JP2015019191A - Optical transceiver and optical receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To receive an optical signal without depending on a modulation/demodulation system.SOLUTION: An optical transmitter 2 comprises: an error correction part 21 for adding an error-correcting code to an inputted electric signal; a differential encoding part 22 for differentially encoding the electric signal to which the error-correcting code is added; a light source 25 which emits light; and a modulator 26 in which emitted light is modulated and converted into an optical signal in accordance with the differentially encoded electric signal. An optical receiver 3 comprises: a light source 31 which emits light; a coherent detection part 32 for performing coherent detection on an inputted optical signal and light from the light source 31; a differential detection part 35 for differentially detecting a coherent-detected electric signal; an error correction part 36 which performs error-correcting processing on the differentially detected electric signal; and a control part 37 for adjusting a frequency of light emitted by the light source 31 so as to minimize the number of error corrections in the error correction part 36.

Description

  The present invention relates to a digital coherent optical transmitter / receiver and an optical receiver capable of receiving an optical signal without depending on a modulation / demodulation method.

  In recent years, with an increase in demand for information communication, there is a demand for an increase in optical transmission capacity. The increase in the number of wavelength multiplexing or the new installation of an optical fiber network cannot sufficiently meet the increase in demand, and therefore it is necessary to improve the transmission rate from the conventional 10 Gbps to 40 Gbps or 100 Gbps. In particular, in an optical transmission system that performs long-distance transmission, transmission penalties such as optical signal waveform distortion due to chromatic dispersion and polarization mode dispersion of an optical fiber in a communication path become serious as speed increases.

  In order to solve this problem, digital coherent communication systems that can compensate for chromatic dispersion and polarization mode dispersion in the electrical domain by using a digital signal processor on the receiving side and that can handle various multilevel modulation systems have recently been developed. Have been actively researched and developed (see, for example, Patent Documents 1 to 3).

  FIG. 5 shows a configuration example of a conventional optical transceiver 101 using a polarization multiplexing quadrature phase shift keying (DP-QPSK) which is a kind of digital coherent communication method. The optical transceiver 101 includes an optical transmitter 102 and an optical receiver 103. The optical transmitter 102 includes an error correction unit 1021, a transmission signal generation unit 1022, a QPSK modulator (hereinafter referred to as a modulator) 1023, 1024, a light source 1025, a polarization beam splitter 1026, and a polarization beam combiner 1027. Yes. The optical receiver 103 includes a coherent detection unit 1031, a light source 1032, a DSP (digital signal processor) 1033, and an error correction unit 1034.

The operation of the conventional optical transceiver 101 will be described below.
In the optical transmitter 102, first, CW (Continuous Wave) light 1061 is output from the light source 1025. The CW light 1061 is input to the polarization beam splitter 1026 and separated into an X polarization component 1062 and a Y polarization component 1063. Thereafter, the signals are input to the modulators 1023 and 1024, respectively. On the other hand, transmission electric signal 1051 is input to error correction section 1021, and parity (error correction code) for error correction is added to transmission electric signal 1051. Transmission electric signal 1052 to which the error correction code is added is input to transmission signal generation section 1022 and converted to high-speed electric signals 1053 and 1054. Further, the high-speed electrical signals 1053 and 1054 are input to the modulators 1023 and 1024, respectively. As a result, the X polarization component 1062 and the Y polarization component 1063 of the CW light 1061 are modulated and converted into optical modulation signals 1064 and 1065, respectively. These are combined by the polarization beam combiner 1027, and the transmission optical signal 1066 is transmitted from the optical transceiver 101.

  Next, the optical receiver 103 first receives the received optical signal 1071. Thereafter, the received optical signal 1071 is input to the coherent detection unit 1031. Further, the CW light 1072 is output from the light source 1032 and input to the coherent detection unit 1031 as local light. The coherent detection unit 1031 performs coherent detection on the X polarization component of the received optical signal 1071 and the X polarization component of the CW light 1072, and the Y polarization component of the received optical signal 1071 and the Y polarization component of the CW light 1072, respectively. , Converted into an electric parallel signal 1081. The electric parallel signal 1081 is input to the DSP 1033, and the electric parallel signal 1082 is output. Finally, the electric parallel signal 1082 is subjected to error correction processing in the error correction unit 1034, and a received electric signal 1083 with reduced bit errors is output.

FIG. 6 shows a functional unit configuration of the DSP 1033.
The first stage of the DSP 1033 is provided with an ADC unit (analog / digital conversion unit) 1035, receives the electric parallel signal 1081 output from the coherent detection unit 1031, performs analog / digital conversion, and outputs a digital parallel signal 1084. Next, the digital parallel signal 1084 is subjected to digital signal processing in the equalization processing unit 1036, and an electric parallel signal 1085 compensated for chromatic dispersion, polarization dependent loss, and polarization mode dispersion is output. The electric parallel signal 1085 is input to the frequency offset compensation unit 1037, and the frequency offset between the signal light and the local light is calculated by digital signal processing. Thereafter, an electrical parallel signal 1086 that compensates the calculated frequency offset is output from the frequency offset compensation unit 1037. The electric parallel signal 1086 is input to the phase synchronization unit 1038, and an electric parallel signal 1087 from which the phase difference between the signal light and the local light is removed by digital signal processing is output. Finally, the electric parallel signal 1087 is input to the decoding unit 1039, and the electric parallel signal 1082 that has been identified and determined is output.

JP 2009-135930 A JP 2012-248944 A JP 2010-268210 A

  In the digital coherent method, a plurality of methods such as a binary phase modulation method and a quaternary phase modulation method are used. However, in the DPS 1033 of FIG. 6, the frequency offset compensation unit 1037 and the phase synchronization unit 1038 depend on the modulation / demodulation method, and therefore there is a problem that the same optical receiver 103 cannot receive different modulation / demodulation methods.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide an optical transceiver and an optical receiver capable of receiving an optical signal without depending on a modulation / demodulation method.

  An optical transceiver according to the present invention includes an optical transmitter that converts an input electric signal into an optical signal and outputs the optical signal, and an optical receiver that converts an optical signal input from an opposite optical transmitter into an electric signal and outputs the electric signal. The optical transmitter includes an error correction unit that adds an error correction code to the input electrical signal, and differential encoding that differentially encodes the electrical signal to which the error correction code is added by the error correction unit A first light source that emits light, and a modulation that modulates the light emitted by the first light source and converts it into an optical signal in accordance with the electrical signal differentially encoded by the differential encoding unit The optical receiver includes: a second light source that emits light; a coherent detector that coherently detects an optical signal input from the optical transmitter and light from the second light source; and a coherent detector Differential for differential detection of electrical signals coherently detected by Light is emitted from the wave source, an error correction unit that performs error correction processing on the electrical signal differentially detected by the differential detection unit, and the second light source so that the number of error corrections in the error correction unit is minimized And a control unit that adjusts the frequency of light.

  According to the present invention, since it is configured as described above, phase estimation and frequency offset compensation are not performed by a DSP (digital signal processor), differential detection with a large tolerance for frequency offset is performed, and the number of error corrections is increased. Accordingly, by adjusting the frequency of light by the second light source, there is an effect that an optical signal can be received without depending on the modulation method.

It is a figure which shows schematic structure of the optical transmitter-receiver which concerns on Embodiment 1 of this invention. It is a flowchart which shows operation | movement of the optical transmitter which concerns on Embodiment 1 of this invention. It is a flowchart which shows operation | movement of the optical receiver which concerns on Embodiment 1 of this invention. It is a figure which shows schematic structure of the optical transmitter-receiver which concerns on Embodiment 2 of this invention. It is a figure which shows schematic structure of the optical transmitter / receiver of the conventional digital coherent communication system. It is a figure which shows the functional block of a general digital signal processor.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
Embodiment 1 FIG.
FIG. 1 is a diagram showing a schematic configuration of an optical transceiver 1 according to Embodiment 1 of the present invention.
As shown in FIG. 1, the optical transceiver 1 includes an optical transmitter 2 and an optical receiver 3.

First, the configuration of the optical transmitter 2 will be described.
The optical transmitter 2 converts the input transmission electric signal 51 into a transmission optical signal 62 and outputs it. The optical transmitter 2 includes an error correction unit 21, a differential encoding unit 22, a transmission signal aggregation unit 23, a driver 24, a light source (first light source) 25, and a modulator 26.

  The error correction unit 21 adds a parity (error correction code) for error correction to the transmission electrical signal 51 input from the outside. The electric signal (transmission electric signal 52) to which the error correction code is added by the error correction unit 21 is output to the differential encoding unit 22.

  The differential encoding unit 22 differentially encodes the transmission electrical signal 52 from the error correction unit 21. The electrical signal differentially encoded by the differential encoding unit 22 (differential encoded signal 53) is output to the transmission signal aggregating unit 23.

  The transmission signal aggregating unit 23 aggregates the differential encoded signals 53 from the differential encoding unit 22. The electrical signal (high-speed electrical signal 54) aggregated by the transmission signal aggregating unit 23 is output to the driver 24.

  The driver 24 amplifies the high-speed electrical signal 54 from the transmission signal aggregation unit 23. The electric signal (high-speed electric signal 55) amplified by the driver 24 is output to the modulator 26.

  The light source 25 emits CW light 61. The CW light 61 emitted from the light source 25 is output to the modulator 26.

  The modulator 26 modulates the CW light 61 from the light source 25 in accordance with the high-speed electrical signal 55 from the driver 24. The optical signal (transmission optical signal 62) modulated by the modulator 26 is output to the outside (opposing optical receiver 3).

Next, the configuration of the optical receiver 3 will be described.
The optical receiver 3 converts the received optical signal 72 input from the opposing optical transmitter 2 into a received electrical signal 85 and outputs it. The optical receiver 3 includes a light source (second light source) 31, a coherent detection unit 32, an ADC unit (analog / digital conversion unit) 33, an equivalent processing unit 34, a differential detection unit 35, an error correction unit 36, and a control unit 37. It has.

  The light source 31 emits CW light. The CW light emitted from the light source 31 is output as the local light 71 to the coherent detection unit 32.

  The coherent detection unit 32 performs coherent detection on the received optical signal 72 input from the outside (opposing optical transmitter 2) and the local light 71 from the light source 31. The electrical signal (electrical parallel signal 81) coherently detected by the coherent detection unit 32 is output to the ADC unit 33.

  The ADC unit 33 performs analog-digital conversion on the electric parallel signal 81 from the coherent detection unit 32 and converts the analog signal into a digital signal. The electric signal (digital parallel signal 82) converted from analog to digital by the ADC unit 33 is output to the equivalent processing unit 34.

  The equivalent processing unit 34 performs digital signal processing on the digital parallel signal 82 from the ADC unit 33 to compensate for chromatic dispersion and the like. The electrical signal (electrical parallel signal 83) subjected to digital signal processing by the equivalent processing unit 34 is output to the differential detection unit 35.

  The differential detection unit 35 differentially detects the electric parallel signal 83 from the equivalent processing unit 34. The electric signal (electrical parallel signal 84) differentially detected by the differential detection unit 35 is output to the error correction unit 36.

  The error correction unit 36 performs error correction processing on the electrical parallel signal 84 from the differential detection unit 35. The electrical signal (received electrical signal 85) that has been subjected to error correction processing by the error correction unit 36 is output to the outside.

  The control unit 37 adjusts the frequency of the CW light emitted from the light source 31 according to the number of error corrections in the error correction unit 36. At this time, the control unit 37 compensates for the frequency offset between the received optical signal 72 and the local light 71 by controlling the frequency of the CW light emitted by the light source 31 so that the number of error corrections is minimized, and thereby the transmission quality. To improve.

Next, the operation of the optical transceiver 1 configured as described above will be described.
First, the operation of the optical transmitter 2 will be described with reference to FIG.
In the operation of the optical transmitter 2, as shown in FIG. 2, first, the error correction unit 21 adds an error correction code to the transmission electric signal 51 input from the outside (step ST201). The electric signal (transmission electric signal 52) to which the error correction code is added by the error correction unit 21 is output to the differential encoding unit 22.

  Next, the differential encoding unit 22 differentially encodes the transmission electrical signal 52 from the error correction unit 21 (step ST202). The electrical signal differentially encoded by the differential encoding unit 22 (differential encoded signal 53) is output to the transmission signal aggregating unit 23.

  Next, the transmission signal aggregating unit 23 aggregates the differential encoded signals 53 from the differential encoding unit 22 (step ST203). The electrical signal (high-speed electrical signal 54) aggregated by the transmission signal aggregating unit 23 is output to the driver 24.

  Next, the driver 24 amplifies the high-speed electrical signal 54 from the transmission signal aggregation unit 23 (step ST204). The electric signal (high-speed electric signal 55) amplified by the driver 24 is output to the modulator 26.

  On the other hand, the light source 25 emits CW light 61 (step ST205). The CW light 61 emitted from the light source 25 is output to the modulator 26.

  Next, the modulator 26 modulates the CW light 61 from the light source 25 according to the high-speed electrical signal 55 from the driver 24 (step ST206). The optical signal (transmission optical signal 62) modulated by the modulator 26 is output to the outside.

Next, the operation of the optical transmitter 2 will be described with reference to FIG.
In the operation of the optical receiver 3, as shown in FIG. 3, first, the light source 31 emits CW light (step ST301). The CW light emitted from the light source 31 is output as the local light 71 to the coherent detection unit 32.

  Next, the coherent detection unit 32 performs coherent detection on the received optical signal 72 input from the outside and the local light 71 from the light source 31 (step ST302). The electrical signal (electrical parallel signal 81) coherently detected by the coherent detection unit 32 is output to the ADC unit 33.

  Next, the ADC unit 33 performs analog-to-digital conversion on the electric parallel signal 81 from the coherent detection unit 32, and converts the analog signal into a digital signal (step ST303). The electric signal (digital parallel signal 82) converted from analog to digital by the ADC unit 33 is output to the equivalent processing unit 34.

  Next, the equivalent processing unit 34 performs digital signal processing on the digital parallel signal 82 from the ADC unit 33 to compensate for chromatic dispersion or the like (step ST304). The electrical signal (electrical parallel signal 83) subjected to digital signal processing by the equivalent processing unit 34 is output to the differential detection unit 35.

  Next, the differential detection unit 35 differentially detects the electrical parallel signal 83 from the equivalent processing unit 34 (step ST305). Here, differential detection is performed by detecting a phase difference between a signal at a certain time and a signal one symbol before, and thereby, the electric parallel signal 84 is demodulated. The electric parallel signal 84 demodulated by the differential detection unit 35 is output to the error correction unit 36.

  Next, the error correction unit 36 performs error correction processing on the electrical parallel signal 84 from the differential detection unit 35 (step ST306). The electrical signal (received electrical signal 85) that has been subjected to error correction processing by the error correction unit 36 is output to the outside.

  Next, the control unit 37 adjusts the frequency of the CW light emitted from the light source 31 according to the number of error corrections in the error correction unit 36 (step ST307). At this time, the control unit 37 compensates for the frequency offset between the received light signal 72 and the local light (CW light) 71 by controlling the frequency of the CW light emitted by the light source 31 so that the number of error corrections is minimized. And improve transmission quality.

  Here, in the optical receiver 3 of the conventional digital coherent communication system, frequency offset compensation / phase synchronization by digital signal processing depends on the modulation system, and therefore, received optical signals having different modulation systems cannot be received. On the other hand, the optical receiver 3 of the present invention has an effect of receiving an optical signal that does not depend on the modulation method by compensating the frequency offset according to the differential detection and the number of error corrections.

  Note that the modulation scheme of the optical transmitter 2 of the present embodiment can also be applied to various digital coherent communication schemes such as a binary phase modulation scheme and a quaternary phase modulation scheme.

  As described above, according to the first embodiment, the optical transmitter 2 includes the error correction unit 21 that adds an error correction code to the input electrical signal, and the error correction unit 21 added the error correction code. A differential encoding unit 22 that differentially encodes an electrical signal, a light source 25 that emits light, and light emitted by the light source 25 according to the electrical signal differentially encoded by the differential encoding unit 22 The optical receiver 3 includes a light source 31 that emits light, a coherent detection of the optical signal input from the optical transmitter 2 and the light from the light source 31. The coherent detection unit 32, the differential detection unit 35 for differential detection of the electrical signal coherently detected by the coherent detection unit 32, and the error correction processing for the electrical signal differentially detected by the differential detection unit 35 An error correction unit 36 to perform, And a control unit 37 that adjusts the frequency of light emitted from the light source 31 so that the number of error corrections in the correction unit 36 is minimized. Therefore, phase estimation / frequency offset compensation is performed by a DSP (digital signal processor). ), And by performing differential detection with a large tolerance for frequency offset and adjusting the frequency of CW light by the light source 31 according to the number of error corrections, an optical signal can be received without depending on the modulation method. effective.

Embodiment 2. FIG.
In the first embodiment, the case where the optical transmitter 2 and the optical receiver 3 are provided with the light sources 25 and 31, respectively, has been described. In contrast, the second embodiment shows a case where the output light of the light source 31 is branched and the branched light is used as the CW light 61 of the optical transmitter 2 and the local light 71 of the optical receiver 3.
4 is a diagram showing a schematic configuration of an optical transceiver 1 according to Embodiment 2 of the present invention. The optical transceiver 1 according to the second embodiment shown in FIG. 4 deletes the light source 25 from the optical transmitter 2 of the optical transceiver 1 according to the first embodiment shown in FIG. 38 is added. Other configurations are the same, and the same reference numerals are given and description thereof is omitted.

  The light branching unit 38 splits the CW light emitted from the light source 31 into two. One CW light branched into two by this optical branching unit 38 is output to the modulator 26 as CW light 61, and the other CW light is output to the coherent detection unit 32 as local light 71.

  Here, the light from the light source 31 is branched into two to be used as the CW light 61 and the local light 71, and the frequency of the CW light from the light source 31 is adjusted by the control unit 37, thereby compensating for the frequency offset in the optical receiver 3. In addition, the CW light 61 of the optical transmitter 2 can be adjusted at the same time. Therefore, by adjusting both transmission and reception according to the facing optical transceiver 1, it is possible to obtain an effect that the adjustment time can be shortened and optimum transmission characteristics can be realized regardless of the frequency offset compensation method of the facing optical transceiver 1. .

  In the present invention, within the scope of the invention, any combination of the embodiments, or any modification of any component in each embodiment, or omission of any component in each embodiment is possible. .

  DESCRIPTION OF SYMBOLS 1 Optical transmitter / receiver, 2 Optical transmitter, 3 Optical receiver, 21 Error correction part, 22 Differential encoding part, 23 Transmission signal aggregation part, 24 Driver, 25 Light source (1st light source), 26 Modulator, 31 Light source (second light source), 32 coherent detection unit, 33 ADC unit (analog / digital conversion unit), 34 equivalent processing unit, 35 differential detection unit, 36 error correction unit, 37 control unit, 38 optical branching unit, 51, 52 Transmission electrical signal, 53 Differential encoding signal, 54, 55 High-speed electrical signal, 61 CW light, 62 Transmission optical signal, 71 Local light emission, 72 Reception optical signal, 81, 83, 84 Electrical parallel signal, 82 Digital parallel signal , 85 Received electrical signal.

Claims (3)

An optical transceiver comprising: an optical transmitter that converts an input electric signal into an optical signal and outputs the optical signal; and an optical receiver that converts an optical signal input from the opposite optical transmitter into an electric signal and outputs the electric signal. In
The optical transmitter is
An error correction unit for adding an error correction code to the input electrical signal;
A differential encoding unit that differentially encodes the electrical signal to which an error correction code is added by the error correction unit;
A first light source that emits light;
A modulator that modulates the light emitted by the first light source and converts it into the optical signal in response to the electrical signal differentially encoded by the differential encoding unit;
The optical receiver is:
A second light source that emits light;
A coherent detection unit for coherently detecting the optical signal input from the optical transmitter and the light from the second light source;
A differential detector for differentially detecting the electrical signal coherently detected by the coherent detector;
An error correction unit for performing error correction processing on the electrical signal differentially detected by the differential detection unit;
An optical transceiver comprising: a control unit that adjusts a frequency of light emitted from the second light source so that the number of error corrections in the error correction unit is minimized. In place of the first light source, a light branching unit that branches the light emitted from the second light source into two parts,
The modulator uses one light branched into two by the light branching unit,
The optical transceiver according to claim 1, wherein the coherent detection unit uses the other light branched into two by the optical branching unit. In an optical receiver that converts an input optical signal into an electrical signal and outputs it,
A second light source that emits light;
A coherent detector for coherently detecting the optical signal modulated according to the differentially encoded electrical signal added with an error correction code by an opposing optical transmitter, and the light from the second light source;
A differential detector for differentially detecting the electrical signal coherently detected by the coherent detector;
An error correction unit for performing error correction processing on the electrical signal differentially detected by the differential detection unit;
An optical receiver comprising: a control unit that adjusts a frequency of light emitted from the second light source so that the number of error corrections in the error correction unit is minimized.

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