JP4761135B2 - Optical signal relay device and relay method - Google Patents

Description

  In the PON (Passive Optical Network) system, the optical signal between the station side device OLT and the home side device ONU is converted into an optical signal by the electrical / optical module after optical / electrical conversion is performed by the optical / electrical module. More particularly, the present invention relates to an optical signal relay apparatus and a relay method for an upstream optical burst signal from a home apparatus ONU to a station apparatus OLT.

  This optical signal relay device and relay method are particularly preferably used in an optical communication system such as GE-PON.

Between the optical subscriber line station side device OLT (Optical Line Terminal: hereinafter referred to as “station side device”) and a plurality of optical subscriber line termination units ONU (Optical Network Unit: hereinafter referred to as “home side device”), There is an optical communication system that performs two-way communication via an optical fiber communication network.
In this optical communication system, an optical fiber communication network having a single star configuration is constructed and put into practical use between the station side device OLT and each home side device ONU with a single optical fiber. . In this network configuration, the configuration of the system and communication equipment becomes simple, but one home-side device ONU occupies one optical fiber, and this optical fiber is directly connected to the station-side device OLT by wiring. Must. Therefore, if the home-side apparatus ONU has N stations, N optical fibers that are directly connected from the station-side apparatus OLT are required, and it is difficult to reduce the price of the optical communication system.

  On the other hand, a PON (Passive Optical Network) system has been put to practical use as an optical communication system in which one optical fiber connected by wiring from the station side device OLT is shared by a plurality of home side devices ONU. This PON system is one of low-cost access methods for optical subscribers applied to FTTx such as FTTH (Fiber To The Home) and FTTB (Fiber To The Building).

In this PON system, in particular, a passive optical branching device (hereinafter also simply referred to as “optical coupler”) that branches and multiplexes a passively input signal without requiring external power supply, and a station side device OLT. Are connected via an optical fiber such as a single mode fiber having a single propagation mode.
In one optical communication system, there are usually a plurality of home-side devices ONU, and optical fibers branched by optical couplers are provided in accordance with the number of home-side devices ONU.

The station-side apparatus OLT and the N-station home-side apparatus ONU are based on 1-to-N transmission connected via an optical fiber and an optical coupler. Thereby, many home side apparatuses ONU can be allocated with respect to one station side apparatus OLT, and the whole installation cost can be held down.
In such an optical communication system such as a PON system, a group of signals (referred to as optical burst signals) including a large number of 0s and 1s are transmitted between the station side device OLT and the home side device ONU for high-speed data transmission. It is transmitting with.
Japanese Patent Laid-Open No. 11-275178

When the distance between the station side device OLT and the optical coupler is long, the optical burst signal is converted into an electric signal by the optical / electric module, and is optically converted again by the electric / optical module and relayed. This repeater is called an “optical signal repeater”.
In an optical signal repeater, it is necessary to restore an optical signal following an optical burst signal whose optical intensity and frequency / phase change for each optical burst.

A synchronization bit portion is provided as a preamble at the head of the optical burst signal.
This synchronization bit portion is originally provided for use by the optical burst signal receiving circuit of the station side apparatus OLT.
For this reason, in the optical signal relay device, it is necessary to accurately reproduce and relay the synchronization bit part so as not to hinder the operation of the optical burst signal receiving circuit of the station side device OLT.

However, even in the optical signal repeater, a certain time is required for the optical burst signal receiving circuit to establish synchronization by following the optical intensity and frequency / phase of the optical burst signal.
For this reason, until the synchronization is established, the optical burst signal cannot be reproduced correctly, the synchronization bit part becomes short, the mark rate (ratio of 0, 1) changes, etc. The optical burst signal receiving circuit may malfunction.

  Therefore, if the data frame is reproduced from the optical burst signal, the synchronization bit portion can be freely reattached, but a large buffer capacity is required. In addition, for example, in GE-PON, since the data signal is encoded in 8B10B, decoding is necessary to reproduce the data frame, which not only complicates the configuration but also stores the signal in units of 10 bits. Since the decoding process is performed, the relay time fluctuates up to 10 bits. When viewed from the station side device OLT, the variation in the reception timing of the optical burst signal becomes large, so that it is necessary to set a large timing margin so that the optical burst signals from different home side devices ONU do not collide due to the variation.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an optical signal relay device and a relay method that can re-start the synchronization bit part of an optical burst signal with a simple configuration.

  The optical signal repeater according to the present invention includes an optical / electric module that converts an optical burst signal into a received signal, and receives and stores the received signal output from the optical / electric module, and the stored received signal is used as a reference clock. And a synchronization pattern having the same pattern as some or all of the synchronization bits of the received signal, and outputting the synchronization pattern signal in accordance with the reference clock A synchronization pattern holding unit, a restoration signal output from the buffer unit, a switching unit that switches the synchronization pattern signal from the synchronization pattern holding unit, and an optical burst period of the received optical burst signal. A timing control unit for performing control of the buffer unit and switching control of the switching unit, and an output signal of the switching unit as an optical burst. And an electric / optical module for converting the signal into a signal.

According to this configuration, the optical burst signal is converted into an electrical reception signal and stored in the buffer unit, and the stored reception signal is output as a restoration signal in accordance with the reference clock.
On the other hand, a synchronization pattern having the same pattern as some or all of the synchronization bits of the received signal is held, and the synchronization pattern signal is output in accordance with the reference clock.
As a result, since the clocks of the restoration signal and the synchronization pattern signal are the same, the frequency / phase are completely aligned.

Then, the synchronization bit portion of the restoration signal output from the buffer portion and the synchronization pattern signal from the synchronization pattern holding portion are switched.
In this way, according to the present invention, the optical burst period can be detected in the state of the encoded signal, and the synchronization bit portion can be reattached. If only the start of reception of the optical burst signal is detected, it is not necessary to synchronize with the optical burst signal, and it can be detected instantaneously. Therefore, the synchronization bit portion can be restored with a simple configuration.

The optical signal repeater may be part of a bidirectional optical signal repeater that bidirectionally relays optical signals from the station side device and the home side device. In this case, it is preferable to use a clock extracted from a downstream continuous signal from the station side device to the home side device as the reference clock (network synchronization). With this configuration, it is possible to synchronize the clocks of the optical signal relay device and the station side device.
When the home-side device ONU operates with a clock extracted from the downstream signal from the station-side device OLT, the optical signal repeater and the home-side device are synchronized with each other, so that the frequency shift between the received signal and the restoration signal is small. Accordingly, the capacity of the buffer unit for absorbing the frequency shift can be reduced, and the delay time can also be reduced. Even when the home-side device ONU is not network-synchronized with the station-side device OLT, the signal from the home-side device ONU seems to be network-synchronized as seen from the station-side device OLT by relay.

Note that a clock created in the optical signal repeater may be used as the reference clock.
If the timing control unit detects the presence or absence of the optical burst signal by comparing the optical intensity of the optical burst signal with a threshold value, it detects the optical burst period based on the output of the detection circuit. Can do.

  The timing control unit may detect the optical burst period by detecting that 0 continues for a predetermined number of times based on the optical burst signal. When there is an optical transmission code rule that the same code continues for a finite number of times during reception of the optical burst signal, the optical burst period ends when the 0 signal continues for a finite number of times. The start of the optical burst period is determined by detecting the next one signal.

  The timing control unit, for each optical burst section of the received optical burst signal, at the time when a time set shorter than the time when the synchronization bit ends from the detection start of the optical burst signal, for the switching unit, If the synchronization pattern signal of the synchronization pattern holding unit is switched to the restoration signal output from the buffer unit, the switching can be completed before the synchronization bit unit is finished. Therefore, the data part is not affected.

  Further, the timing control unit may perform control to switch a no-signal section after the end of the optical burst signal to an output from the synchronization pattern holding unit. As a result, the output from the switching unit becomes a continuous signal, and the frequency component becomes higher than that of the optical burst signal including the no-signal section. For this reason, a high-pass filter with a high cut-off frequency can be used for connection to the electrical / optical module, and the influence of low-frequency noise such as power supply noise can be reduced.

  The optical signal relay method of the present invention is a method according to the same invention as the optical signal relay device.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a schematic diagram showing a configuration example of an optical communication system 1 in which a station side device OLT and a plurality of home side devices ONU are connected by an optical fiber.
The optical communication system 1 includes a station side device OLT2 provided in a control station side station building, and home side devices ONUs 3a, 3b,. . . (Hereinafter collectively referred to as “home-side apparatus ONU3”), a trunk optical fiber 4a connected to the station-side apparatus OLT2, and a branch optical fiber 4b connected to each home-side apparatus ONU3 (hereinafter collectively referred to as “general name”). An optical coupler 5 for connecting the main optical fiber 4a and the plurality of branch optical fibers 4b, and an optical signal repeater 7 inserted in the middle of the main optical fiber 4a. .

The home-side device ONU3 is a device for enjoying the optical network service, and is installed in the subscriber's home. The home apparatus ONU 3 is connected to a terminal device such as a personal computer (hereinafter simply referred to as a PC) 9.
The optical coupler 5 does not require any external power supply and passively branches and multiplexes the signal input from the optical fiber 4 connected to one side and outputs it to the optical fiber 4 connected to the other side. It can be made of a star coupler. Thereby, many home side apparatuses ONU3 can be allocated with respect to one station side apparatus OLT2, and the whole installation cost can be held down.

This optical communication system 1 including the station side device OLT2 and the home side device ONU3 incorporates, for example, Gigabit Ethernet technology, and performs access section communication at a communication speed of 1.25 Gbps using an optical fiber. A GE-PON (Gigabit Ethernet-Passive Optical Network) system has been established.
According to this GE-PON system, the station side device OLT2 and the home side device ONU3 perform mutual communication in units of variable length frames. This frame has a synchronization bit portion including sampling data and a data portion of 64 bytes or more.

Hereinafter, a signal transmission / reception procedure in the downlink direction and the uplink direction of the signals between the home-side apparatus ONU3 and the station-side apparatus OLT2 will be described.
First, the flow of a downstream signal transmitted from a higher-level network such as the Internet network toward the home apparatus ONU 3 will be described.
In the station side device OLT2 that has received the signal from the Internet network, a predetermined bridge process is performed in order to specify the logical link to be relayed. At this time, the station side device OLT2 adds information such as a synchronization bit part including a logical link identifier and a GE-PON header to the frame signal, converts it into an optical signal, and sends it to the trunk optical fiber 4a.

This downstream optical signal is composed of a combination of a transmission signal designating a specific home-side device ONU3 and an idle signal not designating the home-side device ONU3, and is a continuous signal that is not interrupted.
The optical signal sent to the trunk optical fiber 4a passes through the optical signal relay device 7, is branched by the optical coupler 5, and is sent to each home-side device ONU 3 via each branch optical fiber 4b. At this time, only the home-side apparatus ONU3 including the logical link can capture a predetermined optical signal. Then, the home device ONU 3 that has fetched the frame signal relays the home network interface and sends data to the terminal device such as the PC 9.

Next, the flow of an upstream signal sent from each home apparatus ONU 3 to a higher-level network such as the Internet network will be described.
Data from each PC 9 is converted into an optical burst signal via each home-side apparatus ONU3. The transmission rate of bits constituting the optical burst signal is, for example, 1.25 Gbps in the case of GE-PON.

These optical burst signals are transmitted through the branch optical fibers 4, and the optical burst signal 6a from the home-side device ONU 3a, the optical burst signal 6b from the home-side device ONU 3b, and the optical burst signal from the home-side device ONU 3c. 6c. Then, the respective optical burst signals are multiplexed and sent on the trunk optical fiber 4a via the optical coupler 5.
At this time, these optical burst signals are controlled to be transmitted so as not to compete with each other in time. In this control, when data is transmitted from the station-side device OLT2 to each home-side device ONU3, there is a period window (hereinafter also simply referred to as a window) in which an upstream optical signal may be transmitted to each home-side device ONU3. Assigned and notified as a control frame. Therefore, in the same optical communication system 1, the upstream optical signal transmitted from each home-side apparatus ONU 3 can avoid contention.

In this way, mutual communication is performed between the home side apparatus ONU3 and the station side apparatus OLT2. And, one trunk optical fiber 4a connecting the station side device OLT2 and the optical coupler 5 is shared by a plurality of home side devices ONU3, and each home side device ONU3 is communicated by the time division multiplexing method described later. The optical burst transmission to be performed is performed.
FIG. 2 is a schematic diagram showing optical burst transmission of an upstream optical frame signal transmitted from each home-side apparatus ONU 3 to the station-side apparatus OLT 2 via the optical fiber 4 using a time division method.

As described above, in the upstream optical frame signal, the optical burst signal 6a from the home-side apparatus ONU 3a, the optical burst signal 6b from the home-side apparatus ONU 3b, and the optical burst signal 6c from the home-side apparatus ONU 3c are mutually temporally. It is sent under the control of the window so as not to conflict.
The signal included in the optical burst signal from each home-side apparatus ONU3 includes a synchronization bit portion that constitutes the preamble PA and a signal such as a data portion DATA that includes a plurality of frames and cells.

The synchronization bit part is used for bit synchronization establishment of an optical burst bit synchronization circuit provided in the station side apparatus OLT2. The pattern of the synchronization bit part is an 8B10B idle signal in GE-PON. The mark ratio (ratio of 0, 1) is usually 50%, and the number of bits is fixed.
FIG. 3 is a block diagram showing the configuration of the optical signal repeater 7 of the present invention. FIG. 4 is a signal waveform diagram of each part in the optical signal repeater 7.

The optical signal relay device 7 is a device that converts an optical burst signal into an electrical signal (referred to as a received signal; see FIG. 4A), and returns it to the optical signal for relaying.
In the present embodiment, the optical signal repeater 7 is a bidirectional optical signal repeater 7, one of which relays an upstream optical burst signal from the home-side device ONU to the station-side device OLT, and the other is a station. A downstream optical continuous signal from the side device OLT to the home device ONU is relayed.

As shown in FIG. 3, the optical signal repeater 7 that relays the upstream optical burst signal detects the optical / electric module 71 that converts the optical burst signal into a received signal, and the reception start / end of reception of the optical burst signal. And a timing control unit 77 capable of controlling.
The optical / electrical module 71 includes an optical burst signal detection circuit that detects the presence or absence of an optical burst signal, for example, by comparing the optical intensity of the optical burst signal with a threshold value.

The optical / electrical module 71 supplies a signal detection signal indicating the presence of the optical burst signal to the timing control unit 77. The timing control unit 77 can detect the start / end of reception of the optical burst signal based on this signal detection signal.
The timing controller 77 may detect the start / end of reception of the optical burst signal with the following configuration. That is, the timing control unit 77 has a zero continuation detection unit that monitors the output of the optical / electric module 71 and detects the continuation of the zero signal. In the case of GE-PON, since 8B10B encoding is performed, at most 5 bits of the same code continue during reception of the optical burst signal. Therefore, reception ends when the 0 signal continues for 6 bits or more. Then, the reception start is determined by canceling the detection of the 0-continuous signal after completion of the reception (that is, detecting one signal).

Further, the timing control unit 77 may use both the detection of the optical burst signal from the optical / electrical module 71 and the continuous 0 detection.
When the optical burst signal detection circuit is configured with a peak hold circuit, the peak hold circuit charges the capacitor that holds the peak value at a high speed but discharges slowly, so the optical burst signal starts to be received at a high speed. However, detection of the end of reception is delayed.

On the other hand, in the case of zero continuous detection, the end of reception of the optical burst signal can be detected at high speed. However, synchronization is not established at the head of the optical burst signal, and depending on the circuit configuration of the optical / electric module 7, one signal is detected. Detection may be delayed.
By detecting the start of reception of the optical burst signal by detecting the optical burst signal and detecting the end of reception by detecting 0 continuously, it is possible to detect the start / end of reception of the optical burst signal at high speed.

The electrical signal converted by the optical / electrical module 71 is input to the clock regeneration unit 72. The clock recovery unit 72 extracts a clock signal synchronized with each bit of the optical burst signal based on the optical burst signal. This signal is referred to as “regenerated clock”. Then, each bit of the received signal is sampled by the reproduction clock and written into the buffer unit 73.
On the other hand, a reference clock (see FIG. 4B) is input to the optical signal repeater 7.

  This reference clock is a clock having the same frequency as that of the reproduction clock extracted from the downstream signal. Unlike the upstream signal, the downstream signal is always transmitted. Therefore, by using the clock extracted from the downstream optical continuous signal, a reference clock that is not interrupted in time can be created. By extracting the reference clock from the downlink signal in this way, the uplink and downlink signals can be synchronized and network synchronization is possible.

Note that the reference clock does not necessarily have to be extracted from the downstream signal, and may be a clock generated by an oscillator built in the optical signal relay device 7.
The reference clock is supplied to the synchronization pattern holding unit 74, the buffer unit 73, and the timing control unit 77.
The reception signal output from the clock recovery unit 72 is written in the buffer unit 73 and read out based on the reference clock. The buffer unit is cleared by a reset signal from the timing control unit 77 when reception of one optical burst signal is started.

As a result, even if the frequency of the recovered clock and the reference clock is slightly shifted, the time range is limited to one burst signal period, so that the clock shift is absorbed with a small buffer capacity, and the recovered clock is changed to the reference clock. Can be converted.
For example, after accumulating several bits from the start of reception (reset signal), it can also be output sequentially.

As an example, if the deviation of the 1.25 GHz clock is 200 ppm and one burst signal time is 100 μs, the clock deviation within one burst signal time is
(1.25 × 10 ⁹ ) × (100 × 10 ⁻⁶ ) × 200 × 10 ⁻⁶ = 25
Therefore, if the buffer capacity is 50 bits and 25 bits are accumulated from the start of reception and then output, the buffer will not overflow / short. When the network is synchronized, the clock capacity between the home device and the repeater is eliminated, so that the buffer capacity can be further reduced.

The synchronization pattern holding unit 74 is configured by a memory that holds a synchronization pattern having the same pattern as the pattern of the synchronization bit part included in the preamble of the optical burst signal and outputs it based on the reference clock. This synchronous pattern is an 8B10B idle signal (fixed pattern) in the case of GE-PON.
As a result, the synchronization pattern signal output from the synchronization pattern holding unit 74 and the reception signal (referred to as a restoration signal) output from the buffer unit 73 are in phase with the same reference clock and are completely synchronized with each other. Become.

  The switching unit 75 switches between the synchronization pattern signal output from the synchronization pattern holding unit 74 and the restoration signal output from the buffer unit 73 based on the switching signal from the timing control unit 77. That is, the switching unit 75 is connected to the synchronization pattern signal side at the start of reception of one optical burst signal, and switches to the restoration signal side of the buffer unit 73 when receiving the switching signal (see FIG. 4D).

The time when this switching signal is output is the time when a clock corresponding to a predetermined time t is counted from the start of reception of one optical burst signal. The fixed time t is set to be equal to or less than the time T that the synchronization bit part in one optical burst signal lasts. That is,
t ≦ T
It is said. For example, t is 200 nanoseconds and T is 480 nanoseconds.

In particular, if t is shorter than T (t <T), when switching is returned to the buffer unit 73, the synchronization pattern continues, and the synchronization pattern output of the holding unit 74 is synchronized with the synchronization pattern output of the buffer unit 73. Switch to
By this switching, a part or all of the head of the synchronization bit portion of the optical burst signal is replaced with the synchronization pattern output from the synchronization pattern holding unit 74 (see FIG. 4E). As a result, the head of the synchronization bit portion, which is not known whether or not it is correctly reproduced during the reception process, can be replaced with a correct synchronization pattern.

In this case, as described above, the buffer unit 73 and the synchronization pattern holding unit 74 are synchronized with the reference clock, and switching control is also synchronized with the reference clock, so that frequency variation and phase variation due to switching do not occur.
Although there is a possibility that the synchronization pattern is broken at the time of switching, since it is limited to before and after one bit that has been switched, frequency fluctuation / phase fluctuation does not occur, and the mark ratio does not fluctuate greatly. It does not affect the reception of the OLT.

The electrical / optical module converts the restoration signal, in which the head of the synchronization bit part is replaced with the correct synchronization pattern in this way, into an optical burst signal. A signal output from the electrical / optical module is referred to as a “transmission signal”.
In addition, since the electrical / optical module emits dark light even when transmitting a 0 signal, it is desirable to completely stop the light emission in the non-signal section. Therefore, the timing control unit 77 generates an output control signal so that the electrical / optical module emits light only in the optical burst signal section (see FIG. 4E). The electrical / optical module takes in the output control signal from the timing control unit 77 and, based on the output control signal, emits light only when the output control signal is valid.

As described above, the optical burst signal can be relayed while maintaining its accurate code form.
Although the embodiment of the present invention has been described above, the implementation of the present invention is not limited to the above, and the following modifications are possible.
That is, in the processing described so far, the timing control unit 77 still switches the switching unit 75 to the buffer unit 73 side even in the non-signal section after the end of reception of the optical burst signal (see FIG. 4D). .

However, when the reception of the optical burst signal is completed, switching to the synchronization pattern holding unit 74 side may be performed, and the relay signal in the non-signal section until the start of reception of the next optical burst signal may be filled with the synchronization pattern signal.
This has the following advantages. That is, the frequency component of the optical burst signal becomes DC in the no-signal section. Therefore, a DC connection for passing a DC component has to be made as a connection to the electrical / optical module.

  However, the synchronization pattern signal always has a high frequency component. Therefore, when switching to the synchronization pattern signal at the end of reception of the optical burst signal, the output from the switching unit 75 becomes a continuous signal, and the frequency component does not become lower than that of the optical burst signal including the no-signal section. For this reason, the high-pass filter C having a high cutoff frequency can be used for connection to the electrical / optical module, and the influence of low-frequency noise such as power supply noise can be reduced.

It is the schematic which shows the structural example of the optical communication system 1 which connected the station side apparatus OLT and the some home side apparatus ONU with the optical fiber. It is a schematic diagram showing optical burst transmission of an upstream optical frame signal transmitted from each home-side apparatus ONU3 to the station-side apparatus OLT2 via the optical fiber 4 using a time division method. It is a block diagram which shows the structure of the optical signal relay apparatus 7 of this invention. FIG. 6 is a signal waveform diagram of each part in the optical signal relay device 7.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical communication system 7 Optical signal relay apparatus 71 Optical / electrical module 72 Clock reproduction | regeneration part 73 Buffer part 74 Synchronization pattern holding | maintenance part 75 Switching part 76 Electric / optical module 77 Timing control part

Claims (7)

An optical signal repeater that relays an optical burst signal,
An optical / electrical module for converting an optical burst signal into a received signal;
A buffer unit for capturing and storing received signals output from the optical / electrical module, and outputting the stored received signals as a restoration signal in accordance with a reference clock;
A synchronization pattern holding unit for holding a synchronization pattern having the same pattern as part or all of the synchronization bits of the received signal, and outputting the synchronization pattern signal in accordance with the reference clock;
A restoration unit output from the buffer unit, and a switching unit that switches a synchronization pattern signal from the synchronization pattern holding unit;
A timing control unit for detecting an optical burst section of the received optical burst signal and performing control of the buffer unit and switching control of the switching unit;
An optical signal relay apparatus comprising: an electrical / optical module that converts an output signal of the switching unit into an optical burst signal. The optical signal repeater is an optical signal repeater for an upstream burst signal from a home-side device to a station-side device,
It further comprises an optical signal repeater that relays downstream continuous signals from the station side device to the home side device,
The optical signal repeater according to claim 1, wherein a clock extracted from a downstream continuous signal from the station side device to the home side device is used as the reference clock.   The timing control unit detects an optical burst section based on an output of an optical burst signal detection circuit that detects the presence or absence of the optical burst signal by comparing the optical intensity of the optical burst signal with a threshold value. The optical signal relay device described.   2. The optical signal repeater according to claim 1, wherein the timing control unit detects an optical burst section by detecting that 0 of the optical burst signal continues for a predetermined number of times.   The timing control unit, for each optical burst section of the received optical burst signal, at the time when a time set shorter than the time when the synchronization bit ends from the detection start of the optical burst signal, for the switching unit, 5. The optical signal relay device according to claim 1, wherein switching is performed from a synchronization pattern signal of the synchronization pattern holding unit to a restoration signal output from the buffer unit. 6.   The timing control unit holds the synchronization pattern from the restoration signal output from the buffer unit to the switching unit at the end of detection of the optical burst signal for each optical burst period of the received optical burst signal. 6. The optical signal relay device according to claim 5, wherein the switching to a synchronization pattern signal is performed. An optical signal relay method for relaying an optical burst signal,
Optical / electrical conversion of optical burst signal to received signal,
Capture and store the received signal, output the stored received signal as a restoration signal in accordance with a reference clock,
A synchronization pattern signal having the same pattern as part or all of the synchronization bits of the received signal is output in accordance with the reference clock,
For each optical burst section of the received optical burst signal, switching between the restoration signal and the synchronization pattern signal,
An optical signal relay method for converting the output signal after the switching into an optical burst signal and outputting it.

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