JP2016019030A - Optical communication system, optical communication method, and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical communication system, an optical communication method, and a device that are reliable and can avoid a synchronization error even if a transmission path is long in transmission distance and large in cumulative wavelength dispersion.SOLUTION: An optical communication system transmits a signal frame including at least an overhead region and a payload region (204), and performs frame synchronization using a synchronization signal pattern (201) provided in the overhead region. At a transmission side, average optical intensity of the synchronization signal pattern (201) in the overhead region is set smaller than average optical intensity in the payload region. Alternatively, a prescribed region (202, 203) surrounding the synchronization signal pattern is provided, and average optical intensity in the prescribed region is set smaller than the average optical intensity in the payload region.SELECTED DRAWING: Figure 6

Description

  The present invention relates to an optical communication system, and more particularly to an optical communication method and an optical communication apparatus in an optical communication system that performs frame synchronization using a synchronization signal pattern.

  In response to an increase in communication traffic in recent years, introduction of a WDM (Wavelength Division Multiplexing) optical communication system for increasing capacity is also being promoted in backbone long-distance networks. The transmission speed of this WDM optical communication system is realized at 100 Gbps or more per wavelength by digital coherent technology. In a WDM optical communication system, FEC (Forward Error Correction) for correcting a code error occurring in a transmission path is used, and a signal frame in which a correction bit (FEC overhead) is added to a client signal is used.

  For example, an OTU (Optical channel Transport Unit) frame (here, an OTUk (V) frame) as shown in FIG. 1 is standardized by ITU-T, which is a standardization organization related to optical communication (see Non-Patent Document 1). The OTU frame includes a payload (PLD: Payload) in which a client signal is arranged, an overhead (OH: Over Head) in which information necessary for maintenance control is arranged, and an FEC overhead (FEC_OH) for error correction. FEC_OH can be added according to the redundancy of FEC.

  In order to correctly receive such an OTU frame, “frame synchronization” is required to correctly find the head of the frame before error correction by FEC. For this purpose, an FAS (Frame Alignment Signal) for frame synchronization is arranged at the head of the overhead OH. Details of the overhead OH are shown in FIG.

  As shown in FIG. 2, the FAS is a fixed signal pattern in which the signal pattern “1101 0110” continues three times, and then the signal pattern “0010 1000” continues three times. Frame synchronization is performed by detecting FAS on the receiving device side. Further, a 1-byte MFAS (MultiFrame Alignment Signal) is arranged following the FAS. This MFAS value is incremented for each frame, and indicates the number of the multiframe. As shown in FIG. 3, the FAS and the MFAS are arranged at the head of a frame of one lane, and the lanes can be identified by rotating the lane for each frame.

  As described above, since frame synchronization is executed before error correction by FEC, it is executed for a signal having a large number of code errors before error correction. For this reason, in a WDM optical communication system, there is a method of shortening the length of a signal pattern (synchronization signal pattern) detected by frame synchronization or allowing a part of a code error when detecting a synchronization signal. To achieve error tolerance equivalent to FEC (see Patent Document 1).

Japanese Patent No. 4964927

ITU-T Recommendation G. 709 / Y. 1331, Interfaces for the Optical Transport Network (February 2012)

  However, in optical transmission through a long-distance optical fiber transmission line, chromatic dispersion of the optical signal transmitted over a long distance accumulates, and the signal pulse spreads on the time axis. Due to this spread, the signals before and after on the time axis are mutually subjected to deterioration due to phase noise (nonlinear distortion) due to the nonlinearity of the optical fiber, and a burst error in which many errors are concentrated in a short section is generated. If this burst error causes a code error larger than that allowed for the synchronization signal pattern, frame synchronization may fail and communication may not be possible. For example, in a WDM optical communication system using a long-distance optical fiber such as an optical submarine cable, it is known that communication cannot be performed due to such frame synchronization failure.

  Accordingly, an object of the present invention is to provide a highly reliable optical communication system, optical communication method, and apparatus capable of avoiding a synchronization error even in a transmission line having a long transmission distance and a large cumulative chromatic dispersion.

An optical communication system according to the present invention transmits a signal frame including at least an overhead region and a payload region, and performs frame synchronization using a synchronization signal pattern provided in the overhead region. An average light intensity of the synchronization signal pattern is set smaller than an average light intensity of the payload area.
In the optical communication system according to the present invention, on the transmission side, a predetermined area surrounding the synchronization signal pattern is provided in the overhead area, and at least the average light intensity of the predetermined area is set smaller than the average light intensity of the payload area. It is characterized by.
An optical communication apparatus according to the present invention is an optical communication apparatus in an optical communication system that transmits a signal frame including at least an overhead area and a payload area and performs frame synchronization using a synchronization signal pattern provided in the overhead area. A signal frame generation means for generating the signal frame; and an optical transmission means for setting the average light intensity of the synchronization signal pattern to be smaller than the average light intensity of the payload area and transmitting the signal frame as an optical signal. It is characterized by having.
The optical communication apparatus according to the present invention includes a signal frame generating means for generating a signal frame in which a predetermined area surrounding the synchronization signal pattern is provided in the overhead area, and at least the average light intensity of the predetermined area is determined as the average light of the payload area. And an optical transmission unit configured to transmit the signal frame as an optical signal by setting it smaller than the intensity.
An optical communication method according to the present invention transmits a signal frame including at least an overhead region and a payload region from a transmission device to a reception device, and performs frame synchronization using a synchronization signal pattern provided in the overhead region. An optical communication method according to claim 1, wherein the transmitting device sets an average light intensity of the synchronization signal pattern to be smaller than an average light intensity of the payload area.
In the optical communication method according to the present invention, the transmitter generates a signal frame in which a predetermined area surrounding the synchronization signal pattern is arranged in the overhead area, and the average light intensity of the predetermined area is determined as the average light intensity of the payload area. The signal frame is transmitted as an optical signal with a smaller setting, and the receiving apparatus receives the signal frame, performs frame synchronization using the synchronization signal pattern, and deletes the predetermined area from the overhead area. And terminating the signal frame.

  As described above, according to the present invention, the average light intensity of the synchronization signal pattern is set to be smaller than the average light intensity of the payload area, or at least the average light intensity of the predetermined area surrounding the synchronization signal pattern is set in the payload area. By setting it smaller than the average light intensity, it is possible to realize a highly reliable optical communication system, optical communication method and apparatus capable of avoiding a synchronization error even in a transmission line having a long transmission distance and a large cumulative chromatic dispersion.

FIG. 1 is a frame configuration diagram showing an OTUk (V) frame standardized by ITU-T. FIG. 2 is a more detailed configuration diagram of the overhead in the OTUk (V) frame. FIG. 3 is a schematic frame configuration diagram showing the rotation of the FAS in the OTUk (V) frame. FIG. 4 is a system configuration diagram showing an example of an optical communication system used in the embodiment of the present invention. FIG. 5 is a block diagram showing the configuration of the optical communication apparatus according to the first embodiment of the present invention. 6A is a diagram illustrating an example of a signal frame configuration used in the first embodiment, and FIG. 6B is a diagram schematically illustrating a change in average light intensity in a predetermined region including a synchronization signal pattern. is there. FIG. 7 is a block diagram showing the configuration of the optical communication apparatus according to the second embodiment of the present invention. FIG. 8A is a diagram illustrating an example of a signal frame configuration used in the second embodiment, and FIG. 8B is a diagram schematically illustrating a change in average light intensity of the synchronization signal pattern. FIG. 9 is a block diagram showing the configuration of the optical communication apparatus according to the third embodiment of the present invention. FIG. 10 is a diagram illustrating an example of a signal frame configuration used in the third embodiment. FIG. 11 is a signal point arrangement diagram showing an example of symbols mapped as 0 signals in the third embodiment. FIG. 12 is a block diagram showing the configuration of the optical communication apparatus according to the fourth embodiment of the present invention. FIG. 13 is a signal point arrangement diagram showing an example of symbols mapped as 0 signals in the fourth embodiment. FIG. 14 is a diagram showing an example of a signal frame configuration used in the fifth embodiment of the present invention. FIG. 15 is a block diagram showing the configuration of the optical communication apparatus according to the sixth embodiment of the present invention. FIG. 16 is a diagram illustrating a fixed pattern deterioration state after long-distance transmission for explaining the operation of the optical communication apparatus according to the sixth embodiment. FIG. 17 is a block diagram showing the configuration of the optical communication apparatus according to the seventh embodiment of the present invention. FIG. 18 is a diagram showing a frame configuration before synchronization of signal frames used in the seventh embodiment. FIG. 19 is a diagram showing a frame configuration after synchronization of signal frames used in the seventh embodiment. FIG. 20 is a diagram showing a synchronization bit value with respect to the operation state of the seventh embodiment.

<Outline of Embodiment>
According to an embodiment of the present invention, in an optical communication system using a signal frame including at least an overhead region and a payload region, the average light intensity of a synchronization signal pattern arranged in the overhead region of the signal frame is calculated as an average of the payload region. Set smaller than light intensity. Alternatively, at least the average light intensity of a predetermined area surrounding the synchronization signal pattern is set smaller than the average light intensity of the payload area. For example, a block having a low average light intensity is arranged at least in the area before and after the synchronization signal pattern on the time axis or in the surrounding area. Further, the average light intensity of the synchronization signal pattern itself may be set smaller than the average light intensity of the payload area.

  In this way, by reducing the average light intensity of the synchronization signal pattern, or at least the average light intensity of a predetermined region arranged so as to surround the synchronization signal pattern, nonlinear distortion of the synchronization signal pattern can be reduced. As a result, synchronization errors due to burst errors can be avoided. As a result, a stable optical communication system free from synchronization errors can be realized even on a transmission line having a long transmission distance and a large cumulative chromatic dispersion. An example of an optical communication system to which the embodiment of the present invention is applied is shown in FIG.

<System configuration>
In FIG. 4, the optical communication system includes an optical transmission system 11 and a pair of client devices 12A and 12B connected thereby, and the optical transmission system 11 includes a pair of optical communication devices 13A and 13B and a transmission path 14 connecting them. Shall be composed. Since each of the optical communication devices 13A and 13B has the same configuration, hereinafter, when the optical communication devices 13A and 13B are not distinguished from each other, they are referred to as “optical communication device 13”. Similarly, the client devices 12A and 12B are described as “client device 12” when they are not distinguished.

  As will be described later, in the transmission system of the optical communication device 13, when generating a signal frame, control is performed to reduce the average light intensity by providing a predetermined region surrounding the synchronization signal pattern. The transmission line 14 includes N (N is 1 or more) spans, and each span includes an optical fiber 15 and an optical amplifier 16 for compensating for loss in the optical fiber 15. Accordingly, by connecting a plurality of spans, long-distance bidirectional communication is possible between the client apparatuses 12A and 12B. The transmission line 14 may be serial transmission as shown in FIG. 4 or parallel transmission.

  Hereinafter, exemplary embodiments of the present invention will be described in detail by way of example. However, the components described in the following embodiments are merely examples, and are not intended to limit the technical scope of the present invention only to them.

1. First Embodiment An optical communication apparatus according to a first embodiment of the present invention provides a predetermined area surrounding a synchronization signal pattern provided at the head of a management control overhead, and calculates the average light intensity as the average light intensity of a payload area. Lower than. For example, the average light intensity of the blocks added at least before and after the synchronization signal pattern on the time axis is reduced. The average light intensity is the light intensity per unit time. Hereinafter, the first embodiment will be described in detail with reference to FIGS. 5 and 6.

1.1) Optical Communication Device As shown in FIG. 5, the optical communication device 13 includes a transmission system including a signal frame generation unit 101, a D / A conversion unit 102, and an optical transmitter 103, an optical receiver 104, A / A reception system including a D conversion unit 205 and a signal frame termination unit 106; and a control unit 107 that controls the transmission system and the reception system. The signal frame generation unit 101 includes an FEC encoding unit 111, a synchronization control unit 112, and a 0 signal addition unit 113. The signal frame termination unit 106 includes a synchronization control unit 121, an FEC decoding unit 122, and a 0 signal. A deletion unit 123 is provided.

  As shown in FIG. 6A, in the signal frame generated by the signal frame generation unit 101, 0 signal blocks 202 and 203 are arranged at positions before and after the synchronization signal pattern 201 in time. Following this, the payload 204 and the FEC overhead 205 are arranged. Here, an area composed of the 0 signal block 202 and the 0 signal block 203 is a predetermined area sandwiching a synchronization signal pattern of the management control overhead.

  The 0 signal blocks 202 and 203 are preferably immediately before and after the time axis on which the synchronization signal pattern 201 is arranged. This is because the signals immediately before and after affect the synchronization signal pattern 201 from a short distance, and thus the accumulation of signal degradation due to nonlinear distortion is large. However, if the size of the 0 signal blocks 202 and 203 is set too long, the signal transmission efficiency is lowered. In order to secure the necessary transmission amount, it is necessary to increase the transmission speed accordingly, and the demand for optical / electronic devices becomes severe, and the cost increases. Therefore, it is necessary to determine an appropriate size of the 0 signal block in consideration of a trade-off between reducing the influence of nonlinear distortion and ensuring transmission efficiency. For example, the size of the 0 signal blocks 202 and 203 can be about 2% of the frame length, and they can be arranged immediately before and after the synchronization signal pattern 201.

1.2) Operation The signal frame generator 101 of the transmission system divides the client signal from the client device 12 and puts it in the payload 204 of the signal frame. In each signal frame, the FEC encoding unit 111 adds an FEC overhead 205 for error correction, and the synchronization control unit 112 adds a synchronization signal pattern 201 for cueing a frame. Then, the 0 signal adding unit 113 adds 0 signal blocks 202 and 203 before and after the synchronization signal pattern 201.

  The signal frame shown in FIG. 6A generated in this manner is sequentially read from the first bit, converted into an analog signal by the D / A converter 102, and transmitted as an optical signal through the transmission line 14 by the optical transmitter 103. The At that time, as shown in FIG. 6B, the optical transmitter 103 averages the light intensities of the 0 signal blocks 202 and 203 transmitted to the transmission line 14 over the light intensities of the payload 204 and the FEC overhead 205. Set a small value (for example, light intensity 0). Furthermore, the light intensity of the synchronization signal pattern 201 transmitted to the transmission line 14 may be set to be smaller than the light intensity of the payload 204 and the FEC overhead 205 on average. Since the synchronization signal pattern 201 needs to be detected on the receiving side, it is desirable that the average light intensity of the synchronization signal pattern 201 is different from the average light intensity of the zero signal blocks 202 and 203. For example, the average light intensity of the synchronization signal pattern 201 is set so that the nonlinear distortion of the synchronization signal pattern 201 itself is small and the deterioration of the signal band noise ratio (S / N) on the reception side is not large. The average light intensity of the 0 signal blocks 202 and 203 may be set so that nonlinear distortion from signals before and after the synchronization signal pattern 201 can be reduced, and the amplitude can be set to 0.

As an example, in FIG. 6B, the average light intensity when transmitting the 0 signal block 202, the synchronization signal pattern 201 and the 0 signal block 203 transmitted to the transmission line 14 is expressed as the average light of the payload 204 and the FEC overhead 205. It can be set to a level smaller than the intensity I _REF . For example, only the average light intensity when transmitting the 0 signal blocks 202 and 203 can be set to a level I _L1 smaller than the average light intensity I _REF . Further, the average light intensity when transmitting the 0 signal blocks 202 and 203 is set to the level I _L1 , and the average light intensity when transmitting the synchronization signal pattern 201 is larger than the level I _{L1 and} higher than the level I _REF . You may set to small level _IL2 . However, the level I _L2 of the synchronization signal pattern 201 in this case needs to be able to detect the synchronization signal pattern 201 on the receiving side without significant deterioration of the S / N.

  As described above, the reduction of the average light intensity in a predetermined area composed of the 0 signal block 202, the synchronization signal pattern 201, and the 0 signal block 203 is performed by changing the symbol of the predetermined area to I (in-phase) -Q (quadrature-phase). It may be realized by mapping to a signal point having a small amplitude in the signal point arrangement diagram. Alternatively, the symbols of the 0 signal block 202 and the 0 signal block 203 can be mapped to signal points having an amplitude of 0. Further, the transmission light intensity of the optical transmitter 103 may be reduced at the transmission timing of these transmission bits.

  The optical signal that has reached through the transmission path 14 is converted into a digital signal by the optical receiver 104 and the A / D converter 105. The signal frame termination unit 106 transmits the client signal to the client device 12 by terminating the signal frame. More specifically, the synchronization control unit 121 detects the synchronization signal pattern 201 from the received bit string and cues the frame. As described above, since the average light intensity of the synchronization signal pattern 201 at transmission and the average light intensity of the 0 signal blocks 202 and 203 are reduced, the nonlinear distortion of the synchronization signal pattern 302 itself and the synchronization signal pattern 201 are reduced. As a result, the nonlinear distortion from the signals before and after becomes smaller, and the correct frame can be found. Subsequently, the FEC decoding unit 122 performs error correction using the payload 204 and the FEC overhead 205, and the 0 signal deletion unit 123 deletes the 0 signal blocks 202 and 203. In this way, the client signal in the payload 204 is transmitted to the client device 12.

1.3) Effect As described above, according to the first embodiment of the present invention, the synchronization signal pattern is reduced by reducing the average light intensity of the blocks added at least before and after the synchronization signal pattern on the time axis. Non-linear distortion due to the influence of the signals before and after is reduced, and synchronization errors due to burst errors can be effectively avoided. Furthermore, by reducing the average light intensity of the synchronization signal pattern itself, nonlinear distortion of the synchronization signal pattern itself can be reduced, and synchronization errors due to burst errors can be more effectively avoided.

2. Second Embodiment The optical communication apparatus according to the second embodiment of the present invention reduces the average light intensity of the synchronization signal pattern provided at the head of the management control overhead to be lower than the average light intensity of the payload area. Hereinafter, the second embodiment will be described in detail with reference to FIGS. 7 and 8.

  As shown in FIG. 7, the optical communication device 13 has a configuration in which the 0 signal adding unit 113 and the 0 signal deleting unit 123 are excluded from the configuration of the first embodiment, and in a signal frame configuration different from that of the first embodiment. The difference is that control is performed to reduce the average light intensity of only the synchronization signal pattern. Since the other configuration is the same as that of the first embodiment, the same reference numerals are given and description thereof is omitted.

  As shown in FIG. 8A, in the signal frame generated by the signal frame generation unit 101, the payload 204 and the FEC overhead 205 are arranged following the synchronization signal pattern 201. As shown in FIG. 8B, the optical transmitter 103 sets the light intensity of the synchronization signal pattern 201 transmitted to the transmission line 14 to be smaller than the light intensity of the payload 204 and the FEC overhead 205 on average. For example, the average light intensity of the synchronization signal pattern 201 is set so that the nonlinear distortion of the synchronization signal pattern 201 itself is small and the deterioration of the signal band noise ratio (S / N) on the reception side is not large.

As an example, in FIG. 8B, the average light intensity when transmitting the synchronization signal pattern 201 transmitted to the transmission line 14 is set to a level smaller than the average light intensity I _REF of the payload 204 and the FEC overhead 205. be able to. For example, the average light intensity when transmitting the synchronization signal pattern 201 is set to a level I _L2 that is smaller than the level I _REF . However, the level I _L2 of the synchronization signal pattern 201 in this case needs to be able to detect the synchronization signal pattern 201 on the receiving side without significant deterioration of the S / N.

  As described above, according to the second embodiment of the present invention, by reducing the average light intensity of the synchronization signal pattern itself, the nonlinear distortion of the synchronization signal pattern itself is also reduced, and synchronization errors due to burst errors are further reduced. It can be effectively avoided.

3. Third Embodiment An optical communication apparatus according to a third embodiment of the present invention is applied to a multilane transmission system, and is provided with a multilane distribution function in a transmission system and a multilane combination function in a reception system. In multi-lane transmission, in order to reduce nonlinear distortion due to the influence of signals other than the synchronization signal pattern, the average light intensity of a predetermined area surrounding the synchronization signal pattern is made lower than the average light intensity of the payload area. Specifically, not only the 0 signal block is added before and after the time axis, but the 0 signal block is also arranged in an area corresponding to a lane different from the lane of the synchronization signal pattern. Furthermore, in order to reduce nonlinear distortion of the synchronization signal pattern itself, the average light intensity of the synchronization signal pattern can be reduced.

In the third embodiment, it is assumed that polarization multiplexing (DP) -multilevel QAM (Quadrature Amplitude Modulation) is used as a modulation method of the multilane transmission system. As an example, DP-16QAM of 200 Gbps is adopted, and in this case, there are four physical lanes used in multilane transmission:
1) X polarization I channel 2) X polarization Q channel 3) Y polarization I channel and 4) Y polarization Q channel.
That is, the optical signal consisting of the four lanes (channels) propagates in one optical fiber.

  Further, the transmission line 14 can be transmitted over a long distance by connecting a plurality of pure silica core fibers (PSCF), for example. PSCF is suitable for long-distance fiber transmission because of its low loss, large effective cross-sectional area of the core, and low nonlinear distortion. For example, a long distance transmission system of 6000 km can be realized by connecting 100 km of 60 km PSCF. However, the transmission path is not limited to the PSCF transmission path, and a transmission path using other fibers can also be used. Hereinafter, the third embodiment will be described in detail with reference to FIGS. 9 to 11.

3.1) Optical Communication Device As shown in FIG. 9, the optical communication device 13 according to the third embodiment includes a frame generation unit 301, a multilane distribution unit 302, a D / A conversion unit 303, and an optical transmitter 304. And a reception system including an optical receiver 305, an A / D conversion unit 306, a multilane combination unit 307, and a frame termination unit 308.

  The transmission frame generator 301 includes an FEC encoder 311 and a synchronization controller 312 and generates a signal frame. In the present embodiment, the signal frame is an OTUk (V) frame shown in FIGS. 1 to 3 and can accommodate signals such as Ethernet (registered trademark, the same applies hereinafter).

  The multi-lane distribution unit 302 includes a 0 signal addition unit 313, and first distributes the OTUk (V) frame to the four lanes described above. Subsequently, as described later, the 0 signal adding unit 313 arranges the 0 signal block so as to surround the synchronization signal pattern of the OTUk (V) frame. The overhead information of the area where the 0 signal block is arranged is transferred to the subsequent area. The multi-lane distribution unit 302 outputs the OTUk (V) frame distributed to the lanes and added with the 0 signal block to the four D / A converters # 1 to # 4 of the D / A conversion unit 303, respectively. The transmission signal of each lane converted into an analog signal by the D / A converters # 1 to # 4 is transmitted through the transmission line 14 as an optical signal by the optical transmitter 304.

  The optical receiver 305 of the receiving system converts the optical signals of the four lanes that have arrived through the transmission path 14 into electric signals, and the four A / D converters of the A / D converter 10 respectively corresponding to the four physical lanes. # 1 to # 4 convert the received electrical signal into a digital signal corresponding to each lane.

  The multilane combining unit 307 includes a synchronization control unit 314 and a 0 signal deletion unit 315. First, the synchronization control unit 315 detects the synchronization signal pattern 201 from the received bit string, cues the frame, combines the digital signals of the four lanes, and then the 0 signal deletion unit 314 replaces the 0 signal blocks 401 to 403 with each other. The existing OTUk (V) frame is deleted and output to the frame termination unit 308.

  The frame termination unit 308 includes an FEC decoding unit 316, performs FEC processing using the FEC overhead, and transmits a client signal to the client device 12 by terminating the OTUk (V) frame.

3.2) Operation The frame generator 301 of the transmission system divides the client signal from the client device 12 and puts it in the payload of the OTUk (V) frame. In the OTUk (V) frame, the FEC encoding unit 311 adds an FEC overhead for error correction, and the synchronization control unit 312 adds a synchronization signal pattern 201 made up of FAS and MFAS for frame cueing. For example, FAS and MFAS are in lane 1 and are arranged at the head of the frame. In order to identify the lanes, the FAS and MFAS lanes are rotated for each frame as shown in FIGS.

  Subsequently, the multi-lane distribution unit 302 distributes the OTUk (V) frame to each lane, and the 0 signal addition unit 313 inserts 0 signal blocks 401 to 403 around the FAS and the MFAS in the OTUk (V) frame. Distribution to each lane is performed every 16 bytes, which is the minimum unit of the OTUk (V) frame. FIG. 10 shows the configuration of the overhead OH in the OTUk (V) frame generated in this way.

  In FIG. 10, 0 signal blocks 401 and 402 are added at positions before and after the synchronization signal pattern 201, and also in the other lanes 2 to 4 without the synchronization signal pattern 201, A 0 signal block 403 is arranged in an area corresponding to the 0 signal blocks 401 and 402. The ODUk overhead data in the area of the 0 signal block 403 is moved to the subsequent area 404, and the original OTUk overhead, ODUk overhead, and OPUk overhead are arranged after the ODUk overhead 404 after the movement. Here, an area composed of the 0 signal blocks 401 to 403 is a predetermined area surrounding the synchronization signal pattern (or adjacent to the synchronization signal pattern). As described above, any signal in other lanes 2 to 4 that propagates through the same optical fiber affects the synchronization signal pattern 201 arranged in one lane. Therefore, when the synchronization signal pattern 201 is transmitted, the 0 signal block 403 is transmitted simultaneously in the lanes 2 to 4.

  In this embodiment, since multilane transmission is used, FAS and MFAS are used for the synchronization signal pattern 201. The MFAS is arranged after the FAS, and the numbers 0 to 255 are sequentially assigned as described in FIG. In multi-lane transmission, it is necessary to distribute a frame to a plurality of lanes using FAS or MFAS, and to correctly identify and recombine each lane on the receiving side.

  The signal distributed for each lane is transmitted by the D / A converter 303 and the optical transmitter 304 using the above-described four physical lanes 1) to 4). That is, the signal distributed to lane 1 is to the X polarization I channel, the signal distributed to lane 2 is to the X polarization Q channel, the signal distributed to lane 3 is to the Y polarization I channel, and to lane 4 The distributed signal is transmitted through the Y polarization Q channel.

  The optical transmitter 304 sets the average light intensity of the 0 signal blocks 401 to 403 transmitted to the transmission path 14 to be smaller than the average light intensity of the payload and the FEC overhead. Further, the average light intensity of the synchronization signal pattern 201 transmitted to the transmission line 14 may be set smaller than the average light intensity of the payload and the FEC overhead. The average light intensity of the synchronization signal pattern 201 and the average light intensity of the zero signal blocks 401 to 403 may be the same level or different levels. For example, the average light intensity of the 0 signal blocks 401 to 403 is set so that nonlinear distortion from signals around the synchronization signal pattern 201 can be reduced. The average light intensity of the synchronization signal pattern 201 is set so that the nonlinear distortion of the synchronization signal pattern 201 itself is reduced.

  The optical signal that has passed through the transmission path 14 is converted into a digital signal corresponding to each of the four physical lanes through the optical receiver 305 and A / D converters # 1 to # 4 of the A / D converter 306. The multi-lane combination unit 307 detects the synchronization signal pattern 201 by the synchronization control unit 314, identifies frame synchronization and lanes, and reconstructs frames based on the identification information. At this time, the 0 signal deletion unit 315 deletes the 0 signal blocks 401 to 403 arranged around the synchronization signal pattern 201 and returns the data of the moved ODUk overhead 404 to the original frame position.

  Finally, the frame termination unit 308 extracts a client signal from the received OTUk frame and transmits it to the client apparatus 12.

3.3) Signal pattern of 0 signal block As described above, the 0 signal adding unit 313 of the transmission system surrounds the FAS and MFAS (synchronization signal pattern 201) for frame synchronization and lane identification, 403 is inserted. The average light intensity in the 0 signal blocks 401 to 403 is reduced by mapping the symbol of the 0 signal block to a signal point having a small amplitude in the I (in-phase) -Q (quadrature-phase) signal point arrangement diagram. Can do.

  For example, in the case of 16QAM, as shown in FIG. 11, the signal pattern of the 0 signal blocks 401 to 403 in the present embodiment is set so as to be mapped only to four signal points A, B, C, and D having a small amplitude. The

  In FIG. 10, by adding 0 signal blocks 401 and 402 before and after the time axis on which the synchronization signal pattern 201 composed of FAS and MFAS is arranged, the synchronization signal pattern for the existing OTUk (V) frame. The influence of nonlinear distortion due to signals that should be placed before and after 201 can be suppressed. As described above, the 0 signal blocks 401 and 402 are preferably immediately before and after the time axis on which the FAS and MFAS are arranged. In consideration of the relationship between the size of the 0 signal blocks 401 and 402 and the signal transmission efficiency, for example, 96 bits corresponding to about 2% of the frame length can be used for the 0 signal blocks 401 and 402. Specifically, 48 bits are assigned to the 0 signal block 401 immediately before the FAS, and 48 bits are assigned to the 0 signal block 402 immediately after the MFAS. Furthermore, by arranging the 0 signal block 403 in another lane where no FAS or MFAS is arranged, the influence of nonlinear distortion from the other lane can be suppressed.

By arranging the 0 signal blocks 401 to 403 in this way, for example, even if Pin = 0 dBm where a synchronization error has occurred in a long distance transmission of 6000 km, no synchronization error or erroneous synchronization occurs, and the signal is conducted. Here, Pin is the input light intensity in each fiber span. Furthermore, in a wide Pin range from −2 dBm to 0 dBm, a Q margin as high as 2 dB or more (Q value indicating an index of digital signal quality—Q value that can be transmitted error-free by FEC (Q _limit )) is obtained. We were able to construct a highly stable optical communication system that is resistant to disturbances, including pin fluctuations (for Q values, see NS Bergano et al. “Margin measurement in optical amplifier systems” IEEE PTL, Vol. 5, No. 3, pp304-306 , 1993).

3.4) Effect As described above, according to the third embodiment of the present invention, in multi-lane transmission, a predetermined area surrounding the synchronization signal pattern is provided, and the average light intensity is lower than the average light intensity of the payload area. Let As a result, it is possible to reduce nonlinear distortion due to the influence of signals before and after the synchronization signal pattern and signals in lanes other than the lane of the synchronization signal pattern. Furthermore, by reducing the average light intensity of the synchronization signal pattern, the nonlinear distortion of the synchronization signal pattern itself can be reduced.

4). Fourth Embodiment An optical communication apparatus according to a fourth embodiment of the present invention performs multilane transmission according to the signal frame of FIG. 10 as in the second embodiment described above, but the modulation scheme is different. Then, DP-QPSK (Quadrature Phase Shift Keying) is used. Since all QPSK symbols have the same light intensity, there is no signal pattern using symbols with low light intensity as in the third embodiment. Therefore, in the present embodiment, the signal pattern of the 0 signal block is set so as to be mapped to the origin (amplitude 0) of the IQ signal point space. Hereinafter, differences from the third embodiment will be mainly described.

  As shown in FIG. 12, the transmission system of the optical communication apparatus 13 according to the present embodiment includes a timing control unit 505 in addition to the frame generation unit 501, the multilane distribution unit 502, the D / A conversion unit 503, and the optical transmitter 504. Have Other than the timing control by the timing control unit 505, the operation is basically the same as the operation of the transmission system of the third embodiment. Since the receiving system of the optical communication device 13 is the same as that of the second embodiment, the same reference numerals are given and the description thereof is omitted.

  The timing control unit 505 generates a timing signal at a frame period and outputs the timing signal to the frame generation unit 501 and the multilane distribution unit 502. However, the frame period in which the timing signal is generated is determined by the frame size generated by the frame generation unit 501 and the addition amount of the 0 signal block by the 0 signal addition unit 506. The frame generation unit 501 and the multilane distribution unit 502 configure the frame so that the head of the frame is arranged when the timing signal is generated.

  Furthermore, as shown in FIG. 10, the multi-lane distribution unit 502 inserts 0 signal blocks 401 and 402 sandwiching the synchronization signal pattern 201 for a predetermined time in accordance with the timing signal, and for a predetermined time in the other lanes. A zero signal block 403 is inserted and output to the DA converter 503. That is, the 0 signal block 401, the synchronization signal pattern 201, and the 0 signal block 402 are sequentially output to the D / A converter # 1 only in the lane 1 in which the synchronization signal pattern 201 composed of FAS and MFAS is arranged, and the others. In lanes 2 to 4, the 0 signal block 403 is inserted for the same time and output to the D / A converters # 2 to # 4 of the DA converter 503. Operations other than inserting the 0 signal block are the same as those in the second embodiment.

  As shown in FIG. 13, in this embodiment, DP-QPSK is used as a modulation method, so that all symbols have the same amplitude (light intensity). Therefore, the signal patterns of the 0 signal blocks 401 to 403 are set so as to be mapped to the origin (amplitude 0) of the IQ signal point space. Accordingly, the light intensity of the 0 signal patterns 401 to 403 in FIG. 10 becomes 0, and the signal deterioration of the synchronization signal pattern 201 due to the signals before and after the synchronization signal pattern 201 (FAS and MFAS) and the signal of another lane is effectively suppressed. be able to. In addition, even in an optical transmission system using a modulation method such as QPSK in which there is no difference in light intensity between symbols, it is possible to reduce the influence of nonlinear distortion.

  Further, the optical transmitter 504 may reduce the light intensity of the synchronization signal pattern 201 transmitted to the transmission path 14 in accordance with the timing signal of the timing control unit 505. If the light intensity of the signal pattern for synchronization is too small, the signal-to-noise ratio (S / N) deteriorates. For example, by reducing the light intensity by about 5%, burst due to nonlinear distortion more than the deterioration of S / N. Errors can be suppressed.

  As an example, when the optical communication device 13 according to the present embodiment is used in a 12000 km optical transmission system in which a pure silica core fiber (PSCF) 60 km is connected by 200 spans, frame synchronization and lane identification are normal, and disturbances including fluctuations in Pin are also caused. A strong optical communication system could be achieved.

5. Fifth Embodiment An optical communication apparatus according to a fifth embodiment of the present invention is applied to a multi-lane transmission system as in the third embodiment described above, but uses a synchronization signal pattern used for frame synchronization and lane identification. The newly prepared point is different. Since the basic configuration of the optical communication apparatus is the same as that of the third embodiment, the frame configuration used in the fifth embodiment will be described with reference to FIG. Note that FIG. 14 shows only the synchronization signal pattern and the 0 signal block, and the data arranged immediately after that may be the same as the OTU frame or may have another frame configuration.

  As shown in FIG. 14, synchronization signal patterns # 1 to # 4 corresponding to the lanes 1 to 4 to be used are prepared as the synchronization signal patterns 501, respectively. Here, as each synchronization signal pattern, as in the third embodiment, four symbols having a small amplitude among the 16QAM symbols shown in FIG. 11 are used. One symbol includes information for 4 bits. As an example, for the synchronization signal patterns # 1 and # 2, the symbol pattern “ABCABCD” is used among the four symbols shown in FIG. 11, and 2 bits of each symbol are used as the synchronization signal pattern # 1. The remaining 2 bits are used for the synchronization signal pattern # 2. Then, the pattern of “DBACCDBAC” is used for the synchronization signal patterns # 3 and # 4, and 2 bits of each symbol is used as the synchronization signal pattern # 3, and the remaining 2 bits are used as the synchronization signal pattern # 4. Use each one. Thus, four different signal patterns are prepared as synchronization signal patterns.

  Further, zero signal blocks 602 and 603 with a light intensity of 0 are arranged before and after the synchronization signal pattern 601 on the time axis in the same manner as in the fourth embodiment described above. In this embodiment, the size of the 0 signal blocks 602 and 603 is 64 bits.

  According to the present embodiment, four different signal patterns are used as synchronization signal patterns. Therefore, unlike existing lane identification using MFAS, lane identification can be performed using only signal patterns, and erroneous synchronization is unlikely to occur. .

  Furthermore, since the lane identification is completed simultaneously with the completion of the frame synchronization, the time until the synchronization is completed can be shortened. When frame synchronization is completed when the synchronization signal pattern matches twice, all synchronization can be completed in the shortest two frames. On the other hand, in the existing method, the synchronization signal pattern is arranged in only one lane per frame. Therefore, in addition to the frame synchronization time for two frames, the synchronization signal more than the number of lanes used for lane identification is used. Pattern analysis is required. Therefore, when 4 lanes are used, 6 frames are required. Therefore, according to the present embodiment, the synchronization is completed at a maximum three times faster than the existing method.

  As described above, according to the present embodiment, the 0 signal block having the light intensity of 0 is arranged before and after the synchronization signal pattern, thereby suppressing the signal deterioration of the synchronization signal pattern as in the fourth embodiment. can do. Also, according to the present embodiment, since synchronization is completed at high speed, it is possible to switch the optical path at high speed when a failure occurs, and a highly reliable and stable optical communication system can be realized.

  The 0 signal blocks 602 and 603 can use symbols with low light intensity as in the third embodiment. However, it is necessary to use a signal pattern different from the newly prepared synchronization signal patterns # 1 to # 4.

6). Sixth Embodiment An optical communication apparatus according to a sixth embodiment of the present invention performs multi-lane transmission according to the signal frame of FIG. 14 as in the fifth embodiment described above. The difference is that an error state of a signal pattern is detected, and whether or not synchronization processing (frame synchronization, lane identification) in the frame is controlled according to the error state. Hereinafter, differences from the fifth embodiment will be mainly described.

  In FIG. 15, the transmission system of the optical communication apparatus 13 according to the present embodiment includes a frame generation unit 701, a multilane distribution unit 702, a D / A conversion unit 703, and an optical transmitter 704, as in the third embodiment. The multi-lane distribution unit 702 has a 0 signal addition unit 313. Since the configuration and operation of the transmission system are the same as those in the third embodiment, description thereof is omitted.

  The reception system of the optical communication device 13 includes an optical receiver 705, an A / D conversion unit 706, a multilane coupling unit 707, a frame termination unit 708, and a control unit 709. The multilane coupling unit 707 includes lanes 1-4. Are provided with error detectors # 1 to # 4, a synchronization control unit 314 (not shown), and a zero signal deletion unit 314, respectively. The control unit 709 monitors the error state of the multilane combining unit 707 and instructs whether or not the synchronization processing of the multilane combining unit 707 can be performed according to the error state. Since other operations are the same as those of the third embodiment, the details are omitted.

  In multilane combining section 707, error detectors # 1 to # 4 receive synchronization signal patterns # 1 to # 4 transmitted simultaneously from A / D converters # 1 to # 4 of A / D conversion section 706, respectively. Input and count the number of code errors for each lane. The multilane combining unit 707 outputs the number of code errors for each lane to the control unit 709 as error state information.

  The control unit 709 determines whether to perform frame synchronization and lane identification based on the error state information, and outputs a synchronization processing permission instruction to the multi-lane combination unit 707. In this embodiment, when one or more code errors occur simultaneously in all lanes, control is performed so that frame synchronization and lane identification at that time are not performed. A specific example will be described with reference to FIG.

  Usually, in a transmission line with a high cumulative chromatic dispersion, code errors frequently occur in the synchronization signal pattern in all the lanes 1 to 4, and a synchronization error or erroneous synchronization is likely to occur. In the example shown in FIG. 16, in the frames of frame numbers 3, 5, 11, 13, and 19, code errors frequently occur in the received data of synchronization signal patterns # 1 to # 4 transmitted simultaneously in lanes 1 to 4. Yes. When such an error state is detected, the control unit 709 instructs the multi-lane combination unit 707 not to execute frame synchronization and lane identification in the frame.

  As described above, according to the present embodiment, it is possible to detect a code error occurrence state peculiar to a transmission line with a large accumulated chromatic dispersion, so that synchronization processing of a frame in which code errors occur frequently is not performed. Can be controlled. As a result, a synchronization error or erroneous synchronization can be avoided, and the synchronization completion time can be shortened by eliminating the need to perform synchronization processing again.

  Furthermore, according to the present embodiment, there is an advantage that frame synchronization is not easily lost after frame synchronization is completed. Loss of frame synchronization is a situation where the head of the frame is lost and the frame needs to be resynchronized or the lane cannot be identified. Normally, after synchronization is completed, the synchronization signal pattern is not detected more than M times. Determined. According to the present embodiment, since synchronization processing is not performed on a code error frequent frame peculiar to a transmission line with high accumulated chromatic dispersion, the probability that a different pattern is detected M times consecutively is reduced, and frame synchronization is not easily lost. .

  As described above, according to the present invention, it is possible to achieve a stable optical communication system that can complete synchronization at high speed and is less likely to lose frame synchronization.

7). Seventh Embodiment An optical communication apparatus according to a seventh embodiment of the present invention performs multilane transmission according to the signal frame of FIG. 14 as in the fifth embodiment described above, but 0 signal is transmitted in the transmission system and the reception system. The difference is that the block size is variably controlled before and after the synchronization process. Hereinafter, differences from the fifth embodiment will be mainly described.

7.1) Optical Communication Device In FIG. 17, the transmission system of the optical communication device 13 according to the present embodiment includes a frame generation unit 801, a multilane distribution unit 802, a D / A conversion unit 803, and an optical transmitter 804. The lane distribution unit 802 is provided with a variable 0 signal addition unit 810. The reception system of the optical communication device 13 includes an optical receiver 805, an A / D conversion unit 806, a multilane combination unit 807, and a frame termination unit 808, and a variable 0 signal deletion unit 811 is provided in the multilane combination unit 807. ing. Further, the optical communication apparatus 13 includes a 0 signal control unit 809 that controls the variable 0 signal adding unit 810 and the variable 0 signal deleting unit 811 to change the size of the 0 signal block. Since other configurations and operations are the same as those of the fifth embodiment, description thereof is omitted.

7.2) Variable control of 0 signal size As shown in FIG. 18, before frame synchronization and lane identification are completed, a synchronization signal pattern 901-1 (# 1 to # 4) for each lane and before and after A frame composed of the provided 0 signal blocks 902-1 and 903-1 and an OTUk (V) frame 904 is used. The synchronization signal pattern 901-1 includes synchronization signal patterns # 1 to # 4 for each lane, as in the fifth embodiment. The 0 signal blocks 902-1 and 903-1 are arranged to greatly reduce the influence of chromatic dispersion from the data before and after the time axis on the synchronization signal pattern 901-1, and the time width thereof is, for example, It is set to about 1/2 to 1/10 of the spread on the time axis of the pulse when propagating through a transmission line with large chromatic dispersion. Specifically, the time width of the 0 signal blocks 902-1 and 902-1 is set to about 1000 bits.

  As shown in FIG. 19, after the frame synchronization and the lane identification are completed, the 0 signal control unit 809 controls the variable 0 signal adding unit 810 and the variable 0 signal deleting unit 811 to perform the 0 signal block 902-2 and The time width of 903-2 is shortened. Here, as shown in FIG. 19, 0-bit blocks 902-2 and 902-2 each having a 48-bit width are arranged before and after the synchronization signal pattern 901-2.

  As described above, at the time of frame synchronization and lane identification, as shown in FIG. 18, the 0 signal blocks 902-1 and 903-1 having a large time width are arranged before and after the synchronization signal pattern 901-1, so that The influence from certain signal data can be reduced. As a result, synchronization errors or erroneous synchronization can be avoided even during long-distance transmission, and synchronization can be completed in a short time.

  Subsequently, once synchronization is established, loss of synchronization is unlikely to occur if the numerical value of M is appropriately set as described in the sixth embodiment. Accordingly, as shown in FIG. 19, the 0 signal blocks 902-2 and 903-2 having a short time width can be arranged, and the transmission efficiency can be improved.

7.3) Operation As shown in FIGS. 18 and 19, in this embodiment, two unused bits in the overhead of the OTUk frame are used as synchronization bits indicating the synchronization state. As described in Non-Patent Document 1, the overhead of the OTUk frame includes unused bids such as GCC0 that can be used for various purposes, and two of them are used as synchronization bits. When the synchronization bit is 0, the frame is out of frame synchronization, and when the synchronization bit is 1, the synchronization is established.

  First, as shown in FIG. 4, in multilane transmission in which an optical communication device 13A and an optical communication device 13B are connected by a transmission line 14, the optical communication devices 13A and 13B have the configuration shown in FIG.

  In FIG. 20, the values of the synchronization bits 905 and 906 of the frames transmitted from the optical communication devices 13A and 13B, respectively, are shown according to the operating state. The synchronization bits 905A and 906A indicate the synchronization state of transmission from the optical communication device 13A to the optical communication device 13B, and the synchronization bits 905B and 906B indicate the synchronization state of transmission from the optical communication device 13B to the optical communication device 13A.

<Frame synchronization>
Operation S1 (during synchronization processing): All the synchronization bits (905A, 906A, 905B, 906B) are 0, and frame synchronization and lane identification are executed in each of the optical communication devices 13A and 13B.

  Operation S2 (immediately after the completion of synchronization from the optical communication apparatus 13A to the optical communication apparatus 13B): When frame synchronization and lane identification are completed in the optical communication apparatus 13B, the multi-lane coupling unit 807 of the optical communication apparatus 13B sets the synchronization bit 905B to 1. Then, the optical communication device 13A is notified that the synchronization has been completed. When it is confirmed that the synchronization bit 905B of the signal from the optical communication device 13B is 1, the optical communication device 13A sets the synchronization bit 905A to 1 and notifies the optical communication device 13B that the width of the 0 signal block is to be changed.

  Operation S3 (when the 0 signal block is changed by the optical communication apparatus 13A): Transmission of a frame in which the time width of the 0 signal block is changed shortly after X frames after the synchronization bit 905A is set to 1 by the optical communication apparatus 13A is started. In the present embodiment, for example, X = 5 can be implemented in consideration of the setting change time for the change of the frame length. On the other hand, after confirming that the synchronization bit 905B is 1 also in the optical communication device 13B, the setting is changed so that a frame in which the time width of the 0 signal block is shortened after X frames can be received. Then, a frame synchronization method is realized in which the 0 signal block is changed by transmission from the optical communication device 13A to the optical communication device 13B after X frames.

<Out of sync>
Next, the operation when the synchronization loss occurs will be described.
Operation S4 (immediately after loss of frame synchronization): When synchronization is lost in the optical communication device 13B, the synchronization bit 905B is changed from 1 to 0 to notify the optical communication device 13A that synchronization has been lost. At the same time, the optical receiver 13B starts frame synchronization and lane identification assuming the frame shown in FIG.

  Operation S5 (after confirming loss of frame synchronization by the optical communication device 13A): When the optical communication device 13A receives a frame in which the synchronization bit 905B transmitted from the optical communication device 13B is 0, the optical communication device 13A sets the synchronization bit 905A. Change to 0. At the same time, transmission of the frame shown in FIG. 14 is started. Thereafter, the process returns to the above-described operation S1 to execute the synchronization process again.

  The above is the description of the frame synchronization processing from the optical communication device 13A to the optical communication device 13B, but the frame synchronization processing from the optical communication device 13B to the optical communication device 13A is the same using the synchronization bit 906A and the synchronization bit 906B. It can be realized by performing the operation.

  Note that the operation speed is not changed before and after the frame synchronization change, and the operation speed required for the optical / electronic device is the same as that of the previous embodiments. In this embodiment, as shown in FIGS. 18 and 19, two types of frames having different sizes of the 0 signal block are used. However, three or more types of frames may be prepared and used depending on the communication situation. . Furthermore, frames with different 0 signal block amounts can be selected according to the transmission distance. The size change of the 0 signal block can be adjusted not only on the time axis but also by the number of adjacent lanes. That is, the amount of the 0 signal block may be adjusted by arranging the 0 signal block only in one lane.

7.4) Effect As described above, according to the seventh embodiment of the present invention, before synchronization is established, it is arranged before and after the synchronization signal pattern so as to reduce the influence of nonlinear distortion of the synchronization signal pattern. The transmission efficiency can be improved by increasing the time width of the 0 signal block to be changed and changing the time width of the 0 signal block to be small after synchronization is established. Therefore, according to the present embodiment, it is possible to realize stable multi-lane transmission that can effectively avoid a synchronization error or erroneous synchronization without sacrificing transmission efficiency.

8). Additional Notes Part or all of the above-described embodiments may be described as the following additional notes, but are not limited thereto.
(Appendix 1)
In an optical communication system that transmits a signal frame including at least an overhead region and a payload region, and performs frame synchronization using a synchronization signal pattern provided in the overhead region,
An optical communication system characterized in that, on the transmission side, the average signal intensity of the synchronization signal pattern in the overhead area and / or the predetermined area surrounding the synchronization signal pattern is set smaller than the average light intensity of the payload area. .
(Appendix 2)
The supplementary note 1, wherein the signal frame further includes an FEC (Forward Error Correction) overhead region for performing error correction, and frame synchronization is performed using the synchronization signal pattern before performing the error correction. Optical communication system.
(Appendix 3)
3. The optical communication system according to appendix 1 or 2, wherein a low light intensity block is arranged as the predetermined area before and after the synchronization signal pattern on the time axis.
(Appendix 4)
The optical communication system according to appendix 3, wherein the light intensity of the low light intensity block is 0.
(Appendix 5)
The optical communication system according to any one of appendices 1-4, wherein an average light intensity of the synchronization signal pattern is set smaller than an average light intensity of the payload region.
(Appendix 6)
The signal frame is transmitted as an optical signal of multi-level modulation using both intensity modulation and quadrature phase modulation, and the synchronization signal pattern is composed of symbols with low light intensity. system.
(Appendix 7)
Any one of appendix 1-6, wherein the signal frame is transmitted as an optical signal of multilevel modulation using both intensity modulation and quadrature phase modulation, and the predetermined area is configured by a symbol having low light intensity. Item 1 is an optical communication system.
(Appendix 8)
Multi-lane transmission of the signal frame using a plurality of channels within one wavelength of light,
The synchronization signal pattern is disposed in at least one channel;
The predetermined region is a second region having the same time width as the sum of the first region before and after the synchronization signal pattern on the time axis and the synchronization signal pattern and the first region in channels other than the at least one channel. The optical communication system according to any one of supplementary notes 1-7, wherein the optical communication system includes a region.
(Appendix 9)
The optical communication system according to appendix 8, wherein the synchronization signal pattern is simultaneously arranged in all of the plurality of channels.
(Appendix 10)
The receiving side monitors an error state of a synchronization signal pattern arranged in each of the plurality of channels for each channel, and determines whether frame synchronization processing is possible or not according to the error state of the plurality of channels. The optical communication system according to appendix 9.
(Appendix 11)
The optical communication system according to any one of appendices 1-10, wherein when the frame synchronization is completed on the transmission side and the reception side, the size of the predetermined area is made smaller than that before the frame synchronization.
(Appendix 12)
The optical communication system according to appendix 11, wherein the size of the predetermined area is a time width of an area arranged before and after the synchronization signal pattern on the time axis.
(Appendix 13)
The optical communication system according to any one of appendices 1-12, wherein the signal frame is an OTUk frame.
(Appendix 14)
An optical communication device in an optical communication system that transmits a signal frame including at least an overhead region and a payload region and performs frame synchronization using a synchronization signal pattern provided in the overhead region,
A signal frame generating means for generating a signal frame in which a predetermined area surrounding the synchronization signal pattern is arranged in the overhead area;
An optical transmission means for transmitting the signal frame as an optical signal by setting an average light intensity of a predetermined region surrounding the synchronization signal pattern and / or the synchronization signal pattern to be smaller than an average light intensity of the payload region;
An optical communication device comprising:
(Appendix 15)
The signal frame generation means includes
FEC encoding means for adding FEC (Forward Error Correction) overhead for error correction to the payload area;
Synchronization control means for arranging the synchronization signal pattern in the overhead region;
Predetermined area adding means for arranging the predetermined area in the overhead area;
15. The optical communication device according to appendix 14, characterized by comprising:
(Appendix 16)
16. The optical communication apparatus according to appendix 14 or 15, wherein a low light intensity block is arranged as the predetermined area before and after the synchronization signal pattern on the time axis.
(Appendix 17)
The optical communication apparatus according to appendix 16, wherein the light intensity of the low light intensity block is zero.
(Appendix 18)
18. The optical communication device according to any one of appendices 14-17, wherein an average light intensity of the synchronization signal pattern is set smaller than an average light intensity of the payload area.
(Appendix 19)
The optical frame is transmitted as a multi-level modulation optical signal using both intensity modulation and quadrature modulation, and the synchronization signal pattern is composed of symbols with low optical intensity. apparatus.
(Appendix 20)
Any one of Supplementary notes 1-19, wherein the signal frame is transmitted as an optical signal of multi-level modulation using both intensity modulation and quadrature phase modulation, and the predetermined area is configured by a symbol having low light intensity. Item 1 is an optical communication device.
(Appendix 21)
Multi-lane transmission of the signal frame using a plurality of channels within one wavelength of light,
The synchronization signal pattern is disposed in at least one channel;
The predetermined region is a second region having the same time width as the sum of the first region before and after the synchronization signal pattern on the time axis and the synchronization signal pattern and the first region in channels other than the at least one channel. The optical communication device according to any one of appendices 14-20, wherein the optical communication device includes a region.
(Appendix 22)
The optical communication apparatus according to appendix 21, wherein the synchronization signal pattern is simultaneously disposed in all of the plurality of channels.
(Appendix 23)
23. The apparatus according to any one of appendices 14-22, further comprising a control unit that controls the signal frame generation unit so that the size of the predetermined area is smaller than that before frame synchronization when frame synchronization is completed. Optical communication equipment.
(Appendix 24)
24. The optical communication apparatus according to appendix 23, wherein the size of the predetermined area is a time width of an area arranged before and after the synchronization signal pattern on the time axis.
(Appendix 25)
The optical communication device according to any one of appendices 14 to 24, wherein the signal frame is an OTUk frame.
(Appendix 26)
An optical communication apparatus in an optical communication system for transmitting a signal frame including at least an overhead area and a payload area,
Optical receiving means for receiving, as an optical signal, the signal frame in which a predetermined area surrounding the synchronization signal pattern is arranged in the overhead area;
Frame synchronization using the signal pattern for synchronization, signal frame termination means for terminating the signal frame by deleting the predetermined area from the overhead area,
Have
An optical communication apparatus characterized in that at least an average light intensity of the predetermined area is set to be smaller than an average light intensity of the payload area on the transmission side of the optical signal.
(Appendix 27)
27. The optical communication according to appendix 26, wherein the signal frame terminating means includes FEC decoding means for performing apologetic correction using an FEC (Forward Error Correction) overhead for performing error correction included in the signal frame. apparatus.
(Appendix 28)
The signal frame is transmitted in multiple lanes using a plurality of channels within one wavelength of light,
The synchronization signal pattern is disposed in at least one channel;
The predetermined region is a second region having the same time width as the sum of the first region before and after the synchronization signal pattern on the time axis and the synchronization signal pattern and the first region in channels other than the at least one channel. 28. The optical communication device according to appendix 26 or 27, wherein the optical communication device includes an area.
(Appendix 29)
29. The optical communication apparatus according to appendix 28, wherein the synchronization signal pattern is simultaneously arranged on all of the plurality of channels.
(Appendix 30)
30. The method according to any one of appendices 26 to 29, further comprising control means for controlling the signal frame terminating means so that the size of the predetermined area is made smaller than that before frame synchronization when frame synchronization is completed. Optical communication equipment.
(Appendix 31)
31. The optical communication apparatus according to appendix 30, wherein the size of the predetermined area is a time width of an area arranged before and after the synchronization signal pattern on the time axis.
(Appendix 32)
The optical communication device according to any one of supplementary notes 26-31, wherein the signal frame is an OTUk frame.
(Appendix 33)
An optical communication method in an optical communication system that transmits a signal frame including at least an overhead region and a payload region from a transmission device to a reception device, and performs frame synchronization using a synchronization signal pattern provided in the overhead region,
The transmission apparatus generates a signal frame in which a predetermined area surrounding the synchronization signal pattern is arranged in the overhead area, and sets the average light intensity of the predetermined area to be smaller than the average light intensity of the payload area. As an optical signal,
The receiving apparatus receives the signal frame, performs frame synchronization using the signal pattern for synchronization, deletes the predetermined area from the overhead area, and terminates the signal frame;
An optical communication method characterized by the above.
(Appendix 34)
An optical communication method in an optical communication system for transmitting a signal frame including at least an overhead region and a payload region and performing frame synchronization using a synchronization signal pattern provided in the overhead region,
Generate a signal frame in which a predetermined area surrounding the synchronization signal pattern is arranged in the overhead area,
An average light intensity of the predetermined area is set smaller than an average light intensity of the payload area, and the signal frame is transmitted as an optical signal.
An optical communication method characterized by the above.
(Appendix 35)
An optical communication method in an optical communication system for transmitting a signal frame including at least an overhead area and a payload area,
Receiving the signal frame in which a predetermined area surrounding the synchronization signal pattern is arranged in the overhead area as an optical signal;
Frame synchronization is performed using the synchronization signal pattern, the predetermined area is deleted from the overhead area, and the signal frame is terminated.
An optical communication method, wherein an average light intensity of the predetermined area is set smaller than an average light intensity of the payload area on a transmission side of the optical signal.

8). Other Supplementary Notes The present invention can be described as, but not limited to, the following supplementary notes.
(Appendix 1)
A signal frame composed of information data, overhead for management control, and FEC (Forward Error Correction) overhead for error correction is used, and a frame is generated using a synchronization signal pattern in the overhead for management control. An optical communication system that performs synchronization,
An optical communication system, wherein an average light intensity of the synchronization signal pattern is set to be smaller than an average light intensity of the information data.
(Appendix 2)
The optical communication system according to supplementary note 1, wherein blocks having low light intensity are arranged before and after the synchronization signal pattern on the time axis.
(Appendix 3)
The optical communication system according to appendix 2, wherein the light intensity of the block having the small average light intensity is 0.
(Appendix 4)
The signal frame is transmitted as an optical signal of multi-level modulation using both intensity modulation and quadrature phase modulation,
4. The optical communication system according to appendix 2 or 3, wherein the synchronization signal pattern is composed of symbols with low light intensity.
(Appendix 5)
The optical communication system according to appendix 4, wherein the block with low light intensity is configured by a symbol with low light intensity.
(Appendix 6)
The optical communication system according to appendix 1-5, wherein the signal frame is subjected to multilane transmission using a plurality of channels within one wavelength of light,
The synchronization signal pattern is arranged only in one channel,
When transmitting the synchronization signal pattern and a block with low light intensity arranged before and after the time axis, simultaneously transmitting the block with low light intensity to the other channels at the same time width. An optical communication system.
(Appendix 7)
The optical communication system according to appendix 1-5, wherein the signal frame is subjected to multilane transmission using a plurality of channels within one wavelength of light,
The optical communication system according to any one of appendices 1-6, wherein the number of channels to which synchronization signal patterns composed of symbols with low light intensity are distributed is prepared and arranged on all channels simultaneously.
(Appendix 8)
8. The optical communication system according to appendix 7, which has a monitor for monitoring the number of code errors in the synchronization signal pattern of each channel and performs frame synchronization based on information on the number of code errors in each lane.
(Appendix 9)
The optical communication system according to any one of supplementary notes 1-8, wherein the transmission / reception apparatus includes a control unit that adjusts a size of a signal pattern with low light intensity, and reduces the signal pattern with low light intensity after synchronization is completed.
(Appendix 10)
The optical communication system according to any one of supplementary notes 1-9, wherein the signal frame is an OTU frame (OTUk or OTUkV).

  The present invention can be applied to all optical transmission systems in which the influence of nonlinear distortion is a problem.

12A and 12B Client devices 13A and 13B Optical communication device 14 Transmission path 15 Optical fiber 16 Optical amplifier 101 Signal frame generation unit 102 D / A conversion unit 103 Optical transmitter 104 Optical receiver 105 A / D conversion unit 106 Signal frame termination unit 111 FEC encoding unit 112 Synchronization control unit 113 0 signal addition unit 121 synchronization control unit 122 FEC decoding unit 123 0 signal deletion unit 201 synchronization signal pattern 202, 203 0 signal block 204 payload 205 FEC overhead 301 frame generation unit 302 multilane Distribution unit 303 D / A conversion unit 304 Optical transmitter 305 Optical receiver 306 A / D conversion unit 307 Multilane combination unit 308 Frame termination unit 311 FEC encoding unit 312 Synchronization control unit 313 0 Signal addition unit 314 Synchronization control unit 315 0 signal deletion unit 31 6 FEC decoding unit 401, 402, 4030 Signal block 404 ODUk overhead

Claims (10)

In an optical communication system that transmits a signal frame including at least an overhead region and a payload region, and performs frame synchronization using a synchronization signal pattern provided in the overhead region,
An optical communication system, wherein an average light intensity of the synchronization signal pattern is set smaller than an average light intensity of the payload area on a transmission side. In an optical communication system that transmits a signal frame including at least an overhead region and a payload region, and performs frame synchronization using a synchronization signal pattern provided in the overhead region,
An optical communication system characterized in that, on the transmission side, a predetermined area surrounding the synchronization signal pattern is provided in the overhead area, and at least an average light intensity of the predetermined area is set smaller than an average light intensity of the payload area.   The optical communication system according to claim 2, wherein an average light intensity of the synchronization signal pattern is also set smaller than an average light intensity of the payload area. Multi-lane transmission of the signal frame using a plurality of channels within one wavelength of light,
The synchronization signal pattern is disposed in at least one channel;
The predetermined region is a second region having the same time width as the sum of the first region before and after the synchronization signal pattern on the time axis and the synchronization signal pattern and the first region in channels other than the at least one channel. The optical communication system according to claim 2, further comprising: a region.   The receiving side monitors an error state of a synchronization signal pattern arranged in each of the plurality of channels for each channel, and determines whether frame synchronization processing is possible or not according to the error state of the plurality of channels. The optical communication system according to claim 4.   6. The optical communication system according to claim 2, wherein when the frame synchronization is completed on the transmission side and the reception side, the size of the predetermined area is made smaller than that before the frame synchronization. An optical communication device in an optical communication system that transmits a signal frame including at least an overhead region and a payload region and performs frame synchronization using a synchronization signal pattern provided in the overhead region,
A signal frame generating means for generating the signal frame; and an optical transmitting means for setting the average light intensity of the synchronization signal pattern to be smaller than the average light intensity of the payload area and transmitting the signal frame as an optical signal;
An optical communication device comprising: An optical communication device in an optical communication system that transmits a signal frame including at least an overhead region and a payload region and performs frame synchronization using a synchronization signal pattern provided in the overhead region,
A signal frame generating means for generating a signal frame in which a predetermined area surrounding the synchronization signal pattern is provided in the overhead area;
An optical transmitter configured to set at least an average light intensity of the predetermined area to be smaller than an average light intensity of the payload area and transmit the signal frame as an optical signal;
An optical communication device comprising: An optical communication method in an optical communication system that transmits a signal frame including at least an overhead region and a payload region from a transmission device to a reception device, and performs frame synchronization using a synchronization signal pattern provided in the overhead region,
The optical communication method, wherein the transmitter sets an average light intensity of the synchronization signal pattern to be smaller than an average light intensity of the payload area. An optical communication method in an optical communication system that transmits a signal frame including at least an overhead region and a payload region from a transmission device to a reception device, and performs frame synchronization using a synchronization signal pattern provided in the overhead region,
The transmitter generates a signal frame in which a predetermined area surrounding the synchronization signal pattern is arranged in the overhead area, and sets the average light intensity of the predetermined area to be smaller than the average light intensity of the payload area. As an optical signal,
The receiving apparatus receives the signal frame, performs frame synchronization using the signal pattern for synchronization, deletes the predetermined area from the overhead area, and terminates the signal frame;
An optical communication method characterized by the above.

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