JP2006197447A - Constant light emission prevention circuit in optical transmitter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stop a light emission output by automatically detecting abnormal light emission when an optical signal is outputted while the optical signal is not originally outputted due to a failure inside an optical transmitter about a constant light emission prevention circuit in the optical transmitter of a subscriber's line optical terminating unit (ONU) or the like. <P>SOLUTION: A photodiode (PD) 2 monitors an optical output of a laser diode (LD) 1, and the optical output is inputted as a peak detection signal (SPD) to a coincidence determination circuit 6 through a peak detection circuit 5. An AND signal (drive signal of laser diode (LD) 1) of a data signal (SDATA) and a bias signal (BIAS) is inputted to the other terminal of the coincidence determination circuit 6 through a delay circuit 8, and when the coincidence determination circuit 6 determines that a delay signal (SDLY) does not coincide with the peak detection signal (SPD), an optical output interruption circuit 9 performs control so as to prevent the laser diode (LD) 1 from emitting light by making a drive circuit 7 of the laser diode (LD) 1 stop the transmission of drive signal. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a constant light emission prevention circuit for preventing a state in which an optical signal is always output due to a failure or malfunction in an optical transmitter such as a subscriber line optical terminal unit (ONU: Optical Network Unit).

  At present, various communication technologies using optical fiber transmission are being researched and developed in order to construct an ultra-high-speed digital transmission system over a wide range at a low cost in accordance with the information society that is becoming more and more advanced. Here, a conventional optical signal burst transmission system will be described.

  FIG. 5 shows a schematic configuration diagram of a Passive Optical Network (hereinafter referred to as PON) system. The PON system is a network system in which a branching device is inserted in the middle of an optical fiber network and a single fiber is drawn into a plurality of subscriber homes. In the PON system shown in FIG. 5, three subscriber line optical terminal units (ONUs) 111, 112, and 113 are connected to the optical subscriber line terminal unit in the station building 115 through the star force plug 114. A configuration example is shown.

  In the PON system shown in FIG. 5, the optical signals from each of the subscriber line optical terminal units (ONUs) 111 to 113 are time-division multiplexed as a certain set of data strings (burst signal cells) so that they do not overlap each other. Are transmitted in the direction of the station (hereinafter referred to as the upward direction). In this transmission, the optical transmitters of the subscriber line optical termination units (ONUs) 111 to 113 individually monitor each transmission optical signal to determine whether or not a signal with a normal optical output level is being transmitted. It is necessary to have.

  Here, an optical output interruption detection circuit in an optical transmitter of a conventional subscriber line optical termination unit (ONU) will be described with reference to FIG. FIG. 6 shows a circuit diagram of a conventional light output break detection circuit. As shown in FIG. 6, the conventional light output break detection circuit includes a laser diode (LD) 101, a photo diode (PD) 102, a preamplifier 103, an amplifier 104, a peak detection circuit 105, a comparator 106, and a drive. The circuit 107 is configured.

  The drive circuit 107 outputs a signal digitally modulated by the input bias signal (BIAS) and the data signal (DATA) as a drive signal, and causes the laser diode (LD) 101 to emit light. The photo diode (PD) 102 monitors a part of the output light of the laser diode (LD) 101 and generates a photocurrent according to the output light.

  The preamplifier 103 performs current / voltage conversion on the photocurrent and outputs a voltage signal. The amplifier 104 further amplifies the output signal from the preamplifier 103. The peak detection circuit 105 detects the peak value of the voltage signal amplified by the amplifier 104.

  The comparator 106 compares the peak value output from the peak detection circuit 105 with the reference voltage Vref, and detects whether the optical output level is equal to or higher than a required value. As described above, it has a function of detecting whether an optical output level higher than a required value is output or in a state where the output is cut off, and outputting it as an alarm signal when the output cut is detected.

The above-described conventional light output interruption detection circuit is described in the following patent documents.
JP 2000-165323 A Japanese Patent Laid-Open No. 2001-168552

  However, in the conventional light output interruption detection circuit, it is possible to detect whether or not an optical output level exceeding the required value is output, but an optical signal should not be output due to an internal failure of the optical transmitter. When an optical signal is output during the period, it is impossible to detect the abnormality and stop the output of the optical signal.

  In particular, when an optical signal is output during a period in which the optical signal should not be output in the subscriber line optical termination unit (ONU) of the PON system, all other subscriber line optical terminations in time division multiplexing are used. There is a problem that it overlaps with the transmission optical signal from the unit (ONU) and adversely affects the communication of all other normal subscriber line optical terminators (ONUs).

  The present invention has been made in view of the above circumstances, and an optical signal is transmitted during a period in which an optical signal should not be output due to a failure or failure occurring in an optical transmitter such as a subscriber line optical terminal unit (ONU). An object of the present invention is to provide a constant light emission prevention circuit that automatically detects the abnormal light emission when it is output and immediately turns off the light emission output.

  The always-on light emission prevention circuit in the optical transmitter according to the present invention includes (1) a light emitting element that outputs an optical signal, a light detection element that monitors the light output of the light emitting element, and a light emission detection signal detected by the light detection element. A coincidence determination circuit that compares the drive signal to the light emitting element to determine the coincidence between them, and means for stopping light emission of the light emitting element when a signal indicating a mismatch is input from the coincidence determination circuit; It is provided with.

Further, (2) as a means for stopping the light emission of the light emitting element, there is provided a means for stopping transmission of a drive signal to the light emitting element.
Further, (3) as means for stopping light emission of the light emitting element, means for short-circuiting both electrodes of the light emitting element is provided.
(4) A signal indicating a mismatch from the match determination circuit is output as an alarm signal indicating a light output abnormality of the light emitting element.

  (5) In an optical transmitter of a subscriber line optical termination device, a laser diode that outputs an optical signal, a photo diode that monitors the optical output of the light emitting element, and light emission detection detected by the photo diode A coincidence determination circuit that compares the signal and the drive signal to the laser diode to determine whether they match, and stops the light emission of the laser diode when a signal indicating a mismatch is input from the coincidence determination circuit And a means for causing the above to occur.

  According to the present invention, a failure or failure occurs in a drive circuit for a light emitting element such as a laser diode (LD) or a photo detection element such as a photo diode (PD) for monitoring the light emission, and an optical signal is not originally output. When an optical signal is output during the period, it is automatically detected and the light output from the light emitting element is stopped to prevent damage to the light emitting element of its own device and its drive circuit, etc. Damage and deterioration of the light receiving element of the optical receiver can be prevented.

  In a system that transmits optical signals by time division multiplexing with other subscriber line optical termination units (ONUs), such as an optical transmitter of a subscriber line optical termination unit (ONU) in a PON system, It is possible to prevent the adverse effect on the communication of other subscriber line optical terminal units (ONUs) due to the output of the optical signal during the non-output period, and improve the communication quality.

  In addition, an abnormal light emission detection signal obtained from a circuit for detecting a light emission abnormality provided to stop light emission abnormality that is output during a period in which the light signal is not originally output is output as an alarm signal to a maintenance person or the like. Immediate notification of light emission abnormality of the light emitting element can be made.

  An embodiment of a constant light emission preventing circuit according to the present invention will be described in detail with reference to the drawings. FIG. 1 shows a circuit diagram of a first embodiment of a constant light emission preventing circuit according to the present invention. As shown in FIG. 1, the first embodiment of the always-on light emission prevention circuit according to the present invention includes a laser diode (LD) 1, a photo diode (PD) 2, a preamplifier 3, an amplifier 4, The peak detection circuit 5, the coincidence determination circuit 6, the drive circuit 7, the delay circuit 8, and the light output cutoff circuit 9 are configured.

  In FIG. 1, a light output of a laser diode (LD) 1 that is a light emitting element is monitored by a photo diode (PD) 2 that is a light detecting element and converted into an electric signal. The converted electrical signal is output as a peak detection signal (SPD) through the peak detection circuit 5 and input to the coincidence determination circuit 6. The coincidence determination circuit can be constituted by an exclusive OR circuit and its output inverting circuit.

  On the other hand, a logical product signal of the data signal (SDATA) and the bias signal (BIAS) is input to the other one terminal of the coincidence determination circuit 6 via the delay circuit 8. This logical product signal is also input to the drive circuit 7 of the laser diode (LD) 1, and the drive circuit 7 applies this logical product signal to the laser diode (LD) 1 as a drive signal, and the laser diode (LD). 1 is emitted.

  That is, the coincidence determination circuit 6 receives the light emission detection signal detected by the light detection element of the photodiode (PD) 2 as one of the terminals as the peak detection signal (SPD). A delay signal (SDLY) from the delay circuit 8 which is a signal equivalent to a drive signal to the light emitting element of the laser diode (LD) 1 is input to the terminal.

  In the coincidence determination circuit 6, when the delay signal (SDLY) (that is, the driving signal for the light emitting element) output from the delay circuit 8 and the peak detection signal (SPD) (that is, the light emission detection signal) coincide, 6 outputs a high level signal, and an optical output disconnect circuit 9 to which the signal is input causes a drive signal to be sent to the drive circuit 7 of the laser diode (LD) 1, and the laser diode (LD) 1 Control to emit light.

  When the delay signal (SDLY) output from the delay circuit 8 (that is, the driving signal for the light emitting element) and the peak detection signal (SPD) (that is, the light emission detection signal) do not match, the match determination circuit 6 outputs the low level signal. The optical output cutoff circuit 9 to which the output is input stops sending the drive signal to the drive circuit 7 of the laser diode (LD) 1 so that the laser diode (LD) 1 does not emit light. To control.

  The first embodiment of the constant light emission preventing circuit according to the present invention shown in FIG. 1 will be described in more detail. In FIG. 1, a driving circuit 7 outputs an electric signal digitally modulated by a bias signal (BIAS) and a data signal (SDATA) inputted from the outside, and drives a laser diode (LD) 1 with the electric signal. To emit light and output an optical signal.

  The photo diode (PD) 2 monitors a part of the output light of the laser diode (LD) 1 and generates a photo current (photocurrent) corresponding to the light output level of the laser diode (LD) 1. The photocurrent flowing into the preamplifier 3 is converted into an electric signal, output as an electric signal (peak detection signal (SPD)) by the peak detection circuit 5, and input to the input terminal of the coincidence determination circuit 6.

  The other input terminal of the coincidence determination circuit 6 receives a logical product signal (electric transmission signal) of a data signal (SDATA) and a bias signal (BIAS) as a drive signal source of the laser diode (LD) 1 as a delay circuit. 8 is input. A coincidence determination signal (SCOMP) output from the output terminal of the coincidence determination circuit 6 is input to the drive circuit 7 via the light output disconnection circuit 9.

  Next, the operation of the first embodiment of the constant light emission preventing circuit according to the present invention shown in FIG. 1 will be described in more detail with reference to FIGS. 2 and 3 show waveform diagrams of signals output from each part of the constant light emission prevention circuit of FIG.

  FIG. 2 is a waveform diagram when no abnormal light output occurs in the constant light emission prevention circuit of FIG. FIG. 6A shows a case where the data signal (SDATA) is input in bursts. During normal operation, the output signal (SCOMP) of the coincidence determination circuit 6 is a delay signal (SDARY) obtained by delaying a logical product signal (electric transmission signal) of the data signal (SDATA) and the bias signal (BIAS) and a peak detection signal. (SPD) is the same signal, and in this case, a high level signal is output.

  The delay signal (SDLY) input to the A terminal of the coincidence determination circuit 6 is a peak detection signal than the input timing of the logical product signal of the data signal (SDATA) and the bias signal (BIAS) input to the drive circuit 7. (SPD) is a signal delayed by the delay of the output timing.

  In this way, the laser diode (LD) 1 emits light by a signal that has been normally digitally modulated within a predetermined burst signal cell section in accordance with the data signal (SDATA), and the internal drive circuit 7 and the photo signal for monitoring. When the diode (PD) 2 is operating normally, the output match determination signal (SCOMP) of the match determination circuit 6 is in a high level state, indicating that it is operating normally.

  As another example, FIG. 2B shows an operation example in which the data signal (SDATA) is continuously input and the optical signal transmission is turned on / off by the BIAS signal. In this case as well, as in the case of (a) in the figure, the coincidence determination signal (SCOMP) of the coincidence determination circuit 6 is in a high level state, indicating that it is operating normally.

  Next, in the always-on light emission prevention circuit shown in FIG. 1, when an abnormality occurs in the light output, that is, when some failure or failure occurs in the drive circuit 7 or the monitoring photodiode (PD) 2, The figure is shown in FIG.

  FIG. 3A shows a case where the data signal (SDATA) is input in a burst manner. The period of time A shown in the figure is an area in which the peak detection signal (SPD) is originally at a low level, but the drive circuit 7 of the laser diode (LD) 1 or the monitoring photodiode (PD) 2 has failed. Shows an example in which a high-level peak detection signal (SPD) is output. In this case, the delay signal (SDLY) obtained by delaying the data signal (SDATA) does not match the peak detection signal (SPD), and the match determination signal (SCOMP) of the match determination circuit 6 changes to a low level. .

  Thus, at the moment when an abnormality occurs in the optical output of the laser diode (LD) 1, the coincidence determination signal (SCOMP) of the coincidence determination circuit 6 immediately changes to a low level, and the optical output disconnect circuit 9 Stop output. Therefore, the first embodiment of the always-on light emission prevention circuit according to the present invention shown in FIG. 1 can stop the light output when the light output of the laser diode (LD) 1 is abnormal.

  As another example, FIG. 3B shows an operation example in which the data signal (SDATA) is continuously input and the optical transmission signal is on / off controlled by the BIAS signal. Also in this case, as in the case of (a) in the figure, the coincidence determination signal (SCOMP) of the coincidence determination circuit 6 is in a low level state when a mismatch occurs in the input signals (interval of time A in the figure). Thus, the output of the optical signal is stopped by the optical output cutoff circuit 9.

  Next, FIG. 4 shows a configuration of a second embodiment of the constant light emission preventing circuit of the present invention. In the second embodiment, the operation / non-operation of the drive circuit 7 is controlled by the light output disconnection circuit 9 in the first embodiment, whereas the laser output (LD) is directly controlled by the light output disconnection circuit 9. ) A circuit configuration for stopping the light emission of 1.

  That is, as shown in FIG. 4, when the transistor 11 is connected in parallel with the laser diode (LD) 1 and the coincidence determination signal (SCOMP) of the coincidence determination circuit 6 is at a high level, the optical output cutoff circuit From 9, the transistor 11 is controlled to be in a non-conducting state, and the laser diode (LD) 1 is operated without affecting the light emission of the laser diode (LD) 1.

  On the other hand, when the coincidence determination signal (SCOMP) of the coincidence determination circuit 6 becomes a low level due to the occurrence of an optical output abnormality, the transistor 11 is controlled from the optical output disconnection circuit 9 to become conductive, and the laser diode LD) The anode-cathode of 1 is short-circuited to disable light emission. According to the second embodiment of the present invention, it is possible to reliably stop the light emission of the laser diode (LD) 1 even when the interruption circuit of the drive circuit 7 fails.

  Further, in the always-on light emission prevention circuit of the first and second embodiments shown in FIGS. 1 and 4, a mismatch obtained from the match determination circuit 6 due to a failure of the drive circuit 7 or the monitoring photodiode (PD) 2 Can be used as a circuit for reporting an abnormality in the optical output of the laser diode (LD) 1.

1 is a circuit diagram of a first embodiment of a constant light emission prevention circuit of the present invention. It is a wave form diagram of each part when the light output abnormality has not occurred in the constant light emission preventing circuit of the present invention. It is a wave form diagram of each part when the light output abnormality has occurred in the constant light emission prevention circuit of the present invention. FIG. 6 is a circuit diagram of a second embodiment of a constant light emission preventing circuit of the present invention. 1 is a schematic configuration diagram of a PON system to which the present invention is applied. It is a figure which shows the light output interruption detection circuit in the conventional optical transmitter.

Explanation of symbols

1,101 Laser diode (LD)
2,102 Photo diode (PD)
3,103 Preamplifier 4,104 Amplifier 5,105 Peak detection circuit 6 Match determination circuit 7,107 Drive circuit 8 Delay circuit 9 Optical output disconnection circuit 106 Comparator 10,108 AND circuit 111,112,113 Subscriber line light Terminal unit (ONU)
114 Star Coupler 115 Station

Claims (5)

A light emitting element that outputs an optical signal;
A light detecting element for monitoring a light output of the light emitting element;
A coincidence determination circuit that compares the light emission detection signal detected by the light detection element and the drive signal to the light emission element to determine the coincidence of both;
Means for stopping light emission of the light emitting element when a signal indicating a mismatch is input from the match determination circuit;
A constant light emission preventing circuit in an optical transmitter, comprising:   2. The constant light emission preventing circuit in the optical transmitter according to claim 1, further comprising means for stopping transmission of a drive signal to the light emitting element as means for stopping light emission of the light emitting element.   2. The constant light emission preventing circuit in the optical transmitter according to claim 1, further comprising means for connecting both electrodes of the light emitting element in a short-circuited state as means for stopping the light emission of the light emitting element.   4. The always-on light emission prevention circuit in the optical transmitter according to claim 1, wherein a signal indicating mismatch from the match determination circuit is output as an alarm signal indicating a light output abnormality of the light emitting element. 5. A laser diode that outputs an optical signal;
A photodiode for monitoring the light output of the light emitting element;
A coincidence determination circuit that compares the light emission detection signal detected by the photo diode and the drive signal to the laser diode to determine the coincidence of both,
Means for stopping emission of the laser diode when a signal indicating a mismatch is input from the match determination circuit;
A continuous light emission prevention circuit in an optical transmitter of a subscriber line optical termination device.

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