signal.
  • the control unit 13 ends the control for optimizing the bias voltage in the B mode.
  • the deviation from the optimum bias is also within the reference (Yes in step 113), so the control unit 13 ends the operation of optimizing the bias voltage and determines the optimum bias voltage.
  • the light modulator 12 is controlled.
  • control unit 13 starts control of an optimization operation for adjusting the offset value for each component by feedback control (step 133).
  • control unit 13 When the control unit 13 starts the optimization operation of the B mode for adjusting the offset value for each component, the control unit 13 reads the bias reference value and the offset value data from the storage unit 14 (step 141). When the B mode is first executed immediately after startup, 0 is set as the offset value.
  • control unit 13 controls the light modulation unit 12 by applying a bias voltage obtained by adjusting the bias reference value using the offset value to the bias terminal of the light modulation unit 12. (Step 142).
  • the control unit 13 reads BER data from the signal processing unit 16 (step 143).
  • the BER data read from the signal processing unit 16 is a BER obtained by controlling the light modulation unit 12 by applying a bias voltage adjusted by the offset value.
  • the control unit 13 determines whether the BER read from the signal processing unit 16 is within the reference. When the BER is within the reference (Yes in Step 144), the control unit 13 stores the offset value in the storage unit 14 (Step 148). The operations from step 141 to step 148 are sequentially performed on the I-phase component, the Q-phase component, and the Ph component.
  • the control unit 13 compares the BER newly acquired from the signal processing unit 16 with the BER acquired last time. When the newly acquired BER is equal to or higher than the previously acquired BER (No in step 145), the control unit 13 increases or decreases the offset value by the same amount in the opposite direction to the previous time.
  • the increase / decrease direction and increase / decrease amount of the offset value when the offset value is first increased / decreased are set in advance.
  • the control unit 13 adjusts the -1 mV offset value obtained by reversing the positive and negative values from the previous time.
  • the control unit 13 stores the adjusted value in the storage unit 14.
  • the control unit 13 performs the operation from step 143 again.
  • control unit 13 increases or decreases the offset value by the same amount in the same direction as the previous time, and applies a bias voltage to the light modulation unit 12. Is applied (step 146).
  • the control unit 13 increases the +1 mV offset value in the same manner.
  • the control unit 13 stores the adjusted value in the storage unit 14.
  • the control unit 13 performs the operation from step 143 again.
  • the control unit 13 reads BER data from the signal processing unit 16 (step 143).
  • the BER data read from the signal processing unit 16 is a BER obtained by controlling the light modulation unit 12 by applying a bias voltage adjusted by the offset value.
  • the control unit 13 determines whether the BER read from the signal processing unit 16 is within the reference. When the BER is within the reference (Yes in Step 144), the control unit 13 stores the offset value in the storage unit 14 (Step 148). The operations from step 141 to step 148 are sequentially performed on the I-phase component, the Q-phase component, and the Ph component. When the BER is not within the reference (No in Step 144), the control unit 13 further varies the offset value and continues the operation of adjusting the offset value.
  • control unit 13 ends the feedback control in step 112 of FIG. 8 and ends the control for optimizing the bias value in the B mode.
  • the control unit 13 confirms that the bias voltage determined to be optimal, that is, the bias voltage obtained by correcting the reference value of the bias voltage with the offset value is within the reference.
  • the control unit 13 performs again from the operation of optimizing the reference value of the bias voltage in the A mode.
  • control unit 13 ends the operation of optimizing the bias voltage, and controls the light modulation unit 12 with the bias voltage determined to be optimal.
  • the optical transceiver of the present embodiment optimizes the bias voltage in two stages: optimization of the bias voltage reference value by the A mode and optimization of the offset value from the bias voltage reference value by the B mode. .
  • the optical transceiver 10 optimizes the reference value of the bias voltage in the A mode, and if the BER is within the reference when the control in the A mode is finished, the operation of optimizing the bias voltage is completed.
  • the optical transceiver 10 optimizes the offset value of the bias voltage in the B mode.
  • Optimize the bias voltage in consideration of the interaction of the I-phase component, the Q-phase component and the Ph component in the B mode that is, correct for the deviation of the optimum bias voltage as follows.
  • the reference values of the bias voltages of the I-phase component, Q-phase component, and Ph component are set in the A mode
  • the BER of the I-phase component, Q-phase component, and Ph component is confirmed.
  • the offset value in the B mode is optimized for components whose BER is not the reference. For example, when the I-phase component is out of the standard and the Q-phase component and the Ph component satisfy the standard, only the I-phase component is optimized for the offset value by the B mode.
  • the optical transceiver 10 of this embodiment receives an optical signal output from its own apparatus by the optical receiving unit 15, and the control unit 13 optimizes the reference value of the offset voltage based on the signal waveform as the A mode. .
  • the optical transceiver 10 of the present embodiment optimizes the offset value of each component in the B mode based on the BER, that is, the signal quality, after optimization in the A mode.
  • the optical transceiver 10 of the present embodiment can correct the bias voltage shift due to the interaction of the I-phase, the Q-phase, and the Ph component by optimizing the offset value of each component. Therefore, the optical transceiver 10 of the present embodiment can optimize the bias voltage with high accuracy even when there is an interaction between the I phase, the Q phase, and the Ph component.
  • the optical transceiver 10 according to the present embodiment can optimize the bias voltage applied to the optical modulator with high accuracy while suppressing the influence of the interaction of each component even if characteristic variation or the like occurs.
  • the optical transceiver 10 of the second embodiment acquires the data of the signal waveform and the reception quality by receiving the optical signal returned by the relay device after transmission from the own device, and obtains the reference value of the offset voltage. And offset value optimization.
  • feedback control may be performed in the optical transceiver to optimize the reference value of the bias voltage in the A mode.
  • the bias voltage is optimized based on the result of receiving the optical signal branched at the output portion of the light modulation unit 12 by the light receiving element.
  • the reference value of the bias voltage in the A mode may be optimized based on the waveform of the optical signal received by the light receiving element provided in the light modulation unit.
  • the optical transceiver 10 of the second embodiment acquires the BER information of the received signal by receiving the optical signal transmitted from the own device by the own device, but is received by the opposite optical transceiver via the transmission path.
  • the offset value may be optimized based on the BER at the time. In such a configuration, signal information for optimizing the offset value is shared in advance between the optical transceiver on the receiving side and the transmitting side.

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Abstract

[Problem] To provide an optical transceiver capable of optimizing a bias voltage to be applied to an optical modulator while suppressing interaction between components even when a property variation or the like occurs. [Solution] This optical transceiver is configured to be provided with an optical modulation means 1, a control means 2, and an optimization means 3. The optical modulation means 1 applies a bias voltage to light of each of an I phase component and a Q phase component to perform modulation of the light. The control means 2 controls the bias voltage for each component for which modulation is performed. The optimization means 3 optimizes the bias voltage by means of a first mode and a second mode. The first mode is for setting a first bias voltage obtained by optimizing the bias voltage on the basis of an optical signal. The second mode is for adjusting an offset value from the first bias voltage, for each component for which modulation is performed, on the basis of the quality of an optical signal. In addition, the control means 2 controls application of the bias voltage on the basis of a second bias voltage obtained by correcting the first bias voltage on the basis of the offset value.

Description

光トランシーバおよび変調制御方法Optical transceiver and modulation control method
　本発明は、光信号の変調に関するものであり、特に、光変調器の最適な動作点を補正する技術に関するものである。 The present invention relates to modulation of an optical signal, and more particularly to a technique for correcting an optimum operating point of an optical modulator.
　基幹系光ネットワークを中心に、大容量の伝送が可能なデジタルコヒーレント方式の光通信ネットワークシステムが用いられるようになっている。デジタルコヒーレント方式では、光源であるＩＬＴＡ（Integrable Tunable Laser Assembly）から出力した光に、ＬＮ（Lithium Niobate：ＬｉＮｂＯ３）結晶を用いたマッハツェンダー型のＬＮ変調器で位相変調を施すことで光信号が生成される。 Digital coherent optical communication network systems capable of large-capacity transmission have been used mainly in backbone optical networks. In the digital coherent system, the optical signal is generated by phase-modulating the light output from an ILTA (Integrable Tunable Laser Assembly), which is a light source, with a Mach-Zehnder type LN modulator using an LN (Lithium Niobate: LiNbO 3 ) crystal. Generated.
　デジタルコヒーレント方式における光変調器の制御は、同相成分Ｉ（In-Phase）、直交位相成分Ｑ（Quadrature）および位相成分Ｐｈ（Phase）３つの成分を制御するバイアスを印加することで最適な光波形が出力されるように行われる。そのような光変調器では、光変調器内のＩ相成分の影響によって、Ｑ相成分が最適値よりわずかにずれる現象も生じる。そのようなずれの解決は、収束点から手動でバイアスにオフセットをかけることで行われることが多い。しかし、経年劣化によって、Ｉ相成分、Ｑ相成分およびＰｈ成分の最適バイアスが変動するため、最適バイアスが変動に合わせてオフセットの量を最適化する必要がある。そのため、光変調器において、経年劣化等による最適値の変動の影響を抑制するため、Ｉ相成分、Ｑ相成分およびＰｈ成分の最適バイアスやオフセット値を最適化する技術の開発が行われている。そのような光変調器におけるＩ相成分、Ｑ相成分およびＰｈ成分の最適バイアスやオフセット値を最適化する技術としては、例えば、特許文献１のような技術が開示されている。 The optical modulator in the digital coherent system is controlled by applying a bias for controlling the three components in-phase component I (In-Phase), quadrature component Q (Quadrature) and phase component Ph (Phase). Is performed so that is output. In such an optical modulator, a phenomenon in which the Q-phase component slightly deviates from the optimum value also occurs due to the influence of the I-phase component in the optical modulator. Such deviations are often resolved by manually offsetting the bias from the convergence point. However, since the optimum bias of the I-phase component, the Q-phase component, and the Ph component varies due to deterioration over time, it is necessary to optimize the amount of offset according to the variation of the optimum bias. Therefore, in the optical modulator, in order to suppress the influence of fluctuations in the optimum value due to deterioration over time, a technique for optimizing the optimum bias and offset value of the I-phase component, the Q-phase component and the Ph component has been developed. . As a technique for optimizing the optimum bias and offset value of the I-phase component, Q-phase component, and Ph component in such an optical modulator, for example, a technique as disclosed in Patent Document 1 is disclosed.
　特許文献１は、最適バイアスからのずれを補正する機能を有するＭＺ型光変調器を備えた光送信機に関するものである。特許文献１の光変調器は、光変調器に印加するバイアス電圧を変化させ、光変調器の動作点を掃引しながら出力光の計測を行って最適なバイアスの補償量を決定している。また、特許文献２および特許文献３にも特許文献１と同様の光送信機の光変調器のバイアス電圧の最適化に関する技術が開示されている。 Patent Document 1 relates to an optical transmitter including an MZ type optical modulator having a function of correcting a deviation from an optimum bias. The optical modulator disclosed in Patent Document 1 changes the bias voltage applied to the optical modulator and measures the output light while sweeping the operating point of the optical modulator to determine the optimum bias compensation amount. Also, Patent Document 2 and Patent Document 3 disclose techniques related to optimization of the bias voltage of the optical modulator of the optical transmitter similar to Patent Document 1.
特開２０１３－１７４７６１号公報JP 2013-174761 A 国際公開第２０１３／１１４６２８号International Publication No. 2013/114628 特開２０１２-１２８１６５号公報JP 2012-128165 A
　しかしながら、特許文献１、特許文献２および特許文献３の技術は次のような点で十分ではない。特許文献１、特許文献２および特許文献３では、マッハツェンダー型光変調器のバイアス電圧の最適化を行っているが、Ｉ相成分、Ｑ相成分およびＰｈ成分の各成分が互いに及ぼす影響については考慮されていない。そのため、特許文献１、特許文献２および特許文献３では、Ｉ相成分、Ｑ相成分およびＰｈ成分が互いに影響を及ぼすことで、光変調器の動作点が最適値からずれる恐れがある。そのため、特許文献１、特許文献２および特許文献３の技術は、光変調器の特性変動等が生じた際に、光変調器に印加するバイアス電圧を高い精度で最適化するための技術としては十分ではない。 However, the techniques of Patent Document 1, Patent Document 2 and Patent Document 3 are not sufficient in the following points. In Patent Document 1, Patent Document 2 and Patent Document 3, the bias voltage of the Mach-Zehnder optical modulator is optimized. Regarding the influence of the I-phase component, the Q-phase component and the Ph component on each other, Not considered. For this reason, in Patent Document 1, Patent Document 2, and Patent Document 3, the I-phase component, the Q-phase component, and the Ph component affect each other, which may cause the operating point of the optical modulator to deviate from the optimum value. Therefore, the techniques of Patent Document 1, Patent Document 2 and Patent Document 3 are techniques for optimizing the bias voltage applied to the optical modulator with high accuracy when the characteristic variation of the optical modulator occurs. Not enough.
　本発明は、上記の課題を解決するため、光変調器の特性変動等が生じた際に、各成分の相互作用の影響を抑制し、光変調器に印加するバイアス電圧を高い精度で最適化することができる光トランシーバおよびその制御方法を提供することを目的としている。 In order to solve the above-mentioned problems, the present invention suppresses the influence of the interaction of each component when the characteristic variation of the optical modulator occurs, and optimizes the bias voltage applied to the optical modulator with high accuracy. It is an object of the present invention to provide an optical transceiver that can be used and a control method thereof.
　上記の課題を解決するため、本発明の光トランシーバは、光変調手段と、制御手段と、最適化手段を備えている。光変調手段は、入力された光をＩ（In-Phase）相成分とＱ（Quadrature）相成分の光に分波する手段と、分波したそれぞれの光にバイアス電圧を印加して変調を施す手段と、変調を施したＩ相成分とＱ相成分の光を合波した光信号を出力する手段とを有する。制御手段は、光変調手段において印加されるバイアス電圧を、変調を施す成分ごとに制御する。最適化手段は、第１のモードと第２のモードによってバイアス電圧を最適化する。第１のモードは、光変調手段から出力される光信号に基づいてバイアス電圧を最適化した第１のバイアス電圧を設定するモードである。第２のモードは、第１のバイアス電圧からのオフセット量を、光信号の品質を基に変調を施す成分ごとに調整することでバイアス電圧を最適化するモードである。また、制御手段は、最適化手段によって設定された第１のバイアス電圧をオフセット値に基づいて補正した第２のバイアス電圧を基に、光変調手段におけるバイアス電圧の印加を制御する。 In order to solve the above-described problems, the optical transceiver of the present invention includes optical modulation means, control means, and optimization means. The light modulation means demultiplexes the input light into light of an I (In-Phase) phase component and a Q (Quadrature) phase component, and applies a bias voltage to each of the demultiplexed light to perform modulation. And means for outputting an optical signal obtained by combining the modulated I-phase component and Q-phase components. The control unit controls the bias voltage applied in the light modulation unit for each component to be modulated. The optimization means optimizes the bias voltage in the first mode and the second mode. The first mode is a mode for setting a first bias voltage in which the bias voltage is optimized based on the optical signal output from the light modulation means. The second mode is a mode for optimizing the bias voltage by adjusting the offset amount from the first bias voltage for each component to be modulated based on the quality of the optical signal. Further, the control unit controls application of the bias voltage in the light modulation unit based on the second bias voltage obtained by correcting the first bias voltage set by the optimization unit based on the offset value.
　本発明の変調制御方法は、入力された光をＩ相成分とＱ相成分の光に分波する。本発明の変調制御方法は、分波したそれぞれの光に変調を施す成分ごとに制御したバイアス電圧を印加して変調を施す。本発明の変調制御方法は、変調を施したＩ相成分とＱ相成分の光を合波した光信号を出力する。本発明の変調制御方法は、第１のモードと、第２のモードによってバイアス電圧を最適化する。第１のモードは、光変調手段から出力される光信号に基づいてバイアス電圧を最適化した第１のバイアス電圧を設定するモードである。第２のモードは、第１のバイアス電圧からのオフセット値を、光信号の品質を基に変調を施す成分ごとに調整することでバイアス電圧を最適化するモードである。本発明の変調制御方法は、第１のバイアス電圧をオフセット値に基づいて補正した第２のバイアス電圧を基に、バイアス電圧の印加を制御する。 The modulation control method of the present invention demultiplexes input light into I-phase component and Q-phase component light. In the modulation control method of the present invention, modulation is performed by applying a bias voltage controlled for each component to be modulated to each of the demultiplexed light. The modulation control method of the present invention outputs an optical signal obtained by combining modulated I-phase components and Q-phase components. In the modulation control method of the present invention, the bias voltage is optimized by the first mode and the second mode. The first mode is a mode for setting a first bias voltage in which the bias voltage is optimized based on the optical signal output from the light modulation means. The second mode is a mode in which the bias voltage is optimized by adjusting the offset value from the first bias voltage for each component to be modulated based on the quality of the optical signal. The modulation control method of the present invention controls the application of the bias voltage based on the second bias voltage obtained by correcting the first bias voltage based on the offset value.
　本発明によると、特性変動等が生じても、各成分の相互作用の影響を抑制しつつ光変調器に印加するバイアス電圧を高い精度で最適化することができる。 According to the present invention, it is possible to optimize the bias voltage to be applied to the optical modulator with high accuracy while suppressing the influence of the interaction of each component even if characteristic variation or the like occurs.
本発明の第１の実施形態の構成の概要を示す図である。It is a figure which shows the outline | summary of a structure of the 1st Embodiment of this invention. 本発明の第２の実施形態の構成の概要を示す図である。It is a figure which shows the outline | summary of a structure of the 2nd Embodiment of this invention. 本発明の第２の実施形態の光変調器の構成の例を示した図である。It is the figure which showed the example of the structure of the optical modulator of the 2nd Embodiment of this invention. 本発明の第２の実施形態の制御部の構成を示した図である。It is the figure which showed the structure of the control part of the 2nd Embodiment of this invention. 本発明の第２の実施形態の信号処理部の構成を示した図である。It is the figure which showed the structure of the signal processing part of the 2nd Embodiment of this invention. 本発明の第２の実施形態の動作フローを示す図である。It is a figure which shows the operation | movement flow of the 2nd Embodiment of this invention. 本発明の第２の実施形態の動作フローを示す図である。It is a figure which shows the operation | movement flow of the 2nd Embodiment of this invention. 本発明の第２の実施形態の動作フローを示す図である。It is a figure which shows the operation | movement flow of the 2nd Embodiment of this invention. 本発明の第２の実施形態の動作フローを示す図である。It is a figure which shows the operation | movement flow of the 2nd Embodiment of this invention. 本発明の第２の実施形態において、光トランシーバ内でフィードバック制御を行う際の動作を模式的に示した図である。It is the figure which showed typically the operation | movement at the time of performing feedback control within the optical transceiver in the 2nd Embodiment of this invention.
　（第１の実施形態）
　本発明の第１の実施形態について図を参照して詳細に説明する。図１は、本実施形態の光トランシーバの構成の概要を示したものである。本実施形態の光トランシーバは、光変調手段１と、制御手段２と、最適化手段３を備えている。光変調手段１は、入力された光をＩ（In-Phase）相成分とＱ（Quadrature）相成分の光に分波する手段と、分波したそれぞれの光にバイアス電圧を印加して変調を施す手段と、変調を施したＩ相成分とＱ相成分の光を合波した光信号を出力する手段とを有する。制御手段２は、光変調手段１において印加されるバイアス電圧を、変調を施す成分ごとに制御する。最適化手段３は、第１のモードと第２のモードによってバイアス電圧を最適化する。第１のモードは、光変調手段１から出力される光信号に基づいてバイアス電圧を最適化した第１のバイアス電圧を設定するモードである。第２のモードは、第１のバイアス電圧からのオフセット値を、光信号の品質を基に変調を施す成分ごとに調整することでバイアス電圧を最適化するモードである。また、制御手段２は、最適化手段３によって設定された第１のバイアス電圧をオフセット値に基づいて補正した第２のバイアス電圧を基に、光変調手段１におけるバイアス電圧の印加を制御する。 (First embodiment)
A first embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 shows an outline of the configuration of the optical transceiver of this embodiment. The optical transceiver of this embodiment includes an optical modulation unit 1, a control unit 2, and an optimization unit 3. The light modulation means 1 is a means for demultiplexing the input light into light of an I (In-Phase) phase component and a Q (Quadrature) phase component, and a bias voltage is applied to each of the demultiplexed light to modulate it. And means for outputting an optical signal obtained by combining the modulated I-phase component and Q-phase components. The control unit 2 controls the bias voltage applied in the light modulation unit 1 for each component to be modulated. The optimization unit 3 optimizes the bias voltage in the first mode and the second mode. The first mode is a mode in which a first bias voltage is set by optimizing the bias voltage based on the optical signal output from the light modulation unit 1. The second mode is a mode in which the bias voltage is optimized by adjusting the offset value from the first bias voltage for each component to be modulated based on the quality of the optical signal. The control unit 2 controls the application of the bias voltage in the light modulation unit 1 based on the second bias voltage obtained by correcting the first bias voltage set by the optimization unit 3 based on the offset value.
　本実施形態の光トランシーバは、最適化手段３において第１のバイアス電圧を設定する第１のモードと、第１のバイアス電圧のオフセット値を設定する第２のモードの２段階でバイアス電圧を最適化している。本実施形態の光トランシーバは、最適化手段３が２段階で最適化したバイアス電圧を基に、制御手段２が光変調手段１において各成分に印加するバイアス電圧を制御している。本実施形態の光トランシーバは、第２のモードにおいて、成分ごとにオフセット値を最適化することで、各成分に相互作用があった場合にも、バイアス電圧をより最適化することができる。その結果、本実施形態の光トランシーバは、特性変動等が生じても各成分の相互作用の影響を抑制しつつ光変調器に印加するバイアス電圧を高い精度で最適化することができる。 The optical transceiver according to the present embodiment optimizes the bias voltage in two stages: the first mode in which the optimization unit 3 sets the first bias voltage and the second mode in which the offset value of the first bias voltage is set. It has become. In the optical transceiver of this embodiment, the control unit 2 controls the bias voltage applied to each component in the optical modulation unit 1 based on the bias voltage optimized by the optimization unit 3 in two stages. The optical transceiver of this embodiment can optimize the bias voltage even when there is an interaction with each component by optimizing the offset value for each component in the second mode. As a result, the optical transceiver according to the present embodiment can optimize the bias voltage applied to the optical modulator with high accuracy while suppressing the influence of the interaction of each component even if characteristic variation or the like occurs.
　（第２の実施形態）
　本発明の第２の実施形態について図を参照して詳細に説明する。図２は、本実施形態の光トランシーバ１０の構成の概要について示したものである。本実施形態の光トランシーバ１０は、光源部１１と、光変調部１２と、制御部１３と、記憶部１４と、光受信部１５と、信号処理部１６を備えている。 (Second Embodiment)
A second embodiment of the present invention will be described in detail with reference to the drawings. FIG. 2 shows an outline of the configuration of the optical transceiver 10 of the present embodiment. The optical transceiver 10 of the present embodiment includes a light source unit 11, an optical modulation unit 12, a control unit 13, a storage unit 14, an optical reception unit 15, and a signal processing unit 16.
　本実施形態の光トランシーバ１０は、外部から入力される外部信号を基に、伝送路を介して伝送する光信号を生成して出力する光送信機としての機能と、伝送路を介して受信する光信号の復号等を行って外部信号として出力する光受信機としての機能を有する。また、本実施形態の光トランシーバ１０は、デジタルコヒーレント方式の光通信システムに対応した光トランシーバである。すなわち、本実施形態の光トランシーバ１０は、外部信号を元に信号処理部１６で符号化されたデータに基づいて、光変調部１２において、Ｉ相と、Ｉ相の直交位相成分であるＱ相の光に、それぞれ変調を施して出力する。また、本実施形態の光トランシーバ１０は、光受信部１５において、伝送路を介して光受信信号として受信する光信号のコヒーレント検波を行い、信号処理部１６で復号等の信号処理を行った信号を外部信号として出力する。 The optical transceiver 10 according to the present embodiment generates a function of an optical transmitter that generates and outputs an optical signal to be transmitted via a transmission path based on an external signal input from the outside, and receives the function via the transmission path. It has a function as an optical receiver that decodes an optical signal and outputs it as an external signal. The optical transceiver 10 of this embodiment is an optical transceiver compatible with a digital coherent optical communication system. That is, the optical transceiver 10 according to the present embodiment uses the optical modulation unit 12 based on the data encoded by the signal processing unit 16 based on the external signal, and the Q phase that is the quadrature phase component of the I phase and the I phase. The light is modulated and output. In the optical transceiver 10 of the present embodiment, the optical receiver 15 performs coherent detection of an optical signal received as an optical reception signal via a transmission path, and the signal processing unit 16 performs signal processing such as decoding. Is output as an external signal.
　光源部１１は、光信号を送信する際の搬送波の光を出力する光源としての機能を有する。本実施形態の光源部１１は、ＩＴＬＡ（Integrable Tunable Laser Assembly）として構成されている。光源部１１は、連続（ＣＷ：Continuous Wave）を出力する。光源部１１から出力された光は、光変調部１２に入力される。 The light source unit 11 has a function as a light source that outputs light of a carrier wave when transmitting an optical signal. The light source unit 11 of the present embodiment is configured as an ITLA (Integrable Tunable Laser Assembly). The light source unit 11 outputs continuity (CW: Continuous Wave). The light output from the light source unit 11 is input to the light modulation unit 12.
　光変調部１２は、制御部１３の制御に基づいて、光源部１１から入力されるＣＷ光に位相変調を施して光信号を生成する光変調器である。本実施形態の光変調部１２には、マッハツェンダー型のＬＮ（Lithium Niobate：ＬｉＮｂＯ３）変調器が用いられる。光変調部１２には、ＬＮ変調器に代えて、電気光学効果を用いた他の変調器を用いてもよい。 The optical modulation unit 12 is an optical modulator that performs phase modulation on the CW light input from the light source unit 11 and generates an optical signal based on the control of the control unit 13. A Mach-Zehnder type LN (Lithium Niobate: LiNbO 3 ) modulator is used for the light modulator 12 of the present embodiment. The light modulator 12 may be replaced with another modulator using the electro-optic effect instead of the LN modulator.
　図３は、本実施形態の光変調器の構成を模式的に示したものである。図３に示すように光変調器は、２つの光路に分岐された光にＩ－Ｃｈ変調部と、Ｑ－Ｃｈ変調部の２つの変調部を備えている。光変調器は、それぞれの変調部において伝送路で伝送するための符号化が行われた符号データを基にした制御信号が、Ｉ－Ｃｈ変調信号およびＱ－Ｃｈ変調信号としてそれぞれ入力される制御端子を備えている。また、光変調器は、それぞれの変調部においてバイアス電圧を印加するための制御信号がＩ－Ｃｈバイアス電圧信号、Ｑ－Ｃｈバイアス電圧信号として入力されるバイアス印加端子を備えている。また、Ｉ相とＱ相の信号の位相差を調整する位相調整部は、バイアス電圧を制御する制御信号としてＰｈ－Ｃｈバイアス電圧信号が入力されるバイアス印加端子を備えている。光変調器は、各制御信号を基にバイアス電圧が印加された状態で、入力された光に変調を施し、Ｉ相成分とＱ相成分が直交するように合波して出力する。また、本実施形態の光変調部１２は、第１の実施形態の光変調手段１に相当する。 FIG. 3 schematically shows the configuration of the optical modulator of the present embodiment. As shown in FIG. 3, the optical modulator includes two modulation units, an I-Ch modulation unit and a Q-Ch modulation unit, for the light branched into two optical paths. The optical modulator is a control in which a control signal based on code data encoded for transmission on a transmission path in each modulation unit is input as an I-Ch modulation signal and a Q-Ch modulation signal, respectively. It has a terminal. The optical modulator also includes a bias application terminal to which a control signal for applying a bias voltage in each modulator is input as an I-Ch bias voltage signal and a Q-Ch bias voltage signal. In addition, the phase adjustment unit that adjusts the phase difference between the I-phase and Q-phase signals includes a bias application terminal to which a Ph-Ch bias voltage signal is input as a control signal for controlling the bias voltage. The optical modulator modulates the input light in a state where a bias voltage is applied based on each control signal, and multiplexes and outputs so that the I-phase component and the Q-phase component are orthogonal. The light modulation unit 12 of the present embodiment corresponds to the light modulation unit 1 of the first embodiment.
　制御部１３は、光変調部１２における光源部１１からの出力光の変調を制御する機能と、光変調部１２に印加するバイアス電圧の最適化を行う機能を有する。図４は、本実施形態の制御部１３の構成を示したものである。図４に示すとおり、本実施形態の制御部１３は、最適化処理部２１と、変調器制御部２２を備えている。 The control unit 13 has a function of controlling the modulation of the output light from the light source unit 11 in the light modulation unit 12 and a function of optimizing the bias voltage applied to the light modulation unit 12. FIG. 4 shows the configuration of the control unit 13 of the present embodiment. As shown in FIG. 4, the control unit 13 of this embodiment includes an optimization processing unit 21 and a modulator control unit 22.
　最適化処理部２１は、光変調部１２に印加するバイアス電圧を最適化する機能を有する。最適化処理部２１は、信号処理部１６から入力される電気信号の波形と信号の受信品質を基に、I相およびＱ相の変調部と位相変調部にそれぞれ印加するバイアス電圧の最適値を設定する。 The optimization processing unit 21 has a function of optimizing the bias voltage applied to the light modulation unit 12. The optimization processing unit 21 determines the optimum value of the bias voltage to be applied to the I-phase and Q-phase modulation units and the phase modulation unit based on the waveform of the electrical signal input from the signal processing unit 16 and the reception quality of the signal. Set.
　最適化処理部２１は、各バイアス電圧の最適値を、信号の波形を最適化するＡモードと、信号のＢＥＲ（Bit Error Ratio）を最小化するＢモードの２段階によって設定する。すなわち、最適化処理部２１は、Ａモードを第１のモード、Ｂモードを第２のモードとすると、第１のモードによるバイアス電圧の基準値の最適化を行った後、第２のモードによるオフセット値の最適化を行う。 The optimization processing unit 21 sets the optimum value of each bias voltage in two stages: A mode for optimizing the signal waveform and B mode for minimizing the signal BER (Bit Error Ratio). In other words, when the A mode is the first mode and the B mode is the second mode, the optimization processing unit 21 optimizes the reference value of the bias voltage in the first mode, and then performs the second mode. Optimize the offset value.
　Ａモードにおける最適化では、最適化処理部２１は、変調器制御部２２を介して光変調部１２において光信号に低周波の試験信号を重畳する。Ａモードにおいて、最適化処理部２１は、各バイアス電圧を掃引し、Ｉ相およびＱ相の信号の波形およびＩ相とＱ相の位相差が理想的な状態になるバイアス電圧を判断し、理想的な状態と判断したときのバイアス電圧を各成分のバイアス電圧の基準値とする。最適化処理部２１は、光変調部１２から出力された低周波信号の波形を、光受信部１５および信号処理部１６を介して電気信号として取得する。 In the optimization in the A mode, the optimization processing unit 21 superimposes a low-frequency test signal on the optical signal in the optical modulation unit 12 via the modulator control unit 22. In the A mode, the optimization processing unit 21 sweeps each bias voltage, determines the I-phase and Q-phase signal waveforms and the bias voltage at which the phase difference between the I-phase and the Q-phase is in an ideal state. The bias voltage when it is determined to be a typical state is used as a reference value for the bias voltage of each component. The optimization processing unit 21 acquires the waveform of the low-frequency signal output from the light modulation unit 12 as an electrical signal via the light receiving unit 15 and the signal processing unit 16.
　また、Ｂモードにおける最適化では、最適化処理部２１は、Ａモードにおいて設定されたバイアス電圧の基準値にオフセット値を加えたバイアス電圧を、オフセット値を変動させながら光変調部１２において印加する。最適化処理部２１は、成分ごとにオフセット値を変動させ、オフセット値を変動させた際にＢＥＲの変化を監視する。最適化処理部２１は、成分ごとにＢＥＲが最小になるオフセット値を、Ｉ相およびＱ相の変調部と、位相変調部におけるオフセット値としてそれぞれ設定する。 In the optimization in the B mode, the optimization processing unit 21 applies the bias voltage obtained by adding the offset value to the reference value of the bias voltage set in the A mode in the optical modulation unit 12 while changing the offset value. . The optimization processing unit 21 changes the offset value for each component, and monitors the change in the BER when the offset value is changed. The optimization processing unit 21 sets an offset value that minimizes the BER for each component as an offset value in the I-phase and Q-phase modulation units and the phase modulation unit.
　最適化処理部２１は、バイアス電圧の基準値やオフセット値を設定する演算処理に必要なデータおよび設定したバイアス電圧の基準値およびオフセットのデータを記憶部１４に書き込む。また、最適化処理部２１は、演算処理や光変調部１２の制御に必要なデータを記憶部１４から読み出す。また、最適化処理部２１は、例えば、演算処理を行うＣＰＵ（Central Processing Unit）によって構成されている。また、本実施形態の最適化処理部２１は、第１の実施形態の最適化手段３に相当する。 The optimization processing unit 21 writes data necessary for arithmetic processing for setting the reference value and offset value of the bias voltage and the set reference value and offset data of the bias voltage in the storage unit 14. In addition, the optimization processing unit 21 reads data necessary for arithmetic processing and control of the light modulation unit 12 from the storage unit 14. The optimization processing unit 21 is configured by, for example, a CPU (Central Processing Unit) that performs arithmetic processing. The optimization processing unit 21 of the present embodiment corresponds to the optimization unit 3 of the first embodiment.
　変調器制御部２２は、最適化処理部２１の処理結果に基づいて、光変調部１２を制御する制御回路である。変調器制御部２２は、光変調部１２のＩ－Ｃｈ変調部、Ｑ－ｃｈ変調部および位相変調部におけるバイアス電圧の印加を制御するバイアス電圧信号を光変調部１２に出力する。また、変調器制御部２２は、光変調部１２のＩ－Ｃｈ変調部およびＱ－ｃｈ変調部において変調を施す際の制御信号を光変調部１２に出力する。 The modulator control unit 22 is a control circuit that controls the light modulation unit 12 based on the processing result of the optimization processing unit 21. The modulator control unit 22 outputs to the optical modulation unit 12 a bias voltage signal that controls application of a bias voltage in the I-Ch modulation unit, Q-ch modulation unit, and phase modulation unit of the optical modulation unit 12. Further, the modulator control unit 22 outputs a control signal for performing modulation in the I-Ch modulation unit and the Q-ch modulation unit of the optical modulation unit 12 to the optical modulation unit 12.
　変調器制御部２２は、データ通信用の光信号の送信を行う場合には、信号処理部１６から入力される符号データに基づいた変調が行われるように光変調部１２を制御する。また、変調器制御部２２は、バイアス電圧の最適化を行う際には、最適化処理部２１の制御に基づいて、低周波の試験信号が光信号に重畳されるように光変調部１２を制御する。また、本実施形態の変調器制御部２２は、第１の実施形態の制御手段２に相当する。 When transmitting an optical signal for data communication, the modulator control unit 22 controls the optical modulation unit 12 so that modulation based on code data input from the signal processing unit 16 is performed. In addition, when the bias controller optimizes the bias voltage, the modulator controller 22 controls the optical modulator 12 so that a low-frequency test signal is superimposed on the optical signal based on the control of the optimization processor 21. Control. The modulator control unit 22 of the present embodiment corresponds to the control unit 2 of the first embodiment.
　記憶部１４は、光変調部１２の制御およびバイアス電圧の最適化に必要な各データを記憶する機能を有する。記憶部１４は、制御部１３の制御に基づいて、データの保存および読み出しを行う。記憶部１４は、例えば、フラッシュメモリ等のデータの書き込みと読み出しが可能な不揮発性の半導体メモリ素子によって構成されている。 The storage unit 14 has a function of storing each data necessary for controlling the light modulation unit 12 and optimizing the bias voltage. The storage unit 14 stores and reads data based on the control of the control unit 13. The storage unit 14 is configured by a nonvolatile semiconductor memory element capable of writing and reading data, such as a flash memory.
　光受信部１５は、光信号を受信し、電気信号に変換して信号処理部１６に出力する機能を有する。光受信部１５には、伝送路を介して対向する光伝送装置から送信されてくる光信号が入力される。また、バイアス電圧の最適化を行う際に、光受信部１５には、光トランシーバ１０から送信した光信号が、中継装置等で折り返されて入力される。光受信部１５は、光受信信号のコヒーレント検波を行う機能を有し、局発光源および光受信信号の受光素子等を備えている。 The optical receiver 15 has a function of receiving an optical signal, converting it into an electrical signal, and outputting it to the signal processor 16. The optical receiver 15 receives an optical signal transmitted from an optical transmission device facing through the transmission path. In addition, when optimizing the bias voltage, the optical signal transmitted from the optical transceiver 10 is input to the optical receiver 15 after being folded back by a relay device or the like. The optical receiver 15 has a function of performing coherent detection of an optical reception signal, and includes a local light source and a light receiving element for the optical reception signal.
　信号処理部１６は、光受信部１５から入力された信号および外部から入力される外部信号の処理を行う機能を有する。図５は、本実施形態の信号処理部１６の構成を示したものである。図５に示すように本実施形態の信号処理部１６は、受信信号処理部３１と、送信信号処理部３２と、ＢＥＲ計測部３３を備えている。 The signal processor 16 has a function of processing a signal input from the optical receiver 15 and an external signal input from the outside. FIG. 5 shows the configuration of the signal processing unit 16 of the present embodiment. As shown in FIG. 5, the signal processing unit 16 of this embodiment includes a reception signal processing unit 31, a transmission signal processing unit 32, and a BER measurement unit 33.
　受信信号処理部３１は、光受信部１５が受信したバイアス電圧の最適化のための試験信号をＩ相成分とＱ相成分の信号に分離して制御部１３に出力する。また、受信信号処理部３１は、光受信部１５が受信した光受信信号の復号等の処理を行って、外部に出力する信号に変換する。受信信号処理部３１は、外部に出力する信号に変換した信号を外部信号として出力する。 The received signal processing unit 31 separates the test signal for optimizing the bias voltage received by the optical receiving unit 15 into an I-phase component signal and a Q-phase component signal, and outputs them to the control unit 13. The reception signal processing unit 31 performs processing such as decoding of the optical reception signal received by the optical reception unit 15 and converts it into a signal to be output to the outside. The reception signal processing unit 31 outputs a signal converted into a signal to be output to the outside as an external signal.
　送信信号処理部３２は、外部から入力される外部信号を、伝送路で伝送する際の符号データに変換し、符号データを制御部１３に出力する。 The transmission signal processing unit 32 converts an external signal input from the outside into code data for transmission through the transmission path, and outputs the code data to the control unit 13.
　ＢＥＲ計測部３３は、受信信号処理部３１で行われる信号処理を監視し、光受信部１５から入力された光信号のＢＥＲを算出する。ＢＥＲ計測部３３は、算出したＢＥＲの値を制御部１３の要求に基づいて制御部１３に出力する。ＢＥＲ計測部３３は、Ｉ相の信号、Ｑ相の信号のそれぞれのＢＥＲと、Ｐｈ成分のＢＥＲを算出する。ＢＥＲ計測部３３は、例えば、Ｉ相とＱ相間の位相差を示すＰｈ成分のＢＥＲを、検出した信号の位相成分と所定の基準を比較することで誤りの有無を判断して算出する。 The BER measuring unit 33 monitors the signal processing performed by the received signal processing unit 31 and calculates the BER of the optical signal input from the optical receiving unit 15. The BER measurement unit 33 outputs the calculated BER value to the control unit 13 based on a request from the control unit 13. The BER measurement unit 33 calculates the BER of each of the I-phase signal and the Q-phase signal and the BER of the Ph component. For example, the BER measurement unit 33 calculates the BER of the Ph component indicating the phase difference between the I phase and the Q phase by comparing the phase component of the detected signal with a predetermined reference to determine the presence or absence of an error.
　信号処理部１６は、例えば、ＤＳＰ（Digital Signal Processor）によって構成されている。受信信号処理部３１、送信信号処理部３２およびＢＥＲ計測部３３は、同一の基板上に回路パターンとして形成されていてもよく、また、それぞれ別の基板上に回路パターンとして形成されていてもよい。また、信号処理部１６の信号処理は、ＣＰＵや半導体メモリ素子を用いて実行されるプログラムによって実行されてもよい。 The signal processing unit 16 is configured by, for example, a DSP (Digital Signal Processor). The reception signal processing unit 31, the transmission signal processing unit 32, and the BER measurement unit 33 may be formed as circuit patterns on the same substrate, or may be formed as circuit patterns on different substrates. . Further, the signal processing of the signal processing unit 16 may be executed by a program executed using a CPU or a semiconductor memory element.
　本実施形態の光トランシーバ１０において、光変調部１２に印加するバイアス電圧の最適化を行う際の動作について説明する。図６、図７、図８および図９は、本実施形態の光トランシーバ１０において、バイアス電圧の最適化を行う際の動作フローを示したものである。動作フローを示す各図のうち図６は、バイアス電圧の最適化を行う際のメインフローを示している。図７は、Ａモードによる最適化を行う際の動作フローを示している。図８は、Ｂモードによる最適化を行う際の動作フローを示している。また、図９は、Ｂモードの処理において、フィードバック制御によって最適なオフセット値を設定する際の動作フローを示している。 In the optical transceiver 10 of this embodiment, an operation when the bias voltage applied to the optical modulation unit 12 is optimized will be described. 6, FIG. 7, FIG. 8, and FIG. 9 show an operation flow when the bias voltage is optimized in the optical transceiver 10 of the present embodiment. Among the diagrams showing the operation flow, FIG. 6 shows a main flow when the bias voltage is optimized. FIG. 7 shows an operation flow when performing optimization in the A mode. FIG. 8 shows an operation flow when performing optimization in the B mode. FIG. 9 shows an operation flow when an optimum offset value is set by feedback control in the B mode processing.
　光トランシーバ１０が動作を開始すると、光トランシーバ１０は、図６に示されているバイアス電圧の最適化の動作を行う。バイアス電圧の最適化の動作を開始すると、制御部１３は、Ａモードで制御を行って光変調部１２において印加するバイアス電圧の最適化を行う（ステップ１１１）。 When the optical transceiver 10 starts operation, the optical transceiver 10 performs the operation of optimizing the bias voltage shown in FIG. When the operation for optimizing the bias voltage is started, the control unit 13 performs the control in the A mode and optimizes the bias voltage applied in the optical modulation unit 12 (step 111).
　Ａモードによるバイアス電圧の最適化の動作が開始されると、図７に示す動作が実行される。制御部１３は、Ａモードによるバイアス電圧の最適化の動作を開始すると、光変調部１２を制御して出力する光信号に低周波の試験信号を重畳する。制御部１３は、光変調部１２に印加されるバイアス電圧の値を掃引し、信号処理部１６を介して入力される低周波の試験信号の波形変化を基にバイアス電圧の最適化制御を行う（ステップ１２１）。制御部１３は、例えば、低周波の試験信号の振幅が最小となる電圧をバイアス電圧の最適値とする。 When the operation for optimizing the bias voltage in the A mode is started, the operation shown in FIG. 7 is executed. When the control unit 13 starts the operation of optimizing the bias voltage in the A mode, the control unit 13 controls the optical modulation unit 12 to superimpose a low-frequency test signal on the optical signal to be output. The control unit 13 sweeps the value of the bias voltage applied to the light modulation unit 12 and performs optimization control of the bias voltage based on the waveform change of the low frequency test signal input via the signal processing unit 16. (Step 121). For example, the control unit 13 sets the voltage at which the amplitude of the low-frequency test signal is minimum as the optimum value of the bias voltage.
　光変調部１２で光信号に重畳された低周波の信号は、中継装置等で折り返されて光受信部１５に入力される。例えば、バイアス電圧の最適化を行う際に、通信管理システムに制御に基づいて光信号を、光信号の送信元へ向かう側の経路に折り返す機能を有する中継装置を用いることで、自装置から送信した光信号を光受信部１５で受信することができる。 The low-frequency signal superimposed on the optical signal by the optical modulator 12 is turned back by a relay device or the like and input to the optical receiver 15. For example, when optimizing the bias voltage, the communication management system transmits the optical signal from its own device by using a relay device having a function of returning the optical signal to the path toward the optical signal transmission source based on the control. The received optical signal can be received by the optical receiver 15.
　光受信部１５で受信された光信号は、電気信号に変換されて信号処理部１６に入力される。信号処理部１６に入力された低周波信号は、信号処理部１６において処理されて制御部１３に入力される。低周波信号の波形のデータを受け取ると、制御部１３は、波形データの変動を基に印加したバイアス電圧が最適であるかを判断する。 The optical signal received by the optical receiver 15 is converted into an electrical signal and input to the signal processor 16. The low frequency signal input to the signal processing unit 16 is processed by the signal processing unit 16 and input to the control unit 13. When receiving the waveform data of the low frequency signal, the control unit 13 determines whether the applied bias voltage is optimal based on the fluctuation of the waveform data.
　最適なバイアス電圧ではないと判断すると（ステップ１２２でＮｏ）、制御部１３は、Ａモードによるバイアス電圧の最適化の動作を継続する。 If it is determined that the bias voltage is not optimal (No in step 122), the control unit 13 continues the operation of optimizing the bias voltage in the A mode.
　最適なバイアス電圧と判断すると（ステップ１２２でＹｅｓ）、制御部１３は、最適と判断したバイアス電圧の値を記憶部１４に保存する（ステップ１２３）。最適と判断したバイアス電圧の値を記憶部１４に保存すると、制御部１３は、バイアス電圧のオフセット値の初期値を記憶部１４に保存する（ステップ１２４）。オフセット値の初期値は、０として設定される。 If it is determined that the bias voltage is optimal (Yes in Step 122), the control unit 13 stores the value of the bias voltage determined to be optimal in the storage unit 14 (Step 123). When the bias voltage value determined to be optimal is stored in the storage unit 14, the control unit 13 stores the initial value of the offset value of the bias voltage in the storage unit 14 (step 124). The initial value of the offset value is set as 0.
　バイアス電圧のオフセット値の初期値を保存すると、制御部１３は、図６のステップ１１１のＡモードによるバイアス電圧の最適化の制御を終了し、ステップ１１２のＢモードによるバイアス電圧の最適化の制御を開始する。 When the initial value of the offset value of the bias voltage is stored, the control unit 13 ends the control of optimizing the bias voltage in the A mode in step 111 in FIG. 6, and controls the optimization of the bias voltage in the B mode in step 112. To start.
　Ｂモードによるバイアス電圧の最適化の動作が開始されると、図８に示す動作が実行される。Ｂモードによるバイアス電圧の最適化の動作を開始すると、制御部１３は、信号処理部１６からＢＥＲの値を読み出す（ステップ１３１）。信号処理部１６は、光受信部１５を介して受信した信号のＢＥＲを計測している。 When the operation for optimizing the bias voltage in the B mode is started, the operation shown in FIG. 8 is executed. When the operation of optimizing the bias voltage in the B mode is started, the control unit 13 reads the value of BER from the signal processing unit 16 (step 131). The signal processing unit 16 measures the BER of the signal received via the optical receiving unit 15.
　ＢＥＲの値を読み出すと、制御部１３は、ＢＥＲの値をあらかじめ設定された基準値と比較する。ＢＥＲの基準値は、光信号の受信品質として十分な値として設定されている。 When the BER value is read, the control unit 13 compares the BER value with a preset reference value. The reference value of BER is set as a value sufficient as the reception quality of the optical signal.
　ＢＥＲの値が基準値以内であるとき（ステップ１３２でＹｅｓ）、制御部１３は、Ｂモードによるバイアス電圧の最適化の制御を終了する。このとき、図６のステップ１１３において、最適バイアスからのずれも基準以内（ステップ１１３でＹｅｓ）となるので、制御部１３は、バイアス電圧の最適化の動作を終了し最適と判断したバイアス電圧で光変調部１２を制御する。 When the value of BER is within the reference value (Yes in step 132), the control unit 13 ends the control for optimizing the bias voltage in the B mode. At this time, in step 113 of FIG. 6, the deviation from the optimum bias is also within the reference (Yes in step 113), so the control unit 13 ends the operation of optimizing the bias voltage and determines the optimum bias voltage. The light modulator 12 is controlled.
　ＢＥＲの値が基準値よりも大きいとき（ステップ１３２でＮｏ）、制御部１３は、フィードバック制御による成分ごとのオフセット値を調整する最適化動作の制御を開始する（ステップ１３３）。 When the value of BER is larger than the reference value (No in step 132), the control unit 13 starts control of an optimization operation for adjusting the offset value for each component by feedback control (step 133).
　Ｂモードによるオフセット値のフィードバック制御が開始されると、図９に示す動作が実行される。 When the feedback control of the offset value in the B mode is started, the operation shown in FIG. 9 is executed.
　制御部１３は、成分ごとのオフセット値を調整するＢモードの最適化動作を開始すると、記憶部１４からバイアスの基準値とオフセット値のデータを読み出す（ステップ１４１）。立ち上げ直後に、最初にＢモードを実行した際には、オフセット値は、０が設定されている。 When the control unit 13 starts the optimization operation of the B mode for adjusting the offset value for each component, the control unit 13 reads the bias reference value and the offset value data from the storage unit 14 (step 141). When the B mode is first executed immediately after startup, 0 is set as the offset value.
　バイアスの基準値とオフセット値のデータを読み出すと、制御部１３は、バイアスの基準値をオフセット値で調整したバイアス電圧を、光変調部１２のバイアス端子に印加して光変調部１２を制御する（ステップ１４２）。 When the bias reference value and offset value data are read, the control unit 13 controls the light modulation unit 12 by applying a bias voltage obtained by adjusting the bias reference value using the offset value to the bias terminal of the light modulation unit 12. (Step 142).
　バイアスの基準値をオフセット値で調整したバイアス電圧を印加して光変調部１２を制御すると、制御部１３は、信号処理部１６からＢＥＲのデータを読み出す（ステップ１４３）。このとき、信号処理部１６から読み出させるＢＥＲのデータは、オフセット値で調整したバイアス電圧を印加して光変調部１２を制御したＢＥＲである。 When the light modulation unit 12 is controlled by applying a bias voltage obtained by adjusting the bias reference value with the offset value, the control unit 13 reads BER data from the signal processing unit 16 (step 143). At this time, the BER data read from the signal processing unit 16 is a BER obtained by controlling the light modulation unit 12 by applying a bias voltage adjusted by the offset value.
　信号処理部１６からＢＥＲを読み出すと、制御部１３は、信号処理部１６から読み出したＢＥＲが基準内であるかを判断する。ＢＥＲが基準内であるとき（ステップ１４４でＹｅｓ）、制御部１３は、記憶部１４にオフセット値を保存する（ステップ１４８）。ステップ１４１からステップ１４８の動作は、Ｉ相成分、Ｑ相成分およびＰｈ成分それぞれに順に行われる。 When the BER is read from the signal processing unit 16, the control unit 13 determines whether the BER read from the signal processing unit 16 is within the reference. When the BER is within the reference (Yes in Step 144), the control unit 13 stores the offset value in the storage unit 14 (Step 148). The operations from step 141 to step 148 are sequentially performed on the I-phase component, the Q-phase component, and the Ph component.
　ＢＥＲが基準内ではないとき（ステップ１４４でＮｏ）、制御部１３は、信号処理部１６から新たに取得したＢＥＲと、前回取得したＢＥＲとを比較する。新たに取得したＢＥＲが前回取得したBER以上であるとき（ステップ１４５でＮｏ）、制御部１３は、オフセット値を前回と逆方向に同じ量、増減させる。最初にオフセット値を増減させる際のオフセット値の増減方向と増減量はあらかじめ設定されている。 When the BER is not within the standard (No in Step 144), the control unit 13 compares the BER newly acquired from the signal processing unit 16 with the BER acquired last time. When the newly acquired BER is equal to or higher than the previously acquired BER (No in step 145), the control unit 13 increases or decreases the offset value by the same amount in the opposite direction to the previous time. The increase / decrease direction and increase / decrease amount of the offset value when the offset value is first increased / decreased are set in advance.
　制御部１３は、例えば、前回、オフセット値を＋１ｍＶとした場合には、前回と正負を逆転させた－１ｍＶオフセット値を調整する。オフセット値を調整すると、制御部１３は、調整した後の値を記憶部１４に保存する。制御部１３は、オフセット値を変動させると、ステップ１４３からの動作を再び、行う。 For example, when the offset value is +1 mV last time, the control unit 13 adjusts the -1 mV offset value obtained by reversing the positive and negative values from the previous time. When the offset value is adjusted, the control unit 13 stores the adjusted value in the storage unit 14. When the offset value is changed, the control unit 13 performs the operation from step 143 again.
　信号処理部１６から新たに読み出したＢＥＲが前回のＢＥＲより小さいとき（ステップ１４５でＹｅｓ）、制御部１３は、オフセット値を前回と同じ方向に同じ量、増減させて光変調部１２にバイアス電圧を印加する（ステップ１４６）。 When the BER newly read from the signal processing unit 16 is smaller than the previous BER (Yes in step 145), the control unit 13 increases or decreases the offset value by the same amount in the same direction as the previous time, and applies a bias voltage to the light modulation unit 12. Is applied (step 146).
　制御部１３は、例えば、前回、オフセット値を＋１ｍＶとして場合には、同様に、＋１ｍＶオフセット値を増やす。オフセット値を調整すると、制御部１３は、調整した後の値を記憶部１４に保存する。制御部１３は、オフセット値を変動させると、ステップ１４３からの動作を再び、行う。 For example, when the offset value is +1 mV last time, the control unit 13 increases the +1 mV offset value in the same manner. When the offset value is adjusted, the control unit 13 stores the adjusted value in the storage unit 14. When the offset value is changed, the control unit 13 performs the operation from step 143 again.
　すなわち、オフセット値を変動させたバイアス電圧を光変調部１２に印加すると、制御部１３は、信号処理部１６からＢＥＲのデータを読み出す（ステップ１４３）。このとき、信号処理部１６から読み出させるＢＥＲのデータは、オフセット値で調整したバイアス電圧を印加して光変調部１２を制御したＢＥＲである。 That is, when a bias voltage whose offset value is changed is applied to the optical modulation unit 12, the control unit 13 reads BER data from the signal processing unit 16 (step 143). At this time, the BER data read from the signal processing unit 16 is a BER obtained by controlling the light modulation unit 12 by applying a bias voltage adjusted by the offset value.
　信号処理部１６からＢＥＲを読み出すと、制御部１３は、信号処理部１６から読み出したＢＥＲが基準内であるかを判断する。ＢＥＲが基準内であるとき（ステップ１４４でＹｅｓ）、制御部１３は、記憶部１４にオフセット値を保存する（ステップ１４８）。ステップ１４１からステップ１４８の動作は、Ｉ相成分、Ｑ相成分およびＰｈ成分それぞれに順に行われる。ＢＥＲが基準内ではないとき（ステップ１４４でＮｏ）、制御部１３は、オフセット値をさらに変動させてオフセット値の調整の動作を継続する。 When the BER is read from the signal processing unit 16, the control unit 13 determines whether the BER read from the signal processing unit 16 is within the reference. When the BER is within the reference (Yes in Step 144), the control unit 13 stores the offset value in the storage unit 14 (Step 148). The operations from step 141 to step 148 are sequentially performed on the I-phase component, the Q-phase component, and the Ph component. When the BER is not within the reference (No in Step 144), the control unit 13 further varies the offset value and continues the operation of adjusting the offset value.
　ステップ１４８で全ての成分について記憶部１４にオフセット値が保存されると、制御部１３は、図８のステップ１１２におけるフィードバック制御を終了し、Ｂモードによるバイアス値の最適化の制御を終了する。 When the offset values are stored in the storage unit 14 for all the components in step 148, the control unit 13 ends the feedback control in step 112 of FIG. 8 and ends the control for optimizing the bias value in the B mode.
　Ｂモードによるバイアス値の最適化の制御を終了すると、制御部１３は、最適と判断したバイアス電圧、すなわち、バイアス電圧の基準値をオフセット値で補正したバイアス電圧が基準内である確認する。バイアス電圧が基準内ではないとき（ステップ１１３でＮｏ）、制御部１３は、Ａモードによるバイアス電圧の基準値の最適化の動作から再度、実施する。 When the control for optimizing the bias value in the B mode is completed, the control unit 13 confirms that the bias voltage determined to be optimal, that is, the bias voltage obtained by correcting the reference value of the bias voltage with the offset value is within the reference. When the bias voltage is not within the reference (No in step 113), the control unit 13 performs again from the operation of optimizing the reference value of the bias voltage in the A mode.
　バイアス電圧が基準内のとき（ステップ１１３でＹｅｓ）、制御部１３は、バイアス電圧の最適化の動作を終了し、最適と判断したバイアス電圧で光変調部１２を制御する。 When the bias voltage is within the reference (Yes in step 113), the control unit 13 ends the operation of optimizing the bias voltage, and controls the light modulation unit 12 with the bias voltage determined to be optimal.
　バイアス電圧の基準値およびオフセット値の最適化について、より具体的な例を基に説明する。本実施形態の光トランシーバは、バイアス電圧をＡモードによりバイアス電圧の基準値の最適化と、Ｂモードによるバイアス電圧の基準値からのオフセット値の最適化の２段階で、バイアス電圧を最適化する。 Optimize the bias voltage reference value and offset value based on a more specific example. The optical transceiver of the present embodiment optimizes the bias voltage in two stages: optimization of the bias voltage reference value by the A mode and optimization of the offset value from the bias voltage reference value by the B mode. .
　光トランシーバ１０は、Ａモードでバイアス電圧の基準値を最適化し、Ａモードによる制御を終えた際にＢＥＲが基準内であれば、バイアス電圧の最適化の動作を完了する。 The optical transceiver 10 optimizes the reference value of the bias voltage in the A mode, and if the BER is within the reference when the control in the A mode is finished, the operation of optimizing the bias voltage is completed.
　また、Ａモードによる制御を終えた際にＢＥＲが基準よりも大きいとき、光トランシーバ１０は、Ｂモードで、バイアス電圧のオフセット値を最適化する。 Also, when the BER is larger than the reference when the control in the A mode is finished, the optical transceiver 10 optimizes the offset value of the bias voltage in the B mode.
　ＢモードにおけるＩ相成分、Ｑ相成分およびＰｈ成分の相互作用を考慮した、バイアス電圧の最適化、すなわち、最適バイアス電圧のずれに対する補正は、次のように行う。ＡモードでＩ相成分、Ｑ相成分およびＰｈ成分のバイアス電圧の基準値が設定されると、Ｉ相成分、Ｑ相成分およびＰｈ成分のＢＥＲの確認が行われる。Ｉ相成分、Ｑ相成分およびＰｈ成分のＢＥＲを確認すると、ＢＥＲが基準外の成分についてＢモードによるオフセット値の最適化が行われる。例えば、Ｉ相成分が基準外で、Ｑ相成分およびＰｈ成分が基準を満たしているとき、Ｉ相成分のみＢモードによるオフセット値の最適化が行われる。 Optimize the bias voltage in consideration of the interaction of the I-phase component, the Q-phase component and the Ph component in the B mode, that is, correct for the deviation of the optimum bias voltage as follows. When the reference values of the bias voltages of the I-phase component, Q-phase component, and Ph component are set in the A mode, the BER of the I-phase component, Q-phase component, and Ph component is confirmed. When the BER of the I-phase component, the Q-phase component, and the Ph component is confirmed, the offset value in the B mode is optimized for components whose BER is not the reference. For example, when the I-phase component is out of the standard and the Q-phase component and the Ph component satisfy the standard, only the I-phase component is optimized for the offset value by the B mode.
　Ｂモードによる最適化の動作が終わると、オフセット値で調整したバイアス電圧が、Ａモードで調整したバイアス電圧の基準値から所定の範囲内であるかを確認する。これは、Ｂモードで補正を行ったとしても補正後のバイアス電圧は、Ａモードで調整した基準点の近傍にあることを確認して、Ｂモードによる補正が正常に行われたことを判断するために行われる。 When the optimization operation by the B mode is completed, it is confirmed whether the bias voltage adjusted by the offset value is within a predetermined range from the reference value of the bias voltage adjusted by the A mode. Even if correction is performed in the B mode, it is confirmed that the corrected bias voltage is in the vicinity of the reference point adjusted in the A mode, and it is determined that the correction in the B mode has been performed normally. Done for.
　本実施形態の光トランシーバ１０は、自装置から出力した光信号を光受信部１５で受信し、制御部１３において信号の波形を基にオフセット電圧の基準値の最適化をＡモードとして行っている。また、本実施形態の光トランシーバ１０は、Ａモードにおける最適化の後、ＢＥＲ、すなわち、信号の品質を基に各成分のオフセット値の最適化をＢモードとして行っている。本実施形態の光トランシーバ１０は、各成分のオフセット値の最適化を行うことで、Ｉ相、Ｑ相およびＰｈ成分の相互作用によるバイアス電圧のずれを補正することができる。そのため、本実施形態の光トランシーバ１０は、Ｉ相、Ｑ相およびＰｈ成分の相互作用がある場合でも、バイアス電圧を精度よく最適化することができる。その結果、本実施形態の光トランシーバ１０は、特性変動等が生じても各成分の相互作用の影響を抑制しつつ光変調器に印加するバイアス電圧を高い精度で最適化することができる。 The optical transceiver 10 of this embodiment receives an optical signal output from its own apparatus by the optical receiving unit 15, and the control unit 13 optimizes the reference value of the offset voltage based on the signal waveform as the A mode. . In addition, the optical transceiver 10 of the present embodiment optimizes the offset value of each component in the B mode based on the BER, that is, the signal quality, after optimization in the A mode. The optical transceiver 10 of the present embodiment can correct the bias voltage shift due to the interaction of the I-phase, the Q-phase, and the Ph component by optimizing the offset value of each component. Therefore, the optical transceiver 10 of the present embodiment can optimize the bias voltage with high accuracy even when there is an interaction between the I phase, the Q phase, and the Ph component. As a result, the optical transceiver 10 according to the present embodiment can optimize the bias voltage applied to the optical modulator with high accuracy while suppressing the influence of the interaction of each component even if characteristic variation or the like occurs.
　第２の実施形態の光トランシーバ１０は、自装置から送信後に中継装置等で折り返された光信号を自装置で受信することによって信号の波形および受信品質のデータを取得し、オフセット電圧の基準値とオフセット値の最適化を行っている。そのような構成に代えて、図１０に模式的に示すように、光トランシーバ内でフィードバック制御を行ってＡモードにおけるバイアス電圧の基準値の最適化を行ってもよい。そのような構成とする場合には、例えば、光変調部１２の出力部分で分岐した光信号を受光素子で受光した結果を基に、バイアス電圧の最適化が行われる。また、光変調部に備えられた受光素子で受光する光信号の波形に基づいて、Ａモードにおけるバイアス電圧の基準値の最適化が行われてもよい。 The optical transceiver 10 of the second embodiment acquires the data of the signal waveform and the reception quality by receiving the optical signal returned by the relay device after transmission from the own device, and obtains the reference value of the offset voltage. And offset value optimization. Instead of such a configuration, as schematically shown in FIG. 10, feedback control may be performed in the optical transceiver to optimize the reference value of the bias voltage in the A mode. In the case of such a configuration, for example, the bias voltage is optimized based on the result of receiving the optical signal branched at the output portion of the light modulation unit 12 by the light receiving element. Further, the reference value of the bias voltage in the A mode may be optimized based on the waveform of the optical signal received by the light receiving element provided in the light modulation unit.
　第２の実施形態の光トランシーバ１０は、自装置から送信した光信号を自装置で受信することによって受信信号のＢＥＲの情報を取得しているが、伝送路を介して対向する光トランシーバが受信した際のＢＥＲに基づいてオフセット値の最適化を行ってもよい。そのような構成とする場合には、受信側と送信側の光トランシーバの間で、オフセット値の最適化を行う際の信号の情報があらかじめ共有されている。 The optical transceiver 10 of the second embodiment acquires the BER information of the received signal by receiving the optical signal transmitted from the own device by the own device, but is received by the opposite optical transceiver via the transmission path. The offset value may be optimized based on the BER at the time. In such a configuration, signal information for optimizing the offset value is shared in advance between the optical transceiver on the receiving side and the transmitting side.
　以上、上述した実施形態を模範的な例として本発明を説明した。しかしながら、本発明は、上述した実施形態には限定されない。即ち、本発明は、本発明のスコープ内において、当業者が理解し得る様々な態様を適用することができる。 The present invention has been described above using the above-described embodiment as an exemplary example. However, the present invention is not limited to the above-described embodiment. That is, the present invention can apply various modes that can be understood by those skilled in the art within the scope of the present invention.
　この出願は、２０１７年２月６日に出願された日本出願特願２０１７－０１９２１８を基礎とする優先権を主張し、その開示の全てをここに取り込む。 This application claims priority based on Japanese Patent Application No. 2017-019218 filed on Feb. 6, 2017, the entire disclosure of which is incorporated herein.
　１　　光変調手段
　２　　制御手段
　３　　最適化手段
　１０　　光トランシーバ
　１１　　光源部
　１２　　光変調部
　１３　　制御部
　１４　　記憶部
　１５　　光受信部
　１６　　信号処理部
　２１　　最適化処理部
　２２　　変調器制御部
　３１　　受信信号処理部
　３２　　送信信号処理部
　３３　　ＢＥＲ計測部 DESCRIPTION OF SYMBOLS 1 Optical modulation means 2 Control means 3 Optimization means 10 Optical transceiver 11 Light source part 12 Optical modulation part 13 Control part 14 Storage part 15 Optical receiving part 16 Signal processing part 21 Optimization processing part 22 Modulator control part 31 Received signal processing part 32 Transmission signal processing unit 33 BER measurement unit

Claims (10)

  1. 　入力された光をＩ（In-Phase）相成分とＱ（Quadrature）相成分の光に分波する手段と、分波したそれぞれの光にバイアス電圧を印加して変調を施す手段と、変調を施したＩ相成分とＱ相成分の光を合波した光信号を出力する手段とを有する光変調手段と、
    　前記光変調手段において印加される前記バイアス電圧を、変調を施す成分ごとに制御する制御手段と、
    　前記光変調手段から出力される前記光信号に基づいて前記バイアス電圧を最適化した第１のバイアス電圧を設定する第１のモードと、前記第１のバイアス電圧からのオフセット値を、前記光信号の品質を基に前記変調を施す成分ごとに調整することで前記バイアス電圧を最適化する第２のモードによって前記バイアス電圧を最適化する最適化手段と、を備え、
    　前記制御手段は、前記最適化手段によって設定された前記第１のバイアス電圧を前記オフセット値に基づいて補正した第２のバイアス電圧を基に、前記光変調手段における前記バイアス電圧の印加を制御することを特徴とする光トランシーバ。     Means for demultiplexing input light into I (In-Phase) phase component light and Q (Quadrature) phase component light, means for applying a bias voltage to each of the demultiplexed light, and means for modulating Light modulating means having means for outputting an optical signal obtained by combining the applied I-phase component and Q-phase components;
    Control means for controlling the bias voltage applied in the light modulation means for each component to be modulated;
    A first mode for setting a first bias voltage in which the bias voltage is optimized based on the optical signal output from the optical modulation means, and an offset value from the first bias voltage are set as the optical signal. Optimizing means for optimizing the bias voltage by a second mode that optimizes the bias voltage by adjusting each component to be modulated based on the quality of
    The control unit controls application of the bias voltage in the light modulation unit based on a second bias voltage obtained by correcting the first bias voltage set by the optimization unit based on the offset value. An optical transceiver characterized by that.
  2. 　前記光変調手段は、前記Ｉ相成分と前記Ｑ相成分を合波する際の位相差を調整する手段をさらに有し、
    　前記制御手段は、前記光変調手段における前記位相差の調整を、バイアス電圧を印加して制御する手段をさらに有し、
    　前記最適化手段は、前記第１のモードおよび前記第２のモードによって、前記光変調手段において前記位相差の調整する際のバイアス電圧の最適化をさらに行うことを特徴とする請求項１に記載の光トランシーバ。     The light modulation means further includes means for adjusting a phase difference when the I-phase component and the Q-phase component are combined,
    The control means further includes means for controlling the adjustment of the phase difference in the light modulation means by applying a bias voltage,
    The said optimization means further optimizes the bias voltage at the time of adjusting the said phase difference in the said optical modulation means by the said 1st mode and the said 2nd mode. Optical transceiver.
  3. 　前記制御手段は、前記第１のモードにおいて前記Ｉ相成分と前記Ｑ相成分の波形が最適化されるように前記バイアス電圧の前記第１のバイアス電圧を設定し、前記第２のモードにおいて前記光信号のＢＥＲ（Bit Error Ratio）を最小化するように前記オフセット値を設定することを特徴とする請求項１または２に記載の光トランシーバ。 The control means sets the first bias voltage of the bias voltage so that waveforms of the I-phase component and the Q-phase component are optimized in the first mode, and the control unit sets the first bias voltage in the second mode. 3. The optical transceiver according to claim 1, wherein the offset value is set so as to minimize a BER (Bit Error Ratio) of the optical signal.
  4. 　送信した前記光信号を折り返した前記光信号を受信する受信手段と、
    　前記受信手段が受信した前記光信号から前記ＢＥＲを算出する信号処理手段をさらに備え、
    　前記制御手段は、前記信号処理手段が算出した前記ＢＥＲを最小化するように前記オフセット値を設定することを特徴とする請求項３に記載の光トランシーバ。     Receiving means for receiving the optical signal obtained by folding the transmitted optical signal;
    Signal processing means for calculating the BER from the optical signal received by the receiving means;
    4. The optical transceiver according to claim 3, wherein the control unit sets the offset value so as to minimize the BER calculated by the signal processing unit.
  5. 　前記制御手段は、前記光信号の送信先から送られてくる前記光信号のＢＥＲを最小化するように前記オフセット値を設定することを特徴とする請求項３に記載の光トランシーバ。 4. The optical transceiver according to claim 3, wherein the control unit sets the offset value so as to minimize a BER of the optical signal transmitted from a transmission destination of the optical signal.
  6. 　前記制御手段は、前記第２のモードにおいて前記オフセット値の最適化を行った後に、前記第２のバイアス電圧が所定の基準範囲外であったときに前記第１のモードから前記バイアス電圧の最適化を再度、行うことを特徴とする請求項１から５いずれかに記載の光トランシーバ。 After the optimization of the offset value in the second mode, the control means optimizes the bias voltage from the first mode when the second bias voltage is outside a predetermined reference range. 6. The optical transceiver according to claim 1, wherein the conversion is performed again.
  7. 　前記制御手段は、前記光変調手段において低周波信号を重畳するように制御することを特徴とする請求項１から６いずれかに記載の光トランシーバ。 The optical transceiver according to any one of claims 1 to 6, wherein the control means controls the optical modulation means to superimpose a low-frequency signal.
  8. 　入力された光をＩ相成分とＱ相成分の光に分波し、
    　分波したそれぞれの光に変調を施す成分ごとに制御したバイアス電圧を印加して変調を施し、
    　変調を施したＩ相成分とＱ相成分の光を合波した光信号を出力し、
    　前記光信号に基づいて前記バイアス電圧を最適化した第１のバイアス電圧を設定する第１のモードと、前記第１のバイアス電圧からのオフセット値を、前記光信号の品質を基に前記変調を施す成分ごとに調整することで前記バイアス電圧を最適化する第２のモードによって前記バイアス電圧を最適化し、
    　前記第１のバイアス電圧を前記オフセット値に基づいて補正した第２のバイアス電圧を基に、前記バイアス電圧の印加を制御することを特徴とする変調制御方法。     Splits the input light into I-phase and Q-phase light,
    Apply a controlled bias voltage for each component that modulates each demultiplexed light,
    Output an optical signal that combines the modulated I-phase component and Q-phase components,
    Based on the quality of the optical signal, the first mode for setting the first bias voltage that optimizes the bias voltage based on the optical signal and the offset value from the first bias voltage are used for the modulation. Optimize the bias voltage by a second mode that optimizes the bias voltage by adjusting for each applied component,
    A modulation control method, wherein application of the bias voltage is controlled based on a second bias voltage obtained by correcting the first bias voltage based on the offset value.
  9. 　前記Ｉ相成分と前記Ｑ相成分を合波する際の位相差をバイアス電圧の印加によって調整し、
    　前記第１のモードおよび前記第２のモードによって、前記位相差を調整するバイアス電圧の最適化をさらに行うことを特徴とする請求項８に記載の変調制御方法。     Adjusting the phase difference when the I-phase component and the Q-phase component are combined by applying a bias voltage;
    The modulation control method according to claim 8, further comprising: optimizing a bias voltage for adjusting the phase difference according to the first mode and the second mode.
  10. 　前記第１のモードにおいて前記Ｉ相成分と前記Ｑ相成分の波形が最適化されるように前記バイアス電圧の第１の設定値を設定し、前記第２のモードにおいて前記光信号のＢＥＲを最小化するように前記オフセット値を設定することを特徴とする請求項８または９に記載の変調制御方法。 The first set value of the bias voltage is set so that the waveforms of the I-phase component and the Q-phase component are optimized in the first mode, and the BER of the optical signal is minimized in the second mode. The modulation control method according to claim 8 or 9, wherein the offset value is set so as to be equalized.
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