JPS5821386A - Controller for semiconductor laser - Google Patents

Abstract

PURPOSE:To grasp the degree of the degradation of the semiconductor laser by controlling a bias level so that monitor output in case of operation and monitor output in case of initial adjustment equalize and displaying the level. CONSTITUTION:When initial adjustment, monitor output Pmo in the case when prescribed output is obtained, bias voltage VBO and the change DELTAVB of vias voltage required for predetermined output change are set to a register R. The semiconductor laser LD is brought to an ON state for a specified period while the value of the register R is set to a register RVB. When the controller reaches a control period, a microprocessor MPU compares value set to a register RPm and monitor output Pm from a light-receiving element M, and sets the approximate value of the output Pm to the RPm. The MPU detects the output Pm through the operation, controls the bias level so that the output Pm and Pmo agree, and addes difference with the VBO to value set to the RVB. When said operation is completed, value set to the RVB is displayed to a display circuit DSP.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention maintains the output of a semiconductor laser at a constant level, and determines the operating point and deterioration state t? of the semiconductor laser. The present invention relates to a semiconductor laser control device that can grasp lK.

FIG. 1 shows the output characteristics of a semiconductor laser. In this figure, the vertical axis P is the optical output, and the horizontal axis f is the forward current.

The broken line indicates the characteristic tube when it deteriorates.◎ In a semiconductor laser, when the forward current flow f exceeds the threshold tube, the forward current increases sharply and emits light! Start.

The threshold value fluctuates as shown by the broken line due to temperature or aging of the element.In order to obtain a relatively constant optical output, K must change the bias current flowing through the semiconductor laser. A method is used in which a portion of the current is fed back and compared with a reference value t to control the bias current tube. However, with the method described above, it is impossible to know the operating point and deterioration state of the semiconductor laser, and it is inconvenient in terms of maintenance of the device.

The present invention solves the above-mentioned problems, and aims to provide a semiconductor laser control device tII that can maintain a constant output sound of a semiconductor laser and display its deterioration state, and includes: a monitor circuit for monitoring an output tube of a semiconductor laser; The monitor output when the specified output is obtained during initial adjustment, the bias level of the semiconductor laser, and the unit output change Kl! a memory circuit that stores the amount of change in the bias to be generated; It consists of a display circuit that displays the bias level after control.

The present invention will be explained in detail below with reference to FIG. 2. FIG. 2 shows the output characteristics at the time of initial adjustment, and FIG. 3 shows an embodiment of the present invention.

In Figure 2.3, Pm is the monitor output PmO, VB□ is the monitor output when the specified output is obtained, bias voltage, ΔvB is the change in bias voltage required for a constant output change, lMPU is the microprocessor, and OMPq comparison. Vessel D8F
is a display circuit* D/AS, D/A@ is a D/A converter, LAD is a semiconductor laser, M is a light receiving element, RvB, RP
m and R are registers, and RVB and RPm are for bias setting.

R is used for output monitoring, and R is used for data storage during initial adjustment.

The present invention aims to stabilize the output based on nine reference data tubes obtained at the time of initial adjustment, for example, at the time of shipping the device. Therefore, assuming that the output characteristics as shown in FIG. 2 are obtained at the time of initial adjustment, the change in bias voltage ΔvB required for a constant output change in the 72-taper output Pmo and vBo when a specified output is obtained is set in the register RK.

The vibration level is controlled by semiconductor V-the-T- for a certain period of time.
Control is performed by turning it on. For example, in the case of a laser printer, this is done during the paper feeding period.

That is, VBO stored in register R is set to register RVBK in device power #oNw#. When it comes to the control period, is it Magukuro Procera? MPυ is register R
Pm t- Monitor the output tube of the semiconductor laser LD by operating as follows.

First, the microprocessor MPυ lolilcs the most significant bit (M2R) of register RPm. Register RPm
The value set to D/A converter D/A.

QD/A converted by
It is compared with the monitor output Pm from . The microprocessor MPU takes the output t of the comparator OMF and sets the value of the register RPm (Pm) to the register RI'm(0).
Set M8BIO1i to the next digit IOH, and set the value of register RPm) P m, turn MSBI OFF and turn the next digit 'ION' 0 Repeat sequentially toward the lower bits of this operation tube When the approximate value of the output Pm is set in the register RPm, it becomes K. By the above operation, υ microprocessor MPUq knows the monitor output Pm and finds the difference from the reference output PmO. If the difference is, for example, 5×ΔvB, set the value that is currently set in register RVB plus 5×ΔV13, and set P
If the difference between m and Pmo is small, the value added by ΔVBt is set in register RVB and monitoring is performed again. For example, in a trench where t-Pm and pmo are almost the same,
Repeat until m-Pm0l <ΔPm (ΔPm tolerance).

When the above operation is completed, the value set in the register RVB is displayed on the display circuit DBPIC, and it is possible to know the change in bias voltage since the time of cut-off adjustment, that is, the degree of deterioration of the semiconductor laser, and the life span of the semiconductor laser. It is possible to perform maintenance on the replacement ring of the element before reaching the voltage VB, which prevents equipment trouble.In this example, only the bias voltage VB during operation is shown, but the bias voltage VB at the time of initial adjustment is The bias voltage vno may also be displayed at the same time.The difference between the bias voltage vBo during adjustment and the bias voltage during operation is determined by the microprocessor MPU, and if the difference exceeds a certain value, a warning light is turned on. ◎ As explained above, according to the present invention, the output t? of the semiconductor laser may be Keep lK constant and keep the semiconductor laser state 'tNK
Troubles with equipment in which semiconductor lasers are installed can be detected! This makes it possible to prevent accidents from occurring, which is very effective for equipment maintenance.

[Brief explanation of the drawing]

The fgx diagram shows the output characteristics of the semiconductor laser, FIG. 2 shows the output characteristics at the time of initial adjustment, and FIG. 3 shows an embodiment of the present invention. Pm...Monitor output, Pmo, VB□...Monitor output when the specified output is set to □ during initial adjustment, bias voltage, ΔvB is the change in bias voltage required for a constant output change,
MPU is a microprocessor, OMPFi comparator, DS
F is a display circuit, D/mu8. D/Mu. ...D/A converter, LD...semiconductor laser, M...
・Photodetector, RVB, RPm, R...Register Go 51
;・ I 1 and busy l book z8

Claims (1)

[Claims] A monitor circuit that monitors an output tube of a semiconductor laser. Monitoring output when the specified output is obtained during initial adjustment,
A memory circuit that stores the bias level of the semiconductor laser and the amount of bias change required for a unit output change; the semiconductor laser is kept on for a certain period of time, and a monitor output stored in the memory circuit is compared with the monitor output, and the two match. It should consist of a control circuit for controlling the bias level, and at least a display circuit for displaying the bias level after control!
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