JPS61235769A - Method and device for aging or screening semiconductor laser - Google Patents

Abstract

PURPOSE:To calculate a threshold current for deciding the life of a semiconductor laser by linear approximation by applying a bias voltage to a semiconductor photodetector so that the light-current conversion characteristic of the semiconductor photodetector has linearity. CONSTITUTION:A high-temperature thermostatic chamber 2 where the semiconductor laser 1 to be aged or screened is arranged and a room-temperature thermostatic chamber 4 where the semiconductor photodetector 3, i.e. germanium detector is arranged are both provided. An optical transmission means 5 such as an optical fiber is which allows the thermostatic chambers 2 and 4 to communicate optically with each other and guide the light output of the laser 1 to the detector 3. Further, a detecting circuit 6 is provided which makes the driving current of the laser 1 and detects variation in its light output with time by the detector 3, or makes the light output of the laser 1 and detects variation in its driving current with time. Then, the bias voltage is applied to the detector 3 so that the light-current conversion characteristic of the detector 3 is linear.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method and apparatus for aging or screening semiconductor lasers.

Conventional technology Semiconductor lasers have recently been
It is used as a light-emitting source for optical communication used in high-value-added communication networks (VANs), etc.

An aging or screening device has been developed as an evaluation test system for improving the reliability of such semiconductor lasers. Such test systems have also been used to evaluate semiconductor lasers used in video discs and audio discs. Aging of this type of semiconductor laser is also called a lifetime test, and in order to evaluate the characteristics in a short period of time, the semiconductor laser is operated at high temperature and changes in its characteristics are investigated.Normally, this aging is , semiconductor laser at 60℃
This aging is performed by continuously operating for thousands of hours at a high temperature of ~80°C to examine changes in its characteristics.
constant current drive mode called ENT Control), and APC (Automatic Power
There is a constant light output drive mode called Control.

In the constant current drive mode, the drive current of the semiconductor laser is kept constant and temporal changes in the optical output are detected.

On the other hand, in the constant light output drive mode, the light output of the semiconductor laser is kept constant and temporal changes in the drive current are detected.

Semiconductor laser screening is a test similar to the aging described above, but whereas aging tests the lifespan of a semiconductor laser, this is a test to determine initial failure of a semiconductor laser. Therefore, a semiconductor laser is operated at a high temperature of 60° C. to 80° C. for approximately 100 to 150 hours to examine changes in its characteristics.

A conventional method for performing such aging or screening is to keep the semiconductor laser to be aged or screened at a high temperature, keep a semiconductor photodetector at room temperature, and receive the optical output from the semiconductor laser at the semiconductor photodetector. Accordingly, the driving current of a semiconductor laser is kept constant and a temporal change in its optical output is detected, or the optical output of a semiconductor laser is kept constant and a temporal change in the driving current is detected. Conventionally, silicon detectors and germanium detectors have been used as semiconductor photodetectors, and silicon detectors are suitable for short wavelength light output of about 800 nm from semiconductor lasers used in audio discs. There were no particular problems because the linearity of its photo-current conversion characteristics was good.

Problems to be Solved by the Invention However, 1300
A long-wavelength germanium detector for outputting light at a wavelength as long as nanometers has the following problem because its light-to-current conversion characteristics have poor linearity.

That is, when measuring the forward current vs. output characteristic of a semiconductor laser using a semiconductor photodetector with poor linearity of the light-to-current conversion characteristic, as illustrated in FIG. 4 of the accompanying drawings, originally, Although a linear value should be obtained, a non-linear one is obtained. Therefore, when detecting temporal changes in the optical output of a semiconductor laser with a constant drive current during aging or screening, its optical output Since the detection sensitivity of the detector varies depending on the type of light, accurate measurement values cannot be obtained, and troublesome calculations for correction are required to determine the actual light output. Furthermore, even when examining temporal changes in the drive current of a semiconductor laser with the optical output constant, the optical output is
It is necessary to detect temporal changes in the drive current by keeping the value of w constant, and also to detect temporal changes in the drive current by keeping the optical output constant at a value of, for example, 5mW. If the sensitivity of the photodetector changed as the output changed, there was a problem in that the characteristics at 3 mW and the characteristics at 5 mW could not be directly compared.

In addition, the forward drive current at the starting point of light emission due to oscillation of a semiconductor laser is called the threshold current, and there is a method that uses changes in the threshold current as a guide to determine the lifespan or initial failure of the semiconductor laser. . To find this threshold current,
The forward drive current vs. optical output characteristic of a semiconductor laser is originally
Since it has linearity, it is common to measure only two points on the characteristic curve and obtain the values at those two points by linear approximation. However, if the light-to-current conversion characteristics of the photodetector are not linear, the threshold current of the semiconductor laser cannot be determined by such linear approximation.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method and apparatus for aging or screening a semiconductor laser, which eliminates the conventional problems as described above.

Means for Solving the Problems According to the present invention, a semiconductor laser to be aged or screened is placed in a constant temperature bath at high temperature, a semiconductor photodetector is placed in a constant temperature bath at room temperature, and the semiconductor laser to be aged or screened is placed in a constant temperature bath at room temperature. A light transmission means is provided that optically communicates with a room temperature constant temperature bath to guide the light output from the semiconductor laser to the semiconductor photodetector, and the drive current of the semiconductor laser is kept constant and the time of the light output is controlled. In the aging or screening method for a semiconductor laser, the semiconductor laser aging or screening method detects a temporal change in the driving current by the semiconductor photodetector, or the optical output of the semiconductor laser is kept constant and detects a temporal change in the drive current for the purpose. Applying a bias voltage to the semiconductor photodetector so as to provide linearity of current conversion characteristics The present invention also includes a high-temperature thermostat in which the semiconductor laser to be aged or screened is placed;
A room-temperature constant temperature bath in which a semiconductor photodetector is disposed, and optical communication between the high temperature constant temperature bath and the room temperature constant temperature bath to guide optical output from the semiconductor laser to the semiconductor photodetector. a light transmitting means, and a temporal change in the optical output of the semiconductor laser with a constant driving current detected by the semiconductor photodetector, or a temporal change in the driving current for that purpose with the optical output of the semiconductor laser constant. A semiconductor laser aging or screening device comprising: a detection circuit for detecting a first and a first differential amplifier having a second input terminal and one output terminal, a drive level setting means for setting a constant current value in constant current drive mode and a constant light output in constant light output drive mode, 1
and a comparator having a second input terminal and one output terminal, a current bumper having a control gate, and a drive current detection resistor, and the semiconductor photodetector includes a comparator having a second input terminal and one output terminal, and a drive current detection resistor. 1 of the first differential amplifier.
The second input terminal of the first differential amplifier is connected to ground, and the output terminal of the first differential amplifier is connected between the input terminal of the first differential amplifier and the second input terminal of the first differential amplifier. is associated with an optical output read instruction terminal that provides an instruction to read the optical output of the laser, and is connected to the first input terminal of the tenth differential amplifier via a first resistor, so that the voltage thereon is always kept at zero potential. The drive level setting means is connected to the second input terminal of the comparator, and the current buffer and the drive current detection resistor are connected in series to the drive current circuit of the semiconductor laser. The output terminal of the comparator is connected to the control gate of the current buffer, and the connection point between the current buffer and the drive current detection resistor is connected to the drive current of the semiconductor laser. The switching means connects the connection point between the current buffer and the drive current detection resistor to the first input terminal of the comparator in the constant current drive mode. and associating the output terminal of the first differential amplifier with the first input terminal of the comparator in a constant light output drive mode.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described in more detail with reference to embodiments of the present invention based on FIGS. 1, 2, and 3 of the accompanying drawings.

FIG. 1 schematically shows the configuration of a semiconductor laser aging or screening apparatus as an embodiment of the present invention. As shown in FIG. 1, this aging or screening apparatus mainly includes a high-temperature constant temperature bath 2 in which a semiconductor laser 1 to be aged or screened is placed, and a semiconductor photodetector such as a germanium detector. A room-temperature constant temperature bath 4 for arranging the device 3, and an optical communication between the high temperature constant temperature bath 2 and the room temperature constant temperature bath 4 to guide the optical output from the semiconductor laser 1 to the semiconductor photodetector 3. , for example, a light transmission means 5 such as an optical fiber, and a semiconductor laser 1 whose drive current is kept constant and a semiconductor photodetector 3 detects a temporal change in the optical output.
A detection circuit 6 is provided for keeping the optical output constant and detecting temporal changes in the drive current. The high-temperature constant temperature bath 2 is designed to maintain its interior at a constant high temperature of 70° C., and the room temperature constant temperature bath 4 is configured to maintain its interior at a constant normal temperature of 20° C., for example. .

FIG. 2 shows details of the detection circuit 6. As shown in FIG.
A bias voltage means 61 for providing linearity of current conversion characteristics, a first differential amplifier 62 having a positive input terminal, a negative input terminal, and an output terminal, and a first potentiometer as a bias current canceling voltage means. 63, a second differential amplifier 64 having a positive input terminal, a negative input terminal, and an output terminal, and a second differential amplifier 64 for switching between constant current drive mode (ACC) and constant light output drive mode (APC). A switching means 65, a second potentiometer 66 as a drive level setting means for setting a constant current value in the constant current drive mode and a constant light output in the constant light output drive mode, and a positive input terminal, a negative input terminal, and an output terminal. A current buffer 68 having a control gate such as a unijunction transistor with high input impedance, and a drive current detection resistor 69 are provided.

The semiconductor photodetector 3 is connected between the bias voltage means 61 and the negative input terminal of the first differential amplifier 62. The positive input terminal of the differential amplifier 62 is connected to ground,
The output terminal of the differential amplifier 62 is connected to the negative input terminal of the second differential amplifier 64 via a resistor R1, and is also connected to the negative input terminal of the first differential amplifier 62 via a resistor R2. , the voltage at the connection point J1 is always kept at zero potential. That is, the differential amplifier 62 is used as a current amplifier with low input impedance. 1st
The potentiometer 63 is connected to the positive input terminal of the second differential amplifier 64. The output terminal of the 20th differential amplifier 64 is connected to an optical output read instruction terminal T1 that gives an instruction to read the optical output of the semiconductor laser 1, and is connected to a resistor R.
3 to the negative input terminal of the second differential amplifier 64 so as to cancel the bias current caused by the bias voltage output. The second potentiometer 66 is connected to the positive input terminal of the comparator 67. Unijunction transistor 68 and drive current detection resistor 69
is connected in series to the drive current circuit E of the semiconductor laser 1. The output terminal of the comparator 67 is connected to the control gate of the unijunction transistor 68, and the connection point J2 between the unijunction transistor 68 and the drive current detection resistor 69 is connected to the drive current that gives an instruction to read the drive current of the semiconductor laser 1. It is connected to the read instruction terminal T2. The switching means 65 selects a constant current drive mode (AC
In C), the unijunction transistor 68
The connection point J2 between the drive current detection resistor 69 and the drive current detection resistor 69 is connected to the negative input terminal of the comparator 67, and the constant light output drive mode (AP
In C), the output terminal of the second differential amplifier 64 can be connected to the negative input terminal of the comparator 67.

Next, the operation of the aging or screening apparatus having such a configuration will be briefly described.

First, when aging or screening is performed in the constant current drive mode, the switching means 65 is turned on to the ACC side, and the second potentiometer 66 is adjusted to set the voltage corresponding to the desired running current value. is applied to the positive input terminal of the comparator 67 as a reference value. Then, the drive current circuit E is energized and the drive current ■ is applied to the semiconductor laser I. to flow. This drive current 11 is read at the terminal T2 as a voltage drop across the drive current detection resistor 69 and is applied to the negative input terminal of the comparator 67. The comparator 67 compares the voltage corresponding to the actual driving current value I with the voltage reference value corresponding to the desired travel driving current value given by the potentiometer 66, and detects a difference between them. Sometimes, the degree of energization of the unijunction transistor 68 is controlled according to the difference, so that the actual drive current 1. On the other hand, the semiconductor photodetector 3 receives the light output from the semiconductor laser 1 and flows a current according to its light-to-current conversion characteristics.

This current is converted by the first differential amplifier 62, and the second
It is read as the optical output value of the semiconductor laser 1 at the optical output reading instruction terminal T1 via the differential amplifier 64. In this way, in the constant current drive mode, the drive current of the semiconductor laser 1 is 1. It is possible to detect a temporal change in the optical output of the semiconductor laser 1 while keeping it constant.

Next, when performing aging or screening in the constant light output drive mode, the switching means 65 is turned on to the APC side, and the second potentiometer 66 is adjusted to set the voltage corresponding to the desired constant light output value. It is added to the positive input terminal of the comparator 67 as a reference value. Then, the drive current circuit E is energized to supply a drive current l to the semiconductor laser 1.

to flow. This drive current of 1° is read as a voltage drop across the drive current detection resistor 69 at the terminal T2. On the other hand, the semiconductor photodetector 3 receives the optical output from the semiconductor laser 1 and flows a current according to its light-to-current conversion characteristics.This current is converted into a voltage by the tenth differential amplifier 62, and The signal is read as the optical output value of the semiconductor laser 1 at the optical output reading instruction terminal T1 via the two differential amplifiers 64, and is applied to the negative input terminal of the comparator 67. Comparator 67 compares the voltage corresponding to this actual light output with a voltage reference value corresponding to the desired constant light output value given by potentiometer 66, and if there is a difference between them, Accordingly, the energization ring of the unijunction transistor 68 is controlled so that a drive current of 1° is applied so that the actual light output is always equal to the desired constant light output value. In this way,
In the constant light output drive mode, the drive current of the semiconductor laser 1 is 1.
It is possible to detect temporal changes in

In the embodiment described above, the first potentiometer 63 and the second differential amplifier 64 were provided as bias current canceling voltage means, but if the bias current is not a particular problem, these potentiometers 63 and There is no need to provide a differential amplifier 64; in this case,
The output terminal of the first differential amplifier 62 may be directly connected to the APC terminal of the switching means 65 and the optical output reading instruction terminal T1.

In addition, when aging or screening a large number of semiconductor lasers at the same time, as shown by the dotted line in Figure 2,
Circuits 60', 60#, 60"'-- similar to the circuit configuration in the block indicated by reference numeral 60 are provided in accordance with the number of semiconductor lasers to be tested', 1", 1" to form one bias voltage means. 61 and each circuit 60', 60', 60 #----
Each semiconductor laser ′, ′, 1′# between −−・−・
semiconductor photodetectors 3', 3 each receiving optical output from
'', 3'''-------.

Effects of the Invention As described above, in the present invention, by applying a reverse bias of, for example, about 3 V to a semiconductor photodetector, the linearity of the light-to-current conversion characteristic of the semiconductor photodetector is improved. Therefore, the forward drive current vs. optical output characteristic of the resulting semiconductor laser is also more linear and accurate, as illustrated in FIG. 3, compared to that in FIG. 4. Therefore, the threshold current, which is a guide for determining the life span or initial failure of the semiconductor laser, can be more accurately and easily determined by linear approximation.

Furthermore, according to the circuit configuration of the device of the present invention described above, the connection point J1 is always kept at zero potential regardless of the magnitude of the current generated by the photodetector 3. The bias voltage by the bias voltage means 61 is always the same.
Therefore, accurate detection can be performed, and
As shown in FIG. 2, one bias voltage means 61 is used to control multi-channel semiconductor lasers 1', 1#, I In -
---- can be aged or screened simultaneously. Furthermore, if the bias current canceling voltage means 63 and the differential amplifier 64 are used as in the embodiment described above,
Since the bias current is canceled, more accurate detection can be performed.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the configuration of a semiconductor laser aging or screening device as an embodiment of the present invention, FIG. 2 is a detailed diagram of the detection circuit of the device in FIG. 1, and FIG. FIG. 4 is a diagram showing an example of the forward drive current versus optical output characteristic of a semiconductor laser obtained by a conventional detection device; FIG. 4 is a diagram showing an example of the forward drive current versus optical output characteristic of a semiconductor laser obtained by a conventional detection device . 1... Semiconductor laser, 2... High temperature constant temperature chamber, 3...
Semiconductor photodetector, 4... Room temperature constant temperature bath, 5... Optical transmission means, 6... Detection circuit, 61... Bias voltage means, 62... First differential amplifier, 63... - First potentiometer, 64... Second differential amplifier, 65...
- Switching means, 66...second potentiometer, 6
7... Comparator, 68... Unijunction transistor, 69... Drive current detection resistor, R2゜R
3...Resistor, T1...Optical output reading instruction terminal, T2
...Drive current reading instruction terminal. -T -11-----------'' (a) Figure 3

Claims (3)

[Claims] (1) A semiconductor laser to be aged or screened is placed in a high temperature constant temperature bath, a semiconductor photodetector is placed in a room temperature constant temperature bath, and optical communication is established between the high temperature constant temperature bath and the room temperature constant temperature bath. A light transmission means is provided to guide the optical output from the semiconductor laser to the semiconductor photodetector, and the semiconductor photodetector detects a temporal change in the optical output while keeping the driving current of the semiconductor laser constant. or in a method for aging or screening a semiconductor laser, in which the optical output of the semiconductor laser is kept constant and a temporal change in the driving current is detected; A method for aging or screening a semiconductor laser, comprising applying a bias voltage to a semiconductor photodetector. (2) A high-temperature constant temperature chamber for arranging a semiconductor laser to be aged or screened, a room temperature constant temperature chamber for arranging a semiconductor photodetector, and an optical connection between the high temperature constant temperature chamber and the room temperature constant temperature chamber. a light transmitting means for guiding the light output from the semiconductor laser to the semiconductor photodetector by communicating with the semiconductor laser; and a light transmission means for guiding the light output from the semiconductor laser to the semiconductor photodetector; In the semiconductor laser aging or screening apparatus, the semiconductor laser aging or screening apparatus includes a detection circuit for detecting a change in driving current over time while keeping the optical output of the semiconductor laser constant, The light of the vessel
A bias voltage means for providing linearity of current conversion characteristics, a first differential amplifier having first and second input terminals and one output terminal, and a constant current drive mode and a constant light output drive mode. a drive level setting means for setting a constant current value in the constant current drive mode and a constant light output in the constant light output drive mode; The semiconductor photodetector includes a comparator having an output terminal, a current buffer having a control gate, and a drive current detection resistor. The second input terminal of the first differential amplifier is connected to ground, and the output terminal of the first differential amplifier is connected between the input terminal of the first differential amplifier and the second input terminal of the first differential amplifier. is associated with an optical output read instruction terminal that provides an instruction to read the optical output of the laser, and is connected to the first input terminal of the first differential amplifier via a first resistor, so that the voltage thereon is always zero. The drive level setting means is connected to the second input terminal of the comparator, and the current buffer and the drive current detection resistor are connected to the semiconductor laser drive current circuit. The output terminal of the comparator is connected to the control gate of the current buffer, and the connection point between the current buffer and the drive current detection resistor is connected to the drive current of the semiconductor laser. The switching means connects the connection point between the current buffer and the drive current detection resistor to the first input terminal of the comparator in the constant current drive mode. A semiconductor laser aging or screening device, characterized in that the output terminal of the first differential amplifier is connected to the first input terminal of the comparator in a constant light output drive mode. (3) The detection circuit includes bias current canceling voltage means and a second differential amplifier having first and second input terminals and one output terminal, and The output terminal of the amplifier is connected to the first input terminal of the second differential amplifier to be associated with the optical output read instruction terminal, and the bias current canceling voltage means is connected to the first input terminal of the second differential amplifier. The output terminal of the second differential amplifier is connected to the optical output read instruction terminal and the second input terminal of the second differential amplifier is connected to the optical output read instruction terminal through a second resistor. The switching means is connected to the first input terminal of the second differential amplifier to cancel the bias current generated by the bias voltage means, and the switching means is connected to the first input terminal of the second differential amplifier to cancel the bias current generated by the bias voltage means.
The output terminal of the first differential amplifier is associated with the first input terminal of the comparator by connecting the output terminal of the differential amplifier to the first input terminal of the comparator. A semiconductor laser aging or screening device according to item (2).