JP2008177711A - Optical transmission system, its method and optical transmitter/receiver used for the method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve signal processing at a lower signal speed by reducing a circuit scale participating in high-speed signal processing required on the reception side of a multi-value phase modulation long haul high-speed optical transmission system where a plurality of high-speed signals is switched via one clock source. <P>SOLUTION: A circuit for separating an output signal from a transmission side framer circuit into two channels and a circuit for inserting a synchronous pattern and a CH number into the separated signal are provided on the transmission side. CDR circuits 36, 37 performing clock reproduction/retiming individually for 20 Gbps signals of two channels, S/P circuits 38, 39 performing S/P conversion of the CDR output, and circuits 40, 41 for identifying the CH number by taking frame synchronization from the S/P circuit output signal are provided on the reception side. Furthermore, an elastic store 42 for switching the signal of 2CH on the clock of one system and a circuit 43 for determining the read-out phase from the elastic store based on the output phase information from the synchronous circuit are provided. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical transmission system and method and an optical transmission / reception apparatus used therefor, and more particularly to an optical transmission / reception apparatus in a long-distance high-speed optical transmission system using a multi-level phase modulation method.

  In a long-distance high-speed optical transmission system, a multi-level phase modulation method may be used for the purpose of relaxing transmission distance limitation due to polarization mode dispersion of an optical fiber as a transmission medium. As a transmission / reception apparatus in a long-distance high-speed optical transmission system employing a DQPSK (Differential Quadrature Phase Shift Keying) modulation system (see Patent Documents 1 and 2), which is a conventional multilevel phase modulation system, Structures such as the transmitter side shown in FIG. 3 and the receiver side shown in FIG. 4 are known. 3 and 4 is an example in which the DQPSK modulation method is applied to a transmission rate of 40 Gbps.

  Referring to FIG. 3, the transmission apparatus includes a transmission side framer circuit 10, a DQPSK precoder circuit 13, a P / S (Parallel / Serial) circuit and a CMU (Clock Multiplier Unit) circuit 14, a light source 20, an LN (LiNbO3). ) Modulator 21.

  The operation of the transmission apparatus having such a configuration will be described. In the transmission side framer circuit 10, as a logical signal sent to the transmission path, G.P. 707 / G. An STM (Synchronous Transfer Mode) signal / OTN (Optical Transport Network) signal defined in 709 is generated. In the DQPSK precoder circuit 13, a signal suitable for driving the LN modulator 21 is generated from the STM signal / OTN signal. In the P / S circuit and the CMU circuit 14, a plurality of high-speed data signals and high-speed clock signals are generated from the signal pre-coded by the DQPSK precoder circuit 13 and the low-speed clock signal. In the case of this example, in order to perform 40 Gbps RZ-DQPSK modulation, two 20 Gbps data signals and one 10 GHz clock signal are generated.

  The light source 20 generates a CW optical signal that is a transmission carrier. In the LN modulator 21, four CW lights are generated based on the high-speed data signal and the high-speed clock signal generated by the P / S circuit and the CMU circuit 114 by the DQPSK modulation circuit 211 and the RZ (Return to Zero) pulse carver circuit 212. Modulated into a DQPSK optical signal 22 having values (0, π / 2, π, 3π / 2) and sent to the optical transmission line. The symbol rate sent to the transmission line is 20 Gsymbol / s in 40 Gbps QPSK modulation.

  FIG. 4 is a diagram illustrating the configuration of the receiving apparatus. Referring to FIG. 4, the receiving apparatus includes an optical branching unit 31, a 1 symbol + π / 4 delay interferometer 32, a 1 symbol−π / 4 delay interferometer 33, differential receiver circuits 34 and 35, a CDR (Clock Data Recovery) circuits 36 and 37, a bit buffer 142, an S / P circuit 138, and a reception side framer circuit 44.

  The operation of the receiving apparatus having such a configuration will be described. The DQPSK optical signal 30 received from the optical transmission line is branched into two by an optical branching unit 31 and input to a 1 symbol + π / 4 delay interferometer 32 and a 1 symbol−π / 4 delay interferometer 33, respectively. In the differential receiver circuit 34, an electrical signal is regenerated from the two optical signals output from the 1 symbol + π / 4 delay interferometer 33. Similarly, in the differential receiver circuit 35, an electrical signal is regenerated from the two optical signals output from the 1 symbol-π / 4 delay interferometer 33.

  The 20 Gbps electrical signal regenerated by each differential receiver is input to the CDR circuits 36 and 37, respectively, to regenerate the clock, and to retime the data signal. The two re-timed 20 Gbps data signals are synchronized with one clock in the bit buffer 142 in order to reproduce the original 40 Gbps signal (this process is referred to as “clock change”). Will be called). The two 20 Gbps signals after the clock change are input to the S / P circuit 138, a lower-speed 150 Mbps signal is generated, and is output to the reception side frame circuit 44. In the reception side frame circuit 44, various signal processing is performed on the STM / OTN signal.

JP 2006-111538 A JP-T-2004-516743

  In the above-described prior art, it is necessary to transfer two 20 Gbps data signals to one clock by the bit buffer 142 on the receiving device side. At this time, the clock transfer processing is performed using a 20 GHz clock. It is necessary to ensure timing within a period (50 ps). For example, for two systems of 20 Gbps data, if the data processing delay of one side causes a delay variation of 20 GHz clock period (50 ps) or more with respect to the other data, the time order of the data cannot be maintained as 40 Gbps. . For this reason, the clock transfer processing circuit needs to ensure timing within 50 ps, but at present, there is a problem that it is necessary to improve the operation speed of the LSI in order to realize this high-speed signal processing speed. In FIG. 4, a portion indicated by a chain line 150 is a portion where high speed processing is required.

  An object of the present invention is to perform signal processing in which a plurality of high-speed signals are transferred to a single clock source on the receiving side. However, the circuit scale of the portion involved in the high-speed signal processing is reduced, and lower signal An optical transceiver capable of realizing signal processing at a speed and an optical transmission system using the same are provided.

  An optical transmission system according to the present invention is an optical transmission system of a multi-level phase modulation method, wherein a transmission side framer circuit output signal is separated into first and second channels, and a frame synchronization pattern for the separated signals. And first means for inserting the channel identification information, second means for converting the output signal of the first means into a multi-system signal having a speed suitable for an optical transmission path, and the second means And a third means for performing multi-level phase modulation processing of the optical signal based on the plurality of system signals and transmitting the optical signal to the optical transmission path, and the multi-level phase modulation optical signal from the optical transmission path A fourth means for branching into a system and performing photoelectric conversion on each of the branch outputs, and a first speed of the same speed as the signal speed of the first and second channels for each of the outputs of the fourth means. The fifth to convert to the first and second channel signal And a sixth means for identifying the frame synchronization and the channel identification information using the frame synchronization pattern for each of the outputs of the fifth means and the identification information by the sixth means. And a receiving device having a seventh means for performing a process of transferring the first and second channel signals to a single system clock.

  An optical transmission method according to the present invention is an optical transmission method of a multi-level phase modulation method, wherein a transmission side framer circuit output signal is separated into first and second channels in a transmission device, and the separated signal is A first step of inserting a frame synchronization pattern and channel identification information, a second step of converting the output signal of the first step into a plurality of system signals having a speed suitable for an optical transmission line, And a third step of performing multi-level phase modulation processing on the optical signal based on the plurality of system signals in the second step and transmitting the multi-level phase modulation to the optical transmission line. A fourth step of branching an optical signal into the plurality of systems and performing photoelectric conversion on each of the branch outputs; and a signal speed of the first and second channels for each of the outputs of the fourth step. Same speed A fifth step of converting the first and second channel signals, and a sixth step of identifying the frame synchronization and the channel identification information using the frame synchronization pattern for each of the outputs of the fifth step. And a seventh step of performing a process of transferring the first and second channel signals to a single clock based on the identification information obtained in the sixth step.

  A transmission apparatus according to the present invention is a transmission apparatus in an optical transmission system of a multi-level phase modulation method, and separates a transmission-side framer circuit output signal into first and second channels and frames the separated signals. A first means for inserting a synchronization pattern and channel identification information; a second means for converting an output signal of the first means into a plurality of system signals having a speed suitable for an optical transmission line; and the second means And a third means for performing multi-level phase modulation processing of the optical signal based on the plurality of system signals of the means and sending it to the optical transmission line.

  A receiving apparatus according to the present invention separates a transmission side framer circuit output signal into first and second channels, inserts a frame synchronization pattern and channel identification information into the separated signal, and outputs the output signal as follows: Multi-level phase modulation type optical transmission that converts multi-line signals at a speed suitable for the optical transmission line, multi-level phase modulation processing of the optical signal based on the multi-line signal, and sends it to the optical transmission line A receiving device in a system, the first means for branching the multi-level phase-modulated optical signal into the plurality of systems and performing photoelectric conversion on each of the branch outputs, and each of the outputs of the first means For each of the outputs of the third means and third means for converting to the first and second channel signals of the same speed as the signal speed of the first and second channels, the frame synchronization Patterned pattern Fourth means for performing synchronization and identification of the channel identification information, and fifth means for performing the process of changing the first and second channel signals to a single system clock based on the identification information obtained by the four means. It is characterized by including.

  According to the present invention, since the clock transfer process on the receiving device side is performed only with the low-speed clock, high-speed signal processing is not required in the clock transfer circuit part, and signal processing of the high-speed S / P converter circuit There is an effect that there may be a delay variation.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a transmitting apparatus according to an embodiment of the present invention, and FIG. 2 is a block diagram of a receiving apparatus according to an embodiment of the present invention. 1 and 2, the same parts as those in FIGS. 3 and 4 are denoted by the same reference numerals. Further, in this embodiment, it is assumed that the DQPSK modulation method is applied to a transmission rate of 40 Gbps, as in the prior art.

  Referring to FIG. 1, the transmission apparatus according to this embodiment includes a transmission side framer circuit 10, a channel (CH) separation circuit 11, a synchronization pattern / CH (channel) number insertion circuit 12, a DQPSK precoder circuit 13, and a P / S circuit and CMU circuit 14, light source 20, and LN modulator 21. The LN modulator 21 includes a DQPSK modulation circuit 211 and an RZ pulse cover circuit 212 as in the example of FIG.

  The operation of the transmission apparatus having such a configuration will be described. In the transmission side framer circuit 10, as a logical signal sent to the transmission path, G.P. 707 / G. The STM signal / OTN signal defined in 709 is generated. In the channel separation circuit 11, the STM signal / OTN signal is separated into two channels corresponding to 20 Gbps. The synchronization pattern insertion circuit / CH number insertion circuit 12 inserts a synchronization pattern indicating a frame delimiter and a channel pattern for identifying a channel number into the separated two-channel signals.

  In the DQPSK precoder circuit 13, a signal suitable for driving the LN modulator 21 is generated from the signal input from the synchronization pattern / CH number insertion circuit 12. The P / S circuit and the CMU circuit 14 generate a plurality of high-speed data signals and high-speed clock signals from the precoded signal and the low-speed clock signal. In this example, in order to perform 40 Gbps RZ-DQPSK modulation, two 20 Gbps data signals and one 10 GHz clock signal are respectively generated.

  The light source 20 generates a CW optical signal that is a transmission carrier. The LN modulator 21 converts the CW light into four-valued (0, π / 2, π, 3π / 2) DQPSK based on the high-speed data signal and the high-speed clock signal generated by the P / S circuit and the CMU circuit 14. The optical signal 22 is modulated and transmitted to the optical transmission line. The symbol rate sent to the transmission line is 20 Gsymbol / s in 40 Gbps QPSK modulation.

  Next, the receiving apparatus will be described with reference to FIG. The receiving apparatus includes an optical branching unit 31, a 1 symbol + π / 4 delay interferometer 32, a 1 symbol−π / 4 delay interferometer 33, differential receiver circuits 34 and 35, CDR circuits 36 and 37, S / P circuits 38 and 39, synchronization circuit / CH number identification circuits 40 and 41, an elastic store 42, a read phase determination circuit 43, and a reception side framer circuit 44 are configured.

  The operation of the receiving apparatus having such a configuration will be described. The DQPSK optical signal 30 received from the optical transmission path is branched into two by an optical branching unit 31 and input to a 1 symbol + π / 4 delay interferometer 32 and a 1 symbol−π / 4 delay interferometer 33, respectively. In the differential receiver circuit 34, an electrical signal is regenerated from the two optical signals output from the 1 symbol + π / 4 delay interferometer 32. Similarly, in the differential receiver circuit 35, an electrical signal is regenerated from the two optical signals output from the 1 symbol-π / 4 delay interferometer 33.

  The 20 Gbps electrical signal regenerated by each differential receiver is input to CDR circuits 36 and 37, respectively, where clock recovery is performed by the CDR circuit and data signal retiming is performed. In the S / P circuits 38 and 39, the two re-timed 20 Gbps data signals are respectively subjected to S / P conversion in two systems (two channels). The signal subjected to S / P conversion for each channel is frame-synchronized by the synchronization circuit / CH number identification circuits 40 and 41, and the channel number is recognized. At this time, the extracted frame phase information and channel number are passed to the read phase determination circuit 43.

  In the elastic store 42, the two-channel signals output from the synchronization circuit / CH number identification circuit are switched to one system clock. Changing the clock of one system of the elastic store 42 is performed based on information from the read phase determining circuit 43. The signal transferred to one system clock becomes a 40 Gbps signal converted in parallel. In the receiving side frame circuit 44, various signal processing is performed on the STM / OTN signal.

  On the receiving device side, it is necessary to transfer two 20 Gbps data signals to one clock. This transfer process to the clock is performed by the elastic store 42, and the operation of the elastic store 42 is performed by various signal processes using a low-speed clock (150 MHz clock in this example). In FIG. 2, high-speed signal processing with a 20 GHz clock is required only for the region of the chain line 50. In this area 50, CDR processing and S / P conversion processing of 20 Gbps data are performed, but processing is performed independently for each system (channel) for two systems (two channels) of 20 Gbps data. .

  The clock transfer process on the receiving apparatus side shown in FIG. 2 is performed only with the low-speed clock, and in this example, the operation speed is 150 MHz, and the operating speed of the elastic store 42 is 150 MHz. In other words, high-speed signal processing for clock transfer processing becomes unnecessary. In addition, in the region indicated by the chain line 50 in FIG. 2, S / P conversion processing is individually performed for one system (channel) for two systems (two channels) of 20 Gbps data. There is an effect that the phase management within the 20 G clock period (50 ps) in the conversion circuits 38 and 39 becomes unnecessary.

  For example, for two types of 20 Gbps data, even if one S / P processing delay causes a delay variation of 20 GHz clock period (50 ps) or more for the other data, the memory capacity exceeds the delay variation. Is provided in the error stitcher 42, it is possible to align the phase of the signal between the two channels. That is, there is an effect that there may be delay variation in signal processing in the high-speed S / P conversion circuits 38 and 39. These effects facilitate the realization of a transmission / reception device for multilevel phase modulation.

  As another embodiment of the present invention, the basic configuration is as described above. In this example, the synchronization pattern / CH number insertion circuit 12 is provided on the transmission device side. However, for example, when using an OTN signal in which multiframe phase overhead is defined, the multiframe overhead is used as the channel number. Thus, the present invention can be applied to a configuration without the channel number insertion circuit 12.

It is a block diagram of the transmission apparatus of the Example of this invention. It is a block diagram of the receiver of the Example of this invention. It is a block diagram of the conventional transmitter. It is a block diagram of the conventional receiver.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Transmission side framer circuit 11 CH separation circuit 12 Synchronization pattern / CH number insertion circuit 13 DQPSK precoder circuit 14 P / S circuit and CMU circuit 20 Light source 21 LN modulation circuit 31 Optical branching unit 32 1 symbol + π / 4 delay interferometer 33 1 Symbol-π / 4 delay interferometer 34, 35 Differential receiver circuit 36, 37 CDR circuit 38, 39 S / P circuit 40, 41 Synchronization circuit / CH identification circuit 42 Elastic store 43 Read phase determination circuit 34 Reception side framer circuit

Claims (6)

A multi-level phase modulation optical transmission system,
A first means for separating a transmission-side framer circuit output signal into first and second channels and inserting a frame synchronization pattern and channel identification information into the separated signals; and an output of the first means A second means for converting the signal into a multi-system signal having a speed suitable for the optical transmission path; and the optical transmission path by performing multi-level phase modulation processing on the optical signal based on the multi-system signal of the second means. A transmission device having a third means for transmitting to,
A fourth means for branching the multi-level phase-modulated optical signal from the optical transmission line into the plurality of systems and performing photoelectric conversion on each of the branch outputs; and for each of the outputs of the fourth means, Fifth means for converting to the first and second channel signals having the same speed as the signal speed of the first and second channels, and the frame synchronization pattern for each of the outputs of the fifth means. A sixth means for performing frame synchronization and identification of the channel identification information, and a seventh means for performing a process of transferring the first and second channel signals to a single clock based on the identification information obtained by the sixth means. An optical transmission system comprising: a receiving device having:   2. The optical transmission system according to claim 1, wherein a multi-frame overhead of an OTN signal is used instead of the channel identification information. A multi-value phase modulation optical transmission method,
In the transmission device,
A first step of separating a transmission side framer circuit output signal into first and second channels and inserting a frame synchronization pattern and channel identification information into the separated signals, and an output of the first step A second step of converting the signal into a multi-system signal having a speed suitable for the optical transmission line; and the optical transmission line is subjected to multilevel phase modulation processing based on the multi-system signal of the second step. A third step of sending to
In the receiving device,
A fourth step of branching the multi-level phase-modulated optical signal from the optical transmission path into the plurality of systems and performing photoelectric conversion on each of the branch outputs; and for each of the outputs of the fourth step The frame synchronization pattern is used for each of the fifth step of converting to the first and second channel signals having the same speed as the signal rates of the first and second channels and the output of the fifth step. A sixth step of performing frame synchronization and identification of the channel identification information, and a seventh step of performing a process of transferring the first and second channel signals to a single clock based on the identification information obtained in the sixth step. An optical transmission method comprising the steps of:   4. The optical transmission method according to claim 3, wherein a multiframe overhead of an OTN signal is used instead of the channel identification information. A transmission device in a multi-level phase modulation optical transmission system,
A first means for separating a transmission-side framer circuit output signal into first and second channels and inserting a frame synchronization pattern and channel identification information into the separated signals; and an output of the first means A second means for converting the signal into a multi-system signal having a speed suitable for the optical transmission path; and the optical transmission path by performing multi-level phase modulation processing on the optical signal based on the multi-system signal of the second means. And a third means for sending to the transmitter. The transmission side framer circuit output signal is separated into the first and second channels, the frame synchronization pattern and the channel identification information are inserted into the separated signal, and the output signal is transmitted at a speed suitable for the optical transmission line. A multi-level phase modulation type optical transmission system that converts the multi-system signal into a multi-level signal, multi-level phase-modulates the optical signal based on the multi-line signal, and sends it to the optical transmission line. ,
A first means for branching the multi-level phase modulated optical signal into the plurality of systems and performing photoelectric conversion on each of the branch outputs; and the first and second for each of the outputs of the first means. Third means for converting the first and second channel signals at the same speed as the signal speed of the channel, frame synchronization using the frame synchronization pattern for each of the outputs of the third means, and the A fourth means for identifying channel identification information; and a fifth means for performing a process of transferring the first and second channel signals to a single clock based on the identification information obtained by the four means. A receiving apparatus.

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