JP2015065562A - Optical repeater, communication system, and optical repeating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the following problem: In using a 3R receiver for regenerative repeating of an incoming signal in an extension PON system, much time is required for optimization of a photoreceiver for receiving a burst signal.SOLUTION: A delay line and a function for exactly detecting burst optical signal intensity are provided for an incoming optical repeater to make an input current into a TIA small and constant.

Description

  The present invention relates to an optical receiving technique for performing digital signal transmission in an optical communication system, and more specifically, after converting an optical signal into an electric signal (current signal) by a light receiving element, the current signal is converted into a voltage signal, and waveform shaping / It relates to the technology to amplify. In particular, the present invention relates to a high-sensitivity and wide dynamic range reception technique that can respond to a bursty data signal input at a plurality of different transmission speeds at a high speed and can receive a minute signal to a large signal.

  As a typical network configuration of an optical subscriber system, a single-star configuration (Single star) in which a subscriber side device (Optical network unit: ONU) and a station side device (Optical line terminal: OLT) are connected one-to-one. SS) and a passive optical network (PON) configuration in which a plurality of ONUs 92 are connected to one OLT 91. Network configuration diagrams of the SS and PON systems are shown in FIGS. 1 and 2, respectively.

  In the SS system, since the ONU 92 can occupy the OLT 91, high-speed communication is possible, but there is a drawback that the apparatus cost is high. On the other hand, in the PON system, the PON system is adopted in many optical subscriber systems because a plurality of ONUs 92 share one OLT 91 and optical fiber equipment and are excellent in economic efficiency.

  PON downlink transmission is a continuous mode, and signals to each ONU 92 are transmitted by time division multiplexing (TDM). The downstream signal is broadcast to all ONUs, and each ONU selectively receives only the signal addressed to itself. On the other hand, in uplink transmission, each ONU 92 transmits a signal at a timing designated by the OLT 91 in order to avoid signal collision by time division multiple access (TDMA). Since the transmission distance between the ONU 92 and the OLT 91 is different for each ONU 02, the upstream signals from the respective ONUs 92 are characterized by being intermittent with different strengths and phases, and the upstream signals are called a burst mode.

  In general, the optical receiver 80 is a photodiode (PD) which is a light receiving element, an impedance conversion amplifier (TIA), an amplitude limiting amplifier (LIA), a clock data regenerator (Clock and data recovery): CDR). A configuration of a general optical receiver 80 is shown in FIG.

  The PD 81 converts an optical signal propagating through the optical fiber into a current signal, and the subsequent TIA 82 converts and amplifies the current signal into a voltage signal. The LIA 83 further amplifies the TIA 82 input into a voltage signal having a constant amplitude and outputs it to the CDR 84. The CDR 84 at the subsequent stage performs clock extraction based on the input signal, and uses the reproduced clock to identify and reproduce the signal whose amplitude has been limited by the LIA 83.

  In the PON system, since the upstream signal is in burst mode, the TIA 82 and LIA 83 constituting the optical receiver 80 provided in the OLT 91 amplify burst signals having significantly different intensities without distortion, and the CDR 84 clocks from burst signals having different phases. The signal needs to be extracted. In this case, each receiving circuit needs to be optimized for each burst signal, but each circuit requires a certain response time.

  From the viewpoint of providing an uplink communication service, it is necessary to support a large transmission line loss for wide-area accommodation, and therefore, an equalization amplifier is required to have a high sensitivity and a wide dynamic range reception performance. In addition, from the viewpoint of realizing high uplink transmission efficiency, it is necessary to shorten the physical overhead such as the guard time between the uplink burst signals and the preamble length. Therefore, instantaneous response performance is required for TIA82, LIA83, and CDR84. The In order to realize a high-speed PON system, establishment of a high-speed burst signal receiving technique as described above plays an extremely important role.

  In order to achieve both high-sensitivity reception and wide dynamic range reception in an amplifier such as TIA 82, a technique of controlling the gain of the amplifier according to the input signal strength by automatic gain control (AGC) is used. That is, when the input signal strength is small, high-sensitivity reception is enabled by increasing the gain of the amplifier, and when the input signal strength is large, the input overload is increased by decreasing the gain of the amplifier.

  In general, a differential interface is often used in an electric circuit. The reason is that the voltage amplitude may be halved as compared with the single-phase interface, and the common-mode noise resistance is high. In order to use a differential interface in the optical receiver 80, there is a configuration in which a single-phase converter (S / B) is provided at the subsequent stage of the TIA 82.

  Next, as a means of gain control in the amplifier, as described in Non-Patent Document 1, the output amplitude of the amplifier is monitored, and a signal for setting the amplifier gain to a desired value is fed back and given to the amplifier. There is a way to control the gain. Similarly, during single-phase / differential conversion, there is a method of monitoring the DC potential difference between differential pairs at the latter stage of S / B output and performing feedback control. However, since such feedback control requires a long time for TIA gain and single-phase / differential conversion, there is a problem that uplink transmission efficiency may be deteriorated when used in the PON system.

  As a means for speeding up the gain control in the TIA 82 and the single-phase / differential conversion of the transmission circuit in the optical receiver, there is a technique as described in Non-Patent Document 2. High-speed level detection by the hysteresis comparator 72 is used for gain control and single-phase / differential conversion. An example of a feedforward AGC / ATC circuit that can be considered in this case is shown in FIG.

The TIA 82 has two core circuits, a main core 82 _M and a replica core 82 _R , and the circuit constants and the like are completely the same. Those outputs are connected to a single-phase differential converter (S / B) 71. An automatic threshold controller (ATC) 73 is connected to the subsequent stage of the single-phase / differential converter 71. FIG. 5 shows the relationship between the operations of the TIA core 82 and the hysteresis comparator 72. The hysteresis comparator 72 receives two TIA outputs (main and replica). Replica core 82 _R is open input end, since there is no input signal, essentially the output voltage maintains a constant value. Thus, for the hysteresis comparator 72, a DC component is canceled, the form of the output amplitude from the main core 82 _M is inputted as it is.

Although depending on the output amplitude of the TIA core 82, SW1 is turned ON when the output from the single-phase / differential converter 71 (input from the hysteresis comparator 72) exceeds a certain threshold. FIG. 6 shows a circuit diagram of the core circuit provided in the TIA 82. It has two variable resistors R _L and R _f , and a MOSFET type switch is used. The output of the hysteresis comparator 72, that is, SW1, is connected to the MOSFET of the core circuit of the TIA 82, thereby controlling the two resistance values. As a result, by setting a high impedance conversion gain Z _H is relative to the input optical signal intensity is low light, achieving high sensitivity. By setting a low impedance conversion gain Z _L with respect to the input optical signal strength is greater light, increasing the input overload resistance, to achieve a wide dynamic range.

  FIG. 7 shows an example of the ATC circuit 73. A high-speed peak hold circuit 731 is connected to each differential pair. The high-speed peak hold circuit 731 detects and holds the peak voltage to generate a control voltage, thereby realizing high-speed single-phase differential conversion. The voltage corresponding to the input signal voltage to the ATC circuit 73 is detected and held at high speed. Based on the control signal, the offset compensator 732 cancels the DC voltage difference between the differential pairs (voltage offset compensation). The time required for such voltage offset depends on the DC voltage difference (offset amount) between the differential pairs, and the control time becomes longer as the offset amount increases.

  In the PON system in which the above-described gain control and single-phase differential conversion have different upstream signal strengths for each ONU 92, it is necessary to reset the circuit for each upstream signal so that the optimum operation is performed for each upstream signal. Such a reset signal is generally given to the optical receiver 80 of the OLT 91 from the MAC LSI in the subsequent stage in addition to the optical receiver 80.

  By the way, from the viewpoint of reducing the operation cost of the optical subscriber system, widening the PON system is one of the effective means. As shown in FIG. 8, in this case, a configuration example in which the optical repeater 95 is arranged between the ONU 92 and the OLT 91 is given. There are various configurations of the optical repeater, but there are two means for regenerative repeat of uplink signals: a method using an optical amplifier and a 3R regenerative repeater using a burst receiver as described above.

  However, when the 3R receiver is used for regenerative relay of the upstream signal, it is difficult to give the reset signal to the burst receiver at an accurate timing because the optical repeater 95 is located far away from the OLT 91. . Even in a situation where a reset signal can be generated, there is a problem that optimization of the burst receiver, specifically, time is required for gain control and compensation of a DC voltage difference between the differential pair.

Masaki Noda, Satoshi Yoshima, Masamichi Nogami, Jun-ichi Nakagawa, “A Study on Fast Burst Reception Time of TIA for 10G-EPON OLT”, IEICE Society Conference, C-3-72, September 2012 Susumu Nishihara, Makoto Nakamura, Tsuyoshi Ito, Takeshi Kurosaki, Yusuke Ohtomo, and Akira Okada, "A SiGe BiCMOS Burst-mode Transimpedance Amplifier Using Fast and Accurate Automatic Offset Compensation Technique for 1G / 10G Dual-rate Transceiver", in Proc BCTM 2010 , Paper 10.2, September 2009 Susumu Nishihara, Makoto Nakamura, Kazuyoshi Nishimura, Keiji Kishine, Shunji Kimura, and Kazutoshi Kato, "10.3 Gbit / s burst-mode PIN-TIA module with high sensitivity, wide dynamic range and quick response", IET Electronics Letters, Vol . 44, no. 3,31st January 2008

  An object of the present invention is to solve the problem that it takes time to optimize a burst receiver when a 3R receiver is used for regenerative relay of an uplink signal in a long PON system.

  In order to achieve the above object, according to the present invention, an upstream optical repeater is provided with a delay line, and the input current to the TIA is made small and constant.

Specifically, the optical repeater according to the present invention is:
An optical repeater connected between a station side device and a subscriber side device in an optical subscriber system including a station side device, a transmission optical fiber, and a subscriber side device,
An optical branching unit that branches the burst optical signal transmitted from the subscriber side device;
An optical delay device for delaying one of the branched optical signals of the optical branching unit;
An optical receiver for receiving the delayed burst signal of the optical delay device;
An optical transmitter for transmitting a burst signal received by the optical receiver to a station side device;
A signal intensity detection unit for detecting the signal intensity of the other optical signal branched from the optical branch unit;
A current control unit that controls an input current amount to an impedance conversion amplifier included in the optical receiver according to the signal strength detected by the signal strength detection unit;
A threshold control unit that initializes a state of an automatic threshold control circuit included in the optical receiver according to the signal strength detected by the signal strength detection unit;
Is provided.

  In the optical repeater according to the present invention, the delay time of the optical delay unit is required for the voltage control unit to control the impedance conversion amplifier and for the threshold control unit to initialize the automatic threshold control circuit. Longer than time.

  In the optical repeater according to the present invention, the threshold control unit may initialize the state of the automatic threshold control circuit when identifying a specific signal pattern included in the burst signal.

Specifically, the optical subscriber system according to the present invention is:
A subscriber side device;
The optical repeater according to any one of claims 1 to 3, which relays a burst signal transmitted from the subscriber side device;
A station-side device that receives a burst signal relayed by the optical repeater;
Is provided.

Specifically, the optical relay method according to the present invention is:
In an optical subscriber system including a station side device, a transmission optical fiber, and a subscriber side device, a burst signal transmitted from a subscriber side device is received by an optical receiver and then transmitted by an optical transmitter.
An optical branching procedure for branching a burst optical signal transmitted from a subscriber side device;
One optical signal branched in the optical branching procedure is delayed, and the amount of input current to the impedance conversion amplifier of the optical receiver is controlled according to the signal strength of the other optical signal branched in the optical branching procedure. And an optical receiver control procedure for initializing a state of an automatic threshold control circuit included in the optical receiver;
A transmission procedure for transmitting by the optical transmitter after receiving the one optical signal branched in the optical branching procedure by the optical receiver;
In order.

  In the optical repeater according to the present invention, the state of the automatic threshold control circuit may be initialized when a specific signal pattern is included in the burst signal in the optical receiver control procedure.

  The above inventions can be combined as much as possible.

  According to the present invention, in the case of using a 3R repeater for regenerative relay of an upstream signal in the extended PON system, the DC voltage corrected by the automatic threshold control circuit can be reduced, and the response time can be shortened.

The network block diagram which has a single star structure is shown. 1 shows a network configuration diagram having a passive optical network configuration. FIG. An example of a structure of an optical receiver is shown. An example of a feedforward type AGC / ATC circuit is shown. An example of the operation characteristic of a hysteresis comparator is shown. An example of a structure of a TIA core circuit is shown. An example of the circuit configuration of ATC is shown. An example of an optical subscriber system is shown. An example of a structure of an optical repeater is shown. An example of a structure of an uplink 3R repeater is shown. An example of a structure of a receiver control part is shown. The 1st example of the input-output characteristic of a TIA current control part is shown. An example of the timing chart of the uplink 3R repeater which concerns on this embodiment is shown. The 2nd example of the input-output characteristic of a TIA current control part is shown. The 3rd example of the input-output characteristic of a TIA current control part is shown. An example of the reset signal generation part which concerns on Embodiment 2 is shown.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. In the present specification and drawings, the same reference numerals denote the same components.

(Embodiment 1)
A first embodiment of the present invention will be described. The network configuration is as shown in FIG. 8, and a bidirectional optical repeater 95 is arranged between the OLT 91 and the optical splitter 94. The bidirectional optical repeater 95 has a 3R repeater capable of handling burst signals. Yes. The optical access network configuration assumed in the present embodiment is 10G-EPON (IEEE Std 802.3av) in which downlink communication is time division multiplexing (TDM) and uplink communication is time division multiple access (TDMA). -2009). In 10G-EPON, a wavelength of 1.577 μm band is used for downlink communication and a 1.27 μm band is used for uplink communication.

  As shown in FIG. 9, the optical repeater 95 includes a wavelength multiplexing / demultiplexing filter 61A, a wavelength multiplexing / demultiplexing filter 61B, an optical amplifier 62, and an upstream 3R repeater 63. The wavelength multiplexing / demultiplexing filter 61A is connected to the ONU 92 via the passive optical splitter 94.

  The wavelength multiplexing / demultiplexing filter 61A sends a downstream 1.577 μm band signal transmitted from the optical amplifier 62 in the ONU 92 direction, while transmitting an upstream 1.27 μm band signal light transmitted from the ONU 92. It is a passive component that transmits to the 3R repeater 63. The wavelength multiplexing / demultiplexing filter 61B sends the downstream 1.577 μm band signal transmitted from the OLT 91 to the optical amplifier 62, while transmitting the upstream 1.27 μm band signal transmitted from the upstream 3R repeater 63. It is a passive component that is transmitted to the OLT 91. The optical amplifier 62 has a function of amplifying the downstream signal intensity transmitted from the OLT 91 via the wavelength filter 61B and regenerating and transmitting it to the ONU 92 via the wavelength filter 61A.

  Next, the configuration of the uplink 3R repeater 63 will be described with reference to FIG. The upstream 3R repeater 63 includes a 3R receiver 68 that functions as an optical receiver, an optical transmitter 64, a receiver control unit 66, an optical fiber delay line 65, and an optical coupler 67. The optical coupler 67 is branched into 2: 2, and the branching ratio is 50%.

  The 3R receiver 68 includes a PD 81, a TIA 82, an ATC 73, an LIA 83, a CDR 84, and a current amount adjuster 85. In this embodiment, the TIA 82 is fixed in gain and does not perform gain control according to the magnitude of the input current. The configuration of the ATC 73 is the same as that described in the prior art. The current amount adjuster 85 receives a TIA input current amount control signal for controlling the amount of current input from the receiver control unit 66 to the TIA 82, and adjusts the amount of current flowing through the TIA 82 according to the TIA input current control signal. It has a function of maintaining the output voltage at a constant value. A specific configuration of the current amount adjuster 85 may be a configuration in which the voltage applied to the gate terminal of the MOSFET is controlled by an input current amount control signal. A reset signal is also given to the ATC 73 to reset the peak hold circuit as described above. The optical fiber delay line 65 is used to increase the time until the receiver control unit 66 generates the reset signal and the TIA input current amount control signal by giving a delay of τ as a value.

  Next, the configuration and operation of the receiver control unit 66 will be described with reference to FIG. The receiver controller 66 includes a PD 661, a TIA 662, an input optical signal intensity monitor 663 that functions as a signal intensity detector, a reset signal generator 664 that functions as a threshold controller, and a TIA current controller 665 that functions as a current controller. Have.

  The input optical signal intensity monitor unit 663 detects the input optical signal intensity with high accuracy. For example, the input optical signal intensity is always sampled at regular intervals / time periods, and the average value thereof is output to the subsequent-stage reset signal generation unit 664 at regular intervals. For example, the accuracy is improved by means of sampling every 5 ns and obtaining an average every 20 times, that is, an average value in a cycle of 100 ns.

  The reset signal generation unit 664 has a comparator inside, and when the set threshold value is exceeded, it is determined that an input optical signal exists, and the reset signal is output to the 3R receiver 68. For example, since the minimum reception sensitivity of the optical receiver provided in the OLT 91 defined by 10GBASE-PR30-D in 10G-EPON is −28 dBm, a value such as −35 dBm may be set as the threshold of the reset signal generation unit 664.

  The TIA current control unit 665 outputs a TIA input current amount control signal that makes the input current to the TIA 82 equal. An example of input / output characteristics of the TIA current control unit 665 is shown in FIG. In accordance with the input to the TIA current control unit 665, in other words, the input optical signal intensity, the input current to the TIA 82 is linear.

Next, the optical relay method according to this embodiment will be described. The optical relay method according to this embodiment includes an optical branching procedure, an optical receiver control procedure, and a transmission procedure in this order.
In the optical branching procedure, the optical coupler 67 branches the burst optical signal transmitted from the ONU 92.
In the optical receiver control procedure, one optical signal branched by the optical coupler 67 is delayed, and during that time, the receiver control unit 66 detects the burst optical signal and outputs a reset signal and a TIA input current amount control signal.
In the transmission procedure, one optical signal branched in the optical branching procedure is received by the 3R receiver 68 and then transmitted by the optical transmitter 64.

The operation in the time domain of the present invention will be described in detail with reference to FIG.
From different ONU # 1, ONU # 2, as different uplink signal of the light signal intensity is input to the optical repeater 95, there is relation of _P 1> _{P 2} to the input optical signal strength of each, towards _{P 1} Is strong.
The optical signal from the ONU # 1 is input to the receiver control unit 66 at time _{t 1.} On the other hand, the upstream optical signal is input to the 3R receiver 68 due to the delay by the optical fiber delay line 65 at time t ₂ after the delay of time τ. Since intervention of the optical coupler 67, the input light intensity to each becomes _{P 1/2, P 2/} 2 of the half. However, it is assumed that the optical coupler 67 operates near ideal and there is no excess loss.

And it outputs the voltage _{V mon1} as a value indicating the optical power in the input optical signal intensity monitor unit 663 time _{t 3.} Considering sampling delay for a period of time from t ₂ to t ₃ it is considered necessary. Then, the reset signal generator 664 outputs a reset signal pulse to the 3R receiver 68. Similarly, V _TIAin1 is also output from the TIA current control unit 665 to the TIA ₈₂ in the 3R receiver 68.

On the other hand, if the initial value of the peak hold circuit of ATC 73 is V _mon , it is once cleared to 0 upon receipt of a reset signal. Thereafter, the value _{V hold} in accordance with an input signal voltage to converge by time _{t 3.} The reset signal generator 664, a signal from the ONU # 1 is input to the time _{t 4.} When there is no signal, the output values from the input optical signal intensity monitoring unit 663 and the TIA current control unit 665 also become zero.

Next, an optical signal having a weak optical signal intensity is input from ONU # 2. The receiver control unit 66 is input at time t _6. The upstream optical signal is input to the 3R receiver 68 due to the delay by the optical fiber delay line 65 at time t ₇ after the delay of time τ. And it outputs the voltage _{V mon2} as a value indicating the optical power in the input optical signal intensity monitor unit 663 time _{t 7.} The reset signal generation unit 664 outputs a reset signal to the 3R receiver 68. Similarly, V _TIAin2 is also output from the TIA current control unit 665 to the TIA ₈₂ in the 3R receiver 68. On the other hand, if the value of the peak hold circuit of ATC 73 holds V _mon , it is once cleared to 0 in response to the input of the reset signal.

  In the present embodiment, the peak hold voltage of the ATC 73 is assumed to be constant regardless of the magnitude of the input optical signal intensity, but in actuality, it may slightly vary depending on the output variation of the input optical signal intensity monitor unit 663 and the pattern of the input signal. There is sex. For example, the sampling is performed in a time zone in which the same code sequence continues for a long time.

  As an input / output characteristic of the TIA current control unit 665, there may be a configuration in which the output voltage is controlled to be a plurality of discrete values according to the input optical signal intensity as shown in FIGS. That is, two-step control as shown in FIG. 14 or four-step control as shown in FIG. 15 is taken. It is preferable that the number of stages is increased because the amount of offset compensation in the ATC 73 is small and the response time is shortened.

  As described above, the optical fiber delay line 65 delays the burst optical signal, and the receiver controller 66 makes the input current to the TIA 82 small and constant during that time. For this reason, the invention according to this embodiment can provide a reset signal for the 3R receiver 68 at an accurate timing, and can reduce the amount of DC voltage to be corrected in the ATC 73 that is an automatic threshold control circuit. it can. Therefore, the invention according to the present embodiment can shorten the response time of the 3R receiver 68 and improve the uplink transmission efficiency when the 3R receiver 68 is used for regenerative relay of the uplink signal in the extended PON system. become.

  In the present embodiment, the current is drawn from the TIA input terminal as means for controlling the input signal strength to the TIA 82 built in the 3R receiver 68. For example, a variable optical attenuator (VOA) is provided at the front stage of the PD81. ) And a signal corresponding to the TIA input current amount control signal from the receiver control unit 66 may be given. Further, as the configuration of the TIA 82, the switching gain control type TIA using the external reset signal described in the prior art may be used.

  In the present embodiment, the peak hold / feed forward type ATC circuit has been described as an example. However, the present invention is not limited to a specific ATC circuit configuration, and can be applied to any type using an external reset signal.

(Embodiment 2)
A second embodiment of the present invention will be described with reference to the drawings. The configuration of the reset signal generation unit 664 is different from that of the first embodiment, and the others are not changed. As shown in FIG. 16, the reset signal generation unit 664 of the second embodiment includes a PD 6641, a TIA 6642, a pattern discriminator 6643, and a reset signal output circuit 6644. The pattern discriminator 6643 detects a specific pattern in the PON system.

For example, in upstream communication of the PON system, each signal has a redundant pattern section called “preamble”. Although the main signal is not included in the preamble section, gain control of the TIA 82 and clock extraction / data reproduction in the CDR are performed using this section. For example, in 10G-EPON, the following values are defined in binary numbers as a synchronization pattern which is a pattern of a preamble section.
10 1111 1101 0000 0010 0001 1000 1000 1010 0111 1010 0011 1001 0010 1101 1101 1001 1010

  The above pattern is repeatedly transmitted over the preamble period. The pattern discriminator 6643 instantaneously detects that the above pattern has been input, and immediately outputs a reset signal to the 3R receiver 68 upon detecting the input of the synchronization pattern. Other operations are the same as those in the first embodiment.

  The present invention can be applied to the information communication industry.

61A, 61B: Wavelength filter 62: Optical amplifier 63: Up 3R repeater 64: Optical transmitter 641: LDD
65: Optical fiber delay line 66: Receiver control unit 661: PD
662: TIA
663: Input optical signal intensity monitor unit 664: Reset signal generation unit 6641: PD
6642: TIA
6643: Pattern identifier 6644: Reset signal output circuit 665: TIA current controller 67: Optical coupler 68: 3R receiver 71: Single phase / differential converter 72: Hysteresis comparator 73: Automatic threshold controller (ATC)
731: Peak hold circuit 732: Offset compensation unit 80: Optical receiver 81, 642: PD
82: TIA
82 _M : main core 82 _R : replica core 83: LIA
84: CDR
85: Current regulator 90: Optical fiber transmission line 90D: Branch fiber 90J: Relay fiber 91: OLT
92: ONU
93: HGW
94: Splitter 95: Optical repeater

Claims (6)

An optical repeater connected between a station side device and a subscriber side device in an optical subscriber system including a station side device, a transmission optical fiber, and a subscriber side device,
An optical branching unit that branches the burst optical signal transmitted from the subscriber side device;
An optical delay device for delaying one of the branched optical signals of the optical branching unit;
An optical receiver for receiving the delayed burst signal of the optical delay device;
An optical transmitter for transmitting a burst signal received by the optical receiver to a station side device;
A signal intensity detection unit for detecting the signal intensity of the other optical signal branched from the optical branch unit;
A current control unit that controls an input current amount to an impedance conversion amplifier included in the optical receiver according to the signal strength detected by the signal strength detection unit;
A threshold control unit that initializes a state of an automatic threshold control circuit included in the optical receiver according to the signal strength detected by the signal strength detection unit;
An optical repeater.   The delay time of the optical delay device is longer than the time required for the voltage control unit to control the impedance conversion amplifier and the threshold control unit to initialize the automatic threshold control circuit. The optical repeater according to claim 1.   3. The optical repeater according to claim 1, wherein the threshold control unit initializes a state of the automatic threshold control circuit when a specific signal pattern included in a burst signal is identified. A subscriber side device;
The optical repeater according to any one of claims 1 to 3, which relays a burst signal transmitted from the subscriber side device;
A station-side device that receives a burst signal relayed by the optical repeater;
An optical subscriber system comprising: In an optical subscriber system including a station side device, a transmission optical fiber, and a subscriber side device, a burst signal transmitted from a subscriber side device is received by an optical receiver and then transmitted by an optical transmitter.
An optical branching procedure for branching a burst optical signal transmitted from a subscriber side device;
One optical signal branched in the optical branching procedure is delayed, and the amount of input current to the impedance conversion amplifier of the optical receiver is controlled according to the signal strength of the other optical signal branched in the optical branching procedure. And an optical receiver control procedure for initializing a state of an automatic threshold control circuit included in the optical receiver;
A transmission procedure for transmitting by the optical transmitter after receiving the one optical signal branched in the optical branching procedure by the optical receiver;
An optical repeater method comprising:   6. The optical relay method according to claim 5, wherein, in the optical receiver control procedure, the state of the automatic threshold control circuit is initialized when a specific signal pattern is included in the burst signal.

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