JPH07167741A - Semiconductor laser deterioration detector - Google Patents

Abstract

PURPOSE:To readily detect the occurrence of deterioration in semiconductor laser based on a drive efficiency indicating the relationship between the light emission output and drive current of semiconductor laser. CONSTITUTION:A deterioration detection control circuit 6 for outputting output setting pulses P1-P4 for setting different light emission output ranges to an APC circuit 5 for driving and controlling a semiconductor laser 1. capacitors C1 and C2 for retaining a voltage equivalent to the drive current of the semiconductor laser 1 at the light emission output Q1, Q2, Q3, and Q4, a capacitor C3 for retaining the charge voltage difference of the capacitors C1 and C2 between one light emission output range (Q1-Q2). and a capacitor C4 for retaining the charge voltage difference of the capacitors C1 and C2 in the other light emitting output range (Q3-Q4) are provided, thus judging whether the difference between the charge voltage of the capacitor C3 and that of the capacitor C4 is equal to or less than a reference value or not by a differential amplification circuit 8 and a comparison circuit 9 and judging that the semiconductor laser l deteriorated when the difference of both exceeds the reference value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a deterioration detecting device for detecting a deterioration state of a semiconductor laser used in a bar code reader, a digital optical disk device or the like.

[0002]

2. Description of the Related Art Generally, a bar code reader or a digital optical disk device irradiates a bar code or an optical disk with a laser beam emitted from a semiconductor laser to read or write data. In order to accurately read or write data in such a device, it is necessary to keep the light emission output of the semiconductor laser constant, but the drive current for keeping this light emission output constant is the deterioration of the semiconductor laser. Becomes higher as the temperature increases, and if left unattended, the semiconductor laser is damaged by an overcurrent. Therefore, the deteriorated semiconductor laser must be promptly replaced with a new semiconductor laser. However, there is an individual difference in the progressing state of deterioration, and the replacement time of the semiconductor laser is not constant. Therefore, in the device disclosed in Japanese Patent Publication No. 5-44627, the difference between the drive currents when the light emission output of the semiconductor laser is set to the first and second levels is measured, and this drive current difference becomes equal to a predetermined value. It is determined that the semiconductor laser has deteriorated when it disappears. by this,
The deterioration of the semiconductor laser can be detected before the data cannot be normally written to the optical disc.

[0003]

However, in the above-mentioned conventional semiconductor laser deterioration detecting device, the drive current for obtaining the light emission output of the first and second levels determined in advance is detected, and the difference between the two is detected. Since it was determined whether or not the deterioration occurred by comparing with the value in the proper state, the semiconductor in the early stage of the degree that the change does not appear in the comparison in the same temperature environment in the relatively low light emission output range. The deterioration state of the laser could not be detected. Therefore, there is a problem that it is not possible to cope with the rapid deterioration of the semiconductor laser, and an error occurs in the reading process and the writing process of data in the bar code reader and the optical disk device. There was a problem that it could not be used and the replacement work could not be prepared according to the deteriorated state.

An object of the present invention is to notice that the relationship between the light emission output and the driving current in a deteriorated semiconductor laser changes depending on both factors of the environmental temperature and the light emission output. Under two types of conditions, at least one of which is different, the driving efficiency, which represents the relationship between the light emission output and the driving current, is detected, and the two are compared, whereby deterioration of the semiconductor laser can be detected very early. Another object of the present invention is to provide a deterioration detecting device capable of coping with the rapid deterioration of

[0005]

SUMMARY OF THE INVENTION A semiconductor laser deterioration detecting device according to the present invention is a drive current detecting means for detecting a drive current value for realizing a specific light emission output of a semiconductor laser which changes according to a drive current and an ambient temperature. And a drive efficiency detecting unit that detects the relationship between the light emitting output in a specific light emitting output range and the detection result of the drive current detecting unit as drive efficiency, and at least one of the light emitting output range and the ambient temperature is different.
The driving efficiency comparing means compares the driving efficiencies under different driving conditions and determines that the semiconductor laser has deteriorated when the difference between the two exceeds a predetermined value.

The driving efficiency comparing means may compare two kinds of driving efficiencies when the emission output range is changed at the same environmental temperature.

The driving efficiency comparing means may compare two kinds of driving efficiencies when the environmental temperature is changed in the same light emission output range.

Further, the drive efficiency comparing means may compare two types of drive efficiency when both the light emission output range and the ambient temperature are changed.

Further, temperature changing means for changing the ambient temperature near the semiconductor laser may be provided.

[0010]

1A and 1B show the relationship between the light emission output Q (mW) and the drive current I (mA) in the unused state and the initial deteriorated state of the same semiconductor laser. The results are shown in Table 1. The relationship between the emission output Q (mW) of the semiconductor laser and the drive current I (mA) is that the line segment a in FIG.
As is clear from the comparison between the slope of and the slope of the line segment b,
In the range equal to or higher than the constant light emission output, it is substantially constant regardless of the value of the light emission output Q and the environmental temperature. On the other hand, the relationship between the emission output of the deteriorated semiconductor laser and the drive current is as follows: the inclination of the line segment c and the inclination of the line segment d in FIG.
Also, as is clear from the comparison between the slope of the line segment c and the slope of the line segment e, when the light emission output range is changed while the environment temperature is constant, and when the light emission output range is constant and the environment temperature is changed. Change occurs in any of.

Therefore, in the present invention, the driving efficiency is detected under two kinds of driving conditions in which at least one of the light emission output range and the ambient temperature is different, and when the two kinds of driving efficiencies do not match, the semiconductor laser deteriorates. Judge that it has occurred. Therefore, even in the case of a semiconductor laser having an initial deterioration as shown in FIG. 1B, the driving efficiency at a low temperature or at a low level of emission output and the driving efficiency at a high temperature or at a high level of emission output are By comparison, the occurrence of deterioration in the semiconductor laser is detected early in an extremely early stage.

Further, by comparing the two types of driving efficiencies when both the light emission output and the environmental temperature are changed, the difference between the two caused by the deterioration can be detected more remarkably and the deterioration of the semiconductor laser can be prevented. Detected earlier.

Further, by providing the temperature changing means, the environmental temperature in the vicinity of the semiconductor laser can be changed, and the driving efficiency under two driving conditions of low temperature and high temperature can be detected in a short time.

[0014]

2 is a circuit diagram showing the structure of a semiconductor laser deterioration detecting apparatus according to an embodiment of the present invention. The semiconductor laser 1 is driven by an APC (automatic power control) circuit 5. The emission output of the semiconductor laser 1 is the photodiode 2
Monitored by. The light emission output of the semiconductor laser 1 monitored by the photodiode 2 is input to the APC circuit 5 from the I / V conversion circuit 4. The APC circuit 5 feedback-controls the drive current supplied to the semiconductor laser 1 so that the voltage value of the light emission output becomes constant. These semiconductor laser 1, photodiode 2, I / V conversion circuit 4 and A
The PC circuit 5 has a general configuration for a semiconductor laser device.

A deterioration detecting apparatus 10 according to an embodiment of the present invention.
Detects the drive current of the semiconductor laser 1 by the I / V conversion circuit 3, holds this value in the capacitors C1 and C2 via the switches SW1 and SW2, and stores it in the capacitors C1 and C2 in the differential amplifier circuit 7. Amplify the difference in voltage. The output of the differential amplifier circuit 7 is the switch SW3.
It is held in the capacitors C3 and C4 via SW4. Further, in the differential amplifier circuit 8, the capacitors C3 and
The difference between the voltages stored in C4 is amplified. The output of the differential amplifier circuit 8 is compared with the reference value Vref in the comparison circuit 9, and is output via the switch SW5.

Output setting pulses P1 to P4 are input to the APC circuit 5 from the deterioration detection control circuit 6. Each pulse width of the output setting pulses P1 to P4 is set to a time t sufficient for the APC circuit 5 to stabilize the light emission output of the semiconductor laser 1. The output setting pulses P1 and P3 are also supplied to the switch SW1 at the same time, and the switch SW1 closes the I / V conversion circuit 3 and the capacitor C1 while either the output setting pulse P1 or P3 is input. To achieve. The output setting pulses P2 and P4 are also supplied to the switch SW2. The switch SW2 closes the I / V conversion circuit 3 and the capacitor C2 while the output setting pulse P2 or P4 is being input.

Further, the output setting pulses P2 and P4 are also supplied to the switches SW3 and SW4, respectively. The switches SW3 and SW4 close the connection between the differential amplifier circuit 7 and the capacitors C3 and C4 while the output setting pulses P2 and P4 are being input. The capacitors C1 and C2 are provided with a discharge circuit (not shown), and when the signal R output from the deterioration detection control circuit 6 is supplied, the discharge circuit changes the voltage charged in the capacitors C1 and C2. To discharge. Also,
The switch SW5 connected to the subsequent stage of the comparison circuit 9 receives the signal S output from the deterioration detection control circuit 6 to close between the comparison circuit 9 and the output terminal. This output terminal is input to, for example, an indicator light (not shown) for displaying the deterioration state of the semiconductor laser 1 or a warning device for issuing a warning.

FIG. 3 is a timing chart of signals in the semiconductor laser deterioration detecting device. The emission outputs Q1 to Q4 of the semiconductor laser and the drive current have the relationship shown in FIG. In FIG. 4, the line 41 shows the relationship in the room temperature state, and the line 42 shows the relationship in the high temperature state.

When the semiconductor laser device is powered on at time t0, the deterioration detection control circuit 6 outputs an output setting pulse P1 at time t1. The APC circuit 5 controls the light emission output of the semiconductor laser 1 to the first set value Q1 while the output setting pulse P1 is being input. During this time, the switch SW1 closes the I / V conversion circuit 3 and the capacitor C1.
The capacitor C1 is charged with a voltage corresponding to the driving current value I1.

Then, at time t2, the deterioration detection control circuit 6 outputs the output setting pulse P2. During this period, the APC circuit 5 controls the light emission output of the semiconductor laser 1 to the second output value Q2. During this time, the switches SW2 and SW3 close the I / V conversion circuit 3 and the capacitor C2 and the differential amplifier circuit 7 and the capacitor C3, and a voltage corresponding to the drive current I2 of the semiconductor laser 1 at that time. Is charged in the capacitor C2 and the capacitor C
The capacitor C3 is charged with a voltage corresponding to the difference between the charging voltage of 1 and the charging voltage of the capacitor C2, that is, the driving current difference (I2-I1) shown in FIG. Further, at time t3, the deterioration detection control circuit 6 outputs the reset signal R. As a result, the discharging switch DS is closed in the discharging circuit (not shown), and the charging voltage of the capacitors C1 and C2 is discharged.

Thereafter, at time t4, the deterioration detection control circuit 6 outputs the output setting pulse P3. Output setting pulse P
While A3 is being output, the APC circuit 5 maintains the light emission output of the semiconductor laser 1 at the set value Q3, and
The voltage corresponding to the drive current I3 at this time is the switch SW.
The capacitor C1 is charged via 1. Further, at time t5, the deterioration detection control circuit 6 outputs the output setting pulse P4. While the output setting pulse P4 is being output, the APC circuit 5 maintains the light emission output of the semiconductor laser 1 at the set value Q4, and the voltage corresponding to the drive current I4 at this time charges the capacitor C2 via the switch SW2. To be done.

The difference between the charging voltage of the capacitor C3 and the charging voltage of the capacitor C4, that is, the drive current difference (I4
The voltage corresponding to −I3) is charged in the capacitor C4 via the switch SW4. The difference between the charging voltage of the capacitor C3 and the charging voltage of the capacitor C4 is input from the differential amplifier circuit 8 to the comparator 9, and the difference between the two is compared with the reference value. The signal S from the deterioration detection control circuit 6 at time t6.
Is output, the switch SW5 is closed, and the comparison result of the difference between the charging voltages of the capacitors C3 and C4 in the comparison circuit 9 and the reference value is output.

As described above, according to this embodiment, the driving current difference (I2-I1) when the light emission output of the semiconductor laser 1 is changed from Q1 shown in FIG. Driving current difference (I4-
I3) is obtained, and it is determined that the semiconductor laser 1 has deteriorated when the difference between the two drive currents exceeds the reference value represented by the reference voltage Vref in the comparison circuit 9.
As described above, in the present embodiment, the light emission output of the semiconductor laser 1 is changed in two different drive current ranges, and it is determined whether the drive efficiencies in the respective ranges are substantially equal to each other, thereby determining the deterioration state of the semiconductor laser 1. To detect.

FIG. 5 is a circuit diagram of a semiconductor laser deterioration detecting device according to an embodiment of the invention described in claim 3 including the invention described in claim 5. The difference from the configuration of the embodiment shown in FIG. 2 is that a heater 11 for raising the environmental temperature is provided near the semiconductor laser 1 and a drive signal H of this heater 11 is output from the deterioration detection control circuit 6. AND that obtains the logical product of the output setting pulse P2 and the heater drive signal H, and the point where the number of output setting pulses output from the deterioration detection control circuit 6 is two, P1 and P2
The gates 12 and 13 are provided, and the AND gates 12 and 13 are provided.
The respective outputs of the above are supplied to the switches SW3 and SW4.

FIG. 6A is a diagram showing the structure of a heater provided in the semiconductor laser device. As shown in the figure, on the heat sink 21 on which the semiconductor laser 1 is installed,
A heater 11 is provided so as to be in contact with the semiconductor laser 1. The on / off of the heater 11 changes the ambient temperature of the semiconductor laser 1. As shown in FIG. 1B, a Peltier element may be provided on the back surface of the heat sink 21 on which the semiconductor laser 1 is installed, and the ambient temperature of the semiconductor laser 1 may be lowered when the Peltier element is driven. .

FIG. 7 is a timing chart of signals of respective parts in the deterioration detecting device shown in FIG. Time t10
When the power of the semiconductor laser device is turned on at, the output detection pulse P1 is output from the deterioration detection control circuit 6 at time t11. During this period, the APC circuit 5 maintains the light emission output of the semiconductor laser 1 at the set value Q1 corresponding to the output setting pulse P1. At this time, the voltage corresponding to the drive current I1 of the semiconductor laser 1 is charged in the capacitor C1 via the switch SW1.

Next, when the output setting pulse P2 is output from the deterioration detection control circuit 6 at time t12, the APC circuit 5 maintains the light emission output of the semiconductor laser 1 at the set value Q2 corresponding to the output setting pulse P2 during this period. At the same time, the switch SW2 closes between the I / V conversion circuit 3 and the capacitor C2, and the drive current I of the semiconductor laser 1 is increased.
The voltage corresponding to 2 is charged in the capacitor C2. At time t12, the drive signal H of the heater 11 is "L".
o ”, and the inverted signal of the drive signal H is input to A
The output setting pulse P2 is supplied to the switch SW3 via the ND gate 12. Therefore, while the output setting pulse P2 is being output, the switch SW3 closes between the differential amplifier circuit 7 and the capacitor C3, and the voltage corresponding to (I2-I1) is charged in the capacitor C3.

Thereafter, at time t13, the deterioration detection control circuit 6
At the same time that the reset signal R is output from the heater 11, the drive signal H of the heater 11 is set to "Hi". The output of the reset signal R discharges the charging voltage of the capacitors C1 and C2, and the drive signal H is set to "Hi", so that the environmental temperature of the semiconductor laser 1 rises. In addition,
The heater 11 maintains the ambient temperature of the semiconductor laser 1 at a high temperature of a predetermined temperature higher than the normal temperature by a driving circuit (not shown).

At time t14, the deterioration detection control circuit 6 outputs the output setting pulse P1 again, and the APC circuit 5 maintains the light emission output of the semiconductor laser 1 at the set value Q1 during this period. At this time, the switch SW1 is set to I /
The V conversion circuit 3 and the capacitor C1 are closed to charge the capacitor C1 with a voltage corresponding to the drive current I13 shown in FIG. Next, at time t15, the deterioration detection control circuit 6 outputs the output setting pulse P2. During this period, the APC circuit 5 maintains the light emission output of the semiconductor laser 1 at the set value Q2, and at the same time, the switch SW2 sets the I / V.
The conversion circuit 3 and the capacitor C2 are closed. As a result, the capacitor C2 is charged with a voltage corresponding to the drive current I14 that realizes the light emission output Q2.

At this time, the output setting pulse P is output via the AND gate 13 to which the drive signal H of the heater 11 is input.
2 is input to the switch SW4, and the switch SW4 closes the differential amplifier circuit 7 and the capacitor C4. As a result, the difference between the charging voltage of the capacitor C1 and the charging voltage of the capacitor C2, that is, the drive current difference (I
The voltage corresponding to 14-I13) is charged in the capacitor C4. At the same time, the comparison circuit 8 compares the charging voltage of the capacitor C3 and the charging voltage of the capacitor C4, and further compares the difference between the two with the reference voltage Vref.
The output of the comparison circuit 9 is led to the output terminal via the switch SW5 when the signal S is output from the deterioration detection control circuit 6 at time t16.

As described above, according to this embodiment, the drive currents (I1 to I2) at room temperature and the drive current (I at high temperature) in the same light emission output range (Q1 to Q2).
13 to I14), it is possible to determine that the semiconductor laser 1 has deteriorated when the driving efficiencies in both ranges do not match.

FIG. 8 is a circuit diagram showing a configuration of a semiconductor laser deterioration detecting apparatus according to an embodiment of the invention described in claim 4 including the invention described in claim 5. The structure of the deterioration detecting device shown in the figure differs from the structure of the deterioration detecting device shown in FIG. 2 in that a heater 11 is provided in the vicinity of the semiconductor laser 1 and a drive signal H of the heater 11 is supplied to the deterioration detecting control circuit. 6
It is the point that I tried to output from.

FIG. 9 is a timing chart of signals of respective parts in the deterioration detecting device shown in FIG. As shown in the figure, the drive signal H of the heater 11 is set to "Hi" between the time t23 when the reset signal R is output from the deterioration detection control circuit 6 and the time t26 when the signal S is output.
With such a configuration, in FIG. 4, when the light emission output is at a low level (Q1 to Q2), the drive current change (I2-I1) at room temperature and the high level range of the light emission output at high temperature (Q3 to Q4). Drive current change (I24-
I23) can be compared.

The change in the driving efficiency due to the deterioration of the semiconductor laser 1 changes remarkably as the light emission output is at a higher level and the environmental temperature is higher, as is apparent from FIG. Therefore, the deterioration of the semiconductor laser 1 can be detected earlier by comparing the driving efficiency between the low light emission output range in the low temperature state and the high light emission output in the high temperature state as in the present embodiment.

It should be noted that the deterioration state can be detected early by driving the emission output of the semiconductor laser 1 in the vicinity of the maximum rated level in the configuration shown in FIG. 2 or FIG. By providing a shutter that covers the laser light emitted from the device 1 from the outside except the photodiode 2, when the semiconductor laser 1 is driven at a high output level when the deterioration state is detected, the shutter is provided in the vicinity of the device. It is possible to safely detect the deterioration state without affecting the existing human body.

Further, in the above embodiment, FIG. 2, FIG. 5 and FIG.
Although the deterioration detecting device is configured by an analog circuit as shown in FIG. 5, the deterioration detecting device of the present invention may be configured by a digital circuit that executes similar processing in the CPU.

[0037]

According to the present invention, the driving efficiency is measured under two kinds of driving conditions in which at least one of the light emission output range and the environmental temperature is different, and the deterioration state of the semiconductor laser is judged based on the comparison result of the two. Because you can
There is an advantage that the deterioration of the semiconductor laser can be detected at an early stage and a semiconductor laser replacement operation can be prepared according to the deterioration state.

Further, by providing the temperature changing means for changing the environmental temperature in the vicinity of the semiconductor laser, there is an advantage that the driving condition can be largely changed and the deterioration state of the semiconductor laser can be detected earlier.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a light emission output and a drive current when a semiconductor laser to which a deterioration detecting device according to an embodiment of the present invention is applied is normal and deteriorates.

FIG. 2 is a circuit diagram of a deterioration detecting device according to an embodiment of the invention described in claim 2.

FIG. 3 is a timing chart of signals in the deterioration detection apparatus.

FIG. 4 is a diagram showing a relationship between a light emission output of a deteriorated semiconductor laser and a drive current in the deterioration detecting device.

FIG. 5 is a circuit diagram of a deterioration detecting device according to an embodiment of the invention described in claim 3.

FIG. 6 is a diagram showing a main part of the deterioration detecting apparatus.

FIG. 7 is a timing chart of signals in the deterioration detection apparatus.

FIG. 8 is a circuit diagram of a deterioration detecting device according to an embodiment of the invention described in claim 4.

FIG. 9 is a timing chart of signals in the deterioration detection apparatus.

[Description of Reference Signs] 1-semiconductor laser 2-photodiode (light emission output detecting means) 7-differential amplifier circuit (driving efficiency detecting means) 8-differential amplifier circuit (driving efficiency comparing means) 11-heater (temperature changing means) )

Claims (5)

[Claims] 1. A drive current detecting means for detecting a drive current value for realizing a specific light emission output of a semiconductor laser that changes according to a drive current and an environmental temperature, and a light emission output and a drive current detecting means in a specific light emission output range. The driving efficiency detecting means for detecting the relationship with the detection result as the driving efficiency is compared with the driving efficiency under two kinds of driving conditions in which at least one of the light emission output range and the environmental temperature is different, and the difference between the two exceeds a predetermined value. And a drive efficiency comparing means for determining that the semiconductor laser has deteriorated when the semiconductor laser deteriorates. 2. The deterioration detecting device for a semiconductor laser according to claim 1, wherein the drive efficiency comparing means compares the two types of drive efficiencies when the emission output range is changed at the same environmental temperature. 3. The deterioration detecting apparatus for a semiconductor laser according to claim 1, wherein the drive efficiency comparing means compares two types of drive efficiencies when the environmental temperature is changed in the same light emission output range. 4. The deterioration detecting apparatus for a semiconductor laser according to claim 1, wherein the drive efficiency comparing means compares the two types of drive efficiency when both the light emission output range and the ambient temperature are changed. 5. The deterioration detecting device for a semiconductor laser according to claim 3, further comprising a temperature changing means for changing an ambient temperature near the semiconductor laser.