JPH0661530A - Laser emitting output controller - Google Patents

Abstract

PURPOSE:To obtain a light output controller which can enable a stable laser emitting output to be obtained from laser emitting device for plotting pictures by changing its laser emitting output without increasing the circuit scale of the laser emitting device. CONSTITUTION:A laser emitting element LD the laser emitting output of which changes in accordance with a temperature change, electronic heating/cooling element (Peltier element) 20 integrally provided with the element LD, temperature detecting element (temperature sensor) 30 which detects the temperature of the element LD, and control circuit means 5, 6, and 7 which change and control the temperature of the element LD by controlling the element 20 based on the temperature detected by means of the element 30 are provided. Since the temperature of the laser diode is changed, the laser emitting output of the laser diode can be changed and controlled even when the driving current of the diode is constant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a controller for controlling laser light emission output in a light emitting device using a laser diode.

[0002]

2. Description of the Related Art A laser diode used as a light source for a laser printer or the like needs to control its light emission output in order to perform high-quality printing (drawing). For example,
If there is a variation in the sensitivity of the photosensitive drum that scans with the laser light to perform drawing, it is necessary to adjust the light emission output of the laser diode correspondingly. Alternatively, if the print pattern to be drawn has density, if printing is performed with a single laser emission output, the overlap of print dots in the fine pattern portion may increase, and the print may be crushed. In this pattern portion, it is necessary to reduce the laser emission output to reduce the print dot diameter. For this reason, in recent years, an automatic output control circuit, that is, an APC circuit for automatically controlling the light emission output by detecting the light emission output of the laser diode and performing feedback control of the drive current of the laser diode based on the detected value is provided. It has been proposed to control the light emission output of a laser diode by changing and adjusting circuit constants and the like.

[0003]

[Problems to be Solved by the Invention] However, the APC
In the control by the circuit, the drive current of the laser diode is changed by changing the constant value of some elements of the circuit, but it is difficult to set the relationship between the constant change of the circuit element and the drive current uniquely. There is a problem that it is difficult to change and control the light emission output of the diode. Also, a photodiode that detects the light emission output of the laser diode,
There is also a problem that when the characteristics of the active element or the passive element constituting the circuit change due to the change of the environmental temperature, the light emission output of the laser diode also changes accordingly. Further, there is a problem that the entire light emitting device becomes large in scale due to the circuit elements forming the APC circuit. The object of the present invention is to
It is an object of the present invention to provide a laser emission output control device capable of arbitrarily controlling the laser emission output without using a PC circuit.

[0004]

SUMMARY OF THE INVENTION The present invention is directed to a laser light emitting element whose laser light emission output is changed according to a temperature change, an electronic heating / cooling element provided integrally with the laser light emitting element, and a laser light emitting element. A temperature detection element for detecting the temperature,
The electronic heating / cooling element is controlled based on the temperature detected by the temperature detecting element to control the temperature change of the laser emitting element. That is, a laser diode normally used as a laser light emitting element changes its laser light emission output according to a temperature change even when the same drive current is passed, so that a laser diode is output according to a required laser light emission output. The temperature is changed to control the change of the laser emission output.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing the overall configuration of an embodiment in which the present invention is applied to a laser printer. As shown in the figure, it has a laser diode LD as a laser emission source, and the light emitted from this laser diode LD is incident on the imaging optical system 1. The laser light incident on the imaging optical system 1 is reflected by the polygon mirror 2 that is rotationally driven, and passes through the fθ lens 3 to scan the image surface of the photosensitive drum 4 or the like. As shown in FIG. 2, the laser diode LD has, for example, a P-type GaAs substrate 11 on which a current confinement layer 12, a clad layer 13, an active layer 14, a clad layer 15, a cap 16 layer, and the like are sequentially laminated and then formed. Electrodes 17 and 1 on the bottom surface, respectively
8 is formed as a known structure. The Peltier element 20 is integrally attached to the upper surface of the laser diode LD. Further, a temperature sensor 30 composed of a thermistor, a thermocouple or the like is attached to a part of the side surface of the laser diode LD.

In the Peltier element 20, as shown in the principle structure of FIG. 3, semiconductors 21 and 22 of different conductivity types are connected to one side by a metal 23, and electrodes 24 and 25 are respectively provided on the opposite sides to form semiconductors. By passing a current through the semiconductors 21 and 22, a temperature gradient can be generated between the semiconductors, and one of the surfaces can be heated to a high temperature and the other surface can be cooled to a low temperature. Therefore, by controlling the current flow rate and the current flow direction, it is possible to arbitrarily change the temperature of the surface in contact with the laser diode LD, and accordingly change the temperature of the laser diode LD. . In this embodiment, the Peltier device is energized so as to cool the temperature of the surface in contact with the laser diode.

Upper and lower electrodes 17 of the laser diode,
As shown in FIG. 1, 18 is connected to the drive circuit 5 to pass a drive current for causing the laser diode LD to emit light. In addition, the pair of electrodes 2 of the Peltier device 20.
4, 25 and the temperature sensor 30 are connected to the temperature control circuit 6, respectively. The drive circuit 5 and the temperature control circuit 6 are an arithmetic circuit 7 composed of a microcomputer.
The arithmetic circuit 7 outputs a drive current control signal to the drive circuit 5 and a set temperature signal to the temperature control circuit 6 based on a light emission output control signal input from the outside.

The temperature / output characteristics of the laser diode LD are shown in FIG. In the figure, the horizontal axis represents the drive current of the laser diode, the vertical axis represents the emission output of the laser diode, and the characteristics at two different temperatures ta and tb are shown. As can be seen from this, when the constant drive current I _P is passed through the laser diode, if the temperature of the laser diode changes, the light emission output also changes.

Therefore, in the circuit configuration of FIG. 1, when the arithmetic circuit 7 outputs the set temperature signal to the temperature control circuit 6 based on the light emission output control signal, the temperature control circuit 6 outputs the Peltier element 20 based on the set temperature signal. The direction and amount of the current flowing in the laser diode LD are controlled to change and set the surface of the Peltier device 20 on the side in contact with the laser diode LD to a desired temperature. At the time of setting the temperature, feedback control using the temperature of the laser diode LD detected by the temperature sensor 30 is performed, thereby enabling highly accurate temperature control. Then, after the laser diode LD is set to a predetermined temperature, the arithmetic circuit 7 outputs a control signal to the drive circuit 5, and the drive circuit 5 causes a current corresponding to the control signal to flow through the laser diode LD. This allows
The laser diode LD outputs a light emission output corresponding to the set temperature. Further, when the light emission output control signal to be input is changed, the temperature control circuit 6 responds to the change by the Peltier element 20, that is, the laser diode L.
By changing the temperature of D and then passing a current through the drive circuit 5, a light emission output different from the above case is output.

FIG. 5 is a perspective view of a part of another embodiment of the present invention. In this embodiment, the present invention is applied to a packaged laser diode. The packaged laser diode LD has a stem 4 having a lead 41.
The cap 45 mounted on the second mount 43, wire-bonded to the lead 41, and having the window glass 44
It is sealed by. In this example, the APC photodiode 46 is integrally sealed. Then, an annular Peltier element 20A is integrally attached so as to be in close contact with the stem 42 and the cap of such a package type laser diode, and the electrodes 24 'and 25' of this Peltier element 20A are embodied in FIG. The temperature control circuit is connected as in the example. Further, the temperature sensor 30A is attached to the stem or the cap near the laser diode.

Therefore, also in this embodiment, the temperature control circuit 6 controls the current flowing through the Peltier element 20A based on the light emission output control signal to control the temperature of the stem 42 and the cap 45, that is, the laser diode LD to a predetermined temperature. Then, the drive circuit 5 allows a predetermined current to flow therethrough, whereby a desired laser emission output can be obtained. When changing the laser emission output, the temperature control circuit 6
It goes without saying that the temperature of the laser diode may be changed by controlling the above.

In the above embodiment, it is assumed that the laser diode is heated by its own light emission in normal use, and the Peltier element is used for cooling to control the change of the light emission output of the laser diode. It goes without saying that the Peltier element may be used to heat the laser diode to control the change of the light emission output depending on the environment in which the laser diode is used, such as in an extremely cold region. Further, as the electronic heating / cooling element, an element other than the above-mentioned Peltier element can be used. Furthermore,
If the temperature of the laser diode is changed to a large number of different temperatures by using the electronic heating / cooling element, the emission output of the laser diode can be controlled to change to a large number of different output values by following this.

[0013]

As described above, according to the present invention, an electronic heating / cooling element is integrally provided with a laser light emitting element whose laser light emission output is changed according to a temperature change, and the temperature of the laser light emitting element is detected by a temperature detecting element. Then, the temperature of the laser light emitting element is changed by controlling the electronic heating / cooling element, and thereby the emission output of the laser light emitting element is changed and controlled. Therefore, the laser light emitting source is used without using the APC circuit. It is possible to control and stabilize the light emission output from the device, and to simplify the circuit configuration. Further, since the temperature of the laser light emitting element is directly controlled to control the light emission output, it is possible to control the light emission output by using the APC circuit like the APC.
There is an effect that it is possible to eliminate the instability of the light emission output control caused by the characteristics of the elements constituting the circuit.

[Brief description of drawings]

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

FIG. 2 is a perspective view showing configurations of a laser diode and an electronic heating / cooling element according to the present invention.

FIG. 3 is a diagram showing the principle of a Peltier device.

FIG. 4 is a characteristic diagram showing a correlation between a light emission output of a laser diode and temperature.

FIG. 5 is a partially cutaway perspective view showing configurations of a laser diode and an electronic heating / cooling element according to another embodiment of the present invention.

[Explanation of symbols]

 LD Laser diode 5 Driving circuit 6 Temperature control circuit 7 Arithmetic circuit 20,20A Peltier device 30,30A Temperature sensor

Claims (1)

[Claims] 1. A laser light emitting element whose laser light emission output is changed according to a temperature change, an electronic heating cooling element provided integrally with the laser light emitting element, and a temperature detecting element for detecting the temperature of the laser light emitting element. And a control circuit for controlling the electronic heating and cooling element based on the temperature detected by the temperature detecting element to control the temperature change of the laser emitting element.