JPS63144653A - Drive circuit for semiconductor laser array - Google Patents

Abstract

PURPOSE:To attain Automatic Power Control (APC) by one optical detector by driving plural radiation exits one by one channel, receiving the light by a single optical detector and storing the drive current. CONSTITUTION:A main pulser P, delay circuits DP1-DPn and a decoder D switch a multiplexer MP, a transistor TS1 is turned on, a semiconductor laser light emitting diode LD1 is lighted to select the radiation exit of the channel. Then the lighting of the diode LD1 is received by the single photo diode detector and the supplied voltage is adjusted via a comparator CP, the light emitting quantity of the diode LD1 is adjusted to a prescribed quantity and the drive voltage is stored in a capacitor C1. The APC is applied similarly to the other diodes LD1-LDn. All the channels are driven by the stored voltage in the capacitors C1-Ckn via the decoder D and the APC is applied by one detector.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention provides a method for mounting a plurality of semiconductor laser chips on one stem or mounting a semiconductor laser in which a plurality of independent channels are formed on an l-chip. The present invention relates to a drive circuit for a semiconductor laser array having a plurality of so-called independent emission apertures.

<Prior Art> With the aim of increasing the speed and density of laser beam printers or optical disk drives, semiconductor laser arrays having a plurality of independent emission ports in one stem have been commercialized. ' Generally, the optical output of a semiconductor laser fluctuates depending on the temperature, so a photodetector such as a photodiode, which is either external or built into the same stem, is usually used to control the optical output to a constant value. (Aato-a+attc P
(control) circuit.

<Problems to be Solved by the Invention> However, in the case of a semiconductor laser array, APC control has been difficult because laser beams from a plurality of independent emission ports enter one photodiode at the same time. If you really want to control the laser light for each channel, as shown in Figures 3(a) and (b), you will need a semiconductor laser array LD, a photodiode, etc. in which multiple semiconductor lasers LD, LD,... are mounted. photodetector P D l+
A magnifying lens Δ is arranged between P D 2..., and the magnifying lens 8 separates the laser beams LD, LD, .
It is necessary to control the optical output to a constant value using an independent APC circuit.

However, this method is not practical because it is difficult to adjust each optical system and requires multiple photodiodes and independent APC circuits, and it cannot be used particularly for driving alignment reliability tests of a large number of semiconductor laser arrays. There wasn't.

The present invention has been made in view of the above-mentioned problems, and is applicable to lIr! for a plurality of semiconductor lasers. An object of the present invention is to provide a driving circuit for a semiconductor laser array that can be controlled by APC using a photodetector for illumination.

Means for Solving the Problems> The present invention provides means for driving the plurality of emission ports one channel at a time in a semiconductor laser array having a plurality of independent emission ports, and a means for driving the laser beams from the emission ports in a single manner. A means for receiving light with a photodetector of
means for performing constant output driving that provides a driving current value that makes the current value the same as 1; means for storing the driving current value for each channel; and constant current driving that simultaneously lights up all channels using the stored driving current value. (Automatic
Current Control: A CC drive)
It consists of a means to

As described above, the laser beam is turned on one channel at a time, the laser beam is received by a single photodetector, and constant output driving is performed to give a current value that makes all channels have a constant optical output. Constant current drive that lights up all channels simultaneously depending on the current value during drive.

<Example> Hereinafter, an example of the present invention will be described in detail using the drawings.

FIG. 1 and FIG. 2 show a circuit diagram and a time chart according to the present invention. In the figure, MP is connected to each semiconductor laser LD, , L during APC by a signal from the main pulser P.
An analog multiplexer serves as a means for switching channels of D2... and switching between APC and ACC modes, and drives multiple laser exit ports one channel at a time through an operational amplifier AJ transistor 1゛r.PD converts laser light into a single light The photodiode CP, which serves as a means for receiving light in the detector, is connected to the input terminal of the analog multiplexer MP, and serves as a means for constant output driving to provide a drive current value that makes the amount of laser light the same for each channel. C is the comparator of operational amplifier A (-
) The drive current value is stored in the capacitor C by turning off all the channels of the analog multiplexer MP and the switching transistors Ts, and a capacitor provided between the input end and the ground as a means for storing the drive current value for each channel. This is constant current driving means that lights up all channels at the same time using the determined driving current value.

First, when performing APC control on the first channel semiconductor laser LD, the analog multiplexer MP is
Set only the channel number to be in the off state, and output the output of the comparator CP to the operational amplifiers l to 1. Transistor'
A current is caused to flow through the semiconductor laser LD through I"r, and the switching transistor Ts+ is turned off. Here, only the laser light L of the semiconductor laser LD is incident on the photodiode PD, and the laser light, The output of the comparator CP changes depending on the strength of the operational amplifier A, and the drive current is set to a constant optical output.

is applied to the first channel semiconductor laser L D + for APC driving. In addition, the operational amplifier A flows to the semiconductor laser LD by a human-powered voltage signal. It works as a voltage-to-current converter to control the li current.

Next, the first channel of the analog multiplexer MP is turned off, and at the same time, the switching transistor 1's1 is turned on. Then, no current flows through the first channel semiconductor laser LD and the laser beam L1 disappears, but the drive current value during APC drive is held in the form of voltage in the capacitor CI. This completes the APC operation of the first channel semiconductor device LDI. Here, in order to lengthen the holding time, the off-resistance of the analog multiplexer MP and the input resistance of the operational amplifier A1 are made as large as possible. Further, it is necessary to select a capacitor 01 with high insulation resistance and low dielectric absorption.

Thereafter, the channels of the analog multiplexer MP and the switching transistors Ts+-Tsn are switched one after another to APC drive the semiconductor lasers LD+ to LDn of all channels, and the voltage at that time is held in the capacitors C,=Cn. Switching of each channel of the analog multiplexer MP is performed by a decoder D and delay pulsers 〇P, -DPn based on the clock pulse of the main pulser P.

When the APC driving of all semiconductor lasers LDI-LDn is completed, a switching signal to ACC driving from the decoder D causes all channels of the analog multiplexer MP and the switching transistor Ts.

~Tsn are all turned off, and the semiconductor lasers LD + ~LDn of all channels are turned on to perform ACC driving. In this state, the operational amplifiers A1-A n calculate q1.n based on the voltage held in the capacitors 01-Cn. :Works as a ΔCC circuit that extracts the drive current value. Here, since all channels of the analog multiplexer MP are in the off state, each semiconductor laser LD is independent of the voltage generated at the photodiode PD.

~LDn can be driven. In addition, semiconductor laser L D +
The intensity of the laser light of , LD, . . , L2 . . . is determined by the variable resistor VR connected to the analog multiplexer MP.
It can be adjusted by changing the basic voltage set in .

Here, since the fluctuation of the laser light output due to temperature is a slow phenomenon in terms of time, operation with a constant laser light output is possible by performing APC driving from time to time and performing ACC driving at other times. The ACC driving time is set to such an extent that the case temperature of the semiconductor laser array does not change, or to the extent that the capacitor 01
~Choose the electricity stored in Cn to the extent that it does not leak. Furthermore, in order to gain actual working time, it is preferable that the APC drive is as short as possible compared to the CC drive.

In this example, a semiconductor laser array in which a semiconductor laser chip with one emission aperture per semiconductor laser chip is mounted has been described. A similar effect can be obtained by using a semiconductor laser array mounted with .

<Effects of the Invention> As described above, according to the present invention, by using a time-series APC circuit that drives a plurality of exit ports one channel at a time, it is possible to eliminate the need for a complicated optical system or a plurality of photodetectors. Therefore, it is possible to provide a useful semiconductor laser array drive circuit that can control and drive the laser beams of all channels to a constant optical output without any problems.

[Brief explanation of the drawing]

1 and 2 are drive circuit diagrams and time charts showing an embodiment of the present invention, and FIGS. 3(a) and 3(b) are simplified cross-sectional views of a semiconductor laser array and a photodetector showing a conventional example. be. LD to LDn: semiconductor laser, I, 1 to Ln: laser beam, PD: photodetector (photodiode), C3 to Cn
: Capacitor, A : Operational amplifier, Tr to Trn:) transistor, Ts to Tsn switching transistor, MP
: Analog multiplexer, CP: Comparator.

Claims (1)

[Claims] 1. In a semiconductor laser array having a plurality of independent emission apertures, means for driving the plurality of emission apertures one channel at a time, means for receiving laser light from the emission apertures with a single photodetector, and means for each channel. means for performing constant output driving that provides a drive current value that makes the amount of laser light the same; means for storing the drive current value for each channel;
A driving circuit for a semiconductor laser array, comprising constant current driving means for lighting all channels at the same time using the stored driving current value.