JPS63289978A - Circuit for laser detecting deterioration of semiconductor laser - Google Patents

Abstract

PURPOSE:To obtain a circuit capable of exactly detecting deterioration of semiconductor laser without composition being complicated and large-scaled, by using an APC circuit to make a difference, which is formed between a driving current upon the setting of an optical output on a first reference level and the driving current upon the setting of the photo-output on a second reference level, compared with a prescribed threshold value. CONSTITUTION:This circuit is provided with the following means: a variable reference level generation circuit 3 in which a first reference level V1 and a second reference level V2 can be exchanged to be set with a prescribed level difference, and an automatic optical output control circuit 4 in which a driving current Ix of the semiconductor laser 1 is controlled so that the optical output level of the semiconductor laser 1 becomes the reference level set in said variable reference level generation circuit 3. This circuit is provided with the following circuits besides: a difference detecting circuit 6 which detects a difference between a driving current upon the setting of the first reference level V1 and the driving current upon the setting of the second reference level V2, a comparator 7 which discriminates whether said difference is in excess of a prescribed threshold value Vt or not, and a communication means 8 which operates based on a comparison result of the comparator 7.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a semiconductor laser deterioration detection circuit for detecting deterioration of semi-quadramid lasers used in laser printers, optical disk devices, optical beam communications, and the like.

2. Description of the Related Art As shown in FIG. 3, a conventional circuit of this type includes a photo diode 2 that monitors the optical output Lout of a semiconductor laser 1, and a photo diode 2 that monitors the output of the semiconductor laser 1 based on the monitored output of the photo diode 2. an APC circuit (automatic optical output control circuit) 4 that stabilizes the optical output of the semiconductor laser 1 at a predetermined level; a current detection circuit 5 that detects the driving current Ix supplied to the semiconductor laser 1 by the APO circuit 4; The above drive current I detected by the circuit 5
It has a comparator 7 that determines whether x has exceeded a predetermined threshold value Vs, and a transmission means 8 that operates based on the comparison result of this comparator 7, and the drive current Ix When the value exceeds the value Vs, it is determined that the semiconductor laser 1 has deteriorated, and the result of this determination is transmitted or displayed to the outside by the transmitting means 8.

Here, in A Pc times ``N54'', the optical output level LO of the semiconductor laser 1 monitored and detected by the photodiode 2 is a predetermined reference level V.

The circuit includes a differential amplifier circuit 41 that performs negative feedback control on the drive current Ix of the semiconductor sensor 1 so that the drive current Ix of the semiconductor sensor 1 is The drive current supply circuit 42 is controlled by the amplified output of the circuit 41.

As described above, the semiconductor laser deterioration detection circuit described above detects deterioration of the semiconductor laser based on the magnitude of the drive current Ix required to keep the optical output constant. When the semiconductor sensor 1 deteriorates and its luminous efficiency decreases, the drive current Ix supplied to maintain a constant light output increases.

Problems to be Solved by the Invention However, with this configuration, there is a problem in that deterioration of the semiconductor laser is not necessarily detected accurately.

The above problem arises for the following reasons.

In other words, as shown in Figure 4, which shows the characteristics of optical output versus drive current of a semiconductor laser at different temperatures, the drive current required to obtain a constant optical output varies greatly depending on temperature as well as deterioration of the semiconductor laser. do. For this reason, as in the circuit described above, if one attempts to determine whether or not a semiconductor laser has deteriorated based solely on the magnitude of the 5 drive current supplied to obtain a predetermined optical output, errors due to temperature will occur, and the deterioration will also occur. There is a risk that a semiconductor laser that does not reach this level may be determined to be degraded, or a semiconductor laser that has deteriorated may be determined to be normal. Therefore, the deterioration detection of the semiconductor laser using the above-mentioned circuit could only be performed very roughly, taking into account all errors caused by temperature.

Note that as a means of migrating errors due to temperature, it is possible to automatically correct the threshold value that is the standard for determining deterioration according to the environmental temperature of the semiconductor laser, but in order to fully implement this, it is necessary to This requires a complex and large-scale configuration that includes a sensor, an A/D converter, a storage device that stores correction data for each temperature, a D/A converter, and the like.

The present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide a semiconductor laser deterioration detection circuit that can accurately detect deterioration of a semiconductor laser without making the configuration complicated or large-scale.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention controls the driving current of the semiconductor laser using the A20 circuit so that the optical output of the semiconductor laser reaches a predetermined reference level, and variably setting the level between a first reference level and a second reference level having a predetermined remill difference from each other;
The difference between the above-mentioned one-stroke current when the first reference level is set and the above-mentioned drive current when the second reference level is set is detected, and when this difference exceeds a predetermined threshold value, The semiconductor laser is configured to detect deterioration of the semiconductor laser by using a comparator to determine whether or not the semiconductor laser has deteriorated.

According to the above-described structure, the present invention detects the deterioration of the semiconductor laser based on the amount of change in the driving current required to change the optical output level by a predetermined amount.

The amount of change in the drive current represents the rate of change in the optical output with respect to the change in the drive current of the semiconductor laser, so-called slope efficiency. That is, when the slope efficiency is high, the amount of change in the drive current is small, and when the slope efficiency is low, it becomes steep. Furthermore, this slope efficiency is
Figure 4 shows: sea urchin, from threshold point A to maximum rating B-! Within the normal range of use in
It hardly changes even if the temperature changes. From this K, the deterioration of the semiconductor laser is based on the above slope efficiency,
Accurate detection becomes possible almost unaffected by temperature.

As described above, it becomes possible to accurately detect deterioration of a semiconductor sensor without making the configuration complicated and large-scale.

Embodiment FIG. 1 shows a schematic configuration of a semiconductor laser detection circuit according to an embodiment of the present invention, in which 1 is a semiconductor norther which is an object to be detected, 2 is a photo diode for monitoring, and 3 is a variable reference. Level generation circuit, 4 is APC circuit, 5
6 is a current detection circuit, 6 is a difference detection circuit, 7 is a comparator, and 8 is a transmission means.

Semiconductor laser 1 is supplied from APC circuit 4 . Laser light is oscillated by drive current Ix.

A photodiode 2 monitors the level of the optical output Lout of the semiconductor laser 1.

The variable reference level generation circuit 3 is configured to be able to switch between a first reference level V1 and a second reference level V1 having a predetermined level base.

The APO circuit 4 is formed by a differential amplifier circuit 41 and a drive current supply circuit 42, and the optical output level Lo of the semiconductor laser 1 monitored by the photodiode 2 is set by the variable reference level generation circuit 3. The drive current Ix of the semiconductor sensor 1 is subjected to negative feedback control so as to reach the reference level V1 or v2. Note that this APC circuit can also be used as an APC circuit built into a device using a semiconductor V-zer.

The current detection circuit 5 detects the drive current Ix supplied from the APO circuit 4 to the semiconductor laser 1.

The difference detection circuit 6 stores a sample signal which is an analog storage means.
It is composed of a hold circuit 61, a subtraction circuit 62, a switch circuit SW1, etc., and a first circuit is connected to the APO circuit 4.
The above drive current Ix when the reference level v1 of
The difference ΔIx between the drive current Ix and the drive current Ix when the second reference level v2 is set is detected.

The comparator 7 determines whether the difference ΔIx exceeds a predetermined threshold value Vt.

The transmitting means 8 operates based on the determination result of the comparator 7 to transmit or display the presence or absence of deterioration of the semiconductor sensor 1 to the outside.

The operation of the semiconductor V-zer detection circuit configured as described above will be described below.

First, a first reference level v1 is set by the variable reference level generation circuit 3, and the APC circuit 4 is set at this reference level v1.
make it work. As a result, the semiconductor sensor 1 is supplied with a driving current Ix that maintains the optical output level LO at the first reference level V1. The I drive current Ix at this time is input to the difference detection circuit 6 via the current detection circuit 5.

In the difference detection circuit 6, the level of the drive current Ix is held in a sample and hold circuit 61, and the held level of the drive current Ix is applied to one calculation input (-) of the subtraction circuit 62.

Next, the first reference level v1 is switched to the second reference level ■2. Then, the drive current Ix supplied from the APC circuit 4 to the semiconductor laser 1
The light output level LO is changed to a magnitude that maintains the optical output level LO at the second reference level V2. The drive current Ix at this time is input to the difference detection circuit 6 via the current detection circuit 5. In the difference detection circuit 6, the level of the sixth drive stream Ix is applied to the other calculation input (+) of the subtraction circuit 62.

As a result, the difference detection circuit 6 outputs the difference ΔIx between the drive current Ix when the first reference level V1 is set and the drive current Ix when the second reference level V2 is set. be done.

The level of this difference ΔIx is compared with a predetermined threshold value Vt by a comparator 7.

When the comparator 7 determines that the Mine ΔIx exceeds the threshold value Vtf, the output state of the comparator 7 at this time is sent to the transmission means 8 as a detection output 5out representing the deterioration of the semiconductor laser 1. Given. The transmitting means 8 transmits or displays a signal indicating that the semiconductor noser 1 has deteriorated based on the detection output 5out from the comparator 7.

As described above, in the circuit of the embodiment described above, the magnitude of the drive current IxO difference ΔIx required to change the optical output level Lo of the semiconductor sensor 1 from the first reference level v1 to the second reference level v2 Based on this, deterioration of the semiconductor laser 1 is detected.

What should be noted here is that the above-mentioned difference ΔIx, which is the reference for the detection, is equivalent to the slope efficiency of the semiconductor laser 1. That is, the above-mentioned difference .DELTA.x represents the rate of change in the optical output with respect to the change in the drive current of the semiconductor sensor 1, so-called slope efficiency. As the slope efficiency increases, the above difference △Ix becomes smaller,
On the other hand, when it becomes lower, the above-mentioned difference △to x becomes sharper. This slope efficiency decreases as the semiconductor laser 1 deteriorates, but as shown in Figure 4, it hardly changes even if the temperature changes within the normal usage range from threshold point A to maximum dog run point B. .

Therefore, in the actual circuit described above, the deterioration of the semiconductor sensor can be accurately determined almost unaffected by temperature.

In the manner described above, it is possible to accurately detect deterioration of the semiconductor laser without making the configuration complicated and large-scale.

FIG. 2 shows in detail a specific circuit example of the main part of the semiconductor 7 laser deterioration detection circuit described above.

In the figure, the current detection circuit 5 includes the voltage dividing resistor a1 inserted in series in the supply path of the drive current Ix,
It is constituted by an operational amplifier IEiOP1 that amplifies the voltage divided by this resistor R1 with a predetermined gain. Its amplification gain is set by resistors R2, R3, and R4.

The difference detection circuit 6 has a switch circuit SW 1, a sample/hold circuit @61, and a subtraction circuit 62. The switch circuits S to (1) are constituted by, for example, MOS transistors or reed switches, and are switched on and off in conjunction with the switching of the variable reference novel setting circuit 3. The sample and hold circuit 61 is constituted by an input resistor R5, a capacitor C1 as an analog storage element, and an operational amplifier OP2 forming a voltage follower.

The comparator 7 is composed of a variable resistor VRI for setting a predetermined threshold (increase Vt) and an analog comparator CMP1. The resistor 9 is for pull-up and is connected to the power supply potential.

The transmitting means 8 includes a logic gate G1 that performs an AND operation between the comparison output of the comparator 7 and a deterioration detection enable signal applied from the outside, and a light emitting diode LBDQ that is driven to emit light by the logic output of the logic gate G1. The presence or absence of deterioration of the semiconductor sensor 1 is displayed by light emission from the light emitting diode LED. The resistor RIO limits the current of the LED. Here, in order to further improve the detection accuracy of the semiconductor V-zer deterioration detection circuit, the transmission means 8 should be It is desirable to display or transmit the detection results by giving an enable signal to the detector.

By doing so, it is possible to further reduce the influence of temperature changes caused by changes in drive current due to switching of the reference novel. In this case, the state of display or transmission by the transmitting means 8 may be maintained using a latch circuit or the like, if necessary.

Effects of the Invention As is clear from the above description, the present invention controls the driving current of the semiconductor V-zer so that the optical output of the semiconductor V-zer becomes a predetermined reference level using an APC circuit, and The level is variably set between a first reference level and a second reference level having a predetermined level difference from each other, and the drive current and the second reference level are set when the first reference level is set. The deterioration of the semiconductor laser is detected by detecting the difference between the drive current and the drive current when Detection is done based on its slope efficiency, which results in
Deterioration of a semiconductor sensor can be accurately detected without making the configuration complicated and large-scale, and without being substantially affected by temperature. This has the effect of

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of a semiconductor device thermal deterioration detection circuit according to an embodiment of the present invention, FIG. 2 is a detailed circuit diagram of the main part thereof, and FIG. 3 is a schematic diagram of a conventional semiconductor device thermal deterioration detection circuit. The configuration diagram and FIG. 4 are graphs showing the optical output characteristics for one drive current of the semiconductor V-zer at different temperatures. DESCRIPTION OF SYMBOLS 1... Semiconductor V-zer which is the 4 detected object, 2... Photo diode for monitor, 3... Variable reference level generation circuit, 4... APC circuit, 5... Current detection circuit, 6--difference detection circuit, 7-- comparator, 8--transmission means; Name of agent: Patent attorney Toshio Koo and one other name
l diagram

Claims (1)

[Claims] a variable reference level generation circuit that can switch and set a first reference level and a second reference level having a predetermined level difference; and a reference level that allows the optical output of the semiconductor laser to be set by the variable reference level generation circuit. an automatic optical output control circuit that controls the driving current of the semiconductor laser so that the driving current of the semiconductor laser is adjusted so that the driving current when the first reference level is set and the driving current when the second reference level is set; Semiconductor laser deterioration comprising: a difference detection circuit that detects a difference; a comparator that determines whether the difference exceeds a predetermined threshold; and a transmission means that operates based on the comparison result of the comparator. detection circuit.