JPS5970974A - Detection of deterioration in semiconductor laser - Google Patents

Abstract

PURPOSE:To prevent poor operation due to deterioration in a semiconductor laser by detecting deterioration in the semiconductor laser every time or periodically in the initial operation of an optical disc device. CONSTITUTION:A circuit 18 is provided to drive a semiconductor laser 10 and a circuit 19 to detect deterioration in the current flowing through the semiconductor laser 10 which contains a driving current sample holding circuit 14 at the power P1 and a driving current sample holding circuit 15 at the power P2. The switching of the sample holding circuits is controlled by P1-CHK signal 21 and P2-CHK signal 22. These signals are formed from a signal CHK-GATE 20 for indicating initial time of equipment. Values of driving currents held by the sample holding circuits 14 and 15 are compared by a comparator 16 and a resulting differential signal 23 is compared with a signal 24 as reference for the deterioration in the semiconductor laser by a comparator 17 to detect deterioration in a semiconductor.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method for detecting deterioration of a semiconductor laser, and more particularly to a method for detecting deterioration of a semiconductor laser used in a digital optical disk.

[Prior art]

In conventional optical disk devices, the deterioration of the semiconductor laser was not actively detected, and it was replaced periodically or when it deteriorated. It was only possible to use the laser while understanding its characteristics.For this reason, for example, when you wanted to record information on a disk, even if a specified recording current was applied, the recording power would be insufficient due to the deterioration of the semiconductor laser, making it impossible to record information normally. There was a possibility that the problem of not being able to display the data could occur.

[Purpose of the invention]

The purpose of the present invention is to
The purpose is to prevent the above-mentioned recording failure by deteriorating the semiconductor laser every time or periodically.

[Summary of the invention]

In order to achieve the above object, the present invention focuses on the property that the differential quantum efficiency decreases as the semiconductor laser deteriorates, and samples and holds the current value required to output power at any two points during the initial operation of the device. The present invention is characterized in that the state of deterioration of the semiconductor laser is determined by keeping the semiconductor laser cool and detecting the difference.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the current and output power characteristics of a semiconductor laser. Curve 1 shows the characteristics of the semiconductor laser when it is normal, and curve 2 shows the characteristics of the semiconductor laser when it is deteriorated. show. The difference between the current values for producing the powers of pl and P2 when the semiconductor laser is normal (121Ll) and the difference between the current values for producing the powers of P-1 and P when the semiconductor laser is degraded (I22)
'2+) is compared with a certain deterioration reference voltage to detect deterioration of the semiconductor laser.

FIG. 2 shows an example of a circuit that performs the above operation, in which 18 is a circuit for driving the semiconductor laser 10, 19 is a circuit for detecting deterioration of the first-rate flowing through the semiconductor laser 10, and when the power is 21 Drive current sample hold circuit 14
and drive i current sample hold circuit 15 at power P2
Contains. The sample and hold circuit is switched by the fifth
As shown in the figure, <, P, -CHK signal 21 and P2-CHK
It is controlled by the signal 22. These signals do not indicate the initial time of the device and are generated from the signal CHK-GATE20.

The drive current values held in the sample circuits 14 and 15 are compared by a comparator 16, and the difference signal 26 is compared by a comparator 17 with a signal 24 serving as a deterioration reference for the semiconductor laser to detect deterioration of the semiconductor.

The operation of the semiconductor laser drive circuit 18 when changing the laser power is as follows. First, a drive current is set to a certain value in order to output power P to the semiconductor laser 10. This drive current causes the laser 10 to emit light with a power P, and a monitor current proportional to the power flows through the monitor. The monitor current is converted into a voltage by the resistor 4 and amplified by the operational amplifier 5 to become the monitor output signal 28. The automatic power control circuit 8 operates so that the monitor output signal 28 and the reference signal 27 match, and the power P is constant.

is obtained. Next, to obtain the drive current at another point P2, P
, -CHK signal 21 is turned on and the amplification degree of the operational amplifier 5 is changed (in the embodiment, the amplification degree is lowered), the balance between the monitor output signal 28 and the reference circuit pressure 27 is lost, and it is attempted to match by the amount of change. Operate. In the embodiment, when the laser current is applied, it works in the direction of flowing a large amount, and finally becomes stable at the power P. In this way, the power P.

Deterioration detection as described above is performed by obtaining the laser drive currents at 22:00 and 22:00.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, it is possible to know the state of deterioration of the laser before the device is actually used (read/write), thereby eliminating read/write failures due to insufficient power of the semiconductor laser. .

[Brief explanation of drawings]

FIG. 1 shows the relationship between semiconductor laser power and output power, and FIG. 2 shows a circuit that detects the differential quantum efficiency of curves 1 and 2 in FIG. 1 and compares the detected value with a reference value. FIG. 3 shows a timing chart of signals used in the circuit of FIG. 1...Relationship between the semiconductor laser's first-class power and output power during normal operation, 2...Relationship between the semiconductor laser's first-class power and 1') capacitance during deterioration, 3...Semiconductor laser monitor, 4... Monitor load resistance, 5...OP amplifier, 6
．． 7... Resistor, 8... Automatic power control circuit, 9... Semiconductor laser drive transistor, 10... Semiconductor laser, 11... Resistor, 12... Switch 1.1... Switch 2.14... Read zangle bold circuit, 15... Write sample hold circuit, 16.17... Comparator, 18... Semiconductor laser drive circuit, 19... Deterioration detection circuit, 20... Semiconductor laser check signal, 21... Semiconductor laser check signal during read, 22... Semiconductor laser check signal during write, 23... Difference signal between write current and first read current, 24... Deterioration detection Reference signal of 25..." 2CI-1 is the gain changeover switch, 2
6...Resistance, 27...Reference voltage in unit power, 28...Monitor output signal. Representative Patent Attorney Usui Tamaya 2 Figure 3 CHK (rlVE 20-LawCofl-CH BA2
/-[-1]-

Claims (1)

[Claims] A semiconductor laser driven by superimposing a pulse on a DC bias, wherein a laser output value at two or more arbitrary current values is detected using a monitor signal, and deterioration of the laser is detected based on the detected output. Deterioration detection method.