JP2008028504A - Optical communication system and optical transmission module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical transmission module which can ensure reliability of information transmission without using a dedicated modulation circuit where a light emitting element fails, and to provide an optical communication system employing it. <P>SOLUTION: In the optical communication system, cathode electrodes of two semiconductor lasers 131 and 132 are connected in common for a constant current source 133, and a drive signal is supplied commonly from a drive circuit 14 to its anode electrode in response to an input signal. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical transmission module that transmits information by optical communication and an optical communication system using the optical transmission module.

  In an optical communication system, generally high reliability is required. Therefore, it is necessary to provide sufficient redundancy for communication failures caused by device failures and the like. A failure of a device that contributes to a communication failure includes a failure of a light emitting element such as a semiconductor laser that is a light source of an optical transmission module. This is because, in general, a light emitting element such as a semiconductor laser has a shorter life than other devices, and if the light emitting element fails, the optical communication system is completely stopped.

  In order to ensure the reliability of information transmission even in an abnormal state in which the light emitting element has failed, conventionally, in the normal state, two information signals are transmitted as individual optical signals by two semiconductor lasers. In an abnormal state in which one of the two has failed, two information signals are modulated and transmitted as an optical signal using one normal semiconductor laser (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 11-112426

  However, in the above prior art, when one of the two semiconductor lasers fails, the two information signals are modulated, and it is necessary to provide a dedicated modulation circuit for an abnormal time. There is a problem that the circuit configuration becomes complicated and the cost becomes high. Further, by modulating and transmitting the two information signals, it is necessary to demodulate them on the receiving side, so that the circuit configuration is complicated for the optical receiving module along with the provision of a dedicated demodulation circuit, This will increase costs.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide light that can ensure the reliability of information transmission without using a dedicated modulation circuit in an abnormal state in which a light emitting element has failed. An object is to provide a transmission module and an optical communication system using the optical transmission module.

  In order to achieve the above object, an optical transmission module according to the present invention includes a constant current source, a plurality of light emitting elements having a first electrode connected in common to the constant current source, and a drive signal corresponding to an input signal. Is provided with a drive circuit for supplying the second electrode to the second electrodes of the plurality of light emitting elements. This optical transmission module constitutes an optical communication system together with the optical transmission path and the optical reception module.

  In the optical transmission module having the above-described configuration or an optical communication system using the optical transmission module, a drive circuit sends a drive signal to a second electrode of a plurality of light emitting elements commonly connected to a constant current source. By supplying, the total amount of current flowing through the plurality of light emitting elements is always the amount of current of the constant current source. The total light amount of the plurality of light emitting elements is determined by the current amount of the constant current source. Here, when, for example, one of the plurality of light emitting elements fails and is turned off, the soot current flowing through the failed light emitting element flows to the other light emitting elements. Therefore, even if, for example, one of the plurality of light emitting elements fails, the other light emitting elements continue to emit light with the light amount before the failure (total light amount of the plurality of light emitting elements). That is, if at least one of the plurality of light emitting elements is normal, this normal light emitting element outputs an optical signal with the same amount of light as when all are normal.

  According to the present invention, if even one of the plurality of light emitting elements is normal, the normal light emitting element outputs an optical signal with the same amount of light as when all are normal. In an abnormal state where the light emitting element has failed, the reliability of information transmission can be ensured without using a dedicated modulation circuit.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[First Embodiment]
FIG. 1 is a schematic configuration diagram of an optical communication system according to the first embodiment of the present invention. As shown in FIG. 1, the optical communication system according to the present embodiment transmits an optical transmission module 10 that converts an input electrical signal into an optical signal and outputs the optical signal, and transmits an optical signal output from the optical transmission module 10. The optical transmission path 20 includes an optical fiber and the like, and the optical reception module 30 that receives an optical signal transmitted through the optical transmission path 20 and converts it into an electrical signal.

  The optical transmission module 10 includes a light emitting unit 13 including a plurality of light emitting elements, for example, two light emitting elements 11 and 12, and a drive circuit 14 that drives the light emitting elements 11 and 12 to emit light in response to an input electric signal, for example, a pulse signal. It has composition which has. As the light emitting elements 11 and 12, a semiconductor laser (LD) or a light emitting diode (LED) is used. The present embodiment is characterized by a specific configuration of the light emitting unit 13 in the optical transmission module 10. Details thereof will be described later.

  The light receiving module 30 receives a light signal transmitted through the light transmission path 20 and converts the light signal into an electric signal corresponding to the light amount, and waveform shaping for the electric signal output from the light receiving element 31. And a receiving circuit 32 that performs signal processing such as the above and outputs it as a pulse signal, for example. As the light receiving element 31, a photoelectric conversion element such as a phototransistor or a photodiode is used.

  FIG. 2 is a circuit diagram illustrating an example of the configuration of the light emitting unit 13 in the optical transmission module 10. In FIG. 2, the same parts as those in FIG. 1 are denoted by the same reference numerals.

  In the optical transmission module 10 according to this example, for example, semiconductor lasers 131 and 132 are used as the light emitting elements 11 and 12. A cathode electrode, for example, a first electrode of the semiconductor lasers 131 and 132 is connected to one end of the constant current source 133. The other end of the constant current source 133 is grounded. For example, anode electrodes, which are second electrodes of the semiconductor lasers 131 and 132, are connected to one ends of the resistance elements 134 and 135, respectively.

  The other ends of the resistance elements 134 and 135 are commonly connected to the node N. The node N is connected to the output terminal of the drive circuit 14 shown in FIG. As a result, the drive circuit 14 supplies a drive signal corresponding to the input signal to the anode electrodes of the semiconductor lasers 131 and 132 via the node N in common.

  In the light emitting unit 13 having the above configuration, when semiconductor lasers 131 and 132 having the same characteristics are used and the resistance values of the resistance elements 134 and 135 are substantially equal, the current flowing through the constant current source 133 is 2I0. The currents I1 and I2 of I0 flow through the semiconductor lasers 131 and 132, respectively.

  Here, as shown in FIG. 3, when both the semiconductor lasers 131 and 132 are ON (light emission state), that is, when the currents I1 and I2 (= I0) flow in the semiconductor lasers 131 and 132, respectively. Each light quantity of 131 and 132 is P1, and when one of the semiconductor lasers 131 and 132 is OFF (non-light emitting state), that is, when the current of about 2I0 flows through the other of the semiconductor lasers 131 and 132, The light quantity of the semiconductor laser 131/132 is P2.

When a semiconductor laser having a small threshold is selected as the semiconductor lasers 131 and 132, as shown in FIG. 4, the variation in the characteristics of current-light output (light quantity) is small.
P2 ≒ 2P1
Can be considered. As a result, when one of the semiconductor lasers 131 and 132 fails and only the other semiconductor laser 131/132 is in a light emitting state, the amount of light P2 is generated, but the total amount of light is turned on for both the semiconductor lasers 131 and 132. Since it is almost the same as the light quantity 2P1 at a certain time, optical communication can be continued without the system being down.

  As described above, for example, the cathode electrodes of the two semiconductor lasers 131 and 132 are commonly connected to the constant current source 133, and the drive signal corresponding to the input signal is supplied from the drive circuit 14 to the anode electrode in common. By adopting such a configuration, the total amount of current flowing through the two semiconductor lasers 131 and 132 is always the amount of current 2I0 of the constant current source 133, and the total amount of light of the two semiconductor lasers 131 and 132 is the amount of current 2I0 of the constant current source 133. Determined by.

  Therefore, when one of the two semiconductor lasers 131 and 132 fails and is turned off, the soot current flowing in the one failed semiconductor laser 131/132 flows to the other semiconductor laser 132/131. Even when one of the two semiconductor lasers 131 and 132 fails, the other semiconductor laser continues to emit light with a light amount P2 substantially equal to the light amount 2P1 before the failure.

  That is, if at least one of the plurality of light emitting elements is in a normal state, this normal light emitting element outputs an optical signal with the same amount of light as when all the light emitting elements are normal. Even if an abnormal state occurs when the light emitting device fails, the system does not go into a stopped state, and the reliability of information transmission is ensured without using a dedicated modulation circuit as in the prior art. it can.

  Further, the countermeasure for ensuring the reliability of information transmission when the light emitting element fails is performed only by the optical transmission module 10, and all the light emitting elements are used as the light quantity of the optical signal in the abnormal state where the light emitting element has failed. Since it is possible to secure a light amount substantially equal to that in the normal state when the light reception is normal, the optical reception module 30 can perform reception processing in the same manner as in the normal state even in an abnormal state. There is no need to complicate or increase costs.

[Second Embodiment]
FIG. 5 is a schematic configuration diagram of an optical communication system according to the second embodiment of the present invention. In FIG. 5, the same parts as those in FIG.

  The optical communication system according to the present embodiment employs a configuration in which when the light emitting element fails, the light transmitting element 10 ′ itself can automatically identify the failed light emitting element. Specifically, the optical transmission module 10 ′ includes, for example, a detection unit 15 that detects light emission amounts of the two light emitting elements 11 and 12 in addition to the light emitting unit 13 and the drive circuit 14 including the two light emitting elements 11 and 12. , 16 and a display unit 17 for identifying and displaying light emitting elements having a light emission amount equal to or less than a predetermined light amount based on the detection results of the detection units 15 and 16. As the light emitting elements 11 and 12, for example, semiconductor lasers 131 and 132 are used as in the case of the first embodiment (see FIG. 2).

  The detection units 15 and 16 are constituted by, for example, a differential amplifier that monitors the voltage at each anode end of the semiconductor lasers 131 and 132 and compares the voltage at the anode end with a predetermined reference voltage. When the voltage at each anode end becomes equal to or higher than the reference voltage, it is determined that a failure has occurred in the semiconductor lasers 131 and 132.

  The detection units 15 and 16 are not limited to those using a differential amplifier. For example, photoelectric detection elements such as photodiodes that detect the light outputs of the semiconductor lasers 131 and 132 are used. It is also possible to use a configuration in which it is determined that a failure has occurred in the semiconductor lasers 131 and 132 when the output of the photoelectric conversion element falls below a predetermined reference voltage.

  The display unit 17 is configured by a display element such as a light emitting diode provided corresponding to each of the semiconductor lasers 131 and 132, and one of the detection units 15 and 16 has failed in either of the semiconductor lasers 131 and 132. When this is detected, the corresponding display element is turned on to notify the user (maintenance staff) of the semiconductor laser 131/132 in which the failure has occurred.

  As described above, when the semiconductor laser 131/132 breaks down, in the optical transmission module 10 ′ that can ensure the reliability of information transmission without causing the system to stop, the failed semiconductor laser 131 / By automatically specifying 132 and being able to notify it, it is possible to reliably notify the user (maintenance staff) of the occurrence of a failure in the semiconductor laser 131/132.

  As a result, the user (maintenance staff) can quickly start replacing the failed semiconductor laser 131/132, and the failure of one of the semiconductor lasers 131/132 causes the other semiconductor laser 132/131 to be approximately doubled. The other semiconductor laser 132/131 can be quickly released from the burden caused by the current flowing, and the life reduction due to the large current flowing can be minimized.

  In addition, when it is necessary to stop the system when replacing the failed semiconductor laser 131/132, the user (maintenance staff) can be notified of which of the semiconductor lasers 131 and 132 has failed, so that the user (maintenance) The person can immediately identify the device to be replaced and can quickly complete the replacement operation, thereby minimizing the downtime of the system.

[Modification]
In each of the above embodiments, the description has been given on the assumption that the semiconductor laser 131/132 has failed and is turned off. However, the present invention has deteriorated the characteristics of the semiconductor laser 131/132 and reduced the amount of light. Can also handle cases.

  That is, when the characteristic of one semiconductor laser 131/132 deteriorates and the flowing current I1 / I2 decreases and the amount of light of the one semiconductor laser 131/132 decreases, the reduced current flows to the other The semiconductor laser 132/131 flows into the semiconductor laser 132/131, and the other semiconductor laser 132/131 continues to emit light with a light amount P2 substantially equal to the light amount 2P1 before the characteristic degradation of the one semiconductor laser 131/132. As a result, even when the characteristics of the semiconductor laser 131/132 deteriorate, the reliability of information transmission can be ensured.

  FIG. 6 shows the relationship between the drive current of the semiconductor laser 131/132 and the optical output. As one of the characteristic deterioration of the semiconductor laser 131/132, it is known that the value of the differential efficiency obtained by dividing the light output fluctuation amount by the drive current fluctuation amount becomes small. In the case of such an event, generally, there is a deterioration in which only the optical output of the semiconductor laser 131/132 is lowered without any change in the drive current of each of the semiconductor lasers 131/132.

  Even in such a case, an average received light amount measurement generally prepared in a circuit that receives an optical signal output from the semiconductor laser at a distance by setting the current flowing through the semiconductor laser 131/132 to a constant current. There is a system that detects an abnormality in information transmission using an analog signal. By applying the method of the present invention, the drive current of the semiconductor laser is about half that of a single laser, so the degradation rate of the semiconductor laser is slowed down, and the user (maintenance personnel) from the occurrence of the abnormality to the repair is slowed down. Since there is a margin in the repair work time, more reliable measures can be taken and the reliability of the information transmission system can be improved. In this case, it is possible to determine which semiconductor laser 131/132 has deteriorated by monitoring the amount of light emitted from the semiconductor laser 131/132, so that an accurate information transmission system can be restored.

  Further, the light output of the semiconductor lasers 131 and 132 is monitored, and the currents I1 and I2 flowing through the semiconductor lasers 131 and 132 are controlled in accordance with the fluctuations in the amount of light emitted. By combining with APC (Automatic Power Control), it is possible to cope with fluctuations in the current-optical output characteristics of the semiconductor laser due to temperature changes and aging changes.

1 is a schematic configuration diagram of an optical communication system according to a first embodiment of the present invention. It is a circuit diagram which shows an example of a structure of the light emission part in an optical transmission module. It is a figure which shows the relationship between the ON / OFF state of two semiconductor lasers, and a light quantity. It is a figure which shows the electric current-light output (light quantity) characteristic of a semiconductor laser. It is a schematic block diagram of the optical communication system which concerns on 2nd Embodiment of this invention. It is a figure which shows the relationship between the drive current of a semiconductor laser, and optical output.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10,10 '... Optical transmission module, 11, 12 ... Light emitting element, 13 ... Light emission part, 14 ... Drive circuit, 15, 16 ... Detection part, 17 ... Display part, 20 ... Optical transmission path, 30 ... Optical reception module, 31: light receiving element, 32: light receiving circuit, 131, 132: semiconductor laser

Claims (4)

A constant current source;
A plurality of light emitting elements having a first electrode commonly connected to the constant current source;
An optical transmission module comprising: a drive circuit that supplies a drive signal corresponding to an input signal to the second electrodes of the plurality of light emitting elements. Detecting means for detecting each light emission amount of the plurality of light emitting elements;
The optical transmission module according to claim 1, further comprising display means for identifying and displaying a light emitting element having a light emission amount equal to or less than a predetermined light quantity based on a detection result of the detection means. Detecting means for detecting each light emission amount of the plurality of light emitting elements;
The optical transmission module according to claim 1, further comprising: a control unit that controls the amount of light emitted by each of the plurality of light emitting elements based on a detection result of the detection unit. An optical transmission module;
An optical transmission line for transmitting an optical signal output from the optical transmission module;
An optical communication system comprising a light receiving module that receives an optical signal transmitted through the optical transmission path and converts it into an electrical signal,
The optical transmission module includes:
A constant current source;
A plurality of light emitting elements having a first electrode commonly connected to the constant current source;
An optical communication system, comprising: a drive circuit that supplies a drive signal corresponding to an input signal to the second electrodes of the plurality of light emitting elements.

Images