JP6273704B2 - Optical repeater - Google Patents

Description

  The present invention relates to an optical repeater that is provided in the middle of an optical cable and amplifies and transmits attenuated signal light by an optical amplifier. In this specification and drawings, the laser diode is “LD (Laser Diode)”, the LD driver is “LDD (LD Driver)”, the polarization combiner is “PBC (Polarization Beam Combiner)”, and the multiplexer / demultiplexer is “CPL”. (Coupler) ”, optical amplifier“ AMP (amplifier) ”, transistor“ TR (transistor) ”, photodetector“ PD (Photo Detector) ”, resistor“ R (resistor) ”, and zener diode“ ZD (Zener Diode) ”, the remote operation IC is abbreviated as“ SV (supervisor) -IC ”, and the power supply circuit is abbreviated as“ PSC (Power Supply Circuit) ”.

  FIG. 3 is a block diagram showing an optical repeater of Related Technique 1. Hereinafter, description will be given based on this drawing.

  The optical repeater of Related Art 1 is an optical submarine repeater installed in an optical submarine cable path. The optical repeater of Related Art 1 is configured to drive four LDs and excite two AMPs.

  However, the related art 1 optical repeater does not have a backup function in the event of an LD failure. For this reason, the optical output as the optical repeater decreases when the LD fails. For example, when one LD fails, the pumping light power supplied to each AMP decreases to 3/4 of the normal time. In addition, in the optical repeater of the related art 1, four LDs are necessary to excite two AMPs, so that the component cost increases.

  FIG. 4 is a block diagram showing an optical repeater of Related Technique 2 disclosed in Patent Document 1. As shown in FIG. FIG. 5 is a partially enlarged view showing the 3 × 2 coupler in FIG. 4. Hereinafter, description will be given based on these drawings.

  In FIG. 4, a 3 × 2 coupler 110 as a light combining / branching device that combines and branches light input from pumping LDs 121, 122, 123 and input ports I1, I2, I3 and outputs the combined light to output ports O1, O2. An upstream amplification unit 100, a downstream amplification unit 100 ′, optical isolators 101, 101 ′, 102, 102 ′, optical multiplexers 105, 105 ′, erbium doped fibers 103, 103 ′, and the like are disclosed.

  In the optical repeater configured as described above, the pumping light generated from the LDs 121, 122, and 123 is incident on the input ports I1, I2, and I3 of the 3 × 2 coupler 110, respectively. In the 3 × 2 coupler 110, the excitation light incident from each input port is synthesized and branched, and is output to the output ports O1 and O2. That is, almost all of the light incident from the LD 121 to the input port I1 except for the loss is output to the output port O1, and almost all of the excitation light incident from the LD 122 to the input port I2 except for the loss is output port O2. In addition, the excitation light input from the LD 123 to the input port I3 is divided into two and output to the output ports O1 and O2, respectively.

  Then, the excitation light output from the output port O <b> 1 is applied to the optical multiplexer 105 of the upstream amplification unit 100 and is incident on the erbium-doped fiber 103. Thereby, in the erbium-doped fiber 103, the signal light LIN that has passed through the optical isolator 101 is amplified. Uplink signal light amplified in the erbium-doped fiber 103 is output as an output LOUT via the optical isolator 102. On the other hand, the excitation light output from the output port O2 of the 3 × 2 coupler 10 is applied to the optical multiplexer 105 'of the downstream amplification unit 100' and is incident on the erbium-doped fiber 103 '. As a result, the downlink signal light LIN ′ that has passed through the optical isolator 101 ′ is optically amplified in the erbium-doped fiber 103 ′ and output as an output LOUT ′ via the optical isolator 102 ′.

  In FIG. 5, LD 121, 122, 123, 3 × 2 coupler 110, polarization maintaining demultiplexer 111, polarization synthesis coupler 112, 113, and the like are disclosed. The polarization maintaining demultiplexer 111 is a beam splitter that divides the light incident from the input end into two while maintaining the polarization state and outputs the light to two output ends. The polarization combining couplers 112 and 113 are polarization beam splitters having two input ends orthogonal to each other, transmitting P-polarized light as it is, and reflecting S-polarized light by 100%. Are input, S-polarized light is input from the other input end, and the combined light of both is output from a single output end.

  In the 3 × 2 coupler 110 configured as described above, the excitation light generated in each of the LDs 121 to 123 is input to the 3 × 2 coupler 110 via the input ports I1 to I3 while holding the polarization plane. Here, P-polarized light is input from the LD 121 and LD 122, and S-polarized light is input from the LD 123. The P-polarized excitation light oscillated in the LD 121 is incident from one input of the polarization combiner 112 via the input port I1, and the P-polarized excitation light generated by the LD 122 is combined via the input port I2. The light enters from one input of the coupler 113. Further, the S-polarized excitation light oscillated in the LD 123 is divided into two in the polarization holding demultiplexer 111, and the two outputs of the polarization holding demultiplexer 111 are the polarization synthesis coupler 111 and the polarization synthesis coupler, respectively. The other input of 113 is incident. In addition, the vertical line in a figure represents P polarized light and the circle represents S polarized light.

  The P-polarized excitation light generated in the LD 121 and the light having half the power of the excitation light generated by the S-polarized LD 123 incident from the polarization holding demultiplexer 111 are combined in the polarization combiner 112. X2 is output to the output port O1 of the coupler 110. This output light is incident on the optical multiplexer 105 of the upstream amplification unit 100 shown in FIG. Similarly, the P-polarized excitation light generated in the LD 122 and the light having half the power of the excitation light generated by the S-polarized LD 123 incident from the polarization maintaining demultiplexer 111 are combined into a polarization combiner. The combined signal is output to the output port O 2 of the 3 × 2 coupler 110. This output light is incident on the optical multiplexer 105 'of the downstream amplification unit 100' shown in FIG.

  According to the optical repeater of Related Technology 2, even if any one of the LDs 121 to 123 fails, the pumping light power does not become zero. For example, when the LD 121 fails, the pumping light power at the output port O1 is reduced to 1/3 of the normal time. When the LD 122 fails, the pumping light power at the output port O2 is reduced to 1/3 of the normal time. When the LD 123 fails, the pumping light powers at the output ports O1 and O2 are reduced to 2/3 of the normal values.

JP-A-8-304860

  As described above, the optical repeaters of the related techniques 1 and 2 have a problem that the pumping light power is reduced when the LD fails. That is, there is a problem in that the optical output as the optical repeater decreases when the LD fails.

  Therefore, an object of the present invention is to provide an optical repeater in which the pumping light power does not decrease even when an LD fails.

The optical repeater according to the present invention is
Three laser diodes,
Two optical amplifiers,
A photosynthesis branching unit that equally distributes the respective excitation lights output from the three laser diodes to the two optical amplifiers;
A switch unit for individually turning on and off the three laser diodes;
A failure detection unit that individually detects a failure of each of the three laser diodes;
During normal operation, two of the three laser diodes are turned on via the switch unit, and the remaining laser diodes are turned off via the switch unit, and a failure of one of the two laser diodes is detected. A drive control unit that turns off the failed laser diode through the switch unit and turns on the remaining laser diode through the switch unit when detected through the failure detection unit;
Equipped with a,
The switch unit includes three transistors having two main terminals and one control terminal,
The three laser diodes are connected in series with each other,
Two main terminals of the three transistors are respectively connected in parallel to the three laser diodes,
Each one control terminal of the three transistors is connected to the drive control unit,
The failure detection unit includes three photodetectors provided at positions for detecting output lights of the three laser diodes, respectively.
Information detected by these photodetectors is output to the drive controller,
The drive control unit
A fourth transistor connected in series to the three laser diodes connected in series;
Regardless of the failure state of the three laser diodes, feedback control is performed on the fourth transistor so that the total output of the three photodetectors is always constant .

An optical repeater drive control method according to the present invention includes:
Three laser diodes,
Two optical amplifiers,
A photosynthesis branching unit that equally distributes the respective excitation lights output from the three laser diodes to the two optical amplifiers;
A switch unit for individually turning on and off the three laser diodes;
A failure detection unit that individually detects a failure of each of the three laser diodes;
For optical repeaters with
During normal operation, two of the three laser diodes are turned on through the switch unit and the remaining laser diodes are turned off through the switch unit,
When a failure of one of the two laser diodes is detected via the failure detection unit, the failed laser diode is turned off via the switch unit, and the remaining laser diodes are turned on via the switch unit. To
Is.

  According to the present invention, the optical synthesis branching unit that evenly distributes the respective excitation lights output from the three laser diodes to the two optical amplifiers is provided, and the two laser diodes are driven in a normal state. If a failure occurs, the spare laser diode is driven instead, so that the pumping light power does not change before and after the failure. Therefore, an optical repeater that does not decrease the pumping light power even when the laser diode fails can be provided.

1 is a block diagram illustrating an optical repeater according to Embodiment 1. FIG. It is a block diagram which shows the optical repeater of Embodiment 2. It is a block diagram which shows the optical repeater of related technology 1. It is a block diagram which shows the optical repeater of related technology 2. It is the elements on larger scale which show the 3x2 coupler in FIG.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention (hereinafter referred to as “embodiments”) will be described with reference to the accompanying drawings. In the present specification and drawings, the same reference numerals are used for substantially the same components.

  FIG. 1 is a block diagram illustrating an optical repeater according to the first embodiment. Hereinafter, description will be given based on this drawing.

  The optical repeater of the first embodiment includes an A-side configuration driven and controlled by the LDD circuit block A and a B-side configuration driven and controlled by the LDD circuit block B. The configuration on the A side and the configuration on the B side are the same, and a constant voltage is supplied in series from the PSC. Further, the case where only one of the A side and the B side is included in the first embodiment. Hereinafter, only the configuration and operation on the A side will be described, but the same applies to the configuration and operation on the B side. In addition, the drive control method of the optical repeater according to the first embodiment is based on the operation of the “drive control unit” as the invention of the method.

  The optical repeater (A side) of the first embodiment equally distributes the pumping light output from LD1, LD2, LD3, two AMP1, AMP2, and LD1, LD2, LD3 to AMP1, AMP2. Failures of TR1, TR2, TR3, LD1, LD2, and LD3 as “switch units” that individually turn on and off PBC-A and CPL-A as “photosynthesis branching units” and LD1, LD2, and LD3, respectively PD1, PD2, and PD3 as “failure detection units” to detect, and an LDD circuit block A as a “drive control unit”.

  The LDD circuit block A normally turns on LD1 and LD2 via TR1 and TR2 and turns off LD3 via TR3 and detects a failure of either LD1 or LD2 (for example, LD1) via PD1. At that time, LD1 is turned off via TR1 and LD3 is turned on via TR3.

  The “photosynthesis branching unit” includes a PBC-A having two input ends and one output end, and a CPL-A including a 3 dB coupler having two input ends and two output ends. The output sides of LD1 and LD2 are respectively connected to two input ends of PBC-A, one output end of PBC-A is connected to one input end of CPL-A, and the output side of LD3 is connected to CPL-A. Connected to the other input end, the two output ends of CPL-A are connected to the input sides of AMP1 and AMP2, respectively.

  The “switch unit” includes TR1, TR2, and TR3 having two main terminals and one control terminal. Since TR in the first embodiment is a bipolar transistor, the main terminal is a collector and an emitter, and the control terminal is a base. When TR is an FET, the main terminal is the source and drain, and the control terminal is the gate. LD1, LD2, and LD3 are connected in series with each other. The collectors and emitters of TR1, TR2 and TR3 are respectively connected in parallel to LD1, LD2 and LD3 (the anode and cathode thereof). Each base of TR1, TR2 and TR3 is connected to an output terminal of the LDD circuit block A.

  The “failure detection unit” includes PD1, PD2, and PD provided at positions for detecting the output lights of LD1, LD2, and LD3, respectively. The output terminals of PD1, PD2, and PD are connected to the input terminal of the LDD circuit block A. The wirings connecting PD1, PD2, PD and the LDD circuit block A are not shown because the drawing becomes complicated. The PSC in the first embodiment is composed of a plurality of ZDs, for example.

  According to the first embodiment, the PBC-A and the CPL-A that evenly distribute the respective excitation lights output from the LD1, LD2, and LD3 to the AMP1 and AMP2 are provided, and the LD1 and LD2 are driven during normal operation. If the LD fails, the spare LD3 is driven instead, so that the pumping light power does not change before and after the failure. Can be provided.

  Next, the optical repeater of the first embodiment will be described more specifically.

  In the first embodiment, six LDs are connected to one LDD. The LDD is composed of two circuit blocks A and B. The LDD circuit block A drives LD1, LD2 and LD3, and the LDD circuit block B drives LD4, LD5 and LD6, respectively. Hereinafter, the configuration and operation of the LDD circuit blocks A, LD1, LD2, and LD3 will be described, but the same applies to the circuit blocks B, LD4, LD5, and LD6. In the first embodiment, since each of the LDD circuit block A and the LDD circuit block B functions alone, the circuit configuration may be simplified.

  The optical outputs of LD1 and LD2 are synthesized by PBC-A and input to one input terminal of CPL-A. The output of LD3 is input to the other input terminal of CPL-A. The two outputs of CPL-A excite AMP1 and AMP2, respectively. In this optical circuit configuration, the optical powers of LD1, LD2, and LD3 are respectively input to AMP1 and AMP2 in half. That is, from the viewpoint of optical power distribution, LD1, LD2, and LD3 are equal to each other, and AMP1 and AMP2 are also equal to each other.

  On the electric circuit, a current monitoring RA is further inserted in series into LD1, LD2, and LD3 connected in series, and the terminal potential on the LD1 side of this RA is fed back to the LDD circuit block A. The Accordingly, an ACC (Automatic Current Control) loop is formed such that the LDD circuit block A controls TR7.

  The collectors and emitters of TR1, TR2, and TR3 are connected to the anodes and cathodes of LD1, LD2, and LD3, respectively, and TR1, TR2, and TR3 are connected in parallel to LD1, LD2, and LD3, respectively. In a normal operation state, TR3 is on. Therefore, since all the current flowing through the ACC loop is bypassed to the TR3 side at the connection portion between LD3 and TR3, LD3 is in an off state. In the normal operation state, the outputs of the PD1 and PD2 for monitoring the optical power of the LD1 and LD2 are fed back to the LDD circuit block A. In response to this, the LDD circuit block A controls the amount of current bypassed to the TR1 and TR2 sides, so that the LD1 and LD2 operate by APC (Automatic Power Control) control.

  Next, the operation at the time of LD failure will be described. For example, when LD1 fails, the LDD circuit block A detects that the output of PD1 has decreased. Then, the LDD circuit block A turns TR1 on and bypasses all the current flowing through the ACC loop to the TR1 side to turn LD1 off. At the same time, the LDD circuit block A switches the LD3 to the APC operation mode in which the amount of bypass current flowing to the TR3 side is controlled according to the output of the PD3 with respect to the TR3 that is on in the normal operation state. The APC control is turned on. That is, the switching operation of turning off LD1 and turning on LD3 with the failure of LD1 is performed. Although the case where LD1 has failed has been described above, the same applies to the case where LD2 fails.

  As for APC control, feedback may be applied to TR7 so that the total output of PD1, PD2, and PD3 is always constant regardless of the failure state of LD1, LD2, and LD3. By applying feedback in such a manner, LD1, LD2, and LD3 can be controlled by one feedback loop, so that the circuit scale of LDD can be reduced. At this time, a different value may be selected as a reference potential for applying feedback according to the number of failures of the LD. For example, when the reference potential when there is no LD failure or when the number of LD failures is 1 is VREF1, the reference potential VREF2 when the number of LD failures is 2 may be VREF2 = 0.5 × VREF1. Conceivable. By setting the reference potential in this way, it is possible to prevent an excessive current from flowing through the remaining one LD when the number of LD failures is two.

  Next, the SV-IC will be described. In the first embodiment, the SV-IC is connected to the LDD. This SV-IC has the following functions. First, a function of inputting a monitor signal of input / output signal strengths of AMP1 and AMP2, a control signal transmitted superimposed on a normal communication signal, and the like. Second, a function for receiving a monitor signal such as a current value of each LD from the LDD. Third, a function for giving a control signal to the LDD according to the input information. Similarly to the LDD, the SV-IC includes an SV circuit block A and an SV circuit block B. The SV circuit block A is connected to the LDD circuit block A, and the SV circuit block B is connected to the LDD circuit block B. .

  A configuration that includes only the LDD and does not include the SV-IC is also included in the first embodiment.

  Next, the first effect of the first embodiment will be described.

  The optical repeaters of the related techniques 1 and 2 have a problem that there is no backup function in the event of an LD failure, and the optical output as the optical repeater decreases when the LD fails.

  On the other hand, in the first embodiment, for example, even if the LD 1 fails, the LD 3 that has been turned off until then is turned on instead, so that the pumping light power does not decrease. As a result, a decrease in light output can be prevented. The same effect is obtained when LD2, LD4, and LD5 fail. Here, in the configuration of the optical circuit of the first embodiment, LD1, LD2, and LD3 are equal to each other from the viewpoint of optical power distribution, and AMP1 and AMP2 are also equal to each other. Similarly, LD4, LD5, and LD6 are equal to each other, and AMP3 and AMP4 are also equal to each other. Therefore, even if LD1, LD2, LD4, and LD5 fail, the pumping light power when switching to LD3 and LD6 is the same as before switching, so the optical output as an optical repeater is stabilized.

  Next, the second effect of the first embodiment will be described.

  In the optical repeater of the related art 1 shown in FIG. 3, four LDs are required to excite two AMPs, that is, two LDs are required for each AMP, which increases the cost of parts. was there.

  On the other hand, in the first embodiment, four AMPs can be excited by six LDs and one LDD, that is, only 3/2 LDs are required for each AMP, thereby reducing the number of parts. The manufacturing cost is reduced.

  FIG. 2 is a block diagram illustrating an optical repeater according to the second embodiment. Hereinafter, description will be given based on this drawing.

  The optical repeater of the second embodiment includes an A-side configuration driven and controlled by the LDD circuit block A and a B-side configuration driven and controlled by the LDD circuit block B. The configuration on the A side and the configuration on the B side are the same, and a constant voltage is supplied in parallel from the PSC. The first embodiment is different from the first embodiment in that the constant voltage is supplied in series from the PSC in the first embodiment, whereas the constant voltage is supplied in parallel from the PSC in the second embodiment. Is a point. Second, the power supply configuration of the entire electric circuit. In the second embodiment, a feeding current supplied from the outside as a constant current is converted into a constant voltage by the PSC. The constant voltage generated by the PSC is supplied to each circuit block A and each circuit block B of the LDD and SV-IC. Here, the second embodiment is different from the first embodiment in that the circuit blocks A and B of the LDD and SV-IC are connected in parallel to the PSC. Other configurations and operations of the second embodiment are the same as those of the first embodiment. The PSC in the second embodiment is composed of, for example, one or a plurality of ZDs.

  Next, the effect of the second embodiment will be described. In the first embodiment, a constant voltage is supplied in series from the PSC, whereas in the second embodiment, a constant voltage is supplied in parallel from the PSC. Therefore, the voltage drop of the entire electric circuit can be reduced to about half in the second embodiment as compared with the first embodiment.

  Although the present invention has been described with reference to the above embodiments, the present invention is not limited to the above embodiments. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention. Further, the present invention includes a combination of some or all of the configurations of the above-described embodiments as appropriate.

  In other words, the present invention is an optical repeater including an optical circuit in which three LDs are connected to two optical amplifiers, in which the optical power of each of the three LDs is equal to two optical amplifiers. In the normal use state, two of the three LDs are on, one is off, and one of the two LDs is on. When either one fails, the LD that is in the off state is turned on.

  Although a part or all of the above embodiments can be described as the following supplementary notes, the present invention is not limited to the following configurations.

[Appendix 1] Three laser diodes;
Two optical amplifiers,
A photosynthesis branching unit that equally distributes the respective excitation lights output from the three laser diodes to the two optical amplifiers;
A switch unit for individually turning on and off the three laser diodes;
A failure detection unit that individually detects a failure of each of the three laser diodes;
During normal operation, two of the three laser diodes are turned on via the switch unit, and the remaining laser diodes are turned off via the switch unit, and a failure of one of the two laser diodes is detected. A drive control unit that turns off the failed laser diode through the switch unit and turns on the remaining laser diode through the switch unit when detected through the failure detection unit;
Optical repeater with

[Appendix 2] The light combining branching unit includes a polarization combining coupler having two input ends and one output end, and a 3 dB coupler having two input ends and two output ends,
Two output sides of the three laser diodes are respectively connected to two input ends of the polarization combining coupler, and one output end of the polarization combining coupler is connected to one input end of the 3 dB coupler, The remaining one output side of the three laser diodes is connected to the other input end of the 3 dB coupler, and the two output ends of the 3 dB coupler are connected to the input sides of the two optical amplifiers, respectively.
The optical repeater according to appendix 1.

[Supplementary Note 3] The switch unit includes three transistors each having two main terminals and one control terminal.
The three laser diodes are connected in series with each other,
Two main terminals of the three transistors are respectively connected in parallel to the three laser diodes,
Each one control terminal of the three transistors is connected to the drive control unit,
The optical repeater according to appendix 1 or 2.

[Supplementary Note 4] The failure detection unit includes three photodetectors provided at positions for detecting output lights of the three laser diodes, respectively.
Information detected by these photodetectors is output to the drive control unit,
The optical repeater according to any one of appendices 1 to 3.

[Appendix 5] Two sets of the optical repeaters according to any one of Appendices 1 to 4 are provided,
These two sets of optical repeaters are each supplied with a constant voltage in parallel from the power supply circuit.
Optical repeater.

[Appendix 6] Three laser diodes;
Two optical amplifiers,
A photosynthesis branching unit that equally distributes the respective excitation lights output from the three laser diodes to the two optical amplifiers;
A switch unit for individually turning on and off the three laser diodes;
A failure detection unit that individually detects a failure of each of the three laser diodes;
For optical repeaters with
During normal operation, two of the three laser diodes are turned on through the switch unit and the remaining laser diodes are turned off through the switch unit,
When a failure of one of the two laser diodes is detected via the failure detection unit, the failed laser diode is turned off via the switch unit, and the remaining laser diodes are turned on via the switch unit. To
Optical repeater drive control method.

[Appendix 11] An optical repeater including an optical circuit in which three LDs are connected to two optical amplifiers,
In the optical circuit, the optical power of each of the three LDs is equally distributed to the two optical amplifiers, respectively.

[Supplementary Note 12] An optical repeater including the optical circuit according to Supplementary Note 11,
LD1 and LD2 are connected by PBC or the like, the output is connected to one input of the multiplexer / demultiplexer, and the output of LD3 is connected to the other input of the multiplexer / demultiplexer, and the multiplexer / demultiplexer is connected. An optical repeater comprising an optical circuit in which two outputs of a duplexer are connected to an optical amplifier 1 and an optical amplifier 2, respectively.

[Supplementary Note 13] The optical repeater according to Supplementary Note 11 or 12,
In normal use, two of the three LDs are on and one is off.
An optical repeater characterized in that when one of two LDs in the on state fails, the LD in the off state is turned on.

[Appendix 14] An LDD comprising a plurality of circuit blocks,
An LDD in which one circuit block controls one or more LDs.

[Supplementary Note 15] The LDD according to Supplementary Note 14,
A plurality of circuit blocks are each provided with a power supply terminal for supplying power,
An LDD characterized in that a plurality of circuit blocks can be connected in series or in parallel by changing the connection method between the power supply terminals.

[Supplementary Note 16] An optical repeater including the LDD according to Supplementary Note 14 or 15,
An optical repeater characterized in that each of the plurality of circuit blocks controls the three LDs described in appendix 11, 12 or 13.

  The present invention can be used in general for optical repeaters used for optical communication, and is particularly suitable for optical submarine repeaters.

LD Laser diode LDD LD driver PBC Polarization combining coupler CPL multiplexer / demultiplexer AMP Optical amplifier TR Transistor PD Photodetector R Resistor SV-IC Remote operation IC
PSC power circuit

Claims (4)

Three laser diodes,
Two optical amplifiers,
A photosynthesis branching unit that equally distributes the respective excitation lights output from the three laser diodes to the two optical amplifiers;
A switch unit for individually turning on and off the three laser diodes;
A failure detection unit that individually detects a failure of each of the three laser diodes;
During normal operation, two of the three laser diodes are turned on via the switch unit, and the remaining laser diodes are turned off via the switch unit, and a failure of one of the two laser diodes is detected. A drive control unit that turns off the failed laser diode through the switch unit and turns on the remaining laser diode through the switch unit when detected through the failure detection unit;
Equipped with a,
The switch unit includes three transistors having two main terminals and one control terminal,
The three laser diodes are connected in series with each other,
Two main terminals of the three transistors are respectively connected in parallel to the three laser diodes,
Each one control terminal of the three transistors is connected to the drive control unit,
The failure detection unit includes three photodetectors provided at positions for detecting output lights of the three laser diodes, respectively.
Information detected by these photodetectors is output to the drive controller,
The drive control unit
A fourth transistor connected in series to the three laser diodes connected in series;
Regardless of the failure state of the three laser diodes, feedback control is performed on the fourth transistor so that the total output of the three photodetectors is always constant.
Optical repeater.   As the reference potential for the feedback control, when the reference potential when the three laser diodes are not broken or when the number of failures is one is VREF1, the reference potential VREF2 when the number of failures is two is VREF2. = 0.5 × VREF1
  The optical repeater according to claim 1. The light combining / branching unit includes a polarization combining coupler having two input ends and one output end, and a 3 dB coupler having two input ends and two output ends,
Two output sides of the three laser diodes are respectively connected to two input ends of the polarization combining coupler, and one output end of the polarization combining coupler is connected to one input end of the 3 dB coupler, The remaining one output side of the three laser diodes is connected to the other input end of the 3 dB coupler, and the two output ends of the 3 dB coupler are connected to the input sides of the two optical amplifiers, respectively.
The optical repeater according to claim 1. Two sets of the optical repeater according to any one of claims 1 to 3 ,
These two sets of optical repeaters are each supplied with a constant voltage in parallel from the power supply circuit.
Optical repeater.

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