JP6064620B2 - Optical transmitter - Google Patents

Description

  The present invention relates to an optical transmitter that generates an optical signal based on an electrical signal.

  IEEE 802.3ba and IEEE 802.3bg are defined as standards for optical transmission networks in order to eliminate bottlenecks in the transmission capacity of communication between servers. In response to these standards, optical communication modules are required to expand optical transmission capacity to 40 Gbps or 100 Gbps. In order to generate a high-quality optical signal with a communication speed of 40 Gbps, an EA (Electronic Absorption) optical modulator is used as an optical modulator in the optical transmission module, and an optical modulator driving circuit is used for driving the optical modulator. Is used. Further, the optical transmission module is provided with a control circuit. The control circuit receives setting information from the host and controls each part in the module, monitors each part and notifies the host of various information such as an alarm. .

  As an optical modulator driving circuit, for example, Patent Document 1 below discloses a circuit having a cross point adjustment function for adjusting a cross point of a waveform of an optical signal. Patent Document 2 below discloses a circuit capable of adjusting a cross point in a drive signal output from a semiconductor laser drive circuit.

JP 2000-59317 A JP 2004-31396 A JP 2001-257645 A JP 2003-348021 A

  In the conventional optical transmission module as described above, if the electrical signal or the reference clock given from the host device is different from the preset frequency or does not have sufficient amplitude, there is an abnormality on the optical transmission network side. In order to prevent random noise from being transmitted, control is performed to turn off the output of the multiplexed electrical signal. In the optical transmission module having such an output off function and the cross point adjustment function as described in Patent Documents 1 and 2 above, when the multiplexed electrical signal output is turned off, it is more than the on state. In some cases, abnormally high optical power was output (excessive light emission).

  As a measure for solving such a problem, a method of performing feedback control based on the light output intensity as described in Patent Document 3 described above, or a directly modulated laser diode element as described in Patent Document 4 described above is used. There is known a method for preventing excessive light emission by providing an external device for adjusting the light output intensity with an optical transmitter. However, in order to apply any of these measures to driving the EA optical modulator, there is a problem that the circuit configuration becomes complicated and is not economical.

  Accordingly, an object of the present invention has been made in view of the above matters, and provides an optical transmitter capable of preventing over-light emission when a clock signal applied from the outside is abnormal with a simple circuit configuration. It is to be.

  In order to solve the above-described problems, an optical transmitter according to the present invention receives a reference clock and receives a first phase synchronization circuit for removing a jitter component of the reference clock and an output of the first phase synchronization circuit. Generating and outputting a multiplied clock synchronized with the output, and outputting an alarm signal when the frequency of the output is out of the predetermined range and abnormal, a multiplied clock, and an external And an optical transmission circuit that outputs an optical signal modulated based on the electrical signal.

  According to the optical transmitter of the present invention, after the jitter component of the reference clock is removed by the first phase synchronization circuit, the second phase synchronization circuit generates the multiplied clock synchronized with the reference clock, and the reference clock Is detected, and an optical signal is output based on the multiplied clock and the electrical signal output from the second phase synchronization circuit by the optical transmission circuit. This eliminates the delay in detecting the frequency of the reference clock in order to eliminate jitter. By controlling the optical output to stop in response to this error detection, the clock signal can be detected with a simple circuit configuration. In such a case, excessive light emission can be prevented.

  The jitter pass band of the first phase locked loop is preferably narrower than the jitter pass band of the second phase locked loop. With this configuration, it is possible to achieve both clock jitter removal processing and rapid clock abnormality detection processing with a simple circuit configuration.

  It is also preferable that the output response time of the alarm signal of the second phase synchronization circuit is set to be shortened according to the widening of the jitter pass band of the second phase synchronization circuit. In this case, over-light emission can be reliably prevented by optimizing the processing time of the clock abnormality detection processing.

  Furthermore, it is also preferable that the optical transmission circuit has a control terminal for controlling the interruption of the optical signal, and interrupts the optical signal when an alarm signal is received by the control terminal. In this way, the optical output can be reliably stopped in response to the detection of the clock abnormality.

  According to the present invention, it is possible to prevent excessive light emission when a clock signal supplied from the outside is abnormal with a simple circuit configuration.

It is a block diagram which shows schematic structure of the optical transmitter which concerns on embodiment. FIG. 2 is a block diagram illustrating in detail a connection configuration of a control unit of the optical transmitter in FIG. 1. It is a circuit diagram which shows the detailed structure of the optical transmission part 5 of FIG. It is a graph which shows the relationship between the input voltage and optical output of a common EA optical modulator. It is a flowchart which shows the procedure of the control operation | movement by the control part 7 of FIG. It is a figure which shows the connection structure of the EA optical modulator 5b and the optical modulator drive circuit 5c in the optical transmission part 5 of FIG. (A) is a diagram showing the waveforms of the sink current Iout and applied voltage Vea when the multiplexed electrical signal is on, and (b) is the waveform of the sink current Iout and applied voltage Vea when the multiplexed electrical signal is off. FIG. It is a graph which shows the example of calculation of the direct current component Veadc of the applied voltage with respect to the EA optical modulator at the time of multiplexing signal ON and OFF. It is a block diagram which shows schematic structure of the optical transmitter concerning the comparative example of this invention.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the description of the drawings, if possible, the same elements are denoted by the same reference numerals, and redundant description is omitted. The optical transceiver module 1 according to the present embodiment is an apparatus including an optical transmitter that receives an electrical signal input from a host device that is an external device and outputs an optical signal in accordance with the electrical signal.

  The configuration of the optical transceiver module 1 will be described with reference to FIGS. As shown in these figures, the optical transmission / reception module 1 receives a reference clock signal from an external host device and four pairs of electrical signals having a transmission rate of 10 Gbps, for example. A multiplexing unit 3 that multiplexes and outputs an electrical signal of 40 Gbps, an optical transmission unit 5 that generates an optical signal based on the electrical signal received from the multiplexing unit 3 and outputs the optical signal toward the optical transmission network, and a control unit 7.

The multiplexing unit 3 is configured by an integrated circuit (IC) and mainly includes phase synchronization circuits 3a and 3b, a frame processing unit 3d, and a multiplexing processing unit 3e. Phase synchronization circuit 3a receives the reference clock CL ₁ of a predetermined frequency from the outside, the jitter components of the reference clock CL ₁ is removed to output the reference clock CL _2. The phase synchronization circuit 3a, the jitter component of the reference clock CL ₁ to be able to sufficiently removed, the bandwidth of the PLL (phase locked loop) is formed by a narrowed phase synchronizing circuit to 1KHz below. Further, the phase synchronization circuit 3a, when the frequency of the reference clock CL ₁ from the outside is abnormal out of a predetermined frequency, and outputs the reference clock CL ₂ of a predetermined frequency by performing a free-running oscillation. Phase synchronization circuit 3b receives the reference clock CL ₂ output from the phase synchronization circuit 3a, a phase synchronization circuit for generating and outputting a multiplied clock CL ₃ to be synchronized with the reference clock CL _2. In the phase synchronization circuit 3b, the bandwidth of the PLL is widened to about several MHz or more compared to the phase synchronization circuit 3a. Further, the phase synchronization circuit 3b, if the frequency of the reference clock CL ₂ input is out of a predetermined frequency range, or if the amplitude of the reference clock CL ₂ is smaller than the prescribed value, the reference clock CL ₂ An abnormality is detected and an alarm signal ALM ₁ is output.

Phase locked loop 3b of the multiplexing unit 3 receives the reference clock CL ₂ output from the phase synchronization circuit 3a, and outputs the frequency of the reference clock by multiplying. For example, the phase synchronization circuit 3b generates a clock corresponding to the transmission speed of the electrical signal from the host device and a clock corresponding to the transmission speed of the electrical signal multiplexed by the multiplexing processing unit 3e, respectively. The data is output to the frame processing unit 3d and the multiplexing processing unit 3e. The frame processing unit 3d receives four pairs of electric signals D ₁ , D ₂ , D ₃ , and D ₄ input from the host device, and executes frame processing using the clock generated by the phase synchronization circuit 3b. . By the frame processing, the time series data included in the four pairs of electrical signals are sequentially output to the multiplexing processing unit 3e in synchronization. The frame processing section 3d, when the electrical signal _{D 1, D 2, D 3} , and detects the frequency or abnormal state of the amplitude of the _{D 4} is carried out also generates and outputs an alarm signal ALM _1. The multiplexing processing unit 3e receives four pairs of time-series data from the frame processing unit 3d, and executes multiplexing processing using the clock generated by the phase synchronization circuit 3b. By this multiplexing processing, an electric signal D ₀ in which four pairs of time-series data are multiplexed is generated and output to the optical transmitter 5.

Here, the optical transceiver module 1 is configured so that the alarm signal ALM ₁ output from the multiplexing unit 3 can be notified to the control unit 7. For example, the multiplexing unit 3 and the control unit 7 may be electrically connected so as to be notified to the control unit 7 via the hard pin (control terminal) 3f of the IC including the multiplexing unit 3, Information may be notified from the multiplexing unit 3 to the control unit 7 by storing alarm state information based on the alarm signal ALM ₁ in a register in the IC. In the present embodiment, it is preferable to employ a configuration for notifying the alarm signal ALM ₁ via the hard pin 3f in order to speed up the control of stopping optical output. That is, as will be described later, hard pin 3f is provided for controlling the interruption of the optical signal by the control unit 7, the control unit 7 blocks the light signal upon receipt of the alarm signal ALM ₁ through hard pin 3f It is configured as follows.

The optical transmitter 5 includes a laser diode element 5a that generates an optical signal, an EA optical modulator 5b that modulates the optical signal, and an optical modulator drive circuit 5c that drives the EA optical modulator 5b. Yes. Optical modulator driving circuit 5c, by increasing or decreasing the drive voltage applied to the EA modulator 5b based on an electrical signal D ₀ output from the multiplexer 3, the light transmitted from the laser diode element 5a to the outside signal, to modulate the data contained in the electrical signal D ₀ based. In the optical transmitter 5 having such a configuration, a current source 9a for supplying a bias current to the laser diode element 5a is connected to the laser diode element 5a via a switch 9b, and the EA optical modulator 5b has an EA A bias voltage source 9c for applying a bias voltage to the optical modulator 5b is connected.

  The control unit 7 is an arithmetic circuit including a microprocessor, a DA converter, an AD converter, and the like. The control unit 7 receives various setting information from the host device and controls each unit of the optical transmission / reception module 1. The state of the signal is monitored, and various information such as an alarm signal is notified to the host device according to the monitoring result. Specifically, the control unit 7 is connected to a current source 9a, a switch 9b, a bias voltage source 9c, a hard pin 3f, and an optical modulator driving circuit 5c. The control unit 7 sets the light emission intensity of the laser diode element 5a by controlling the current source 9a, and controls on / off of the current flowing through the laser diode element 5a by controlling the switch 9b. Toggle on / off. The control unit 7 also adjusts the bias voltage applied to the EA optical modulator 5b by controlling the bias voltage source 9c. Further, the control unit 7 adjusts the cross point of the optical signal by controlling the optical modulator driving circuit 5c.

At this time, in the control unit 7, the microprocessor generates a control value for various controls with a digital value, converts the control value into an analog value with a DA converter, and outputs the analog value. For this reason, in the control processing in the control unit 7, a delay corresponding to the time of the periodic processing of the microprocessor occurs. Therefore, in the on / off control of the optical signal, a switch 9 b for shutting down the optical signal at high speed is provided. . When the control unit 7 receives the alarm signal ALM ₁ from the multiplexing unit 3 and recognizes the occurrence / recovery of the abnormality of the reference clock CL ₂ or the electric signals D ₁ , D ₂ , D ₃ , and D ₄ by the interrupt processing, The optical signal is turned off / on by directly controlling the switch 9b via the digital port.

FIG. 3 is a circuit diagram showing a detailed configuration of the optical transmitter 5 of FIG. As shown in the figure, the light transmission unit 5, two differential signal Din is generated from the electrical signals _{D 0,} two differential output Dout undergoing DinB, a buffer circuit 11 which generates a DoutB, control voltage A cross-point adjusting circuit 15 that receives the voltage from the source 13 and adjusts the cross-point of the two differential outputs Dout and DoutB, termination resistors 17a and 17b that terminate the two differential outputs of the buffer circuit 11, and termination resistors A capacitor 19 connected in series to 17a and 17b to cut the DC component of the two differential outputs Dout and DoutB, and a bias voltage source connected to the two differential outputs Dout and DoutB via termination resistors 17a and 17b 9c. Further, the EA optical modulator 5b is output to the differential output Dout of the buffer circuit 11 through the transmission line 21, and a terminal resistor 23 and a DC component cutting capacitor are connected to both ends of the EA optical modulator 5b. 25 is connected.

  FIG. 4 shows the relationship between the input voltage and the optical output of a general EA optical modulator. As described above, in the EA optical modulator, the relationship between the input voltage and the modulated light output is nonlinear, and in order to adjust the cross point of the optical output, it is necessary to adjust the cross point of the input voltage. Therefore, in the optical transmission unit 5 configured as described above, the voltage of the control voltage source 13 is adjusted by the control of the control unit 7, thereby providing an offset potential between the differentials of the buffer circuit 11, thereby providing two differentials. Adjustment of the cross points of the outputs Dout and DoutB is made possible.

  Next, an operation procedure of optical signal on / off control by the control unit 7 of the optical transceiver module 1 will be described with reference to FIG. FIG. 5 is a flowchart showing the procedure of the control operation by the control unit 7.

The monitoring process and the control process by the control unit 7 are executed by a periodic process by the microprocessor. First, when this periodic process is activated, the alarm signal ALM ₁ from the multiplexing unit 3 is accepted by the interrupt process, and an abnormality occurs in the reference clock CL ₂ or the electric signals D ₁ , D ₂ , D ₃ , D _4. (Hereinafter, simply referred to as “signal abnormality occurrence”) is confirmed (step S01, abnormality confirmation processing). As a result, when the occurrence of signal abnormality is not confirmed (step S02; NO), the abnormality confirmation process is repeated again in the next cycle. On the other hand, if an abnormality is confirmed (step S02; YES), the optical signal is shut down by controlling the switch 9b by the controller 7 (step S03).

Thereafter, the abnormality confirmation process is repeated again in the periodic process, and the occurrence of the abnormality of the reference clock CL ₂ and the electric signals D ₁ , D ₂ , D ₃ , and D ₄ is continuously performed N times (N is a specified integer). It is determined whether or not a state in which there is no error (hereinafter simply referred to as “normal state”) has been confirmed (step S04). As a result of the determination, when a normal state is confirmed N times consecutively (step S04; YES), the counter stored in the control unit 7 is reset (step S05). The drive current of the laser diode element 5a, the cross point in the output of the buffer circuit 11, and the bias voltage of the EA optical modulator 5b are set to normal values (normal setting values), and the optical output is returned to the normal state (step). S06). Then, the process is returned to step S01, and the abnormality confirmation process is repeated. As described above, when the recovery from the abnormality is determined several times in succession, the normal state is restored, and thus the phase synchronization circuit 3b erroneously returns the alarm signal due to the harmonics of the reference clock or the like. However, excessive light emission can be prevented.

  On the other hand, if the signal abnormality has continued, or if it has not been confirmed that it has recovered to a normal state but has been continuously recovered N times (step S04; NO), the control unit 7 Set to low light output state. That is, the control unit 7 sets any one or all of the drive current of the laser diode element 5a, the cross point in the output of the buffer circuit 11, and the bias voltage of the EA optical modulator 5b so that the preset over-emission does not occur ( (Low light output set value) (step S07). Thereafter, the bias current of the laser diode element 5a shut down in step S03 is turned on by the control of the switch 9b (step S08).

  Next, it is determined whether or not the counter inside the control unit 7 has reached a predetermined value (step S09). If the counter has not reached the predetermined value (step S09; NO), 1 is added to the counter (incremented), and the process returns to step S04 (step S10). On the other hand, when the counter reaches a predetermined value (step S09; YES), it is determined that the signal abnormality has continued for a long time, and the initialization processing of the control unit 7 and the multiplexing unit 3 is executed. The Specifically, after the counter of the control unit 7 is reset (step S11), the bias current of the laser diode element 5a is turned on (step S12), and initialization processing of the control unit 7 and the multiplexing unit 3 is executed. (Step S13). Thereafter, the process returns to step S01, and the abnormality confirmation process is repeated. As a result, the automatic return can be smoothly executed after the reference clock or the like is normally returned. Here, the predetermined value that is referred to in the determination in step S09 is set to a value that does not make the operation unstable by repeating the initialization process due to noise or the like, for example, a value corresponding to a sufficiently long time of about 3 seconds. Is done.

According to the optical transceiver module 1 described above, the jitter component of the reference clock CL ₁ from the outside after being removed by the phase synchronization circuit 3a, the phase synchronization circuit 3b, the reference clock CL ₂ output from the phase synchronization circuit 3a Reproduction and frequency abnormality detection of the reference clock CL ₂ are performed, and the frame processor 3d, the multiplexing processor 3e, and the optical transmitter 5 receive the reference clock CL ₃ output from the phase synchronization circuit 3b and an external signal. An optical signal is output based on the electric signals D ₁ , D ₂ , D ₃ , D ₄ . Further, the control unit 7 controls the optical signal to be shut down when the alarm signal ALM ₁ is received from the phase synchronization circuit 3b. As a result, the abnormality detection of the frequency of the reference clock is not delayed due to the jitter removal function, and the clock signal can be generated with a simple circuit configuration by controlling the optical output to stop according to the abnormality detection. Excessive light emission in the case of an abnormality can be prevented.

  Here, since the jitter pass band of the phase synchronization circuit 3a is narrower than the jitter pass band of the phase synchronization circuit 3b, the jitter removal process of the reference clock and the rapid abnormality detection process of the reference clock can be made compatible.

Further, the output response time of the alarm signal ALM ₁ of the phase synchronization circuit 3b is set to be shortened in accordance with the widening of the jitter pass band of the phase synchronization circuit 3b. Over light emission can be reliably prevented by optimizing the time. For example, since the PLL band of the phase synchronization circuit 3b is set as wide as several MHz, the output response time of the alarm signal ALM1 can be shortened to ₁ μsec or less.

Further, the phase synchronization circuit 3a, when the reference clock CL ₁ is abnormal, outputs the reference clock CL ₂ of a predetermined frequency by performing a free-running oscillation. Thus, the clock of the reference clock abnormality prescribed frequency to multiplexing section 3 even when it is supplied, it is possible to prevent the multiplexing section 3 becomes excessive emission will be off the multiplexed electrical signal D _0.

The operation and effect of the optical transceiver module of this embodiment will be described in more detail in comparison with a comparative example. FIG. 9 shows a configuration of an optical transceiver module 901 according to a comparative example of the present invention. The optical transmission / reception module 901 shown in the figure is different from the optical transmission / reception module 1 according to this embodiment in that the phase synchronization circuits 3b and 3a having a two-stage configuration are changed to a phase synchronization circuit 903a having a one-stage configuration. is there. The phase synchronization circuit 903a provided in the optical transceiver module 901 is a circuit having a narrow PLL bandwidth of 1 KHz or less in order to satisfy a jitter standard allowed for an optical transmission signal in a public communication network having an optical transmission capacity of 40 Gbps. Required. In such a configuration, the response time is the alarm signal ALM ₂ to the output of multiplexer 903 changes according to the time constant of the phase synchronization circuit 903a in the multiplexing unit 903, if the bandwidth of the degree 1KHz below The response time is about several milliseconds. In such a response time, the shutdown of the optical signal is delayed, and a failure may occur in the reception circuit facing the optical transmission / reception module 901. In contrast, in the present embodiment, two-stage and is phase synchronous circuit 3a, because it uses the 3b, while satisfying the requirements of jitter suppression, since the response time of the alarm signal ALM ₁ is sufficiently short Excessive light emission can be reliably prevented.

In the optical transceiver module 1 according to this embodiment, when a signal abnormality is detected by the alarm signal ALM _1, by the bias current of the laser diode element 5a is turned off, the optical signal is shut down. On the other hand, in the conventional general optical transceiver module, in order to prevent random noise from being transmitted to the public communication network when the reference clock or an external electric signal is abnormal, multiplexing is performed. The electrical signal is turned off. However, in an optical transmission / reception module having a cross-point adjustment function as described in Japanese Patent Application Laid-Open No. 2000-059317 and Japanese Patent Application Laid-Open No. 2004-31396, when the multiplexed electric signal is turned off, it is higher than the on state. Optical power may be output.

  Such a conventional problem will be described more specifically. FIG. 6 shows a connection configuration of the EA optical modulator 5b and the optical modulator drive circuit 5c in the optical transmitter 5. Normally, when the EA optical modulator is driven, the cross point in the applied voltage Vea is shifted to the high level side in order to compensate for nonlinearity of the input / output characteristics (FIG. 4). In such a state, when the multiplexed electric signal is turned off, the sink current Iout of the buffer circuit 11 disappears, so that the voltage drop due to the termination resistor 17a of the resistance value Rout decreases, and the bias voltage applied by the bias voltage source 9c. Vbias itself appears as the applied voltage Vea. This means that the applied voltage Vea rises above the cross-point potential when the multiplexed electrical signal is on. Therefore, the optical output Pout of the EA optical modulator 5b rises from the average output level when the multiplexed electrical signal is on when the multiplexed electrical signal is off, and enters an over-light emission state.

FIG. 7 shows changes in the waveforms of the sink current Iout and the applied voltage Vea when the multiplexed electrical signal is turned on / off. The average DC component value of the applied voltage Vea is given by the following formula:
Veadc = −Ioutdc × Rout + Vbias
(Ioutdc is a direct current component of the sink current Iout). The DC component Ioutdc of the sink current converges to the current value at the cross point when the multiplexed electrical signal is off. This is because the cross point is adjusted by applying an offset potential between the differentials. Further, when the multiplexed signal is on, the DC component Ioutdc is a value obtained by integrating and averaging the suction current Iout along the time axis, but from 50% of the peak current even when the cross point is shifted. It does not change greatly.

  FIG. 8 shows an example in which the DC component Veadc when the multiplexed signal is on and off is specifically calculated using the above formula. Here, the peak value of the sink current Iout is set to 80 mA, and the cross point when the multiplexed signal is turned on is set to 85% at the applied voltage Vea, that is, 15% at the sink current Iout. The ratio of the direct current component Ioutdc to the peak is 15% when off, but is approximately 45% when on, depending on the rise time, fall time, or signal pattern. As a result of calculating the direct current component Vedc, it was -2.3V when turned on and -1.1V when turned off. As the applied voltage Vea is higher, the light output Pout is larger, and therefore, the light emission is excessive when compared to when it is turned on.

In the present embodiment, when the occurrence of a signal abnormality is detected by the alarm signal ALM ₁ , the optical signal is shut down, so even if an optical modulator driving circuit having a crosspoint adjustment function is used, Excessive light emission can be reliably prevented.

  While the principles of the invention have been illustrated and described in the preferred embodiments, it will be appreciated by those skilled in the art that the invention can be modified in arrangement and detail without departing from such principles. The present invention is not limited to the specific configuration disclosed in the present embodiment. We therefore claim all modifications and changes that come within the scope and spirit of the following claims.

For example, the optical transceiver module 1 of this embodiment, the drive current supplied to the laser diode element 5a has been controlled to be turned off when a signal abnormality is detected by the alarm signal ALM _1, over Other methods may be adopted as a control method for preventing light emission. Specifically, as shown in FIG. 8, the control unit 7 controls the control voltage source 13 when the multiplexed electrical signal is off so that the DC component Veadc does not change between when the multiplexed electrical signal is off and when it is on. The control voltage value may be changed to a value that causes the cross point of the current Iout to be 45%, which is the same as the ON time.

  DESCRIPTION OF SYMBOLS 1 ... Optical transmission / reception module (optical transmitter) 3 ... Multiplexing part, 3a, 3b ... Phase synchronization circuit, 3d ... Frame processing part, 3e ... Multiplexing processing part, 3f ... Hard pin (control terminal), 5 ... Optical transmission part (Optical transmission circuit), 7... Control unit.

Claims (4)

A first phase synchronization circuit that receives a reference clock and removes a jitter component of the reference clock;
A second clock that receives the output of the first phase synchronization circuit, generates and outputs a multiplied clock synchronized with the output, and outputs an alarm signal when the frequency of the output is out of a predetermined range and is abnormal. A phase synchronization circuit;
An optical transmission circuit that receives the multiplied clock and an external electric signal, and outputs an optical signal modulated based on the electric signal;
An optical transmitter comprising: A jitter pass band of the first phase locked loop is narrower than a jitter pass band of the second phase locked loop;
The optical transmitter according to claim 1. The output response time of the alarm signal of the second phase synchronization circuit is set to be shortened according to the widening of the jitter pass band of the second phase synchronization circuit.
The optical transmitter according to claim 1 or 2. The optical transmission circuit has a control terminal for controlling the interruption of the optical signal, and interrupts the optical signal when the alarm signal is received by the control terminal.
The optical transmitter according to any one of claims 1 to 3.

Images