JPS61174692A - Evaluation circuit for semiconductor laser - Google Patents

Abstract

PURPOSE:To prevent automatically a semiconductor laser from deteriorating beyond a prescribed degree by a construction wherein a driving current circuit for the semiconductor laser is broken in response to an output signal of a comparator which determines the relationship in amplitude between a driving current value of the semiconductor laser and a reference value being settable arbitrarily. CONSTITUTION:A voltage of Re.IL is generated at a resistor 6 by a driving current IL of a semiconductor laser 4 to be tested which is made luminant by a power set by a variable reference voltage generator 1. When the driving current IL increases with the deterioration of the semiconductor laser 4, an emitter voltage Re.IL of a transistor 5 increases also in proportion to the increase of the current IL. When the level of a deterioration reference level setter 8 is set at a value equivalent to an emitter voltage generated when the deterioration proceeds to a precetermined reference current value, accordingly, the outputs of a level comparator 9 and a flip-flop circuit 10 become H when the value Re.IL increases beyond the set voltage due to the deterioration. Therefore a switch element 3 is opened, and a current ceases to flow to the semiconductor laser 4. By this constitution, various semiconductor lasers being different in the degree of deterioration can be obtained simply.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a semiconductor laser life test circuit, and is capable of testing a test semiconductor up to a predetermined value.

<Prior Art> Performing a deterioration analysis of a semiconductor laser and elucidating the deterioration process is a necessary condition for developing a semiconductor laser with a longer life. For this purpose, various test semiconductor lasers with different degrees of deterioration are required. In order to obtain this test semiconductor laser, the semiconductor laser is continuously operated under certain conditions, the emission power and drive current values are monitored, and when a predetermined state of deterioration is reached, the operation is stopped and the semiconductor laser is used. Use as a trial sample. Conventionally, in order to obtain this test sample, there is a problem in that, as is clear from the above explanation, the emission power and drive current value of the semiconductor laser in the operating state must be constantly monitored.

<Object of the Invention> The present invention has been made in view of the above conventional problems, and its purpose is to prevent people from constantly stopping the vehicle.
This will prevent further deterioration of the semiconductor laser. Embodiment The attached drawing is a block diagram of a semiconductor laser evaluation circuit showing an embodiment of the present invention.

In the figure, reference numeral 1 denotes a variable reference voltage generator for setting the emission power of the semiconductor laser to an arbitrary value. Reference numeral 2 denotes a semiconductor laser drive circuit composed of a differential voltage amplifier, which drives a transistor 5 with this output voltage to cause a current to flow through the semiconductor laser 4 connected to the collector terminal of the transistor 5. 3 is a switching element connected to the semiconductor laser 4; 07 is a photoelectric conversion system for converting the laser emission power output from the semiconductor laser 4 into an electric signal. The output of this photoelectric conversion system 7 is fed back to the differential voltage amplifier 2 of the drive circuit 2. 6 is an emitter resistance.

The system constituted by the above-mentioned symbols 1 to 7 is a so-called semiconductor. Now, assuming that the switch element 3 is in the ON state, the operation of the feedback control system will be described below.

It is assumed that the semiconductor laser 4 emits light with a constant power in accordance with the voltage determined by the variable reference voltage generator l.

Next, when the semiconductor laser 4 decreases in light emission power for the same drive current IL due to deterioration or the like, the output voltage of the photoelectric conversion system 7 irradiated with the output light also decreases. This output voltage is input to the drive circuit 2, so that the differential voltage amplifier output of the drive circuit 2 increases and the pace voltage of the transistor 5 increases. In response to this, the drive current IL increases, and increases by the amount that the emission power of the semiconductor laser 4 decreases. That is, in this system, the semiconductor laser 4 continues to emit laser light at a value determined by the variable reference voltage generator 1.

Therefore, the semiconductor laser 4 is driven so that the input light emission power to the photoelectric conversion system 7 is always constant, and the deterioration of the semiconductor laser 4 can be determined by the amount of increase in the drive current IL.

This is the principle for achieving output stabilization of the drive circuit No. 4, but when this principle is used as a deterioration characteristic evaluation circuit for the semiconductor laser 4, the following will occur. The deterioration reference level voltage which is the deterioration reference level setter 8 is set and the level comparator 9
input to one terminal of The other input terminal of the level comparator 9 is the terminal voltage of the emitter resistor 6 provided for converting the drive current IL of the semiconductor laser 4 flowing through the transistor 5 into a voltage, that is, the resistance value of the emitter resistor 6.
Then, a voltage Re.IL is introduced.

Level comparator 9 output deterioration standard and health setting device 8
The voltage from the emitter resistor 6 is compared with the voltage from the emitter resistor 6, and if the former is larger than the latter, the output is at the Low level, and vice versa, so that the output is at the HighC level.
The value voltage is set.

A flip-flop circuit 10 is connected to the level comparator 9 and operates based on the output of the level comparator 9. This flip-flop output is connected to operate the switch element 3.

It is assumed that light is emitted with the power set in 1.

The voltage generated at the resistor 6 by the drive current IL of the semiconductor laser 4 is Re.IL. When the test semiconductor laser 4 deteriorates due to long-term continuous operation and its driving current IL increases, the emitter voltage of the transistor 5 (Re @ I
Naturally, L) also increases in proportion to IL. Therefore, the deterioration reference level setter 80 level is set to voltage R1! IIIL
If the initial value of is set to a value corresponding to the emitter voltage when it deteriorates to a predetermined reference current value, then when the semiconductor laser 4 deteriorates beyond that value, Re@IL will increase and exceed the set voltage. This is input to the level comparator 9, and the output of the level comparator 9 is High.
Flip-flop circuit 1 connected to the next stage
Set the output of 0 to High. In response to this output signal, the switch element 3 is opened, and no current flows through the semiconductor laser 4. At this time, the voltage Re@IL also becomes zero and the output of the null level comparator 9 becomes Low again. In other words, when the semiconductor laser 4 under test deteriorates to the value determined by the deterioration reference level setter 8, the semiconductor laser 4 automatically operation will stop and no further deterioration will occur.

<Effects of the Invention> As described above, when a semiconductor laser emits light with the same emission power, the degree of deterioration can be determined by monitoring the increase characteristic of the current value.

According to the present invention, the degree of deterioration can be arbitrarily set in advance, and further deterioration is automatically stopped when the test semiconductor laser has deteriorated to that value. Therefore, there is no need for constant human monitoring, and it is possible to easily obtain semiconductor lasers that have deteriorated to a predetermined value, making it easy to obtain various semiconductor lasers with different degrees of deterioration that are required for deterioration analysis. be able to.

[Brief explanation of drawings]

The attached drawings show a semiconductor laser switch element showing an embodiment of the present invention, 4... semiconductor laser, 5... transistor,
6... Emitter resistance, 7... Photoelectric conversion system, 8...
Deterioration reference level setter, 9... level conoperator,
IO...Flip-flop circuit.

Claims (1)

[Claims] 1. In a drive circuit having a feedback system that maintains the light emission output of the laser at a constant value by feeding back at least a part of the light emission output of the semiconductor laser to the drive circuit of the semiconductor laser, the drive current value of the semiconductor laser and A comparator that compares a reference value that can be set arbitrarily and determines the magnitude relationship between the two, and a switch element that shuts off a drive current circuit to the semiconductor laser according to an output signal of the comparator. A semiconductor laser evaluation circuit characterized by: