JPS6222495A - Stabilizing circuit for semiconductor laser light output - Google Patents

Abstract

PURPOSE:To obtain the stabilizing circuit for semiconductor laser light output which is easily operated and simply constituted at low cost, by stabilizing the light output of all of other semiconductor laser elements by using the control signal to stabilize the light output of at least one element from among a plurality of semiconductor laser elements constituted on the same semiconductor substrate. CONSTITUTION:The output signal of a photoelectric conversion circuit 8 is inputted to a control circuit 9, and the output signal thereof is inputted to driving circuits 2 and 3. An LD5 and an LD6 are formed at least on the same semiconductor substrate 4. The output current of the driving circuit 3 is so designed that the light output of the LD6 is equal to or proportional to the mean value of a specified value of light output when the LD5 is ON and that of light output when the LD5 is OFF. A part or all the light output 7 of LD6 is delivered to a photoelectric conversion circuit 8, and is converted to an electric signal whose value is proportional to the light output of the LD6. A control circuit 9 compares the output level of the photoelectric conversion circuit 8 with a predefined value, and controls the driving circuit 2 and the driving circuit 3 by the result of said comparison.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a circuit for stabilizing the optical output of a semiconductor laser, and more particularly to a circuit for stabilizing the optical output of a plurality of semiconductor lasers formed on the same semiconductor substrate.

[Conventional technology]

Generally, the optical output of a semiconductor laser (hereinafter referred to as LD) is
Since it fluctuates greatly due to operating temperature, aging, etc., a light output stabilization circuit is required to keep the light output constant.

Conventionally, in this type of optical output stabilizing circuit, as shown in FIG.
and the control circuit 15, the output signal of the drive circuit 2 drives the LD 5, a part 7 of the optical output of this LD 5 is input to the photoelectric conversion circuit 8, and the output signal of this photoelectric conversion circuit 8 is input to the control circuit 15, and the output signal of this control circuit 15 is input to the drive circuit 2. Also 1, drive circuit 2
changes the drive current of LD5 according to the electrical input signal,
This LT) 5 outputs an optical signal according to an electrical input signal. A portion 7 of the optical output of this LD 5 is taken out and input to a photoelectric conversion circuit 8, where it is converted into an electrical signal.

The control circuit 15 inputs the output signal of the photoelectric conversion circuit 8 and the electrical input signal which are proportional to the optical output of the LD 5, and outputs a control signal to the drive circuit 2 to keep the optical output of the LD 5 constant.

In general, the control circuit 15 removes the influence of the data pattern of the electrical input signal, rectifies it, and controls vI so that the value becomes a constant value corresponding to a predetermined optical output of the LD 56. When the output increases more than a predetermined value, the output signal of the photoelectric conversion circuit 8 changes, so the optical output level of the LD 5 is adjusted by reducing the driving current of the driving circuit 2 by an amount commensurate with the change. be controlled at a constant level.

[Problem that the invention seeks to solve]

In the conventional optical output stabilization circuit described above, the influence of the data pattern of the electrical input signal is eliminated by the control circuit 15, but the slant control circuit becomes complicated, especially when the same code continues for a long time. The drawback was that it was difficult to control.

Furthermore, when operating multiple semiconductor lasers, it is necessary to stabilize the optical output of each semiconductor laser individually because the characteristics of the semiconductor lasers vary widely.
As many optical output stabilizing circuits as there are semiconductor lasers are required.

Therefore, the number of components and the mounting area are large, and the price is also high.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical output stabilizing circuit for a semiconductor laser which can solve these problems and can be easily controlled and constructed simply and inexpensively.

[Means for solving problems]

The optical output stabilization circuit for a semiconductor laser of the present invention includes first and second semiconductor lasers formed on the same semiconductor substrate, and a current 1 of the first semiconductor laser driven by a data input signal and a control signal. a first drive circuit, a second drive circuit that drives the current of the second semiconductor laser according to the control signal, and a photoelectric conversion that inputs the optical output of the second semiconductor laser and converts it into an electrical signal. circuit, and a control circuit that supplies the output signal of the photoelectric conversion circuit as the control signal to the first and second drive circuits to stabilize and control the optical output of the second semiconductor laser. be done.

The optical output stabilizing circuit for a semiconductor laser of the present invention uses a control signal to stabilize the optical output of at least one semiconductor laser among a plurality of semiconductor lasers configured on the same semiconductor substrate. It is characterized by stabilizing the optical output of a semiconductor laser.

[Principle of the invention]

Generally, the main factors that cause variations in the characteristics of an LD, such as threshold current and differential quantum efficiency, include variations in the properties of the semiconductor substrate forming the LD, variations in various manufacturing conditions, and variations in operating temperature.

By using it in the optical output stabilizing circuit of the present invention or configuring D on the same semiconductor substrate, variations in characteristics can be reduced to an extent that does not interfere with stabilizing the optical output. That is, even if there are variations in the characteristics of semiconductor substrates or variations in various manufacturing conditions, they affect each LD equally within the same substrate, so variations in the characteristics of the LDs can be reduced. Furthermore, since the thermal resistance of the substrate is low within the same substrate and the substrate can also be made small, each LD is strongly coupled thermally, so that almost no temperature difference occurs between the LDs.

In the present invention, optical output is stabilized for at least one LD among a plurality of LDs configured on the same semiconductor substrate, and a control signal for stabilization is sent to the other LDs. This stabilizes the optical output of other LDs by supplying the same amount of light. In this way, L on the same board
Since D has small variations in characteristics, it can be sufficiently stabilized even if it is controlled by at least one control signal.

〔Example〕

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

FIG. 1 is a block diagram of a first embodiment of the present invention, showing a case where two LDs are provided on the same semiconductor substrate.

The electrical input signal input to the input terminal 11 is input to the drive circuit 2, and the output of the drive circuit 2 is connected to the LD 5, which outputs an optical output 10. On the other hand, the output of the other drive circuit 3 is connected to the LD 6 , and part or all of the first cuff of this LD 6 is supplied to the photoelectric conversion circuit 8 .

The output signal of this photoelectric conversion circuit 8 is input to a control circuit 9, and the output signal of the control circuit 9 is input to a drive circuit 2 and a drive circuit 3. Further, at least LD5 and LD6 are formed on the same semiconductor substrate 4.

The output current of the drive circuit 3 is set such that the optical output of the LD 6 is equal to or proportional to the average value of the predetermined optical output when the LD 5 is on (ON>) and the predetermined optical output when the LD 5 is off (OFF). A part or all of the first cuffs of this LD 6 are input to a photoelectric conversion circuit 8 and converted into an electrical signal, whose value becomes a value proportional to the optical output of the LD 6.

Control circuit 9 compares the output level of photoelectric conversion circuit 8 with a predetermined value, and controls drive circuit 2 and drive circuit 3 based on the result. If the optical output of the LD6 becomes larger than the set value for some reason, the photoelectric conversion circuit 8
The output level of the control circuit 9 changes, and the output signal of the control circuit 9 changes to the output level of the LD6.
The drive circuit 3 is controlled to reduce the drive current.

The reason why the optical output of LD6 increases is the same as <LD5
The optical output of the LD 5 also increases because the control circuit 9. By similarly controlling the drive circuit 2 using the output signal, the optical output of the LD 5 can also be controlled to a predetermined value.

FIG. 2 is a circuit diagram of the main part of the embodiment shown in FIG. The electrical input signal input to the input terminal 1 is input to the base of the transistor 20 of the drive circuit 2, the emitter of the transistor 20 is connected to the current source 22, its collector is connected to the power supply VC, and the base of the transistor 21 is connected to the reference voltage VRI. , its emitter is connected to the current source 22, its collector is connected to the cathode crystal of LD5, the collector of transistor 23 is connected to the cathode of LD5, the resistor 24 is connected between the emitter of transistor 23 and ground, and light from LD5 is connected. Outputs output 10.

On the other hand, the current source 25 of the drive circuit 3 is connected to the collector of the transistor 26 together with the cathode of the LD6, and its emitter is grounded via a resistor 27, and the first cuff is outputted from the LD6.

Further, the anode of the light receiving element 28 of the photoelectric conversion circuit 8 is connected to the power supply VB, the cathode of the light receiving element 28 is connected to the input of the inverting amplifier 30, and the resistor 29 is connected between the input and output of the inverting amplifier 30. , the output of the inverting amplifier 30 is
It is connected to the negative phase input of the voltage comparator 31 of the control circuit 9, the positive phase input of this voltage comparator 31 is connected to the reference voltage VR2, and the positive phase input of this voltage comparator 31 is connected to the reference voltage VR2, The output of this voltage comparator 31 is connected to a grounded capacitor 33 and a transistor 26 via a resistor 32.
and the base of transistor 23. At least these LD5 and LD6 are constructed on the same semiconductor substrate 4.

As a driving method for LD, a bar with a value close to the threshold current is used.
The device is driven by superimposing a pulse current that changes depending on the input signal on the bias current, and the optical output is stabilized by controlling only the bias current.

Transistor 20 and transistor 21 of drive circuit 2 are current switching circuits, and when the input signal voltage is lower than reference voltage VRI, current IP1 of current source 22 flows to LD5, and conversely, when it is higher, it does not flow. Further, the transistor 23 and the resistor 24 are a circuit that flows a bias current IBI to the LD 5, and this bias current IBI changes depending on the base voltage of the transistor 23. When the input signal voltage is at a low level, the LD5 is turned on and outputs light, and when it is at a high level, it is turned off and outputs almost no light.The stabilization of this optical output is achieved when the LD5 is turned on and when it is turned off. The purpose is to control the average value of the optical output 10 of the light output 10 to always be a predetermined value.

Further, the current IP2 of the current source 25 of the drive circuit 3 is always connected to the LD
Also, the transistor 26 and the resistor 27 are connected to LD6.
Although bias current IB2 is applied to .

This bias current IB2 changes depending on the base voltage of the transistor 26. For ease of understanding, the resistor 27 is set to the same value as the resistor 24, and the base of the transistor 23 and the base of the transistor 26 are connected, so that the bias currents IBI and IB2 always have the same value. Also, the current I
P2 is set to 1/2 of the current IPI, and when LD5 is ON and O
A current corresponding to the average value of the current during FF is passed through LD6 6
．． Since these LD5 and LD6 are formed on the same semiconductor substrate 4, variations in characteristics are small, and the optical output of LD6 is an average value of optical output 10 when LD5 is ON and OFF.

A part or all of the first cuff of the LD 6 is input to the light receiving element 28 of the photoelectric conversion circuit 8 and converted into a current, which is then converted into a voltage and amplified by the inverting amplifier 30 and the resistor 29. The output signal of this inverting amplifier 30 is transmitted to the control circuit 9
is input to the negative phase input of the voltage comparator 31, and is compared with a reference voltage VR2 corresponding to a predetermined optical output level of the LD6. The output signal of voltage comparator 31 is connected to resistor 32 and capacitor 3.
Due to the integral effect with 3, it is slowly input to the bases of transistors 23 and 26.

If the optical output of the LD6 becomes larger than a predetermined value for some reason, the output voltage of the inverting amplifier 30 becomes higher than the reference voltage VR2, and the output of the voltage comparator 31 becomes a low level. Then, the base voltages of the L-transistor 26 and the transistor 23 gradually decrease, the bias current IB2 decreases, and the optical output of the LD6 decreases.
The light output of LD6 is set to a predetermined value. The factors that increase the optical output of LD6 are the same (it also acts on LD5, so L
Although the optical output 10 of D5 also increases, it is controlled in the same way as LD6 by the output signal of the control circuit 9, and the bias current IBI
becomes smaller, and as a result, the optical output of the LD 5 becomes smaller and returns to a predetermined value.

In the end, by stabilizing the first cuff of LD6, LD5
The optical output of 10 can be stabilized.

FIG. 3 is a block diagram of a second embodiment of the present invention.
3, and each electrical input signal input to the N input terminals 1-1 to 1-N indicates the case where there are three or more LDs on the same semiconductor substrate. N corresponding to
drive circuits 2-1 to 2-H respectively, and drive circuits 2-1 to 2-N to the corresponding N LDs 5-1 to 5-H.
LDs 5-1 to 5-N output optical outputs 10-1 to 10-N according to each electrical input signal. On the other hand, the output of the drive circuit 3 drives the LD 6, part or all of the first cuff of the LD 6 is input to the photoelectric conversion circuit 8, and the output signal of the photoelectric conversion circuit 8 is input to the control circuit 9, which controls the circuit 9
The output signals of drive circuits 2-1 to 2-N and drive circuit 3
and at least D5-1 to 5-N and LD
6 are formed on the same semiconductor substrate 4.

LD5-1 to 5-N and LD6 are the same semiconductor substrate 4
Since the LD 5 is formed on the top of the LD 6, variations in characteristics can be ignored. -1 to 5-N optical outputs can be stabilized all at once. The other operations are exactly the same as the embodiment shown in FIG.
Since the optical output of the LD can be stabilized, the amount of circuitry can be significantly reduced compared to the case where LDs are individually stabilized.

In addition, in these examples, L used for stabilizing the optical output
D6 and LD5 and LD5-1 to LD5-5-N used for signals do not have to have the same characteristics, and may have a correlation in characteristics. It can also be applied to LDs.

〔Effect of the invention〕

As explained above, the present invention stabilizes the optical output of at least one LD among a plurality of LDs with small variations in characteristics configured on the same semiconductor substrate, and sends a control signal for this stabilization. By using this method to stabilize the optical output of other LDs, the optical output can be stabilized regardless of the data pattern of the electrical input signal, and the number of circuits required for stabilization can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the first embodiment of the present invention, FIG. 2 is a circuit diagram of the main part of FIG. 1, FIG. 3 is a block diagram of the second embodiment of the present invention, and FIG. In Figure 0, which is a block diagram of an example of a conventional optical output stabilization circuit, 1.1-1 to N...input terminals, 2.2-1 to 2-N,
3... Drive circuit, 4... Semiconductor substrate, 5.5-1~
5-N, 6... semiconductor laser, 7.10.10-1~
'l O-N... Optical output, 8... Photoelectric conversion circuit,
9... Control circuit, 20.21.23.26... Transistor, 22.25... Current source, 24.27, 29
32... Resistor, 28... Light receiving element, 30... Inverting amplifier, 31... Voltage comparator, 33... Capacitor.

Claims (2)

[Claims] (1) First and second semiconductor lasers formed on the same semiconductor substrate, a first drive circuit that drives the current of the first semiconductor laser using an electrical input signal and a control signal, and a second drive circuit that drives the current of the semiconductor laser using the control signal; a photoelectric conversion circuit that inputs the optical output of the second semiconductor laser and converts it into an electrical signal; and an output signal of the photoelectric conversion circuit. a control circuit for stabilizing and controlling the optical output of the second semiconductor laser by supplying the control signal to the first and second drive circuits as the control signal. (2) A patent claim in which the first semiconductor laser includes a plurality of semiconductor lasers, and the first drive circuit includes a plurality of drive circuits that respectively drive each current of the plurality of semiconductor lasers according to each electrical input signal. An optical output stabilization circuit for a semiconductor laser according to scope 1.