JPH11177174A - Light emitting module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent runaway of a semiconductor light emitting device due to malfunction of an APC control system. SOLUTION: When photocurrent becomes zero due to malfunction of an APC control system, the output voltage of a current-voltage converting part 3 becomes maximum and higher than a reference voltage Vth2 and the output level of an anomaly detecting part 5 becomes high. Then intermittent operation signals from an intermittent operation signals generating part 6 appear at the output of an AND gate 7 and at the output of a NOR gate 8. In response to the intermittent operation signals, a transistor 901 of a bias current controlling part 9 is intermittently driven and a transistor 1103 of a modulation current controlling part 11 is also intermittently driven.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting module for controlling an output of a semiconductor light emitting device based on a detection output of the semiconductor light emitting device.

[0002]

2. Description of the Related Art In an optical communication, an electric signal is converted into an optical signal on a transmitting side, and the electric signal is converted into an optical signal, for example, as shown in FIG. Light emitting modules are known.

In this light-emitting module, the drive of the laser diode 32 is controlled by the modulation current controller 31 based on the input digital data signal, and the modulation current of the laser diode 32 is controlled. A part of the laser light emitted from the laser diode 32 is monitored by the photodiode 33, and the photocurrent flowing through the photodiode 33 is converted to a voltage by an APC (auto power control) control unit 34 and smoothed. The difference voltage between the applied voltage and the predetermined reference voltage is applied to the bias current control unit 35, and the bias current according to the difference voltage flows to the laser diode 32 by the bias current control unit 35, so that the light emission output of the laser diode 32 is constant. Is controlled so that FIG. 4 shows an example of the relationship between the bias current and the modulation current value and the emission intensity of the laser diode 32.

[0004]

As described above, since the laser diode 32 is APC-controlled, if a failure occurs in the APC control system and no photocurrent is detected by the APC control unit 34, the bias current control unit 35 As a result, an excessive bias current flows to the laser diode 32, and the laser diode 32 runs away. Therefore, in such a case, the user sets the laser diode 3
2 is forcibly stopped, the fault location is identified and the AP
The C control system is restored, and thereafter, the laser diode 32 is driven again. However, if the APC control system still does not function and positive feedback is applied to the APC control system again, the laser diode 3
2 may emit too much light, and an output of 8.8 mW or more, which is specified in Class 1 of the IEC-825 standard, which is an international standard that regulates the safety of laser diode light, may occur.

It is an object of the present invention to provide a light emitting module which can solve the above-mentioned problems and can prevent runaway of a semiconductor light emitting element due to a failure in an APC control system.

[0006]

A light emitting module according to the present invention includes a semiconductor light emitting device, drive control means for driving and controlling the semiconductor light emitting device to have a predetermined output, and drive control by the drive control means. A light emitting module having output detection means for detecting the output of the semiconductor light emitting element, wherein the comparison means compares whether the output detected by the output detection means is lower than a predetermined reference value, and the comparison means And an intermittent drive control means for intermittently controlling the semiconductor light emitting element when the detection output is lower than a predetermined reference value.

The module according to the present invention may further include a forced stop means for forcibly stopping the driving of the semiconductor light emitting element, and the forced stop means operates with priority over the intermittent drive control means. Can be.

The semiconductor light emitting device can be a semiconductor laser diode, and can be a light emitting diode.

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. FIG.
In the figure, reference numeral 1 denotes a laser diode, which causes laser light from an emission end face to enter an optical fiber (not shown) and laser light leaking from a rear end face to enter a photodiode 2. The reflectivity of the rear end face of the laser diode 1 (usually set near 100%) is reduced by several percent. Instead of such a configuration, a part of the laser light from the emission end face of the laser diode 1 is extracted by a half mirror (not shown) and is incident on the photodiode 2, and the laser light passing through the half mirror is incident on an optical fiber (not shown). You may do so.

Reference numeral 3 denotes a current-voltage converter, which converts the photocurrent Ipd generated by the photodiode 2 into a voltage (the output voltage is inversely proportional to the photocurrent Ipd). Is detected. In the current-voltage converter 3, since the input impedance of the amplifier 301 is high, the photocurrent Ipd is not introduced into the input, and the feedback resistor 302
Flows to the output side of the amplifier 301 through the feedback resistor 302. As a result, a voltage of Ipd × R is generated between the feedback resistors 302, and the generated voltage is connected to the capacitor 303 connected in parallel to the feedback resistor 302.
And current-voltage conversion is realized. The time constant determined by the feedback resistor 302 and the capacitor 303 is longer than the data signal repetition time.
Reference numeral 4 denotes a light intensity detector which outputs a difference voltage between a predetermined reference voltage and an output voltage of the current-voltage converter 3.
Reference numeral 5 denotes an abnormality detection unit that detects when the output voltage of the current-voltage conversion unit 3 is lower than a predetermined reference voltage (set lower than the maximum output voltage of the abnormality detection unit 5), that is, detects an abnormality of the photodiode 2. In this case, the output signal level is changed to a high level, and when it is high, the output signal level is changed to a low level. Reference numeral 6 denotes an intermittent operation signal generation unit that generates an intermittent operation signal that is a pulse signal whose duty is set so that the average output is suppressed even when the laser diode 1 emits excessive light. Reference numeral 7 denotes an AND gate.
The intermittent operation signal is output from the intermittent operation signal generating section 6 when the output level of the abnormality detecting section 5 transits to the high level, and the output level is transited to the low level when the output level of the abnormality detecting section 5 is the low level. It is. Reference numeral 8 denotes a NOR gate that performs a NOR operation on the level of the optical output stop signal and the output level of the AND gate 7.

Reference numeral 9 denotes a bias current control unit which controls a bias current of the laser diode 1, and includes a bipolar transistor (hereinafter, referred to as a transistor) 902 for flowing a current corresponding to an output voltage of the light intensity detection unit 4. ,
The transistor 901 is connected in series to the laser diode 1 via a transistor 901. The transistor 901 becomes active when the output of the OR gate 8 is at a high level, and becomes inactive when the output of the OR gate 8 is at a low level. 1
Reference numeral 0 denotes an amplifier that outputs a complementary signal corresponding to digital input signals 0 and 1. Reference numeral 11 denotes a modulation current control unit which connects the emitters of the transistors 1101 and 1102 in common, and supplies a current corresponding to the modulation current control signal to the commonly connected emitter.
Are connected in series via a transistor 1103,
The laser diode 1 is connected to the collector of the transistor 1102, and the transistor 1103 becomes active when the output level of the NOR gate 8 is at the high level, becomes inactive when the output level of the NOR gate 8 is at the low level, and the transistors 1101 and 1102 are: One is turned on and the other is turned off by a complementary signal from the amplifier 10 input to the base, and the current flowing to the collector of the transistor 1104 is switched.

Next, the operation will be described. When an optical signal from the laser diode 1 is received by the photodiode 2, a photocurrent is generated in the photodiode 2 according to the intensity of the received laser light. The photocurrent generated in the photodiode 2 is converted into a voltage (the output voltage is inversely proportional to the photocurrent) by the current / voltage converter 3, and the output voltage of the current / voltage converter 3 is converted into a predetermined reference voltage by the light intensity detector 4. Voltage Vth
1 and, at the same time, the reference voltage V
Compared to th2.

The transistor 902 of the bias current control unit 9 is driven by the light intensity detection unit 4 according to the difference voltage between the output voltage of the current-voltage conversion unit 3 and the reference voltage Vth1. On the other hand, when the photocurrent is not zero, the output level of the abnormality detection unit 5 becomes low because the output voltage of the current-voltage conversion unit 3 is lower than the reference voltage Vth2. Abnormality detector 5
Becomes low level, the intermittent operation signal becomes A
It does not appear at the output of the ND gate, and the output level of the AND gate 7 goes low. At this time, if the light output stop signal is at a low level (light output), the transistor 901 of the bias current control unit 9 is turned on and does not affect the bias current. The bias current of the laser diode 1 is controlled according to the difference voltage between the output voltage of the current-to-voltage converter 3 and the reference voltage Vth1, and increases when the photocurrent is small and decreases when the photocurrent is large. Is controlled to
The output of the laser diode 1 is made constant.

On the other hand, when the photocurrent becomes zero due to a failure in the APC control system, the output voltage of the current-to-voltage converter 3 becomes the maximum voltage, becomes higher than the reference voltage Vth2, and the output level of the abnormality detector 5 Becomes high level. Then
The intermittent operation signal from the intermittent operation signal generator 6 appears at the output of the AND gate 7 and also at the output of the NOR gate 8 regardless of the state of the optical output stop signal. The transistor 901 of the current control unit 9 is intermittently driven, and the transistor 1103 of the modulation current control unit 11 is also intermittently driven. That is, when the transistors 901 and 1103 are inactive, the modulation current and the bias current do not flow through the laser diode 1 at all. On the other hand, when the transistors 901 and 1103 are active, the modulation current has a predetermined current value. And the bias current is feedback-controlled as described above. However, since the failure of the APC control system has been recovered, the bias current tends to be maintained at the maximum value. When the duty of the intermittent operation signal is, for example, 10% and the output of the laser diode is, for example, 10 mW, the average output of the laser diode is 1.0 mW,
IEC-825 standard can be cleared.

Here, when the level of the optical output stop signal changes to the low level during the operation of the laser diode 1 (including the intermittent operation), the output level of the NOR gate 8 remains at the low level, and the bias is maintained. The transistor 901 of the current control unit 9 is turned off, the transistor 1103 of the modulation current control unit 11 is turned off, and the modulation current and the bias current do not flow through the laser diode 1 at all. 1
Can be stopped.

When the laser diode 1 emits light after the failure recovery work, the output voltage of the current-to-voltage converter 3 becomes the maximum voltage again, becomes higher than the reference voltage Vth2, and the output level of the abnormality detector 5 becomes lower. When the signal goes high, the intermittent operation signal from the intermittent operation signal generator 6 appears at the output of the AND gate 7 and at the output of the NOR gate 8 as described above. In response, the transistor 901 of the bias current control unit 9
Are intermittently driven, and the transistor 1103 of the modulation current control unit 11 is intermittently driven.

Transistor 110 of modulation current control section 11
Complementary signals from the amplifier 10 are input to 1, 1102, so that one is turned on and the other is turned off. When the transistor 1102 is turned on, a current flows through the laser diode 1 and the laser diode 1 is turned off. In this case, no current flows and the laser diode 1 blinks based on the digital input signal of the amplifier 10.

Although the operation of the light emitting module has been described with reference to FIG. 1, essentially the same operation can be performed even when the light emitting module is configured as shown in FIG. In FIG. 2, 1 to 7, 10, 301 to 303, 1
Reference numerals 101 and 1102 denote the same parts as in FIG. The light emitting module of FIG. 2 employs an OR gate 208 instead of the NOR gate 8 of FIG. 1, and in comparison with the light emitting module of FIG. 1, the configuration of the bias current control unit and the modulation current control unit Are different.

That is, the bias current control unit 209 shown in FIG. 2 connects the transistor 2902 for flowing a current corresponding to the output voltage of the light intensity detection unit 4 to the laser diode 1 in series, and connects the base of the transistor 2902 to the transistor 2901. When the output level of the OR gate 208 is at a high level, the transistor 2901 becomes active and the transistor 290
No bias current flows because the base potential of No. 2 is substantially clamped to the ground potential. When the base level is low, the transistor 2901 becomes inactive and a bias current flows.

The modulation current control unit 211 shown in FIG. 2 includes a transistor 211 for supplying a current according to a modulation current control signal to the commonly connected emitters of the transistors 1101 and 1102.
4 and a resistor are connected in series so that the base of the transistor 2114 is grounded via the transistor 2113. When the output of the OR gate 208 is at a high level, the transistor 2113 becomes active and no modulation current flows, When the level is low, the transistor 2113 becomes inactive and a modulation current flows.

In the embodiment described above, the example in which only the bias current of the laser diode is APC controlled has been described. However, in the example in which the APC control is performed on both the bias current and the modulation current, the intermittent operation is performed in substantially the same manner. Operation control is possible.

In this embodiment, an example has been described in which the average value of the laser diode output is detected.
C control may be performed.

Further, in this embodiment, an example in which a laser diode is employed as a semiconductor light emitting element has been described.
LED (light emitting diod) instead of laser diode
e) can be controlled essentially in the same way, and a field effect transistor (FET) can be used instead of a bipolar transistor.
It is a matter of course that other elements such as an anistor can be adopted, and an element in which a bipolar transistor and an FET are mixed can also be adopted.

[0025]

As described above, according to the present invention,
With the configuration described above, runaway of the semiconductor light emitting element due to a failure in the APC control system can be prevented.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram showing a modification of the light emitting module shown in FIG.

FIG. 3 is a block diagram showing a conventional example of a light emitting module.

FIG. 4 is a diagram illustrating an example of a relationship between a bias current and a modulation current of a laser diode and light emission intensity.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Laser diode 2 Photodiode 3 Current-voltage converter 4 Light intensity detection part 5 Abnormality detection part 6 Intermittent operation signal generation part 7 AND gate 8 NOR gate 9 Bias current control part 10 Amplifier 11 Modulation current control part 208 OR gate 301 Amplifier 302 Feedback resistor 303 Capacitor 901,902 Transistor 1101,1102,1103,1104 Transistor

Claims (5)

[Claims] 1. A semiconductor light emitting device, drive control means for driving and controlling the semiconductor light emitting device to have a predetermined output, and output detection for detecting an output of the semiconductor light emitting device being driven and controlled by the drive control means Means for comparing whether the output detected by the output detecting means is lower than a predetermined reference value, and a result of the comparison by the comparing means, wherein the detected output is higher than a predetermined reference value. An intermittent drive control means for intermittently controlling the semiconductor light emitting element when the power is low. 2. The light emitting module according to claim 1, further comprising a forced stop means for forcibly stopping the driving of the semiconductor light emitting element. 3. The light emitting module according to claim 2, wherein the forcible stop means operates with priority over the intermittent drive control means. 4. The light emitting module according to claim 1, wherein said semiconductor light emitting device is a semiconductor laser diode. 5. The light emitting module according to claim 1, wherein the semiconductor light emitting device is a light emitting diode.