JPH0399485A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To enable a semiconductor laser to operate stably at an output proportional to a modulation signal input by a method wherein the fluctuation of the semiconductor laser in threshold current and slope efficiency attendant on temperature change is corrected, and the semiconductor is modulated in optical intensity corresponding to the modulation signal. CONSTITUTION:A threshold current correction means 22 and a slope efficiency correction means, which correct the fluctuation of a semiconductor laser 1 in threshold current slope efficiency attendant on the change of it in temperature respectively, are provided. That is, the light intensity modulation of the semiconductor laser 1 is carried out corresponding to modulation signals inputted from the outside. A correction coefficient or a reciprocal number of a slope efficiency is computed basing on the temperature data of the semiconductor laser 1. A correction circuit 2 which outputs a correction modulation signal obtained by multiplying the modulation signal input by the correction coefficient and a threshold current generating circuit 3 which generates the threshold current of the semiconductor laser 1 and outputs a driver current obtained by adding the threshold current concerned to the correction modulation signal of the correction circuit 2 are provided. A current drive circuit 4 which drives the semiconductor laser 1 basing on the drive current of the threshold current generating circuit 3 is provided.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a semiconductor laser device used in an exposure device, etc., and more specifically, the present invention relates to a semiconductor laser device that is used in an exposure device or the like. The present invention relates to a semiconductor laser device that performs modulation.

[Prior Art] Conventionally, in this type of semiconductor laser device, when driving the semiconductor laser with a current based on a modulation signal input from the outside and modulating the intensity of its optical output, it is necessary to avoid changes in the ambient temperature of the semiconductor laser. If so, the threshold current of the semiconductor laser changes and the intensity of the optical output changes, making it impossible to obtain an optical output with an intensity corresponding to the input modulation signal. Therefore, conventionally,
In order to avoid malfunctions due to temperature changes in step 4, temperature control means are used to keep the semiconductor laser at a constant temperature, and the operating point of the semiconductor laser is changed to follow changes in the threshold current due to temperature changes in the semiconductor laser. Threshold current correction means are commonly employed.

The former temperature control means keeps the temperature constant by heating a semiconductor laser or using a Peltier element, but since precise temperature control is difficult and unreliable, Threshold current correction means are often used.

A semiconductor laser device equipped with this threshold current correction means monitors the optical output of the semiconductor laser with a photodiode, detects changes in the threshold current, and controls the drive current of the semiconductor laser by following this change. It is equipped with a control circuit that compensates for changes in the threshold current of the semiconductor laser due to temperature changes and modulates the intensity of the optical output of the semiconductor laser in response to the modulation signal input. It has become.

[Problems to be Solved by the Invention] However, in conventional semiconductor laser devices, the threshold current of the semiconductor laser changes with temperature changes, and
The external differential quantum efficiency (hereinafter referred to as slope efficiency), which is the luminous efficiency of the semiconductor laser, also changes. For example, FIG. 2 shows the optical output P of a semiconductor laser. and drive current 1. As shown in the relationship, the threshold current under a certain temperature condition is I th.

When the slope efficiency is η, it is expressed as Po=(IF I th)η. The slope efficiency η is the optical output P. As shown in FIG. 3, this ratio changes almost linearly with changes in the temperature of the semiconductor laser.

Therefore, in a semiconductor laser device that performs intensity modulation of the optical output of a semiconductor laser in response to a modulation signal input, even if the threshold current is corrected due to temperature changes in the semiconductor laser, the slope efficiency changes and the optical output decreases. Since the intensity sometimes decreases as the temperature rises and increases as the temperature decreases, there is a problem in that it is difficult to accurately correspond the modulation symbol input and the light intensity modulation.

The present invention has been made in view of the above points, and its purpose is to eliminate the cause of errors in light intensity modulation due to temperature changes in semiconductor lasers, and to perform light intensity modulation in accurate correspondence with modulation signal input. An object of the present invention is to provide a semiconductor laser device that performs the following steps.

[Means for Solving the Problems] The semiconductor laser device of the present invention achieves the above object by comprising a threshold current correction means for correcting a change in the temperature of the semiconductor laser and a slope efficiency correction means for correcting a change in slope efficiency. It achieves this and consists of the following configuration: That is, the semiconductor laser device of the present invention modulates the light intensity of the semiconductor laser in response to an external modulation signal input, and calculates a correction coefficient of the reciprocal of the slope efficiency based on temperature information of the semiconductor laser. A correction circuit that outputs a corrected modulation signal obtained by multiplying the modulation signal input by a correction coefficient, and a threshold current generator that generates a threshold current for the semiconductor laser and outputs a drive current that is added to the corrected modulation signal of the correction circuit. circuit, and a current drive circuit that drives the semiconductor laser based on the drive current of the threshold current generation circuit.

[Function] According to the semiconductor laser device of the present invention having the above configuration, the correction circuit outputs a correction modulation signal that corrects a change in slope efficiency due to a temperature change of the semiconductor laser to the threshold current generation circuit. , the threshold current generation circuit outputs a drive current that is the sum of the threshold current caused by the temperature change of the semiconductor laser and the correction modulation signal to the current drive circuit to drive the semiconductor laser, so the semiconductor laser has a slope efficiency. It is driven with an optical output proportional to the manual modulation signal, with the threshold current corrected and therefore less error sensitive to temperature changes.

[Example] Hereinafter, an example embodying the present invention will be described with reference to FIG. 1.

FIG. 1 is a block diagram for explaining the entire configuration of the semiconductor laser device of the present invention. As shown in FIG. 1, the slope efficiency η( a correction circuit 2 for correcting the change in FIG. 2);
A threshold current generation circuit 3 that generates a threshold current of the semiconductor laser l, a current drive circuit 4 that drives the semiconductor laser l with current, and a signal that detects the temperature of the semiconductor laser l and corrects the signal converted into an electrical signal. It is comprised of a temperature sensor 5 that outputs an output to the circuit 2, and a light receiving element, for example a photodiode 6, that converts the optical output of the semiconductor laser l into an electrical signal and outputs it to the threshold current generation circuit 3. The temperature sensor 5 is thermally coupled to the semiconductor laser 1 and sends temperature information of the slope efficiency η (FIG. 2) according to the temperature of the semiconductor laser 1 to the correction circuit 2. The photodiode 6 is optically coupled to the semiconductor laser 1 and sends a signal determining the threshold current of the semiconductor laser 1 to the threshold current generation circuit 3.

I will explain in more detail. The correction circuit 2 calculates a correction coefficient, which is the reciprocal of the slope efficiency η (FIG. 2) determined by the temperature of the semiconductor laser I, based on the temperature information from the temperature sensor 5! /η
It has a function of calculating the correction coefficient I/η and a function of multiplying the correction coefficient I/η by a modulation signal D6 manually input from the outside, or outputting a correction modulation signal of 1/η.

The threshold current generation circuit 3 has a function of generating a threshold current Ith according to the temperature of the semiconductor laser l based on a signal from the photodiode 6, and a function of generating a threshold current Ith from the generated threshold current 1th and the correction circuit 2. The current drive circuit 4 adds /η to the correction modulation signal of /η+I th.
It has the ability to output to. Threshold current generation circuit 3
The threshold current generation is performed as follows. That is,
Using a control command signal input from the outside at a predetermined period, the input modulation data from the correction circuit 2 is cut off, only the threshold current is output to the current drive circuit 4, and the output current is gradually increased from zero. let Then, the threshold current 1th is fixed at the time when the optical output of the semiconductor laser 1 suddenly increases and the photodiode 6 detects light at a predetermined level, and the cutoff of the input modulation data from the correction circuit 2 is released. do.

The current drive circuit 4 controls the semiconductor laser 1 based on the drive current (D, /η+I th) from the threshold current generation circuit 3.
drive. This semiconductor laser! optical output P. is expressed as Po=(Ip 1th)77 from the graph of FIG. 2, where the drive current is IF, but the drive current 1. As mentioned above, is (D, /η+I th), so
Substituting this into the above equation gives the optical output P.

is as follows.

PO-(D, /77 + I th-I th) 77
=D.

That is, the optical output P of the semiconductor laser 1. is not affected by changes in the threshold current 11h and slope efficiency η due to temperature changes, and the modulation signal D6 input from the outside is
It will be proportional to.

[Effects of the Invention] As is clear from the detailed description above, the semiconductor laser device of the present invention corrects the threshold current and slope efficiency accompanying temperature changes of the semiconductor laser, and adjusts the modulation signal input from the outside. Since the light intensity modulation of the semiconductor laser is performed in response to the change in temperature of the semiconductor laser, it is not affected by changes in the temperature of the semiconductor laser, and the semiconductor laser can be stably driven with an optical output proportional to the modulation signal human power. can be made,
High precision, high reliability, and effectiveness. In addition, there is no need for precise temperature control of the semiconductor laser, making the entire device more compact.
Another effect is that maintenance can be facilitated.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the semiconductor laser device according to the present invention, Fig. 2 is a graph showing the characteristics of optical output and drive current in the semiconductor laser, and Fig. 3 is the slope efficiency (external differential FIG. 2 is a graph diagram showing characteristics of quantum efficiency (quantum efficiency) and temperature. l... Semiconductor laser, 2... Correction circuit, 3... Threshold current generation circuit, 4... Current drive circuit, 5...
Temperature sensor, 6...photodiode.

Claims (1)

[Claims] A semiconductor laser device that performs intensity modulation of the optical output of a semiconductor laser in response to a modulation signal input from the outside, comprising: a correction coefficient of the reciprocal of external differential quantum efficiency based on temperature information of the semiconductor laser; a correction circuit that calculates the correction coefficient and outputs a correction modulation signal by multiplying the modulation signal by this correction coefficient; and a correction circuit that generates a threshold current of the semiconductor laser and outputs a drive current that is added to the correction modulation signal of the correction circuit. What is claimed is: 1. A semiconductor laser device comprising: a threshold current generation circuit; and a current drive circuit that drives a semiconductor laser based on a drive current of the threshold current generation circuit.