JPS6333884A - Measuring method of deviation of optical axis of semiconductor laser and device used for said method - Google Patents

Abstract

PURPOSE:To rapidly and simply measure the deviation of optical-axis of a semiconductor laser without measuring a far field pattern by moving a pair of photodetectors in the direction of optical-axis deviation required, obtaining a position where outputs from a pair of the photodetectors are equalized and measuring the deviation of the central axis of a package and the optical axis of a semiconductor laser chip. CONSTITUTION:When optical axes are deviated, the maximum light intensity point of a far field pattern 44 is deviated from the central axis of a package, and outputs from photodiodes 28, 29 are shown in curves 46, 47. Consequently, positive and negative polarity are inverted where deviated from an angle 0, the maximum light intensity point of the far field pattern 44, as shown in a curve 42 in an output from a differential amplifier 30. Accordingly, the position of a pointer 24 at the reference point of a holder 22 at a position where an output 49 from a positive and negative sign discrimination circuit 32 is changed is read, thus acquiring the angle of optical-axis deviation. The holder 22 fixing the photodiodes 28, 29 is moved by a servomotor, and the holder 22 is controlled by an output from the positive and negative sign discrimination circuit 32, thus automatically measuring the angle of optical-axis deviation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a method for measuring the characteristics of a semiconductor laser, particularly optical axis deviation, and an apparatus used therefor.

(Prior Art) As shown in FIG. 4, a semiconductor laser generally includes a semiconductor laser chip (4) fixedly enclosed within a package (3) having a glass window (2). The output light of the semiconductor laser (1) is diffused light whose light emitting point is one point on the semiconductor laser chip (4). The direction in which the intensity of light emission is maximum is the optical axis a'''C- of the semiconductor laser chip (4), and the angle α between this axis a and the mechanical center axis of the package (3) is
is the optical axis deviation angle of the semiconductor laser (1).

Since the semiconductor laser (1) is generally incorporated into various optical devices based on the outer diameter of the package (3), it is important to keep the optical axis deviation angle α within a predetermined range. For this reason, in the semiconductor laser (1), after the laser chip (4) is enclosed in the package (3), the optical axis deviation angle is measured and the quality of the semiconductor laser (1) is determined. Since the intensity change of the emitted light is minute in the vicinity of the direction where the light intensity of the laser chip (4) is maximum, when measuring the optical axis deviation angle, it is necessary to measure the optical axis over a wide range of distance in order to accurately determine the optical axis. Measure the visual field image,
It is calculated from its shape.

FIG. 5 shows an example of a far-field image measuring device used for such a purpose. This device includes a holding/rotating device (5) that holds and rotates the semiconductor laser (1), and an angle detecting device (6).
) and a light intensity measuring device (7). Angle detection device (6
), an arithmetic device (8) for calculating the optical axis from the obtained far-field image is connected to the light intensity measuring device (7).

The measurement begins with a holding and rotating device (5) that holds the semiconductor laser (1).
It is held with high accuracy and rotated by a holding/rotating device (5), and the change in the output of the light intensity measuring device (7) with respect to the rotation angle is recorded with a recorder or the like or stored in a computer to obtain a far-field image.

FIG. 6 shows an example of a far-field image of the obtained semiconductor laser. To find the optical axis, use the far-field image (9) to find the angles (1) and (11) of the two points where the light intensity is 1/2 of the maximum light intensity.
) and calculate its central angle ■. This central angle is 0
The direction is defined as the optical axis direction a of the laser chip (4), and the angle formed between this direction and the central axis of the package (3) is the optical axis deviation angle α of the laser chip (4).

However, in the measurement method of determining the optical axis deviation angle using such conventional measurement equipment, detailed information cannot be obtained over a wide angular range.
It is necessary to measure a far-field image. Therefore, it has the disadvantage that measurement requires a large amount of time. In addition, some kind of calculation is required to determine the optical axis from the far-field image, and in order to automate the measurement, it is necessary to digitize the angle and output light and a computer with a storage device, making the equipment complicated. The disadvantage is that the measurement time becomes longer.

<Problems to be Solved by the Invention> As described above, in measuring the optical axis deviation of a semiconductor laser, the method of measuring a far-field image and calculating the optical axis deviation from the result requires a long time for measurement. It has disadvantages such as complexity.

The present invention provides a method for quickly and simply measuring the optical axis deviation of a semiconductor laser without measuring a far-field pattern, and an apparatus used therefor.

[Structure of the Invention] (Means for Solving the Problems) The present invention measures the deviation between the central axis of the package and the optical axis, which is the central axis of light emission of the semiconductor laser chip, in a semiconductor laser in which a semiconductor laser depth is fixed in the package. In the method of A method for measuring optical axis misalignment of a semiconductor laser, characterized by measuring the misalignment between the central axis of the package and the optical axis of the semiconductor laser chip by moving the package in the direction and determining the position where the outputs of a pair of photodetectors are equal. It is.

In addition, in the method of measuring the deviation between the central axis of the package of a semiconductor laser with a semiconductor laser deep fixed in the package and the optical axis, which is the central axis of light emission of the semiconductor laser chip, the optical axis is determined in a plane perpendicular to the central axis of the package. A pair of photodetectors fixed at a certain distance in the direction of deviation are respectively moved in the direction of the desired optical axis deviation to positions corresponding to the maximum positive and negative allowable values of the optical axis deviation angle,
The magnitude relationship between the outputs of the pair of photodetectors at the position corresponding to the maximum positive allowable value and the magnitude relationship between the outputs of the pair of photodetectors at the position corresponding to the negative maximum allowable value are determined, and both positions are determined. If the magnitude relationship of the outputs of the pair of photodetectors at both positions is different, the optical axis is within the allowable optical axis deviation range, and if the magnitude relationship of the outputs of the pair of photodetectors at both positions is the same, the optical axis is within the allowable optical axis deviation range. This is a method for measuring optical axis deviation of a semiconductor laser, characterized in that the optical axis deviation is determined to be outside the deviation range.

Furthermore, in a semiconductor laser optical axis deviation measuring device that measures the deviation between the central axis of a package of a semiconductor laser in which a semiconductor laser chip is fixed in the package and the optical axis that is the central axis of light emission of the semiconductor laser chip, a pair of photodetectors fixed at a certain distance in the direction of optical axis deviation in a plane perpendicular to the central axis of the package; This is a semiconductor laser optical axis deviation measuring device characterized by having a means for moving the optical axis of a semiconductor laser, and a means for comparing outputs of a pair of photodetectors.

<Function> According to the method for measuring the optical axis deviation of a semiconductor laser of the present invention, by utilizing the symmetry of the light emitted from the laser chip, a pair of fixed distances are fixed at a certain distance in the direction of the desired optical axis deviation. By using a photodetector and moving it in the desired optical axis deviation direction and finding the position where the outputs of a pair of photodetectors are equal, the central axis of the light emitted from the laser chip, that is, the optical axis, can be determined. The deviation between the central axis of the package and the optical axis of the semiconductor laser chip can be easily measured.

Therefore, according to the present invention, there is no need to measure a far-field image, and it is possible to provide a method for quickly and easily measuring the optical axis deviation of a semiconductor laser, and a device used therefor.

(Example) Hereinafter, the present invention will be explained with reference to FIGS. 1 and 2 showing one example.

The optical axis deviation measuring device for a semiconductor laser according to the present invention is constructed as shown schematically in FIG.
A holder (20) is provided to hold and fix the semiconductor laser (1) so that the central axis of the package (3) of the semiconductor laser (1) is well reproduced. On the other hand, the holder (20)
A photodetector holder (22) that moves linearly on a base (34) in a plane perpendicular to the central axis of the package (3) by means of a guide (21) is provided in front of the package (3).

A pointer (24) indicating a reference point is written on the holder (22), and a scale (23) indicating the amount of displacement of the holder (22) is written on the base (34). J3, guidelines (24
) on the base (34), and the scale (23) on the holder (2
2) may be provided. The photodetector holder (22) includes:
A pinhole (25L) is inserted as a photodetector at a position passing through the central axis of the package (3) of the semiconductor laser (1) and equidistant from the pointer (24) which is the reference point of the holder (22).
Photodiode (28) with (26), (29)
is installed.

And these two photodiodes (28), (29
) is connected to a differential amplifier (30) which extracts the output as a difference signal, and further connected to the differential amplifier (30) is a sign discrimination circuit (32) which converts the output into a digit.

To measure the optical axis deviation using the semiconductor laser optical axis deviation measuring device configured as described above, first the semiconductor laser (
1) is attached to the holder (20). Next, while making the semiconductor laser (1) emit light, the photodiode (28),
The holder (22) to which (29) is fixed is moved along the guide (21), and the position of the holder (22) where the output signal of the positive/negative sign discrimination circuit (32) changes is determined. Then, a pointer (24) indicates the reference point of the holder (22) at that position.
The distance of deviation of the base (34) from the reference position (35) is read. In this case, the distance from the reference position (35) of the base (34) to the pointer (24) of the reference point of the holder (22) where the output of the positive/negative sign discrimination circuit (32) changes is d;
If the distance from the light emitting point of the semiconductor laser (1) to the slit moving surface is assumed, the optical axis deviation angle is arctan (d
/L). When the optical axis deviation angle is smaller than 5 degrees, the optical axis deviation angle is approximately (180/
By multiplying the positional deviation of Holter page 22) by a certain constant, the optical axis deviation angle can be immediately determined from the deviation distance d.

Note that if a scale corresponding to the optical axis deviation angle is written in advance on the scale (23) of the base (34), the optical axis deviation angle can be directly read.

Next, the operation of the above-mentioned device will be explained.

Figure 2 shows the outputs of the photodiodes (28) and (29), the output of the differential amplifier (30), and the positive/negative sign discrimination circuit (32) with respect to the position of the holder (22) holding the photodiodes (28) and (29). ) shows the output of In addition,
A far-field image is also shown. FIG. 2A shows the case of a semiconductor laser with no optical axis deviation, and FIG. 2A shows the case of a semiconductor laser with optical axis deviation.

As shown in Figure 2a, if the optical axis is not shifted, the maximum light intensity point of the far-field image (29) coincides with the central axis of the package, and the outputs of the photodiodes (28) and (29) are curved (40). ), as shown in (41). Then, the polarity of the output of the differential amplifier (30) is reversed at an angle O as shown by a curve (42). Therefore, the output (43) of the positive/negative sign discrimination circuit (32) changes exactly when the pointer (24) at the reference point of the holder (22) changes at the reference position (35) of the base (34). That is, in this case, the optical axis deviation angle can be read as 0 degrees.

On the other hand, as shown in Figure 2, if there is an optical axis misalignment,
The maximum light intensity point of the far-field image (44) is shifted from the central axis of the package, and the outputs of the photodiodes (2B) and (29) are as shown by curves (46) and (/17).

Therefore, as shown by the curve (42), the output of the differential amplifier (30) is at a position different from the angle O, that is, the far-field image (44).
) The positive and negative polarities are reversed at the maximum light intensity point. Therefore, the optical axis deviation angle can be obtained by reading the position of the pointer (24) of the reference point of the holder (22) at the position where the output (49) of the positive/negative sign discrimination circuit (32) changes.

In this way, according to the present invention, it is possible to quickly and easily measure the optical axis deviation of a semiconductor laser without measuring a far-field image.

Note that in the above embodiment, the photodiode (28)
, (29) is moved by a servo motor, and this servo motor is controlled by the output of a positive/negative sign discrimination circuit (32).
By stopping at the position where the output of 32) changes,
It becomes possible to automatically measure the optical axis deviation angle.

Further, in the above embodiment, a pinhole is formed in the photodiode, but a slit may be formed perpendicular to the movable direction of the holder (22). In this case, the output of the photodiode is averaged in the direction of the pinhole, so if there are particles floating in the air or there is some dirt on the glass window of the semiconductor laser, interference of the laser light may occur. It is possible to reduce errors in angle measurement due to disturbances in the far-field image.

Regarding other embodiments of the present invention, similarly, FIG.
This will be explained using figures.

This embodiment does not measure the optical axis deviation angle itself of the semiconductor laser, but moves the holder (22) to a position corresponding to the maximum positive and negative values θ1 and θ2 of the optical axis deviation angle allowed for the semiconductor laser. A device that determines the magnitude relationship between the outputs of the photodiodes (28) and (29) at each position, compares them, and determines whether the optical axis deviation angle is within an allowable range based on the results. It is.

Therefore, in this embodiment, as shown in FIG.
stoppers (50) and (51) that limit the movable range of
) is provided on the base (34). This stopper (50), (
The regulation positions d2 and 51) are set corresponding to the positive and negative maximum values θ1 and θ2 of the allowable optical axis deviation angle, respectively. And both stoppers (50), (51
) to the positions di, d2 of the photodiode (28), (
29) is moved, and the output of the positive/negative sign determining circuit (32) is checked at each position. If the outputs of the positive/negative sign discriminating circuit (32) at the positions of the stoppers (50), (51) and d2 are different, the optical axis deviation angle is within an allowable range, and the positive/negative sign discriminating circuit (32) ) are the same, it means that the optical axis deviation angle is outside the allowable range.

Figure 3 shows a far-field image, a photodiode (2B), (
29) shows the relationship between the output of the positive and negative sign discriminating circuit (32) and the position of the holder (22) holding the holder (29). Figure 3a shows the case where the optical axis deviation of the semiconductor laser is larger than the permissible range in the negative direction, Figure 3 shows the case where the optical axis deviation is within the permissible range, and Figure 3C shows the case where the optical axis of the semiconductor laser is shifted in the negative direction. This shows a case where the axis misalignment is greater than the allowable range in the positive direction.

As shown in FIG. 3a, when the optical axis misalignment is greater than the allowable range in the negative direction, the maximum light intensity point of the far-field image (53) is outside the range of 01 to θ2. Therefore, at the position d2 of the stoppers (50) and (51), the output (54) of the sign determining circuit (32) remains 1 and does not change. As shown in FIG. 3, when the optical axis deviation is within a permissible range, the output (54) of the positive/negative sign discrimination circuit (32) is d
Ol at the l position and 1 at the d2 position, and the outputs are different between the old and d2 positions. Further, as shown in FIG. 3C, if the optical axis misalignment is greater than the allowable range in the positive direction, the output (54
) remains unchanged at position old and d2 at O.

In this embodiment, it is possible to easily determine whether the optical axis deviation angle is within an allowable range by measuring only at two locations, and it is possible to perform screening of semiconductor lasers as to whether they are good or bad with extremely high efficiency.

[Effects of the Invention] As described above, according to the present invention, the optical axis deviation of a semiconductor laser can be easily measured.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing one embodiment of the present invention, FIG. 2 is a diagram showing a far-field image, the output of the photodiode, the output of the differential amplifier, and the output of the positive/negative sign discrimination circuit (32). FIG. Far-field image and positive/negative sign discrimination circuit (32) in other embodiments
Figure 4 is a diagram showing an example of a semiconductor laser, Figure 5 is a schematic diagram of a device for measuring a far-field image, and Figure 6 explains a method for determining optical axis deviation from a far-field image. This is a diagram. (1)...Semiconductor laser (3)...Package (4)...Semiconductor laser chip (20)...
... Semiconductor laser holder (24) ... Photodetector holder (25), (26) ... Slit (30) ... Differential amplifier (32) ...Positive sign discrimination circuit (34)...
...base

Claims (6)

[Claims] (1) In a method of measuring the deviation between the central axis of the package and the optical axis, which is the central axis of light emission of the semiconductor laser chip, in a semiconductor laser in which a semiconductor laser chip is fixed in the package, the semiconductor laser chip is in a state where the semiconductor laser chip is emitting light. Then, a pair of photodetectors fixed at a certain distance in the direction of the desired optical axis deviation in a plane perpendicular to the central axis of the package are moved in the direction of the desired optical axis deviation, and the pair of photodetectors are detected. 1. A method for measuring optical axis deviation of a semiconductor laser, characterized in that the deviation between the central axis of the package and the optical axis of the semiconductor laser chip is measured by determining a position where the outputs of the semiconductor laser chips are equal. (2) In a method of measuring the deviation between the central axis of the package and the optical axis, which is the central axis of light emission of the semiconductor laser chip, in a semiconductor laser in which a semiconductor laser chip is fixed in the package, a plane perpendicular to the central axis of the package; A pair of photodetectors fixed at a certain distance apart in the direction of the optical axis deviation to be sought in the optical axis deviation direction are respectively moved to positions corresponding to the maximum positive and negative allowable values of the optical axis deviation angle in the direction of the desired optical axis deviation. and a magnitude relationship between the outputs of the pair of photodetectors at a position corresponding to the positive maximum allowable value, and a magnitude relationship between the outputs of the pair of photodetectors at a position corresponding to the negative maximum allowable value. If the magnitude relationship of the outputs of the pair of photodetectors at both positions is different, it is within an allowable optical axis deviation range,
A method for measuring an optical axis deviation of a semiconductor laser, characterized in that when the outputs of the pair of photodetectors at both positions are the same, it is determined that the optical axis deviation is outside the permissible optical axis deviation range. (3) In a semiconductor laser optical axis deviation measuring device for measuring the deviation between the center axis of the package and the optical axis, which is the light emission center axis of the semiconductor laser chip, in a semiconductor laser having a semiconductor laser chip fixed in the package, the semiconductor laser includes: means for holding the package of a laser chip; a pair of photodetectors fixed at a constant distance in a direction of optical axis deviation in a plane perpendicular to the central axis of the package; and the pair of photodetectors. An apparatus for measuring an optical axis deviation of a semiconductor laser, comprising: means for moving the optical axis in the direction of the desired optical axis deviation; and means for comparing outputs of the pair of photodetectors. (4) The device for measuring optical axis deviation of a semiconductor laser according to claim 3, wherein the pair of photodetectors has a slit or a pinball on the front surface. (5) The means for comparing the outputs of the pair of photodetectors includes a differential amplifier.
A device for measuring optical axis deviation of a semiconductor laser as described in 2. (6) means for moving the pair of photodetectors in the desired optical axis deviation direction to a position corresponding to the positive and negative maximum permissible values of the optical axis deviation angle of the semiconductor laser in the desired optical axis deviation direction; 4. The apparatus for measuring optical axis deviation of a semiconductor laser according to claim 3, further comprising a stopper for restricting movement of the pair of photodetectors.