JPH0835881A - Device for measuring shape of light beam - Google Patents

Abstract

PURPOSE:To provide a three dimensional light beam shape measuring device capable of measuring not only the shape of a light beam from a measuring light device on an X-Y plane but also the focal distance and astigmatism in the traveling derection of the light beam. CONSTITUTION:Constituted are of a scanning means 26 for moving a photoconductor 21 having electrodes 23, 24 constituted on a InP base in a direction perpendicular to a light beam 11, a scanning means 6 for moving in the traveling direction of the light beam 11, a resistance measuring means 27 for measuring the resistance between a pair of electrodes 23, 24, a converter means 28 for converting the resistance value to light intensity, and a display means 35 after obtaining the diameter of the light beam 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention measures the diameter and shape of a light beam such as a recording detection light beam of a compact disc recorder and an output light beam of an optical fiber collimator used for various optical components. The present invention also relates to a light beam shape measuring instrument capable of measuring focal length, astigmatism, and the like.

[0002]

2. Description of the Related Art The present applicant has previously filed Japanese Patent Application No. 5-19045.
0 "Light beam shape measuring instrument" (filing date: July 30, 1993)
(JP), a light beam shape measuring instrument on an XY plane using a photoconductor (photoconductor) as a photoelectric conversion element was disclosed. The present invention uses this to accurately measure not only on the XY plane but also on the Z axis, that is, the focal length and astigmatism in the vertical axis direction with good resolution.

Conventionally, in measuring the diameter of a light beam, FIG.
As shown in FIG.
Light receiving element 13 such as a photodiode that passes through 2
The slit 12 is moved in the direction perpendicular to the light beam 11, the output of the light receiving element 13 is measured for each unit movement, and the light beam is output from the state of the output level of the light receiving element 13 with respect to the movement of the slit 12. The light intensity shape of the cross section of 11 is measured.

As described above, since the slit 12 is conventionally moved, there is always a gap D between the slit 12 and the light receiving element 13, and the gap D is about several mm. When the width W of the slit 12 is reduced to increase the resolution, the diffraction effect of the slit 12 becomes large, and the light passing through the slit 12 spreads and reaches the light receiving element 13, as shown in FIG. 4B. The intensity of the light passing through the slit 12 cannot be measured correctly. On the other hand, if the width W of the slit 12 is widened, the spread due to the diffraction effect is reduced,
Since the slit width is wide, the measurement resolution is reduced.

[0005]

[Patent Document 1] Japanese Patent Application No. 5-19
In 0450, a photoconductor having a pair of electrodes formed at intervals smaller than the diameter of the light beam to be measured is provided on the light receiving surface, and the light beam to be measured is made incident on the light receiving surface of the photoconductor. The photoconductor and the photoconductor are moved by the scanning means in the arrangement direction of the electrodes, that is, in the direction perpendicular to the light beam to be measured. The resistance value between the electrodes at that time is measured by a resistance measuring means, the measured resistance value is converted into light intensity, and the diameter of the light beam to be measured is obtained from the change of the converted light intensity based on the movement. The result is displayed.

The light beam shape measuring instrument using the above photoconductor has a higher resolution than the conventional one and can measure the light beam with high accuracy, but it considers only the XY plane, and the Z axis, that is, It was not possible to measure the focal length or astigmatism. This invention measures the focal length and astigmatism of an optical device to be measured that generates a light beam.

[0007]

In order to achieve the above object, the present invention uses a light beam shape measuring instrument using a photoconductor described in Japanese Patent Application No. 5-190450 and uses the light beam traveling direction, that is, Z direction. A Z stage that moves back and forth in the axial direction is provided, an optical device to be measured is mounted on the Z stage, and the optical device to be measured on the Z stage is moved along the Z axis to determine the shape of the light beam at each point. It is what is measured and displayed.

That is, a control signal from the control unit of the light beam shape measuring instrument is applied to the step motor, and the measured optical device is moved by the step motor in the Z-axis direction at every minute interval. The diameter of the beam is measured and displayed. The shorter the distance of this step movement and the larger the number of samplings, the higher the resolution. Examples of the present invention will be described below.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is data and drawings of measurement results when an optical device to be measured on a Z stage is moved, and FIG. The shape figure of is shown. The light beam shape measuring instrument of the present invention will be described with reference to FIG. As shown in FIG. 1B, the photoconductor 21 has an electrode portion (23, 24) formed of a metal film on an Fe-doped InP substrate. The electrode structure has an electrode width L of about 400 μm. And the gap width W is about 3μ
m counter electrode. When light enters the electrode gap, the electrode portion is electrically conducted, and a resistance value corresponding to the amount of light is generated.

This resistance value is measured by the resistance measuring section 27 shown in FIG. Since the resistance value is inversely proportional to the optical power, the reciprocal of the resistance value can be used as the relative value of the light intensity, so that the intensity conversion unit 28 converts it into the light intensity. Therefore, the photoconductor 21 is connected to the X stage 25.
Then, the stepper motor 26 is moved in a direction perpendicular to the light beam 11 and the light intensity is measured for each movement to obtain the shape of the light beam.

The electrode shape correction unit 29 performs a calculation for obtaining the correct intensity characteristic of the light beam 11. That is, the intensity distribution of the light beam 11 is usually a Gaussian distribution, and the function f (x,
y). In addition, the interval shape of the electrodes of the photoconductor 21 is represented by a function g (x, y). When the electrode of the photoconductor 21 scans the irradiation point of the light beam 11, the output waveform at that time is expressed by the following equation.

∫∫f (τ, σ) g (x−τ, y−σ) dτdσ The integral is from −infinity to + infinity, that is, f (x, y) and g (x, y) are convoluted. The result is John. Therefore, when the output of the intensity conversion unit 28 is deconvoluted by g (x, y) in the electrode shape correction unit 29, the correct intensity characteristic of the light beam can be obtained.
This deconvolution may be based on the Gauss-Seidel method, for example.

The peak of the output waveform of the electrode shape correction unit 29
The diameter of the light beam may be determined from the width of 1 / e2 of the beam.
However, the output waveform is often relatively wavy due to distortion of the lens or the like. Therefore, this waveform is calculated by the Gaussian fit calculation unit 32 to form a smooth Gaussian function curve, and the width at the 1 / e2 of the peak of the corrected curve is calculated by the beam diameter calculation unit 34, and the value is calculated. The measurement light beam diameter is displayed on the display unit 35. In addition to this, various kinds of waveforms and numerical values relating to the measurement can be displayed on the display unit 35. With the above procedure, the light beam shape can be measured on the XY plane.

Next, the measurement in the Z-axis direction will be described. The light beam 11 is emitted right above the photoconductor 21 from the Z-axis direction. Therefore, in order to measure the focal length, astigmatism, etc. of the optical device to be measured 1, the optical device to be measured 1 is moved in small intervals on the Z axis, and the light beam diameter is measured at each point. indicate. The display includes a data diagram as shown in FIG. 2 (A) and a graph diagram as shown in FIG. 2 (B).

For this purpose, the Z stage 5 is provided directly above the photoconductor 21 of FIG.
The optical device 1 to be measured is mounted on, and the step motor 6 is driven by the control signal from the control unit 36, and the optical device 1 to be measured on the Z stage 5 is moved along the Z axis by driving the step motor 6. . Then, the diameter of the light beam 11 is measured for each movement.

The measurement resolution is considered to be about 5 μm because the electrode gap width is about 3 μm as described above. Figure 2
Shows an example of the measurement result. 2A and 2B that the measured optical device 1 has a focal length of 5.45 mm and the diameter of the light beam 11 at that time is 20.0 μm. This improvement in measurement resolution can be realized by narrowing the gap between the electrodes of the photoconductor 21. Since the on-resistance is inversely proportional to the square of the gap width, it is possible to realize high-sensitivity and high-resolution measurement without lowering the sensitivity accompanying the narrowing of the gap.

FIG. 3 shows the shape of the light beam measured by this light beam shape measuring instrument. The light beam diameter is as small as 6.3 μm. .

[0018]

As described above, according to the present invention, not only the shape of the light beam 11 from the measured optical device 1 but also the
The focal length and astigmatism can also be measured, that is, the light beam
It can be measured in two dimensions, and the resolution is significantly improved compared to the conventional one, and its technical effect is great.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention, and FIG.
Is an overall configuration diagram, and FIG.
FIG.

FIG. 2 is a diagram of a measurement result by the light beam measuring device of the present invention, FIG. 2 (A) is a diagram of measurement data, and FIG.
[Fig. 4] is a graph of measurement data.

FIG. 3 is a diagram of a light beam diameter as a measurement result by the light beam measuring device of the present invention.

FIG. 4 is a diagram showing a conventional measurement method.

[Explanation of symbols]

 1 Optical device to be measured 5 Z stage 6 Step motor 11 Light beam 21 Photoconductor 22 Light receiving surface 23, 24 Electrode 25 X stage 26 Step motor 27 Resistance measuring unit 28 Intensity converting unit 29 Electrode shape correcting unit 32 Gaussian fit computing unit 34 Beam Diameter calculation unit 35 Display unit 36 Control unit

Claims (2)

[Claims] 1. A photoconductor (21) having a pair of electrodes formed on a light receiving surface at an interval smaller than a diameter of a light beam (11) from an optical device under test (1), and the photoconductor (21). Scanning means for moving the incident point in the arrangement direction of the pair of electrodes in a state where the light beam (11) is incident on the light receiving surface of the light beam, and the light beam (11) on the light receiving surface of the photoconductor (21). Scanning means for moving the measured optical device (1) forward and backward in the traveling direction of the optical beam (11), and resistance measuring means for measuring the resistance value between the pair of electrodes. A conversion means for converting the measured resistance value into light intensity; and a change in the converted light intensity due to movement in the traveling direction of the light beam (11) and movement in the arrangement direction of the electrodes, the optical device to be measured. The light beam from the 1) (1
A means for obtaining and displaying the diameter of 1), and a light beam shape measuring instrument. . 2. The light beam shape measuring instrument according to claim 1, wherein the photoconductor (21) is composed of a pair of electrodes facing each other at a minute interval with a metal film on the InP substrate.