JPH04245691A - Semiconductor laser device drive circuit - Google Patents

Abstract

PURPOSE:To embody an automatic output control type laser device drive circuit wherein the light emitting output of a laser diode is affected by disturbances, such as fluctuations in power supply voltage and outside noise. CONSTITUTION:Three reference current sources 4, 5, and 6, which output reference currents I4, I5 and I6 respectively are provided. The output current of a photodiode 2 which monitors the output of a laser diode 1 is amplified by an amplifier 7 into which the reference current I4 Is input and then the amplified current enters a peak hold circuit 10 and a bottom hold circuit 11. The output of the peak hold circuit 10 and the output of an amplifier 8 which inputs the reference current I5 are input into a differential amplifier 12 where the modulating current of the laser diode is decided with the difference between the reference currents I. and I5 as the reference. Then, the output of the bottom hold circuit 11 and the output of the amplifier 9 which inputs the reference current I6 are made to enter a differential amplifier 13, thereby determining the bias current of the laser diode 1 with the difference between the reference currents I4 and I6 as their reference.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device driving circuit. More specifically, the present invention relates to a semiconductor laser element drive circuit of an optical transmitter using a semiconductor laser element used in an optical communication system.

0002

2. Description of the Related Art FIG. 3 shows a block diagram of an example of a conventional semiconductor laser device drive circuit. The semiconductor laser element drive circuit shown in FIG. 3 monitors the output light of the laser diode 1 with a photodiode 2, and changes the current flowing through the laser diode 1 so that the maximum and minimum values of the light emission output of the laser diode 1 are always constant. The configuration is such that The purpose of the semiconductor laser element drive circuit having this configuration is to correct a decrease in the light emission output of the laser diode 1 due to a rise in temperature during operation. That is, in the semiconductor laser device drive circuit of FIG. 3, an input signal DATA and an inverted input signal DATA* (* symbol indicates an inverted signal) are applied to the bases of transistors Q1 and Q2 via the buffer circuit 3, respectively. Laser diode 1 is power supply VCC
and the collector of transistor Q1 in the forward direction.

The collector of transistor Q1 is further connected to the collector of transistor Q4 via a solenoid 14, and the collector of transistor Q2 is connected to power supply VCC. In addition, transistors Q1 and Q2 are
Their emitters are commonly connected to the collector of a transistor Q3, and the emitter of the transistor Q3 is grounded via a resistor R1.

The output of the differential amplifier 12 is applied to the base of the transistor Q3, and the differential amplifier 12 receives the output of the peak hold circuit 10 which receives the output of the photodiode 2 amplified by the amplifier 7, and the reference current. The output of the amplifier 8 which converts I1 into voltage is input. On the other hand, the output of the differential amplifier 13 is applied to the base of the transistor Q4. The output of the amplifier 9 which converts the voltage into the voltage is input. The emitter of transistor Q4 is grounded via resistor R2. One end of the photodiode 2 is connected to the power supply VCC.

In the above semiconductor laser device drive circuit, the maximum value of the output current of the photodiode 2 and the reference current I1
The value of the modulation current flowing through the laser diode 1 is determined by the output of the differential amplifier 12 which receives as input. Further, the value of the bias current flowing through the laser diode 1 is determined by the output of the differential amplifier 13 which receives the minimum value of the output current of the photodiode 2 and the reference current I2. Therefore, the maximum optical output of the laser diode 1 is determined by the reference current I1, the minimum optical output is determined by the reference current I2, and the average optical output and extinction ratio are determined by the reference currents I1 and I2.

[0006]

In the conventional semiconductor laser device drive circuit described above, the minute reference currents I1 and I2, which determine the light emission output of the laser diode 1, are converted into voltages and sent to the differential amplifiers 12 and 13, respectively. It was entered directly. The reference currents I1 and I2 are minute currents and are susceptible to power supply voltage fluctuations, external noise, etc., and their current values easily change. Therefore, there is a drawback that the laser light output tends to fluctuate due to power supply voltage fluctuations, external noise, and the like.

SUMMARY OF THE INVENTION An object of the present invention is to provide a semiconductor laser element drive circuit which solves the problems of the prior art described above and which oscillates laser light with stable output.

[0008]

[Means for Solving the Problems] According to the present invention, there is provided a semiconductor laser device, a measuring means for measuring the light emission output of the semiconductor laser device, and standards for the maximum and minimum values of the light emission output of the semiconductor laser device, respectively. a reference current output means for outputting a reference current of and a semiconductor laser element driving means for supplying current, wherein the reference current is provided as a difference between a plurality of currents output from different current sources. is provided.

[0009]

[Operation] The main feature of the semiconductor laser device drive circuit of the present invention is that the reference currents of the modulation current and bias current applied to the semiconductor laser device are respectively given as the difference between the currents output from a plurality of current sources. There are some characteristics. In the semiconductor device drive circuit of the present invention, even if the current values of the individual current sources fluctuate due to fluctuations in the power supply voltage or the influence of external noise, the fluctuations in the individual current sources change by approximately the same amount in the same direction. The difference in current hardly changes, and the respective reference currents of the modulation current and bias current applied to the semiconductor laser device do not change. Therefore, the light emission output of the semiconductor laser element is not affected by power supply voltage fluctuations or external noise, and operates stably.

[0010] The present invention will be explained in more detail with reference to Examples below, but the following disclosure is merely an example of the present invention and is not intended to limit the technical scope of the present invention in any way.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a block diagram of an example of a semiconductor laser device driving circuit according to the present invention. The semiconductor laser element drive circuit of FIG. 1, like the conventional semiconductor laser element drive circuit shown in FIG. 3, monitors the output light of the laser diode 1 with the photodiode 2, The configuration is such that the current flowing through the laser diode 1 is controlled so that the value is always constant. Therefore,
Components that are the same as those in the semiconductor laser device drive circuit of FIG. 3 are given the same reference numerals, and the following description will focus on the points that are different from the semiconductor laser device drive circuit of FIG. 3.

In the semiconductor laser device drive circuit shown in FIG. 1, the differential amplifier 12 receives the output of the peak hold circuit 10 and the output of the amplifier 8 as inputs. The peak hold circuit 10 connects the output of the photodiode 2 and the reference current source 4.
The input is the output of the amplifier 7 which receives the output current I4 of . Further, the amplifier 8 receives the output current I5 of the reference current source 5 as an input.

On the other hand, the differential amplifier 13 receives the output of the bottom hold circuit 11 and the output of the amplifier 9 as inputs. The bottom hold circuit 11 is the peak hold circuit 10.
Similarly, the output of photodiode 2 and the reference current source 4
The input is the output of the amplifier 7 which receives the output current I4 of . The amplifier 9 receives the output current I6 of the reference current source 6 as an input. Furthermore, the emitter of transistor Q4 is connected to resistor R2.
is grounded through. One end of the photodiode 2 is connected to the power supply VCC.

In the semiconductor laser device drive circuit configured according to the present invention, the modulation current of the laser diode 1 is determined using the difference between the currents I4 and I5 as a reference current, and the bias current of the laser diode 1 is determined by the difference between the currents I4 and I5. The current difference from I6 is determined as the reference current. Therefore, if the reference current sources 4, 5, and 6 are affected by power supply voltage fluctuations, external noise, etc., the currents I4, I5, and I6
changes in the same direction and by approximately the same amount, so the current I
The difference between currents I4 and I5 and the difference between currents I4 and I6 hardly change. Therefore, the modulation current and the reference current of the bias current of the laser diode 1 hardly change. Therefore, in the semiconductor laser device drive circuit of the present invention, the light emission output of the laser diode is stabilized.

FIG. 2 shows a more specific example of the configuration of the semiconductor laser device drive circuit of the present invention. The semiconductor laser device drive circuit of FIG. 2 has the reference current sources 4, 5, and 6, the amplifiers 7, 8, and 9, the peak hold circuit 10, and the bottom hold circuit 11 of the semiconductor laser device drive circuit of FIG. This is a detailed description. Therefore, the basic structure of both is the same, and the same reference numerals are given to the same components. In order to avoid duplication, the following description will focus on the parts of the semiconductor laser device drive circuit in FIG. 2 that are different from those in FIG. 1.

In the semiconductor laser device drive circuit shown in FIG. 2, the photodiode 2 is inserted between the power supply VCC and the base of the transistor Q22 of the transimpedance type preamplifier 20 for current/voltage conversion. The collector of transistor Q22 is connected to the power supply VC through resistor R21.
C and its emitter is grounded. The base of the transistor Q21 is also connected to the collector of the transistor Q22. The collector of the transistor Q21 is connected to the power supply VCC via a resistor R23, and the emitter is grounded via forward-connected diodes D21 and D22 and a resistor R24. Furthermore, the base of a transistor Q23 is connected to the collector of the transistor Q21. The collector of transistor Q23 is connected to power supply VCC, and the emitter is grounded via resistor R25. A reference current source 4 through which a reference current I4 flows is further connected between the base of the transistor Q23 and the ground. Furthermore, the base of the transistor Q22 is
Diode D22 and resistor R24 via resistor R22
connected between.

Both amplifiers 21 and 22 are preamplifiers 20
This dummy is equipped with reference current sources 5 and 6 that flow reference currents I5 and I6, respectively. Further, the configurations of the amplifiers 21 and 22 are completely the same as that of the preamplifier 20, except that the output of the photodiode 2 is not inputted, and therefore a description thereof will be omitted.

The peak hold circuit 10 includes a preamplifier 2
The differential amplifier A21 is provided with an output of 0 inputted to a positive phase input and whose output terminal is grounded via a diode D27 and a capacitor C21 connected in the forward direction. The anti-phase input terminal of differential amplifier A21 is connected between diode D27 and capacitor C21.

The bottom hold circuit 11 is connected to the preamplifier 2
The differential amplifier A22 is provided with an output of 0 inputted to the positive phase input and whose output terminal is grounded via a diode D28 and a capacitor C22 connected in the opposite direction. The anti-phase input terminal of differential amplifier A22 is connected between diode D28 and capacitor C22.

In the semiconductor laser device drive circuit of the present invention, the output voltage V1 of the amplifier 20 is controlled by the transistor Q23.
If the base-emitter voltage of is VBE, then V1 =
VCC-VBE (R23/R24+1)+IPDR23
(R22+R24)/R24-I4R23 The output voltage V2 of the dummy amplifier 21 is V2 = VCC-VBE (R23/R24+1)-I5
The output voltage V3 of the R23 dummy amplifier 22 is V3 = VCC - VBE (R23/R24 + 1) - I6
R23 Therefore, the input voltage Vin12 of the differential amplifier 12
is Vin12 = R23 (I4 - I5 ) - IPDma
x R23(R22+R24)/R24...(1)
The input voltage Vin13 of the differential amplifier 13 is Vin13=R
23(I4-I6)-IPDmin R23(R2
2+R24)/R24...(2) From the above,
In the semiconductor laser device drive circuit of the present invention, the reference currents that determine the modulation current and bias current flowing through the laser diode 1 are R24/(R22+R24) times I4-I5 and I4-I6, respectively.

In the semiconductor laser element drive circuit described above, when the maximum and minimum values of the laser light output of the laser diode 1 change due to temperature changes during operation, etc.,
The maximum value IPDmax and the minimum value IPDmin of the output current of the photodiode 2 each change. IPDm
When ax and IPDmin change, the above (
From equations 1) and (2), the modulation current and bias current of the laser diode 1 change in a direction that cancels the change in the laser light output of the laser diode 1, and the laser light output becomes stable. Also, the reference currents I4 - I5 and I4 -
By adjusting I6, the laser light output of the laser diode 1 can be set arbitrarily.

Furthermore, in the semiconductor laser device drive circuit of the present invention, for example, when the power supply voltage fluctuates or when external noise occurs, the reference current sources 4, 5, and 6 are similarly affected, and each Reference current I4 to output,
I5 and I6 vary similarly. On the other hand, the modulation current and bias current flowing through the laser diode 1 are
As mentioned above, since it is based on I4 - I5 and I4 - I6, it is not affected by power supply voltage fluctuations or external noise. Therefore, the laser light output becomes more stable without being affected by disturbances.

[0023]

As explained above, the semiconductor laser device drive circuit of the present invention not only prevents the laser light output from decreasing due to temperature rise during operation, but also prevents the laser light output from decreasing due to power supply current fluctuations and external noise. Fluctuations in output can be suppressed. Therefore, it is effective to use it as a drive circuit for a laser transmitter, especially in the field of optical communications.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an example of a semiconductor laser device drive circuit of the present invention.

FIG. 2 is a more detailed block diagram of an example of the semiconductor laser device drive circuit of the present invention.

FIG. 3 is a block diagram of an example of a conventional semiconductor laser device drive circuit.

[Explanation of symbols]

1 Laser diode 2 Photodiode 3 Buffer circuit 4, 5, 6 Reference current source 7, 8, 9 Amplifier 10 Peak hold circuit 11 Bottom hold circuit 12, 13 Differential amplifier

Claims (1)

[Claims] 1. A semiconductor laser device, a measuring means for measuring the light emission output of the semiconductor laser device, and a reference current output for outputting a reference current serving as a reference for each of the maximum and minimum values of the light emission output of the semiconductor laser device. means, and semiconductor laser element driving means for supplying current to the semiconductor laser element so that the maximum and minimum values of the light emission output of the semiconductor laser element measured by the measuring means respectively match the values determined by the reference current. 1. A semiconductor laser device drive circuit comprising: a semiconductor laser device drive circuit, wherein the reference current is provided as a difference between a plurality of currents output from different current sources.