JPH0727004B2 - Semiconductor laser device life evaluation method - Google Patents

Description

The present invention relates to a method of estimating the life of a semiconductor laser device, and more particularly to a method of estimating the life useful in a production factory.

[Prior Art and Problems] In order to measure various characteristics of a semiconductor laser device, it is basically necessary to use an analyzer for necessary characteristics, but the analyzer is expensive and requires a long time for analysis. It is troublesome to handle, such as costly, and is unsuitable as a measuring method in a production factory of semiconductor laser devices or products using the same. In particular, when measuring the life characteristics, it is necessary to perform high temperature acceleration operation (high temperature acceleration life test) in an environment with a relatively wide temperature change range. (Device) is subject to temperature stress and may damage the semiconductor laser device, which is extremely inappropriate as a method for measuring the life of the device incorporated in the product.

Further, unlike the case of the laboratory, the characteristic measurement of the semiconductor laser device in the production factory generally does not require strict characteristics, and it is often sufficient to obtain rough data, for example, life tendency.

[Object of the Invention]

In view of the above, it is an object of the present invention to obtain a method for estimating and evaluating the life of a sample (semiconductor laser element) without the need to subject the sample (semiconductor laser element) to a wide range of temperature changes and by a relatively simple method.

[Outline of Invention]

For the above-mentioned purpose, the present invention is to measure the intensity of laser light emitted from a semiconductor laser device which is a specimen while sweeping surfacewise in front of the light emitting surface of the device, and plot the received light intensity at each sweep point. The life of the semiconductor laser device is estimated and evaluated from the presence or absence of dark lines and dark spots appearing in the figure (far field pattern) obtained by the method.

Example of Invention

The inventor of the present invention previously described a device for drawing a far field pattern of emission light intensity of a semiconductor laser element or the like in the "signal transmission / reception characteristic pattern measurement device" of Japanese Patent Application No. 211683 of 1984. Proposed. This device uses a semiconductor laser element (specimen) or a photoreceptor as a two-dimensional space (plane coordinates).
Sweeping, measuring the received light intensity of the laser light from the semiconductor laser device at each sweep point, and plotting it on three-dimensional coordinates to three-dimensionally draw the far field pattern of the semiconductor laser device. It was done like this.

In order to create a far field pattern of a semiconductor laser diode, as shown in FIG. 4 (A), a semiconductor laser diode to be measured (hereinafter referred to as a laser diode) 1 is a light emitting drive device that outputs a constant power pulse power. Pulse driving is performed at 2, and the intensity of light received on the plane S in front of the light emitting surface of the laser diode 1 is measured while sweeping in a plane with the device, and the intensity of light received at each sweep point is plotted. The far field patterns prepared for each of the three samples are shown in FIGS. 1 to 3. The relationship between the axial direction of this far field pattern and the direction of the chip 101 of the laser diode 1 is as shown in FIG. 4 (B).

Further, FIG. 5 schematically shows the received light intensity pattern drawn for one sweep in the X-axis direction in the far field pattern.

As is well known, the ideally created laser diode has a Gaussian distribution characteristic in which the received light intensity distribution at a point separated by a certain distance has a peak at the light receiving center point X _10, as shown by the solid line in FIG. Show. However, in practice, due to the non-uniformity of the refractive index of the waveguide layer of the laser diode chip, the non-uniformity of the light emitting surface, etc., the emission light intensity (emission intensity) from the laser diode chip becomes the fundamental mode (Gaussian distribution characteristic). On the other hand, the characteristic becomes distorted. That is, there are a portion receiving light with an intensity equal to or higher than the Gaussian distribution characteristic and a portion receiving light with an intensity equal to or lower than the Gaussian distribution characteristic. The former appears as a line, and is called a bright line (BL) here. The latter appears as a line or a dot, so it is called a dark line (DL) or a dark spot (Micro Spot) here. .

The bright line appears as a maximum value extending outward from the Gaussian distribution curve as shown in FIG.
The linear shape appears continuously on the heat sink 102 side (see FIG. 4B) in the direction parallel to (Y axis direction). Further, the dark line or dark point appears as a minimum value extending inward from the Gaussian distribution curve as shown in FIG. 5B, and the dark line is a continuous line in the Y-axis direction. It is a scotoma that is not continuous with the dots.

The presence or absence of a bright line, dark line or dark point is determined by the presence or absence of a bright line, dark line or dark point peak value b with respect to the Gaussian distribution line peak value a, for example 10% or more. It shall be.

From the above viewpoint, referring to FIGS. 1 to 3, the laser diode having the characteristic shown in FIG. 1 does not have any bright line, dark line or dark spot, and the laser diode having the characteristic shown in FIG. Has a bright line as indicated by "BL", a dark line as indicated by "DL" and a dark spot as indicated by "MS" in the laser diode shown in FIG.
In addition, in FIG. 3, there are many dark lines and dark spots other than those indicated by "DL" and "MS", and the drawn far field pattern has a very collapsed shape.

Existence of the bright line, dark line, and dark spot described above, and the light output of the laser diode (peak value of light output at a temperature of 25 ° C) and temperature coefficient of light output (above-mentioned light output at a temperature of 60 ° C and temperature of 25 ° C) (Expressed as a ratio to the light output above)
FIG. 6 shows the correlation of the above.

As is clear from FIG. 6, the laser diode having either one or both of the dark line and the dark spot has a small light output and a low light output temperature coefficient. However, the presence of dark lines and dark spots, or only the presence of bright lines, has a large light output or a high light output temperature coefficient.

By the way, in general, in a laser diode having a small light output and a low light output temperature coefficient, the driving energy applied from the outside is not sufficiently converted into light energy, and the energy accumulated in the laser diode chip is large. This causes the temperature of the laser diode itself to rise, and the time of thermal destruction of the laser diode is shortened, which shortens the life of the laser diode. Therefore, it can be estimated that the lifetime of the laser diode in which the presence of dark lines or dark spots is recognized is short. In this way, by observing the dark line or the dark spot from the far field pattern, it becomes possible to evaluate the life of the laser diode. By the way, in the high-power pulse laser diode, the lifespan is 5000 hours or more, although dark lines or dark spots are not recognized, whereas the lifespan is 500 hours or so, which is extremely short (environmental temperature 25 ℃,
Period 100 microns _sec, the rated drive a pulse width 100n _sec (drive current 3
0-40A) and measured).

The method of detecting the presence of a dark line or a dark spot from the far field pattern is to estimate a reference distribution curve showing the Gaussian distribution characteristic from the slope of a part of the received light intensity characteristic, and calculate a minimum value protruding from this reference distribution curve. , And all of them can be obtained by processing by MPU (microprocessor).

〔The invention's effect〕

As described above in detail, the present invention is designed to evaluate the life of the laser diode by observing the presence of dark lines or dark spots from the far field pattern of the laser diode, which is very simple. Not only is it possible to evaluate the lifetime with the method, but there is no need to subject the sample to temperature changes, so there is no deterioration of the laser diode due to the measurement itself, which is extremely useful in assessing the lifetime required at the production plant. Is the way.

[Brief description of drawings]

1 to 3 are views showing a far field pattern of a laser diode, and FIG. 4 (A) is a view explaining a measuring method.
FIG. 4 (B) is a diagram for explaining the axial relationship between the laser diode and the far field pattern, FIG. 5 is a diagram showing the light receiving characteristic of the emitted light of the laser diode, and FIG. 6 is the existence of bright lines, dark lines or dark spots. It is a figure which shows the correlation of lifetime. (Main symbols) 1 ... Laser diode, BL ... Bright line DL ... Dark line, MS ... Dark spot.

Claims (1)

[Claims] 1. A method of evaluating the life of a semiconductor laser device, which is carried out in the measurement of characteristics during production, in which the intensity of laser light emitted from the semiconductor laser device is swept over the plane in front of the emission surface of the semiconductor laser device. While observing the far field pattern measured and created, the lifetime evaluation method of the semiconductor laser device is such that the lifetime is estimated from the presence or absence of either or both of a dark line and a dark spot appearing in the far field pattern.