JP2019047338A - Digital signal processing circuit, optical transceiver, and method of driving the same - Google Patents

Abstract

To simply measure transfer characteristics of an optical receiver without introducing an additional device when measuring a transfer function.SOLUTION: The optical transceiver includes: an optical transmitter that generates an optical signal whose frequency is shifted by a known amount from local light in an optical receiver; an optical receiver that causes the local light to interfere with the optical signal to output an electric signal of a difference frequency; and a digital signal processing circuit that measures a frequency response of a transfer function on the basis of the electrical signal.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a digital signal processing circuit, an optical transceiver, and a method of driving the optical transceiver.

  In order to cope with the increase in communication traffic, it is required to increase the speed and capacity of the optical transmission system. In recent years, optical transmission systems that are being introduced are based on digital coherent technology combining digital signal processing (DSP) and coherent detection.

  In an optical transmission system of 100 Gb / s per wavelength, the Baud rate and modulation scheme are, for example, 32 Gbaud PDM-QPSK (polarization multiplexing-four phase shift keying). The optical transmitter generates a PDM-QPSK optical signal by modulating the orthogonal linear polarization (X polarization and Y polarization) with the QPSK base band signal. The receiver demodulates the optical signal into a baseband signal by coherently detecting the received optical signal and the local light, and the DSP demodulates the QPSK signal.

  By using coherent detection, higher reception sensitivity can be realized as compared to the on-off-keying (OOK) method. Furthermore, the polarization multiplexing transmission QPSK that combines different signals on X polarization and Y polarization of optical fiber and polarization multiplexing transmission and separation at the receiving side is four times as large as OOK by polarization multiplexing QPSK. It is possible to improve the frequency utilization efficiency.

  In order to increase the transmission capacity per wavelength, in the 400 Gb / s optical transmission system, for example, 64 Gbaud PDM-16 QAM (polarization multiplexing-16 Quadrature amplitude modulation) or 43 Gbaud PDM-64 QAM is used as the Baud rate and modulation method. can give. As described above, in the future optical transmission system, in order to expand the transmission capacity per wavelength, the increase in Baud rate and the multi-value modulation of the modulation scheme proceed.

  With the increase in Baud rate and multi-leveling, the optical transmitter / receiver is required to have a wide band transfer characteristic. In general, the optical transceiver uses a plurality of lanes (in-phase component of X polarization: XI, orthogonal component of X polarization: XQ, in-phase component of Y polarization: YI, orthogonal component of Y polarization: YQ) Since signals are transmitted and the difference in transfer function between lanes causes deterioration of the overall system transmission characteristics, it is also required to sufficiently reduce the difference in transfer function between lanes. If the frequency characteristic of the transfer function of the optical transceiver is insufficient or if there is a difference between the lanes, it is necessary to compensate, for example, the frequency response of the transfer function or the difference in the transfer function between the lanes by a DSP.

  Also, in recent optical transmission apparatuses, CFP2-ACO (CFP-ACO) is a transceiver module whose mechanism, control, power, etc. are defined by CFP (C form-factor pluggable) MSA (multi-source agreement) and OIF (optical interconnection forum). Analog coherent optics) is used. The CFP2-ACO module includes optical components and an analog electrical circuit, and is connected to a DSP (application specific integrated circuit) ASIC mounted on a host board via a pluggable connector. Therefore, in addition to the optical components and analog electrical circuits mounted on the CFP2-ACO module, the analog-to-digital converter (ADC) and DAC (digital-to-analog converter), which are interface parts of pluggable connectors and DSP ASICs, are transmitted. It is necessary to take into account the frequency characteristics of the function and compensate for the frequency response of the transfer characteristic and the difference in frequency response between the lanes.

  In order to compensate the transfer function of the optical receiver, it is necessary to measure the frequency response of the transfer function of the optical receiver.

Elliot Eichen, John Schlafer, William Rideout, and John McCabe “Wide-Bandwidth Receiver / Photodetector Frequency Response Measurements Using Amplified Spontaneous Emission from a Semiconductor Optical Amplifier”, Journal of Lightwave Technology, vol. 8, no. 6, June 1990

  Prior art references show how to measure the frequency response of the transfer function of an optical receiver using an optical white noise source.

  FIG. 7 shows a conventional optical transceiver 700, which comprises an optical transmitter 701 and an optical receiver 702. The receiver 702 is connected to a light white noise source 703.

  The optical transmitter 701 includes a transmission signal processing unit 704, a DAC 705, a driver amplifier 706, a laser 707, and a modulator 708.

  The transmission signal processing unit 704 performs necessary digital signal processing on the input electrical signal. The DAC 705 converts the digital signal output from the transmission signal processing unit into an analog electrical signal. The driver amplifier 706 amplifies the analog electrical signal to an appropriate amplitude and sends it to the modulator 708. The modulator 708 separates linearly polarized CW (Continuous Wave) light transmitted from the laser into orthogonal linearly polarized light, and modulates each linearly polarized light with an electrical signal to generate a light modulation signal. The X polarization 708a and the Y polarization 708b are combined by the polarization beam combiner 708c.

  A part or all of the transmission signal processing unit 704 of the optical transmitter and the DAC 705 can be configured by hardware such as an ASIC or an FPGA (Field-Programmable Gate Array). In addition, part or all of them can be configured by software that functions when a processor such as a CPU (Central Processing Unit) executes a program stored in the storage unit.

  In the case of the CFP2-ACO transceiver module, among the optical transmitters, a driver amplifier which is an analog electric circuit, a laser which is an optical component, and a modulator are included in the CFP2-ACO transceiver module.

  The optical receiver 702 includes a laser 709, a polarization splitter 710, a polarization diversity 90 degree hybrid 711, a PD (photo diode) 711a, a TIA (transimpedance amplifier) 712, an ADC 713, and a received signal processor 714. Prepare.

  Some or all of the ADC 713 of the optical receiver and the reception signal processing unit are hardware functional units such as an ASIC or an FPGA. In addition, part or all of them can be configured by software that functions by causing a processor such as a CPU to execute a program stored in a storage unit.

  In the case of the CFP 2-ACO transceiver module, the transceiver module includes a laser which is an optical component of an optical receiver, a polarization diversity 90 degree hybrid, a PD, and a TIA which is an analog electric circuit.

  Fig. 2 shows a method for measuring the frequency response of the transfer function of a coherent light receiver according to the method described in the prior art document. The light white noise source 703 generates light white noise having a light spectrum that is sufficiently broad band and flat compared to the band of the light receiver. The light white noise is interfered with the local light by the light receiver and converted into a digital signal by the ADC 713 after photoelectric conversion. By Fourier transforming this digital signal, it is possible to measure the frequency response of the transfer function of the optical receiver.

  The optical transmission apparatus using the CFP2-ACO transceiver module has a plurality of slots into which the CFP2-ACO module is inserted, and the CFP2-ACO transceiver is added according to the transmission capacity required for the optical transmission apparatus. Therefore, it is necessary to measure the frequency characteristic of the transfer function of the optical receiver in an actual field such as a communication facility.

  However, it is difficult to measure the frequency characteristic of the transfer function of the optical receiver by bringing a measuring instrument such as an optical white noise generator into the real field.

  The present invention has been made to solve the problems as described above, and an object thereof is that the optical transceiver can measure or compensate the frequency characteristic of the transfer function of the optical receiver without using a measuring instrument. An optical receiver characteristic measurement method, an optical receiver compensation method, an optical receiver measurement system, and an optical receiver compensation system are obtained.

  One aspect of the digital signal processing circuit of the present invention is a digital signal processing circuit for measuring the frequency response of the transfer function of an optical receiver, which comprises only a known amount of local light from the optical transmitter to the optical receiver. An optical signal of CW light whose frequency is shifted is generated, and an optical signal of a difference frequency is obtained by causing local light and the optical signal to interfere with each other by the optical receiver, and transmission of the optical receiver based on the electric signal. Measuring a frequency response of the function.

  It is characterized in that the frequency characteristic of the transfer function is measured by controlling the oscillation frequency of the laser of the optical transmitter and giving a frequency difference between the oscillation frequency of the CW light and the oscillation light of the local light. .

  A shift difference of a frequency f is given to the frequency of the CW light and the frequency of the local light by single sideband modulation.

  The CW light is input to an optical amplifier to make the output light intensity constant.

  Further, one aspect of the digital signal processing circuit of the present invention is a digital signal processing circuit for measuring the frequency response of the transfer function of the optical receiver, which outputs ASE light generated from the optical amplifier of the optical transmitter. The optical receiver interferes with local light and the ASE light to obtain an electrical signal, and the frequency response of the transfer function of the optical receiver is measured based on the electrical signal.

  The optical modulator constituting the optical transmitter is a semiconductor optical modulator.

  One aspect of the optical transceiver according to the present invention is an optical transmitter for generating an optical signal whose frequency is shifted by a known amount from local light in the optical receiver, and interference between the local light and the optical signal to generate a difference frequency And a digital signal processing circuit that measures the frequency response of a transfer function based on the electrical signal.

  Further, according to one aspect of the optical transceiver of the present invention, an optical transmitter for outputting ASE light generated from an optical amplifier, an optical receiver for causing interference between local light and the ASE light and outputting an electric signal, the electricity And digital signal processing circuit for Fourier-transforming the signal to measure the frequency response of the transfer function.

  One aspect of a method of driving an optical transmitter and receiver includes: generating an optical signal whose frequency deviates by a known amount from local light in the optical transmitter; and interfering the local light with the optical signal to generate an electrical signal of a difference frequency And driving the frequency response of the transfer function based on the electrical signal.

  In one aspect of the method of driving an optical transceiver, the steps of: outputting ASE light generated from an amplifier; outputting an electric signal by causing interference between local light and the ASE light; and Fourier-transforming the electric signal And measuring the frequency response of the transfer function.

  According to the present invention, the transfer function of the optical receiver can be measured and compensated.

FIG. 1 is a diagram showing a configuration of an optical transceiver according to a first embodiment of the present invention. It is a figure which shows the structure of the optical transmitter / receiver which concerns on the 2nd Embodiment of this invention. It is a figure which shows the structure of the optical transmitter / receiver which concerns on the 3rd Embodiment of this invention. It is a figure which shows the structure of the optical transmitter / receiver which concerns on the 4th Embodiment of this invention. It is a figure showing composition of an optical transceiver concerning a 5th embodiment of the present invention. It is a figure which shows the structure of the optical transmitter / receiver which concerns on the 6th Embodiment of this invention. It is a figure which shows the structure of the conventional optical transmitter-receiver.

  Hereinafter, the form of the optical transmitter-receiver of this invention is demonstrated in detail using figures. However, it is obvious for those skilled in the art that the present invention is not limited to the description contents of the embodiments shown below, and that various modifications can be made in the form and details without departing from the spirit of the invention disclosed in the present specification. is there.

First Embodiment
FIG. 1 is a diagram showing a configuration of an optical transceiver according to a first embodiment of the present invention.

  The optical transceiver 100 is composed of an optical transmitter 101 and an optical receiver 102.

  The optical transmitter 101 includes a transmission signal processing unit 103, a DAC 104, a driver amplifier 105, a laser 106, and a modulator 107.

  The transmission signal processing unit 103 performs necessary digital signal processing on the input electrical signal. The DAC 104 converts the digital signal output from the transmission signal processing unit into an analog electrical signal. The driver amplifier 105 amplifies the analog electrical signal to an appropriate amplitude and transmits it to the modulator 107. The modulator 107 separates linearly polarized CW (Continuous Wave) light transmitted from the laser into orthogonal linearly polarized light, and modulates each linearly polarized light with an electrical signal to generate a light modulation signal. The X polarization 107a and the Y polarization 107b are multiplexed by the polarization beam combiner 107c.

  Part or all of the transmission signal processing unit 103 of the optical transmitter and the DAC 104 can be configured by hardware such as an ASIC or an FPGA (Field-Programmable Gate Array). In addition, part or all of them can be configured by software that functions when a processor such as a CPU (Central Processing Unit) executes a program stored in the storage unit.

  In the case of the CFP2-ACO transceiver module, among the optical transmitters, a driver amplifier which is an analog electric circuit, a laser which is an optical component, and a modulator are included in the CFP2-ACO transceiver module.

  The optical receiver 102 includes a laser 108, a polarization separation unit 109, a polarization diversity 90 degree hybrid 110, a PD (photo dio 8 de) 110a, a TIA 111 (transimpedance amplifier), an ADC 112, and a reception signal processing unit 113. .

  The laser 108 sends local light to the polarization diversity 90 degree hybrid 110. The polarization diversity 90 degree hybrid 110 causes local light to interfere with the received optical signal. The photodiode 110a converts the interference light into an analog current signal. The TIA 111 converts an analog current signal into an analog voltage signal. The ADC 112 converts an analog voltage signal to a digital signal. The reception signal processing unit performs necessary digital signal processing on the input digital signal.

  Some or all of the ADC 112 of the optical receiver and the reception signal processing unit are hardware functional units such as an ASIC or an FPGA. In addition, part or all of them can be configured by software that functions by causing a processor such as a CPU to execute a program stored in a storage unit.

  In the case of the CFP2-ACO transceiver module, the transceiver module includes a laser which is an optical component of the optical receiver, a polarization diversity 90 degree hybrid 110, a PD 110a, and a TIA 111 which is an analog electric circuit.

  In the first embodiment, in such an optical transceiver, the frequency response of the transfer function of the optical receiver is measured by controlling the oscillation frequency of the laser. Then, based on the measurement result, for example, the DSP 113a compensates for the frequency response of the transfer function and the difference between the lanes.

  Here, a specific configuration and procedure when measuring the frequency characteristic of the transfer function of the optical receiver in the first embodiment will be described.

  At the time of frequency response measurement, the input of the analog electrical signal to the modulator 107 is stopped. This can be achieved by setting the output voltage swing of the DAC 104 to zero or by shutting down the output of the driver amplifier. Of the biases of the four-element Mach-Zehnder modulator (XI, XQ, YI, YQ) of the modulator, only one child Mach-Zehnder modulator is set to a bias at which CW light is maximally transmitted, and the remaining three Mach-Zehnder modulations. Sets the bias so that the CW light is minimally transmitted (null point). Also, the bias settings of the two parent Mach-Zehnder modulators are arbitrary. As a result, CW light of a single polarization is output from the modulator.

  The output light from the optical transmitter 101 is input to the optical receiver 102 using a short optical fiber, and the difference frequency between the oscillation frequency of the laser of the optical transmitter and the oscillation frequency of the laser of the optical receiver 102 is specified in advance The laser is controlled to have a constant value. Then, the CW light and the local light output from the optical transmitter interfere with each other in the optical receiver, and a sine wave of electricity having the same frequency as the difference frequency between the two lasers is output from the TIA 111. The electrical sine wave signal is converted to a digital signal by the ADC 112 and the frequency and amplitude are recorded.

  The amplitude of the electrical sine wave signal changes in accordance with the frequency characteristics of the transfer function (including the pluggable connector in the case of CFP2-ACO) of the PD 110 a constituting the optical receiver, the TIA 111 and the ADC 112. Therefore, the transfer function of the optical receiver is obtained by sequentially changing the difference frequency between the two lasers so as to obtain the frequency range to be measured, and sequentially measuring the frequency and the amplitude of the digital signal converted into a digital signal by the ADC112. It can be measured.

  Based on this measurement data, for example, by applying the DSP 113a in the reception signal processing unit 113, it is possible to compensate for the frequency response of the transfer function of the optical receiver and the difference in transfer function between the lanes.

  Thus, the optical transceiver 100 according to the first embodiment can measure and compensate for the transfer function of the optical receiver 102 and the difference between the lanes.

Second Embodiment
FIG. 2 is a diagram showing the configuration of an optical transceiver 200 according to the second embodiment of the present invention.

  The optical transmitter 201 includes a transmission signal processing unit 203, a DAC 204, a driver amplifier 205, a laser 206, and a modulator 207.

  The transmission signal processing unit 203 performs necessary digital signal processing on the input electrical signal. The DAC 204 converts the digital signal output from the transmission signal processing unit into an analog electrical signal. The driver amplifier 205 amplifies the analog electrical signal to an appropriate amplitude and sends it to the modulator 207. The modulator 207 separates linearly polarized CW (Continuous Wave) light transmitted from the laser into orthogonal linearly polarized light, and modulates each linearly polarized light with an electrical signal to generate a light modulation signal. The X polarization 207a and the Y polarization 207b are multiplexed by the polarization beam combiner 207c.

  A part or all of the transmission signal processing unit 203 of the optical transmitter and the DAC 204 can be configured by hardware such as an ASIC or an FPGA (Field-Programmable Gate Array). In addition, part or all of them can be configured by software that functions when a processor such as a CPU (Central Processing Unit) executes a program stored in the storage unit.

  In the case of the CFP2-ACO transceiver module, among the optical transmitters, a driver amplifier which is an analog electric circuit, a laser which is an optical component, and a modulator are included in the CFP2-ACO transceiver module.

  The optical receiver 202 includes a polarization separation unit 208, a polarization diversity 90 degree hybrid 209, a PD (photo diode) 209a, a TIA 210 (transimpedance amplifier), an ADC 211, and a reception signal processing unit 212.

  Some or all of the ADC 211 of the optical receiver and the reception signal processing unit are hardware functional units such as an ASIC or an FPGA. In addition, part or all of them can be configured by software that functions by causing a processor such as a CPU to execute a program stored in a storage unit.

  In the case of the CFP2-ACO transceiver module, the polarization diversity 90-degree hybrid which is an optical component of the optical receiver, the PD, and the TIA which is an analog electric circuit are included in the transceiver module.

  In the first embodiment, each of the light transmitter and the light receiver is provided with a laser, whereas in the second embodiment, the light transmitter / receiver shares one laser 206. . The CW light from one laser is branched, and one is input to the optical transmitter 201 and the other is input to the optical receiver 202. In this configuration, since only one laser is used, there is an advantage that the power consumption of the CFP 2-ACO transceiver module can be reduced. However, since there is only one laser, the oscillation frequency of the laser is controlled as in the first embodiment to give a frequency difference between the oscillation frequency of the CW light and the local oscillation light output from the optical transmitter, It is not possible to measure the frequency characteristics of the transfer function of

  In the second embodiment, in such an optical transceiver 200, the frequency response of the transfer function of the optical receiver is measured using single side band (SSB) modulation. Then, based on the measurement result, for example, the DSP 212a compensates for the frequency response of the transfer function and the difference between the lanes.

  Here, a specific configuration and procedure when measuring the frequency characteristic of the transfer function of the optical receiver 202 in the second embodiment will be described.

  At the time of frequency response measurement, sine waves of the same frequency f whose phases are shifted by 90 degrees from the outputs of the two lanes corresponding to the same polarization among the outputs of the four lanes of the DAC are output. The remaining 2 lanes of DAC are not output.

  For example, when outputting from two lanes corresponding to the X polarization 207a, assuming that the sine wave output from the XI lane of the DAC 204 is cos 2πft, the sine wave output from the XQ lane of the DAC 204 is sin 2πft. Then, the YI and YQ lanes of the DAC 204 are not output. Here, f is frequency and t is time.

  The modulator 207 has the same bias setting as in normal operation. That is, the bias of the child Mach-Zehnder modulator among the modulators is set to the null point, and the bias of the parent Mach-Zehnder modulator is set such that the phase difference between the I lane and the Q lane is 90 degrees.

  Then, the frequency of the output light from the modulator 207 is shifted by f from the frequency of the input light to the modulator (SSB modulation). Thus, the frequency difference f can be added to the CW light and the local light output from the optical transmitter.

  When the output light from the optical transmitter is input to the optical receiver using a short optical fiber, the CW light shifted by the frequency f output from the optical transmitter interferes with the local light at the optical receiver and the same as the difference frequency f An electrical sine wave of frequency is output from TIA 210. The electrical sine wave signal is converted to a digital signal by the ADC 211, and the frequency and amplitude are recorded.

  The amplitude of the electrical sine wave signal changes in accordance with the frequency characteristic of the transfer function (including the pluggable connector in the case of CFP2-ACO) of the PD 209a constituting the optical receiver, the TIA 210, and the ADC 211. Therefore, the frequency f of the sine wave output from the DAC 204 is sequentially changed so that the frequency range to be measured is obtained, and the frequency and amplitude of the digital signal converted into a digital signal by the ADC 211 are sequentially measured. The transfer function can be measured.

  Based on this measurement data, for example, by applying the DSP 212a in the received signal processing unit 212, it is possible to compensate for the frequency response of the transfer function of the optical receiver 202 and the difference in transfer function between the lanes.

  Thus, the optical transceiver 200 of the second embodiment can measure and compensate for the transfer function of the optical receiver and the difference between the lanes.

Third Embodiment
FIG. 3 is a diagram showing a configuration of an optical transceiver according to a third embodiment of the present invention. The optical transceiver 300 comprises an optical transmitter 301, an optical receiver 302, and a laser 306.

  The optical transmitter 301 includes a transmission signal processing unit 303, a DAC 304, a driver amplifier 305, and a modulator 307.

  The transmission signal processing unit 303 performs necessary digital signal processing on the input electrical signal. The DAC 304 converts the digital signal output from the transmission signal processing unit into an analog electrical signal. The driver amplifier 305 amplifies the analog electrical signal to an appropriate amplitude and sends it to the modulator 307. The modulator 307 separates linearly polarized CW (Continuous Wave) light transmitted from the laser into orthogonal linearly polarized light, and modulates each linearly polarized light with an electrical signal to generate a light modulation signal. The X polarization 307a and the Y polarization 307b are multiplexed by the polarization beam combiner 307c.

  A part or all of the transmission signal processing unit 303 of the optical transmitter and the DAC 304 can be configured by hardware such as an ASIC or an FPGA (Field-Programmable Gate Array). In addition, part or all of them can be configured by software that functions when a processor such as a CPU (Central Processing Unit) executes a program stored in the storage unit.

  In the case of the CFP2-ACO transceiver module, among the optical transmitters, a driver amplifier which is an analog electric circuit, a laser which is an optical component, and a modulator are included in the CFP2-ACO transceiver module.

  The optical receiver 302 includes a polarization separation unit 310, a polarization diversity 90 degree hybrid 311, a PD (photo diode) 311a, a TIA 312 (transimpedance amplifier), an ADC 313, and a reception signal processing unit 314.

  Some or all of the ADC 313 of the optical receiver and the reception signal processing unit are hardware functional units such as an ASIC or an FPGA. In addition, part or all of them can be configured by software that functions by causing a processor such as a CPU to execute a program stored in a storage unit.

  In the case of the CFP2-ACO transceiver module, the polarization diversity 90-degree hybrid which is an optical component of the optical receiver, the PD, and the TIA which is an analog electric circuit are included in the transceiver module.

In the first embodiment, each of the light transmitter and the light receiver is provided with a laser, while in the third embodiment, the light transmitter / receiver shares one laser 306. .
The third embodiment is different from the second embodiment in that an optical amplifier 308 and an optical band pass filter 309 are provided downstream of the modulator 307. The optical amplifier is, for example, an EDFA (erbium doped optical fiber amplifier) or an SOA (semiconductor optical amplifier).

  In the second embodiment, a sine wave of frequency f is output from the DAC 204, and the frequency of output light from the modulator is shifted by f from the frequency of input light to the modulator 207 using SSB modulation. However, the amplitude of the sine wave changes according to the frequency response of the transfer function of the optical transmitter (DAC 204, driver amplifier 205, and modulator 207).

  Therefore, each time the frequency f of the sine wave output from the DAC 204 is sequentially changed, the intensity of the single polarization CW light whose frequency output is shifted from the modulator 207 is f according to the frequency response of the optical transmitter 201. Because of the change, the frequency of the transfer function of the optical receiver 202 can not be measured accurately.

  Therefore, the optical transceiver 300 according to the third embodiment of the present invention includes the optical amplifier 308 at the subsequent stage of the modulator 307. The optical amplifier 308 can operate under automatic power control (APC) in which the output light intensity of the optical amplifier is constant.

  Therefore, by inputting the SSB modulated CW light from the modulator 307 into the optical amplifier 308 and performing APC control, the light intensity corresponding to the frequency characteristic of the transfer function of the optical transmitter 301 generated when the frequency f is changed The change can be compensated to obtain a constant output light intensity.

  The optical band pass filter 309 is a filter for removing unwanted amplified spontaneous emission (ASE) noise generated in the optical amplifier 308. The optical band pass filter 309 has a sufficiently wide band characteristic as compared to the frequency characteristic of the optical receiver 302, so the contribution to the change of the intensity of the SSB modulated CW light in the frequency range of the measurement object can be ignored.

  When the output light from the optical transmitter 301 is input to the optical receiver 302 using a short optical fiber, the CW light shifted by the frequency f output from the optical transmitter 301 interferes with the local light by the optical receiver, and the difference frequency A sine wave of electricity with the same frequency as f is output from the TIA 312. The electrical sine wave signal is converted to a digital signal by the ADC 313 and the frequency and amplitude are recorded.

  The amplitude of the electrical sine wave signal changes in accordance with the frequency characteristic of the transfer function (including the pluggable connector in the case of CFP2-ACO) of the PD 311a constituting the optical receiver 302, the TIA 312 and the ADC 313. Therefore, the frequency f of the sine wave output from the DAC 304 is sequentially changed so that the frequency range to be measured is obtained, and the frequency and amplitude of the digital signal converted into a digital signal by the ADC 313 are sequentially measured. The transfer function of can be measured.

  Based on this measurement data, for example, by applying the DSP 314a in the reception signal processing unit 314, it is possible to compensate for the frequency response of the transfer function of the optical receiver and the difference in transfer function between the lanes.

  As a result, the optical transceiver 300 of the third embodiment can measure and compensate for the transfer function of the optical receiver 302 and the difference between the lanes thereof.

Fourth Embodiment
FIG. 4 is a diagram showing the configuration of an optical transceiver 400 according to the fourth embodiment of the present invention.

  The optical transceiver 400 comprises an optical transmitter 401 and an optical receiver 402.

  The optical transmitter 401 includes a transmission signal processing unit 403, a DAC 404, a driver amplifier 405, a laser 406, and a modulator 407.

  The transmission signal processing unit 403 performs necessary digital signal processing on the input electrical signal. The DAC 404 converts the digital signal output from the transmission signal processing unit into an analog electrical signal. The driver amplifier 405 amplifies the analog electrical signal to an appropriate amplitude and sends it to the modulator 407. The modulator 407 separates linearly polarized CW (Continuous Wave) light transmitted from the laser into orthogonal linearly polarized light, and modulates each linearly polarized light with an electrical signal to generate a light modulation signal. The X polarization 407a and the Y polarization 407b are multiplexed by the polarization beam combiner 407c.

  Part or all of the transmission signal processing unit 403 of the optical transmitter and the DAC 404 can be configured by hardware such as an ASIC or an FPGA (Field-Programmable Gate Array). In addition, part or all of them can be configured by software that functions when a processor such as a CPU (Central Processing Unit) executes a program stored in the storage unit.

  In the case of the CFP2-ACO transceiver module, among the optical transmitters, a driver amplifier which is an analog electric circuit, a laser which is an optical component, and a modulator are included in the CFP2-ACO transceiver module.

  The optical receiver 402 includes a laser 411, a polarization separation unit 410, a polarization diversity 90 degree hybrid 412, a PD (photo diode) 412a, a TIA 413 (transimpedance amplifier), an ADC 414, and a reception signal processing unit 415. .

  Some or all of the ADC 414 of the optical receiver and the reception signal processing unit are hardware functional units such as an ASIC or an FPGA. In addition, part or all of them can be configured by software that functions by causing a processor such as a CPU to execute a program stored in a storage unit.

  In the case of the CFP 2-ACO transceiver module, the transceiver module includes a laser which is an optical component of an optical receiver, a polarization diversity 90 degree hybrid, a PD, and a TIA which is an analog electric circuit.

  The fourth embodiment is different from the first embodiment in that an optical amplifier 408 and an optical band pass filter 409 are provided downstream of the modulator 407. The optical amplifier 408 is, for example, an EDFA or an SOA.

  In the first embodiment, the oscillation frequency of the two lasers is controlled to give a frequency difference between the CW light and the local light output from the optical transmitter 401 to measure the frequency characteristic of the transfer function of the optical receiver. In the fourth embodiment, the ASE noise output from the optical amplifier 408 is used to measure the frequency characteristic of the transfer function of the optical receiver.

  Here, a specific configuration and procedure when measuring the frequency characteristic of the transfer function of the optical receiver 402 in the fourth embodiment will be described.

  During frequency response measurement, the laser 406 of the optical transmitter 401 is extinguished. The output amplitude of the DAC 404 and the bias settings of the child Mach-Zehnder modulator of the modulator and the parent Mach-Zehnder modulator are arbitrary.

  Only ASE noise is generated from the optical amplifier in the absence of output light from the modulator. When the optical amplifier is an EDFA, pumping light is input to an optical fiber doped with erbium ions, and transition of the erbium ions from the pumping state to the ground state generates ASE noise.

  Unnecessary ASE noise is suppressed by setting the center frequency of the transmission band of the optical band pass filter 409 to be the same as the oscillation frequency of the laser. Here, the optical band pass filter has a sufficiently wide band characteristic as compared with the frequency characteristic of the optical receiver. Therefore, ASE noise that has passed through the band pass filter 409 can be regarded as light white noise.

  When the light white noise from the light transmitter 401 is input to the light receiver 402 using a short optical fiber, the light white noise output from the light transmitter is interfered with the local light by the light receiver, and is photoelectrically converted by the ADC 414. It is converted to a digital signal. By Fourier-transforming this digital signal, the frequency response of the transfer function of the optical receiver 402 can be measured.

  Based on this measurement data, for example, by applying the DSP 415a in the reception signal processing unit 415, it is possible to compensate for the frequency response of the transfer function of the optical receiver and the difference in transfer function between the lanes.

  Thus, the optical transceiver according to the fourth embodiment can measure and compensate for the transfer function of the optical receiver 402 and the difference between the lanes.

Fifth Embodiment
FIG. 5 is a diagram showing the configuration of an optical transceiver 500 according to the fifth embodiment of the present invention. The configuration is the same as the optical transceiver according to the third embodiment. The optical transceiver 500 includes an optical transmitter 501, an optical receiver 502, and a laser 506.

  The optical transmitter 501 includes a transmission signal processing unit 503, a DAC 504, a driver amplifier 505, and a modulator 507.

  The transmission signal processing unit 503 performs necessary digital signal processing on the input electrical signal. The DAC 504 converts the digital signal output from the transmission signal processing unit into an analog electrical signal. The driver amplifier 505 amplifies the analog electrical signal to an appropriate amplitude and transmits it to the modulator 507. The modulator 507 separates linearly polarized CW (Continuous Wave) light transmitted from the laser into orthogonal linearly polarized light, and modulates each linearly polarized light with an electrical signal to generate a light modulation signal. The X polarization 507 a and the Y polarization 507 b are multiplexed by the polarization beam combiner 507 c.

  A part or all of the transmission signal processing unit 503 of the optical transmitter and the DAC 504 can be configured by hardware such as an ASIC or an FPGA (Field-Programmable Gate Array). In addition, part or all of them can be configured by software that functions when a processor such as a CPU (Central Processing Unit) executes a program stored in the storage unit.

  In the case of the CFP2-ACO transceiver module, among the optical transmitters, a driver amplifier which is an analog electric circuit, a laser which is an optical component, and a modulator are included in the CFP2-ACO transceiver module.

  The optical receiver 502 includes a polarization separation unit 510, a polarization diversity 90-degree hybrid 511, a PD (photo diode) 511a, a TIA 512 (transimpedance amplifier), an ADC 513, and a reception signal processing unit 514.

  Some or all of the ADC 513 of the optical receiver and the reception signal processing unit are hardware functional units such as an ASIC or an FPGA. In addition, part or all of them can be configured by software that functions by causing a processor such as a CPU to execute a program stored in a storage unit.

  In the case of the CFP2-ACO transceiver module, the polarization diversity 90-degree hybrid which is an optical component of the optical receiver, the PD, and the TIA which is an analog electric circuit are included in the transceiver module.

  In the fourth embodiment, each of the optical transmitter 401 and the optical receiver 402 includes a laser, whereas in the fifth embodiment, the optical transceiver 500 shares one laser. Is different. The CW light from one laser is branched and one is input to the optical transmitter and the other is input to the optical receiver. In this configuration, since only one laser is used, there is an advantage that the power consumption of the CFP2-ACO transceiver module can be reduced. However, since there is only one laser, it is not possible to input local light to the optical receiver while quenching the laser to the optical transmitter as in the fourth embodiment.

  In the fifth embodiment, in such an optical transceiver 500, light white noise is used to measure the frequency response of the transfer function of the optical receiver. Then, based on the measurement result, for example, the DSP 514a compensates for the frequency response of the transfer function and the difference between the lanes.

  Here, a specific configuration and procedure when measuring the frequency characteristic of the transfer function of the optical receiver 502 in the fifth embodiment will be described.

  At the time of frequency response measurement, CW light from the laser 506 is branched and input to the light transmitter 501 and the light receiver 502, respectively. In addition, the input of the analog electrical signal to the modulator 507 is stopped. This can be achieved by setting the output voltage swing of the DAC 504 to zero or by shutting down the output of the driver amplifier. In the modulator 507, the bias of the child Mach-Zehnder modulator is set such that CW light is minimally transmitted (null point), and the bias setting of the parent Mach-Zehnder modulator is arbitrary.

  Only the ASE noise is generated from the optical amplifier with the output light power from the modulator being minimized. When the optical amplifier is an EDFA, pumping light is input to an optical fiber doped with erbium ions, and transition of the erbium ions from the pumping state to the ground state generates ASE noise.

  Unnecessary ASE noise is suppressed by setting the center frequency of the transmission band of the optical band pass filter 509 to be the same as the oscillation frequency of the laser. Here, the optical band pass filter 509 has a sufficiently wide band characteristic as compared with the frequency characteristic of the optical receiver. Accordingly, ASE noise that has passed through the optical band pass filter 509 can be regarded as light white noise.

  When the light white noise from the light transmitter 501 is input to the light receiver 502 using a short optical fiber, the light white noise output from the light transmitter is interfered with the local light by the light receiver, and is converted by the ADC 513 after photoelectric conversion. It is converted to a digital signal. By Fourier transforming this digital signal, the frequency response of the transfer function of the optical receiver 502 can be measured.

  Based on this measurement data, for example, by applying the DSP 514a in the reception signal processing unit 514, it is possible to compensate for the frequency response of the transfer function of the optical receiver and the difference in transfer function between the lanes.

  As a result, the optical transceiver 500 of the fifth embodiment can measure and compensate for the transfer function of the optical receiver 502 and the difference between the lanes.

Sixth Embodiment
FIG. 6 is a diagram showing the configuration of an optical transceiver 600 according to the sixth embodiment of the present invention.

  Although the fifth embodiment does not particularly refer to the material for realizing the modulator 507, the sixth embodiment is characterized in particular by using a semiconductor material.

  In the fifth embodiment, at the time of frequency response measurement, the input of the analog electrical signal to the modulator 507 is stopped, and the bias of the child Mach-Zehnder modulator is set to the minimum transmission (null point) setting of CW light. The input light power to the amplifier was minimized. However, since the extinction ratio of the child Mach-Zehnder modulator is limited, a minute CW light is input to the optical amplifier, and the minute CW light may be amplified to fail to generate a flat light white noise.

  Therefore, the optical transceiver according to the sixth embodiment of the present invention uses a semiconductor modulator 607. The optical transceiver 600 comprises an optical transmitter 601, an optical receiver 602, and a laser 606.

  The optical transmitter 601 includes a transmission signal processing unit 603, a DAC 604, a driver amplifier 605, and a modulator 607.

  The transmission signal processing unit 603 performs necessary digital signal processing on the input electrical signal. The DAC 604 converts the digital signal output from the transmission signal processing unit into an analog electrical signal. The driver amplifier 605 amplifies the analog electrical signal to an appropriate amplitude and sends it to the modulator 607. The modulator 607 separates linearly polarized CW (Continuous Wave) light transmitted from the laser into orthogonal linearly polarized light, and modulates each linearly polarized light with an electrical signal to generate a light modulation signal. The X polarization 607 a and the Y polarization 607 b are combined by the polarization beam combiner 607 c.

  Part or all of the transmission signal processing unit 603 of the optical transmitter and the DAC 604 can be configured by hardware such as an ASIC or an FPGA (Field-Programmable Gate Array). In addition, part or all of them can be configured by software that functions when a processor such as a CPU (Central Processing Unit) executes a program stored in the storage unit.

  In the case of the CFP2-ACO transceiver module, among the optical transmitters, a driver amplifier which is an analog electric circuit, a laser which is an optical component, and a modulator are included in the CFP2-ACO transceiver module.

  The optical receiver 602 includes a polarization separation unit 610, a polarization diversity 90-degree hybrid 611, a PD (photo diode) 611a, a TIA 612 (transimpedance amplifier), an ADC 613, and a reception signal processing unit 614.

  Some or all of the ADC 613 of the optical receiver and the reception signal processing unit are hardware functional units such as an ASIC or an FPGA. In addition, part or all of them can be configured by software that functions by causing a processor such as a CPU to execute a program stored in a storage unit.

  In the case of the CFP2-ACO transceiver module, the polarization diversity 90-degree hybrid which is an optical component of the optical receiver, the PD, and the TIA which is an analog electric circuit are included in the transceiver module.

  During normal operation, a negative reverse bias voltage is applied to the semiconductor layer 607 to the p layer and a positive bias to the n layer. When this bias voltage is applied to the p layer and a negative bias voltage is applied to the n layer, light is absorbed in the semiconductor modulator 607, and the semiconductor modulator 607 operates as an optical attenuator.

  Therefore, when measuring the frequency response, stop the input of the analog electric signal to the semiconductor modulator 607, set the bias of the child Mach-Zehnder modulator to the minimum transmission (null point) setting of CW light, and proceed to the semiconductor modulator 607 in turn. By applying a bias voltage, the output light power from the modulator can be suppressed sufficiently low, and only ASE noise can be generated from the optical amplifier. When the optical amplifier is an EDFA, pumping light is input to an optical fiber doped with erbium ions, and transition of the erbium ions from the pumping state to the ground state generates ASE noise.

  By setting the center frequency of the transmission band of the optical band pass filter 609 to be the same as the oscillation frequency of the laser, unnecessary ASE noise is suppressed. Here, the optical band pass filter 609 has sufficiently wide band characteristics as compared to the frequency characteristics of the optical receiver. Accordingly, ASE noise that has passed through the optical band pass filter 609 can be regarded as light white noise.

  When the light white noise from the light transmitter 601 is input to the light receiver 602 using a short optical fiber, the light white noise output from the light transmitter 601 is interfered with the local light by the light receiver, and after photoelectric conversion, the ADC 613 Converted to a digital signal. By Fourier transforming this digital signal, the frequency response of the transfer function of the optical receiver 602 can be measured.

  Based on this measurement data, for example, by applying the DSP 614a in the reception signal processing unit 614, it is possible to compensate for the frequency response of the transfer function of the optical receiver and the difference in transfer function between the lanes.

  By this, the optical transceiver 600 of the sixth embodiment can measure and compensate for the transfer function of the optical receiver 602 and the difference between the lanes.

100, 200, 300, 400, 500, 600, 700 Optical transceivers 101, 201, 301, 401, 501, 601, 701 Optical transmitters 102, 202, 302, 402, 502, 602, 702 Optical receivers
703 Optical white noise source 103, 203, 303, 403, 503, 603, 704 Transmission signal processing unit 104, 204, 304, 404, 504, 604, 705 DAC
105, 205, 305, 405, 505, 605 Driver amplifier 106, 108, 206, 306, 406, 411, 506, 606, 707, 709 Laser (LD)
107, 207, 307, 407, 507, 607, 708 Modulators 107a, 207a, 307a, 407a, 507a, 607a, X polarizations 107b, 207b, 307b, 407b, 507b, 607b, 708b Y polarizations 107c, 207c , 307c, 407c, 507c, 607c, 708c Polarized beam combiners 308, 408, 508, 508, 508 Optical amplifiers 309, 409, 509, 609 Optical bandpass filters 109, 208, 310, 410, 510, 610, 710 Polarized Wave separation unit 110, 209, 311, 412, 511, 611, 711 Polarization diversity 90 ° C. hybrid 110a, 209a, 311a, 412a, 511a, 611a, 711a PD
111, 210, 312, 413, 512, 612, 712 TIA
112, 211, 313, 414, 513, 613, 713 ADC
113, 212, 314, 415, 514, 614, 714 Received signal processing unit 113a, 212a, 314a, 415a, 514a, 614a DSP

Claims (10)

A digital signal processing circuit for measuring the frequency response of the transfer function of an optical receiver, comprising:
Generating an optical signal of CW light whose frequency is shifted by a known amount from the local light from the optical transmitter and the optical receiver side,
Interference of local light and the optical signal in the optical receiver to obtain an electrical signal of a difference frequency,
A digital signal processing circuit measuring a frequency response of a transfer function of the optical receiver based on the electric signal. In the digital signal processing circuit of claim 1,
A digital signal processing circuit characterized in that the frequency characteristic of the transfer function is measured by controlling the oscillation frequency of the laser of the optical transmitter to give a frequency difference between the oscillation frequency of the CW light and the local oscillation light. In the digital signal processing circuit of claim 1,
A digital signal processing circuit characterized by giving a shift difference of a frequency f to the frequency of the CW light and the frequency of the local light. In the digital signal processing circuit of claim 3,
A digital signal processing circuit characterized in that the CW light is input to an optical amplifier to make the output light intensity constant. A digital signal processing circuit for measuring the frequency response of the transfer function of an optical receiver, comprising:
Output ASE light generated from the optical amplifier of the optical transmitter,
Interference between local light and the ASE light in the optical receiver to obtain an electrical signal;
A digital signal processing circuit measuring a frequency response of a transfer function of the optical receiver based on the electric signal. In the digital signal processing circuit of claim 5,
A digital signal processing circuit characterized in that an optical modulator constituting the optical transmitter is a semiconductor optical modulator. An optical transmitter that generates an optical signal whose frequency is shifted by a known amount from local light in the optical receiver;
An optical receiver that interferes with the local light and the optical signal to output an electrical signal of a difference frequency;
And a digital signal processing circuit that measures the frequency response of a transfer function based on the electrical signal. An optical transmitter that outputs ASE light generated from the optical amplifier;
An optical receiver that outputs an electric signal by causing local light emission and the ASE light to interfere with each other;
A digital signal processing circuit that Fourier-transforms the electric signal to measure a frequency response of a transfer function. Generating an optical signal whose frequency is shifted by a known amount from local light in the optical transmitter;
Interference between the local light and the optical signal to output an electrical signal of a difference frequency;
Measuring the frequency response of a transfer function based on the electrical signal;
And a driving method of an optical transmitter-receiver. Outputting ASE light generated from the amplifier;
Interference between local light and the ASE light to output an electrical signal;
Fourier transforming the electrical signal to measure the frequency response of the transfer function;
And a driving method of an optical transmitter-receiver.

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