JP2826475B2 - Optical transmitter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical transmitter, and more particularly, to an optical transmitter capable of blocking output light from a semiconductor light emitting device.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 4, for example, as shown in FIG. 4, a semiconductor laser module 1 comprising a semiconductor laser 1a and a light receiving element 1b for monitoring light behind the semiconductor laser 1a, An external modulator 2 for inputting and modulating the output light of the above, an optical coupler 3 for inputting and modulating the modulated light from the external modulator 2, and a rear light monitor signal of the light receiving element 1b of the semiconductor laser module 1. , An automatic output stabilization circuit (APC) 4 for automatically controlling the output light of the semiconductor laser 1a to a constant level, and a modulator drive circuit for receiving a data signal and outputting a drive signal for the external modulator 2. (MDD) 5, a light receiving element circuit 6 that receives the branched modulated light from the optical coupler 3 and outputs an abnormality detection signal when the amount of received light is abnormal, and automatically inputs an abnormality detection signal from the light receiving element circuit 6 The semiconductor laser 1a to force stabilization circuit 4
And a shutdown circuit 8 that outputs a light cutoff signal of
Its main part was composed. Note that in FIG.
Denotes optical components such as an optical fiber and a lens constituting an optical transmission line.

In such a conventional optical transmitter, the output light of the semiconductor laser 1a is maintained at a constant level by an automatic output stabilization circuit 4 based on a rear light monitor signal of the semiconductor laser 1a by a light receiving element 1b. However, if the light amount of the modulated light from the external modulator 2 increases or decreases from a certain range due to an abnormality of the semiconductor laser 1a, a failure of the automatic output stabilization circuit 4, a displacement of the optical component 9, or the like,
An abnormality detection signal is output from the light receiving element circuit 6, an optical cutoff signal is output from the shutdown circuit 8 to the automatic output stabilization circuit 4, and the optical output of the semiconductor laser 1a is stopped by the automatic output stabilization circuit 4. Had become.

[0004]

In the above-described conventional optical transmitter, the branched modulated light is monitored, and if the amount of light increases or decreases from a certain range, the optical output of the semiconductor laser 1a is stopped. External modulator 2
Even if the drive current is interrupted or an excessive drive current flows, the output light of the semiconductor laser 1a is not interrupted unless the amount of the modulated light from the external modulator 2 increases or decreases from a certain range, and the optical transmission There is a problem that output light is sent to the downstream side of the road.

SUMMARY OF THE INVENTION In view of the foregoing, it is an object of the present invention to monitor both a modulated light from an external modulator and a drive signal of the external modulator, and simultaneously monitor an abnormal state of the external modulator. It is an object of the present invention to provide an optical transmission device capable of reliably preventing output light from being transmitted to the downstream side of an optical transmission line, not only when the modulated light is abnormal, but also when the drive signal of the external modulator is abnormal. .

The prior art is disclosed in Japanese Patent Application Laid-Open No. 3-245.
There is an "optical modulation circuit" disclosed in Japanese Patent Publication No. 21-213, in which the modulated light is monitored by a photodiode and input to an automatic output stabilization circuit so that the peak value of the modulated light becomes constant. This is to constitute a circuit, and cannot cut off the output light of the semiconductor laser unlike the present invention.

Japanese Patent Application Laid-Open No. 4-132428 discloses a configuration in which the rear light of a semiconductor laser is monitored and the light output of the semiconductor laser is controlled to be constant by an automatic output stabilization circuit. However, the optical output of the semiconductor laser cannot be cut off as in the present invention.

[0008] Further, the "optical transmitting apparatus having an external modulator" disclosed in Japanese Patent Application Laid-Open No. 1-192231 has two
There is disclosed a configuration in which output light from the other output end of a switch-type external modulator having two output ends is transmitted through a downstream transmission line to become loop-back light. It is not designed to block output light.

[0009]

An optical transmitting apparatus according to the present invention comprises:
A semiconductor light emitting element that emits light to output a constant level of output light; an external modulator that inputs and modulates output light of the semiconductor light emitting element; and inputs a data signal and outputs a drive signal of the external modulator. Modulator driving circuit, an optical coupler that inputs and branches modulated light from the external modulator, and a light receiving element that receives the branched modulated light from the optical coupler and outputs an abnormality detection signal when the amount of received light is abnormal. And a shutdown circuit for inputting an abnormality detection signal from the light receiving element circuit and outputting a light cutoff signal for the semiconductor light emitting element, wherein a drive signal of the external modulator in the modulator drive circuit is provided. A drive signal monitoring circuit for monitoring an error and outputting an abnormality detection signal when the drive signal is abnormal; an abnormality detection signal from the light receiving element circuit and an abnormality detection from the drive signal monitor circuit And a OR circuit for inputting the shutdown circuit taking the logical sum of the items.

[0010] Further, the optical transmission apparatus of the present invention has a certain level.
A semiconductor light emitting device module including a semiconductor light emitting device that emits light so as to output an output light of the semiconductor light emitting device, a light receiving device that monitors light behind the semiconductor light emitting device, and an external modulator that inputs and modulates the output light of the semiconductor light emitting device An automatic output stabilization circuit for inputting a rear light monitor signal of a light receiving element of the semiconductor light emitting element module and automatically controlling output light of the semiconductor light emitting element to a constant level; A modulator driving circuit for outputting a modulator driving signal; an optical coupler for inputting and branching the modulated light from the external modulator; and receiving a branched modulated light from the optical coupler and receiving an abnormality when the amount of received light is abnormal. A light receiving element circuit for outputting a detection signal; and a system for receiving an abnormality detection signal from the light receiving element circuit and outputting a light cutoff signal of the semiconductor light emitting element to the automatic output stabilizing circuit. A drive signal monitoring circuit that monitors a drive signal of the external modulator in the modulator drive circuit and outputs an abnormality detection signal when the drive signal is abnormal; and An OR circuit for calculating a logical sum of the abnormality detection signal and the abnormality detection signal from the drive signal monitoring circuit and inputting the logical sum to the shutdown circuit;

[0011]

In the optical transmitter according to the present invention, the external modulator has a fixed level.
The output light of the semiconductor light emitting element that emits light to output the bell output light is input and modulated, the modulator driving circuit inputs the data signal and outputs the driving signal of the external modulator, and the optical coupler outputs the driving signal of the external modulator. The modulated light from the modulator is input and branched, and the light receiving element circuit receives the branched modulated light from the optical coupler and outputs an abnormality detection signal when the amount of received light is abnormal. Further, the drive signal monitor circuit monitors the drive signal of the external modulator in the modulator drive circuit and outputs an abnormality detection signal when the drive signal is abnormal. Then, the OR circuit takes the logical OR of the abnormality detection signal from the light receiving element circuit and the abnormality detection signal from the drive signal monitoring circuit and inputs the logical sum to the shutdown circuit. Outputs the light blocking signal of the element.

Further, in the optical transmitter according to the present invention, the semiconductor light emitting element module outputs a predetermined level of output light.
A semiconductor light-emitting element and a light-receiving element that monitors the light behind the semiconductor light-emitting element. An external modulator inputs and modulates the output light of the semiconductor light-emitting element. The rear light monitor signal of the light receiving element is input to automatically control the output light of the semiconductor light emitting element to a constant level, and the modulator driving circuit inputs the data signal and outputs the driving signal of the external modulator, and the optical coupler. Receives the modulated light from the external modulator and branches, and the light receiving element circuit receives the branched modulated light from the optical coupler and outputs an abnormality detection signal when the amount of received light is abnormal. Further, the drive signal monitor circuit monitors the drive signal of the external modulator in the modulator drive circuit and outputs an abnormality detection signal when the drive signal is abnormal. Then, the OR circuit takes the logical sum of the abnormality detection signal from the light receiving element circuit and the abnormality detection signal from the drive signal monitor circuit and inputs the result to the shutdown circuit. The shutdown circuit receives the output signal of the OR circuit and automatically outputs the signal. A light blocking signal of the semiconductor light emitting device is output to the stabilizing circuit.

[0013]

Next, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit block diagram showing a configuration of an optical transmission device according to one embodiment of the present invention. The optical transmitter of the present embodiment includes a semiconductor laser module 1 including a semiconductor laser 1a and a light receiving element 1b for monitoring light behind the semiconductor laser 1a, and an external modulator 2 for inputting and modulating output light from the semiconductor laser 1a. And an optical coupler 3 for inputting modulated light from the external modulator 2 and branching the light into two, and a rear light monitor signal for the light receiving element 1b of the semiconductor laser module 1 to input the output light of the semiconductor laser 1a to a predetermined level. An automatic output stabilization circuit (APC) 4 for automatically controlling the optical modulator 3, a modulator drive circuit (MDD) 5 for inputting a data signal and outputting a drive signal for the external modulator 2, and a branch modulation from the optical coupler 3. The light receiving element circuit 6 which receives light and outputs an abnormality detection signal of "H" level when the amount of received light is abnormal, and the driving signal of the external modulator 2 in the modulator driving circuit 5 is monitored to determine whether the driving signal is A drive signal monitor circuit (MON) 10 which outputs an "H" level abnormality detection signal, and a logical sum of the abnormality detection signal from the light receiving element circuit 6 and the abnormality detection signal from the drive signal monitor circuit 10 for shutdown. An OR circuit 11 input to the circuit 8; and a shutdown circuit 8 that outputs a light cutoff signal of the semiconductor laser 1a to the automatic output stabilization circuit 4 when the output signal from the OR circuit 11 becomes “H” level. Its main part is configured. In FIG. 1, reference numeral 9 denotes an optical component such as an optical fiber and a lens that constitute an optical transmission line. Also, portions corresponding to those of the conventional optical transmitter shown in FIG. 4 are denoted by the same reference numerals.

The external modulator 2 is a switch type external modulator,
For example, it includes a deflection type optical modulator, an absorption type optical modulator, an interferometer type optical modulator and the like.

The modulator driver circuit 5, for example, as shown in FIG. 2, a field effect transistor TR1, a resistor R ₁ is configured is coupled as shown, to the gate of the field effect transistor TR1 A pulsed data signal is applied.

As shown in FIG. 2, for example, the drive signal monitor circuit 10 includes an operational amplifier 21, comparators 22 and 23, an OR circuit 24, and resistors R _{2 to} R
₁₅ and capacitors C ₁ and C ₂ are connected as shown, and the output of the OR circuit 24 is connected to one input of the OR circuit 11.

The shutdown circuit 8, for example, as shown in FIG. 3, a comparator 31, a PNP-type transistor TR2, a resistor R ₂₁ is constituted are connected as shown, the output voltage of the OR circuit 11 When the voltage becomes “H” level and becomes higher than the comparison voltage V _ref3 , the PNP transistor TR2 is turned on. The ON signal of the PNP transistor TR2 corresponds to a light blocking signal.

As shown in FIG. 3, for example, the automatic output stabilizing circuit 4 includes a current / voltage conversion circuit (I / V) 32, operational amplifiers 33 and 34, and a variable resistor VR.
When an NPN transistor TR3, the resistor R ₂₂ and R
_When the PNP transistor TR2 of the shutdown circuit 8 is turned on, the comparison voltage _Vref4 becomes higher than the output voltage of the current / voltage conversion circuit 32. The output voltage becomes higher than the comparison voltage _Vref5 , the output voltage of the operational amplifier 34 becomes “L” level, and NP
The N-type transistor TR3 is cut off, and the drive current to the semiconductor laser 1a is cut off.

Next, the operation of the optical transmission apparatus of the present embodiment configured as described above will be described.

The output light from the semiconductor laser 1a is maintained at a constant level by an automatic output stabilizing circuit 4 based on a rear light monitor signal of the semiconductor laser 1a by the light receiving element 1b.

For example, in the automatic output stabilizing circuit 4 illustrated in FIG. 3, the backward light monitor current of the light receiving element 1b is converted into a voltage by the current / voltage conversion circuit 32, and if this voltage is larger than the comparison voltage _Vref4 , The output voltage of the operational amplifier 33 becomes lower than the comparison voltage _Vref5 , and NPN
The type transistor TR3 is turned on to control the drive current to the semiconductor laser 1a. Thereby, a feedback circuit is formed, and the output light of the semiconductor level 1a is maintained at a constant level.

However, the light amount of the modulated light from the external modulator 2 increases or decreases from a certain range due to any cause such as abnormality of the semiconductor laser 1a, failure of the automatic output stabilizing circuit 4, and displacement of the optical component 9. Then, the amount of the branched modulated light received by the light receiving element circuit 6 increases or decreases from a certain range, and the light receiving element circuit 6 outputs an "H" level abnormality detection signal. The abnormality detection signal is input to the shutdown circuit 8 via the OR circuit 11, and the shutdown circuit 8 outputs a light cutoff signal of the semiconductor laser 1a to the automatic output stabilization circuit 4, thereby stopping the light output of the semiconductor laser 1a. Is done.

For example, in the shutdown circuit 8 illustrated in FIG. 3, when the output voltage of the OR circuit 11 becomes "H" level and becomes higher than the comparison voltage _Vref3 , the comparator 31
Becomes "L" level, the PNP transistor TR2 is turned on, and the light cutoff signal of the semiconductor laser 1a is output to the automatic output stabilization circuit 4.

For example, in the automatic output stabilizing circuit 4 illustrated in FIG.
, The comparison voltage _Vref4 becomes higher than the output voltage of the current / voltage conversion circuit 32, and the output voltage of the operational amplifier 33 becomes higher than the comparison voltage _Vref5 . And the output voltage of the operational amplifier 34 becomes “L” level, the NPN transistor TR3 is cut off, and the drive current to the semiconductor laser 1a is cut off. Thereby, the optical output of the semiconductor laser 1a is stopped.

If an abnormality occurs in the drive signal of the external modulator 2 for some reason, the drive signal monitor circuit 1
An abnormality detection signal of “H” level from 0 is output. The abnormality detection signal is input to the shutdown circuit 8 via the OR circuit 11, and the shutdown circuit 8 outputs a light cutoff signal of the semiconductor laser 1a to the automatic output stabilization circuit 4, thereby stopping the light output of the semiconductor laser 1a. Is done.

For example, in the drive signal monitoring circuit 10 illustrated in FIG. 2, when the field effect transistor TR1 is damaged and the drive current does not flow through the external modulator 2, the output voltage of the operational amplifier 21 becomes "L" level. , The output voltage of the comparator 23 becomes “H” level. Further, the output voltage of the comparator 22 becomes “L” level. These output voltages are ORed by the OR circuit 24 and applied to one input of the OR circuit 11 as an "H" level abnormality detection signal.

When the field effect transistor TR1 operates abnormally and an excessive drive current flows through the external modulator 2,
The output voltage of the operational amplifier 21 becomes “H” level, and the output voltage of the comparator 22 becomes “H” level. Further, the output voltage of the comparator 23 becomes “L” level. These output voltages are logically ORed by an OR circuit 24 and output as an "H" level abnormality detection signal.
1 is applied to one input.

Therefore, the field effect transistor TR
In the case where the drive current stops flowing due to the abnormality of No. 1 and the case where an excessive drive current starts flowing, an “H” level abnormality detection signal is input to the shutdown circuit 8 via the OR circuit 11. Shutdown circuit 8
Outputs an optical cutoff signal of the semiconductor laser 1a, and the automatic output stabilization circuit 4 stops the optical output of the semiconductor laser 1a.

For example, in the shutdown circuit 8 illustrated in FIG. 3, when the output voltage of the OR circuit 11 becomes “H” level and becomes higher than the comparison voltage V _ref3 , the comparator 31
Becomes "L" level, the PNP transistor TR2 is turned on, and the light cutoff signal of the semiconductor laser 1a is output to the automatic output stabilization circuit 4.

For example, in the automatic output stabilizing circuit 4 illustrated in FIG.
, The comparison voltage _Vref4 becomes higher than the output voltage of the current / voltage conversion circuit 32, and the output voltage of the operational amplifier 33 becomes higher than the comparison voltage _Vref5 . And the output voltage of the operational amplifier 34 becomes “L” level, the NPN transistor TR3 is cut off, and the drive current to the semiconductor laser 1a is cut off. Thereby, the optical output of the semiconductor laser 1a is stopped.

In the above embodiment, the semiconductor laser module 1 is provided with the light receiving element 1b, and the rear light monitor signal of the semiconductor laser 1a from the light receiving element 1b is input to the automatic output stabilizing circuit 4 to output the output of the semiconductor laser 1a. Although an optical transmitter that automatically controls light to a certain level has been described as an example, the present invention is also applicable to an optical transmitter in which a semiconductor laser module includes only a semiconductor laser and an automatic output stabilization circuit is simply a semiconductor laser drive circuit. Can of course be applied as well.

In the above embodiment, detailed circuit examples of the modulator drive circuit 5, drive signal monitor circuit 6, shutdown circuit 8 and automatic output stabilization circuit 4 are shown in FIGS. 2 and 3. It goes without saying that the circuit is not limited to those illustrated in FIGS.

[0034]

As described above, according to the present invention, in an optical transmitter using an external modulator, the light receiving element circuit monitors the modulated light from the external modulator and the driving signal monitor circuit drives the external modulator. By monitoring the signal and inputting the abnormality detection signal from the light receiving element circuit and the abnormality detection signal from the drive signal monitoring circuit to the shutdown circuit via the OR circuit, the modulated light from the external modulator and the external modulation If any of the drive signals of the
An optical cutoff signal of the semiconductor light emitting element is output from the shutdown circuit via the R circuit, and the output of the output light to the downstream side of the optical transmission line is reliably prevented.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram illustrating a configuration of an optical transmission device according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a more detailed circuit example of a modulator drive circuit and a drive signal monitor circuit in FIG. 1;

FIG. 3 is a circuit diagram showing a more detailed circuit example of a shutdown circuit and an automatic output stabilization circuit in FIG. 1;

FIG. 4 is a circuit block diagram illustrating a configuration of a conventional optical transmission device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Semiconductor laser module 1a Semiconductor laser 1b Light receiving element 2 External modulator 3 Optical coupler 4 Automatic output stabilization circuit 5 Modulator driving circuit 6 Light receiving element circuit 8 Shutdown circuit 9 Optical component 10 Drive signal monitor circuit 11 OR circuit 21 Operational amplifier 22 , 23 comparator 24 OR circuit 31 a comparator 32 the current / voltage conversion circuit 33 operational amplifier C _1, C ₂ capacitors _{R 1 ~R 15, R 21 ~R} 23 resistor TR1 field effect transistor TR2 PNP type transistor TR3 NPN-type transistor VR Variable resistor V _{ref1 to} V _ref5 Comparison voltage

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H04B 10/26

Claims (4)

(57) [Claims] 1. A light source for outputting a predetermined level of output light.
A semiconductor light emitting element that emits light, an external modulator that inputs and modulates output light of the semiconductor light emitting element, a modulator drive circuit that inputs a data signal and outputs a drive signal of the external modulator, An optical coupler that receives modulated light from the optical coupler and splits the light, a light-receiving element circuit that receives the branched modulated light from the optical coupler and outputs an abnormality detection signal when the amount of received light is abnormal, and an abnormality from the light-receiving element circuit. A shutdown circuit for inputting a detection signal and outputting a light cutoff signal of the semiconductor light emitting element, wherein the drive signal of the external modulator in the modulator drive circuit is monitored to detect an abnormality when the drive signal is abnormal. A drive signal monitoring circuit that outputs a detection signal; and Optical transmission apparatus characterized by having an OR circuit for inputting the down circuit. 2. A light source for outputting output light of a constant level.
A semiconductor light emitting element module comprising a light emitting semiconductor light emitting element and a light receiving element for monitoring light behind the semiconductor light emitting element; an external modulator for inputting and modulating output light of the semiconductor light emitting element; An automatic output stabilization circuit for inputting a rear light monitor signal of a light receiving element and automatically controlling output light of the semiconductor light emitting element to a constant level; and inputting a data signal and outputting a drive signal of the external modulator A modulator driving circuit, an optical coupler that inputs and branches modulated light from the external modulator, and a light receiving element circuit that receives the branched modulated light from the optical coupler and outputs an abnormality detection signal when the amount of received light is abnormal. And a shutdown circuit that receives an abnormality detection signal from the light receiving element circuit and outputs a light cutoff signal of the semiconductor light emitting element to the automatic output stabilization circuit. In the transmission device, a drive signal monitoring circuit that monitors a drive signal of the external modulator in the modulator drive circuit and outputs an abnormality detection signal when the drive signal is abnormal, an abnormality detection signal from the light receiving element circuit and the drive An optical transmission device, comprising: an OR circuit that calculates a logical sum of an abnormality detection signal from a signal monitoring circuit and inputs the logical sum to the shutdown circuit. 3. The optical transmitter according to claim 1, wherein the drive signal monitoring circuit detects an interruption and an excessive amount of the drive signal of the external modulator and outputs an abnormality detection signal. 4. The optical transmitter according to claim 1, wherein the semiconductor light emitting device is a semiconductor laser.