JPH02205754A - Apparatus and method for measuring double refraction - Google Patents

Abstract

PURPOSE:To make it possible to measure a double refraction value in a short time highly accurately by inserting a double refraction member between a first polarizing plate and a second polarizing plate which are provided in such a way that the polarizing directions of the plates are orthogonally intersected, and measuring the amount of light after the transmission through the second polarizing plate. CONSTITUTION:In a double refraction measuring apparatus 10, a double refraction member 4 can be inserted between a first polarizing plate 1 and a second polarizing plate 2 which are set at a pattern wherein the polarizing directions are orthogonally intersected. Collimated light rays which are emitted from a laser diode train 11 are vertically inputted into the second polarizing plate 2 from the first polarizing plate 1. The amount of the light rays after the light rays have been transmitted through the second polarizing plate 2 can be measured with photoelectric transducer element train 12. The correlation between the measured value of the amount of light and the double refraction value in the optical system that is composed of the polarizing plates 1 and 2, the diode train 11 and the element line 12 is determined by using a double refraction member whose double refraction value is known beforehand. When the double refraction member 4 as an object to be measured is inserted and the amount of leaking light which has been transmitted through the polarizing plate 2 is measured, the double refraction value can be obtained.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a birefringence measuring device and method.

[Prior Art] Conventionally, for example, in the manufacturing process of magneto-optical disks, it has been necessary to reduce the birefringence value, which is a factor that deteriorates the signal-to-noise ratio (SN ratio), which is an evaluation item of the disk. It is desired to establish a method for measuring this value.

The conventional method for measuring birefringence is called the Senarmont method, and is as follows. First, the collimated laser light is transmitted through a polarizing plate, and the linearly polarized light is transmitted at an angle of 45 degrees to the optical axis of the 0th-order disk to produce linearly polarized light in the same direction as the polarization direction of the polarizing plate. At this time, the linearly polarized light becomes elliptically polarized light due to the influence of the birefringence of the disk, but the plane of polarization of the elliptically polarized light does not rotate.However, when this elliptically polarized light is transmitted through a 174-wave plate, the plane of polarization changes. It rotates and becomes linearly polarized light again.

This rotation angle changes depending on the magnitude of birefringence, and the larger the birefringence, the larger the rotation angle. Therefore, by measuring the rotation angle with an analyzer, the birefringence value can be measured.

[Problems to be Solved by the Invention] However, the conventional birefringence measuring method using the Senarmont method has the following problems (1) to (4).

■It is necessary to rotate the analyzer for each measurement point of the birefringent member, which requires complicated equipment and takes a long time to measure.

■Since it amplifies and clarifies the light intensity distribution of linearly polarized light measured by an analyzer, measurement errors are likely to occur.

(2) The analyzer can only measure one point at a time, and cannot measure multiple measurement points simultaneously, making it difficult to complete measurements over the entire surface of a birefringent member in a short period of time.

An object of the present invention is to measure the birefringence value of a birefringent member in a short time and with high precision using a simple device.

Another object of the present invention is to measure birefringence values at multiple points of a birefringent member in a short time.

[Means for Solving the Problems] The birefringence measurement device of the present invention according to claim 1 includes a birefringence member installed between a first polarizing plate and a second polarizing plate whose polarization directions are set to be perpendicular to each other. an optical system capable of vertically entering a collimated light beam from a first polarizing plate toward a second polarizing plate and measuring the amount of light after the light beam passes through the second polarizing plate. This is how it was done.

According to the second aspect of the present invention, a birefringent member can be inserted between the first polarizing plate and the second polarizing plate whose polarization directions are set to be orthogonal, and the collimated light beam is transferred from the first polarizing plate to the second polarizing plate. An optical system is configured that allows the light beam to be incident perpendicularly toward a second polarizing plate and measures the amount of light after passing through the second polarizing plate, and the correlation between the measured light amount value and the birefringence value in the optical system is determined. The measurement of the birefringent member is determined in advance and is based on the above-mentioned light intensity measurement value at a measurement point of the birefringent member measured by the above-mentioned optical system in which the birefringent member to be measured is inserted, and the above-mentioned correlation. This method calculates the birefringence value for a point.

The present invention according to claim 3 uses a laser diode array in which a plurality of laser diodes are arranged in a line as the light amount of the optical system, and as a light receiving device of the optical system, a plurality of laser diode arrays are used as the light receiving device of the optical system. Using a photoelectric conversion element array in which photoelectric conversion elements are arranged in a row, the light amount is simultaneously measured at a plurality of measurement points on the birefringent member.

The present invention as set forth in claim 4 is characterized in that the birefringent member is moved relative to the line-shaped beam bundle emitted by the laser diode array in a direction perpendicular to the beam, and the amount of light at a plurality of measurement points of the birefringent member is simultaneously adjusted. The measurement operation is performed continuously within the plane of the birefringent member.

[Function] According to the present invention as set forth in claim 1.2, there are the following effects (1) and (2).

■Using an optical system consisting of light intensity, first and second polarizing plates, and a light receiving device, a collimated light beam is incident from the first polarizing plate, and after this light beam passes through the second polarizing plate, The birefringence value of a birefringent member can be measured by simply measuring the amount of light. Therefore, birefringence values can be measured in a short time using a simple device.

■Since the birefringence value is determined by measuring the amount of light,
Birefringence values can be measured with higher accuracy than the Senarmont method, which measures light intensity distribution.

According to the present invention as set forth in claim 3, there is the following effect (2).

■By using a laser diode array and a photoelectric conversion element array, the second
The amount of light transmitted through the polarizing plate can be measured simultaneously, and the birefringence values at multiple measurement points can be measured in a short time.

According to the present invention as set forth in claim 4, there is the following effect (2).

(2) By using a laser diode array and a photoelectric conversion element array, and further moving a birefringent member in a direction perpendicular to the linear beam emitted by the laser diode array,
The operation of simultaneously measuring the amount of light at a plurality of measurement points in (2) above is made continuous within the plane of the birefringent member.

Therefore, the birefringence values at multiple points of the birefringent member can be measured in a short time.

[Example] Fig. 1 is a schematic diagram showing an example of the present invention, Fig. 2 is a schematic diagram showing the principle of the present invention, and Fig. 3 is a diagram showing the relationship between the measured light amount and the birefringence value in the present invention. It is a line diagram.

First, regarding the principle behind the establishment of the present invention, Fig. 2 (A) and (B)
Explain with reference to.

As shown in FIG. 2(A), a pair of first and second polarizing plates 1
．． 2 polarization directions IA and 2A are set to be perpendicular to each other,
The collimated light beam is passed from the first polarizing plate 1 to the second polarizing plate 2.
Make the light incident perpendicularly to the target. At this time, the first polarizing plate 1
The incident light oscillates in multiple directions like natural light, and is polarized by the first polarizing plate 1 to produce linearly polarized light 3, but this linearly polarized light 3 does not pass through the second polarizing plate 2.

However, as shown in FIG. 2(B), the first polarizing plate 1 and the second polarizing plate
When a birefringent member 4 is inserted between the polarizing plates 2, linearly polarized light 3 polarized by the first polarizing plate 1 passes through the birefringent member 4 and becomes elliptically polarized light 5, and a part of the elliptically polarized light 5 becomes second polarized light. The light passes through the plate 2 and becomes leaked light 6. The amount of this leaked light 6 changes depending on the magnitude of the birefringence value of the birefringent member 4, and increases as the birefringence value increases.

Therefore, as in the present invention, if the correlation between the measured value of the light amount of the leaked light 6 and the birefringence value in the optical system consisting of the polarizing plate 1.2 is determined in advance, the birefringent member 4 as the object of measurement this time can be The birefringence value of the birefringent member at the measurement point can be determined from the current measurement value of the amount of leaked light 6 at the measurement point measured by the optical system in which the birefringence member is inserted and the above correlation.

Next, one embodiment of the present invention will be described with reference to FIG.

In FIG. 1, 10 is a birefringence measuring device, 1 is a first polarizing plate, 2 is a second polarizing plate, 4 is a birefringent member such as a magneto-optical disk, 11 is a laser diode array that constitutes the amount of light,
12 is a photoelectric conversion element array such as a line CCD constituting the light receiving device; 13 is a rotating shaft; 14 is a chuck; and 15 is a motor.

The birefringence measurement device 10 can insert a birefringence member 4 between a first polarizing plate 1 and a second polarizing plate 2 whose polarization directions are set to be orthogonal, and can measure the collimated light beams emitted by the laser diode array 11. The light beam is made perpendicularly incident from the first polarizing plate 1 toward the second polarizing plate 2, and the amount of light after passing through the second polarizing plate 2 can be measured by the photoelectric conversion element array 12.

At this time, in the birefringence measuring device 10, the polarizing plate 1
．． 2. Laser diode row 11, photoelectric conversion element row 12
The correlation between the light amount measurement value and the birefringence value in the optical system composed of the above is determined in advance, for example, as shown in FIG. 3.

Note that this correlation can be obtained by mounting a birefringent member whose birefringence value is known between the first polarizing plate 1 and the second polarizing plate 2 using a conventional birefringence measuring method such as the Senarmont method. It is determined by measuring the amount of leaked light 6 (see FIG. 2) transmitted through the second polarizing plate 2 at that time using the photoelectric conversion element array 12. At this time, the photoelectric conversion element array 12 photoelectrically converts the amount of received light and displays it as a voltage. The larger the output voltage of the photoelectric conversion element array 12, the larger the birefringence value.

Therefore, if the birefringence member 4 to be measured this time is inserted into the optical system of the birefringence measuring device 10 and the amount of leaked light 6 transmitted through the second polarizing plate 2 is measured, this light amount measurement value can be obtained. The birefringence value of the birefringent member 4 can be determined from the correlation shown in FIG.

Further, the birefringence measuring device 10 uses a laser diode array 11 in which a plurality of laser diodes are arranged in a line as the light amount of its optical system, and uses a plurality of laser diode arrays 11 as light receiving devices of the optical system to correspond to the laser diode array 11. By using a photoelectric conversion element array 12 in which photoelectric conversion elements of It is possible to measure the amount of light at the same time. This makes it possible to instantaneously measure all birefringence values at each point in the radial direction of the magneto-optical disk, for example.

The birefringence measurement device 10 also uses a chuck 14 to hold the birefringence member 4 (for example, the center of a magneto-optical disk) on the rotating shaft 1.
3 and by rotating this rotating shaft 13 with a motor 15, the birefringent member 4 is rotated in a direction perpendicular to the linear beam flux emitted by the laser diode array 11 (for example, in the circumferential direction of the magneto-optical disk). , the photoelectric conversion element array 12 can continuously measure the amount of light at a plurality of measurement points of the birefringent member 4 within the plane of the birefringent member 4 .

The birefringence measuring device 10 uses the data of the light intensity measurement value obtained for each measurement point of the birefringence member 4 as the position of the measurement point (for example, the radial and circumferential position of the magneto-optical disk).
The above-mentioned birefringence value can be obtained through data processing by a microcomputer. Thereby, for example, the birefringence value of the entire surface of the magneto-optical disk can be measured in a short time, and abnormal points can be easily found.

Next, the operation of the above embodiment will be explained.

■Laser diode array 11 and first and second polarizing plates 1.
2 and a photoelectric conversion element array 12, a collimated light beam is incident from the first polarizing plate 1,
The birefringence value of the birefringent member 4 can be measured by a simple operation of measuring the amount of light after passing through the second polarizing plate 2. Therefore, birefringence values can be measured in a short time using a simple device.

■Since the birefringence value is determined by measuring the amount of light,
Birefringence values can be measured with higher accuracy than the Senarmont method, which measures light intensity distribution.

■By using the laser diode array 11 and the photoelectric conversion element array 12, the light transmitted through the second polarizing plate 2 is measured at a plurality of measurement points of the birefringent member 4 corresponding to the laser diode array 11 and the photoelectric conversion element array 12. The subsequent light intensity can be measured simultaneously, and birefringence values at multiple measurement points can be measured in a short time.

(2) Using a laser diode array 11 and a photoelectric conversion element array 12, a birefringent member 4 is further attached to the laser diode array 11.
By moving relative to the direction perpendicular to the line-shaped light beam emitted by the birefringent member 4, the simultaneous measurement operation of the light amount at a plurality of measurement points in (2) above is made continuous within the plane of the birefringent member 4. Therefore, the birefringence values at multiple points of the birefringent member 4 can be measured in a short time.

In addition, in implementing the present invention, the amount of light may be made of, for example, a single laser diode that emits a single beam of light.

Further, in carrying out the present invention, the birefringent member is not rotated relative to the collimated light beam, but is moved linearly, so that the measurement point on the birefringent member is continuously expanded. Furthermore, in carrying out the present invention, any other device other than a laser diode may be used as long as the amount of light is the same and the wavelength is the same at each arbitrary point in the direction in which the light ray travels.

[Effects of the Invention] As described above, according to the present invention, the birefringence value of a birefringent member can be measured in a short time and with high precision using a simple device.

Further, according to the present invention, birefringence values at multiple points of a birefringent member can be measured in a short time.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing an embodiment of the present invention, Fig. 2 is a schematic diagram showing the principle of the invention, and Fig. 3 is a diagram showing the relationship between the measured light amount and the birefringence value in the present invention. . DESCRIPTION OF SYMBOLS 1... First polarizing plate, 2... Second polarizing plate, 4... Birefringence member, 10... Birefringence measuring device, 11... Laser diode row, 12... Photoelectric conversion element Column 13...Rotation axis. Patent applicant Sekisui Chemical Co., Ltd. Representative Hiroshi 1) Kaoru Figure 1 Figure 3 Light intensity measurement value (mv)

Claims (4)

[Claims] (1) A first polarizing plate and a second polarizing plate whose polarization directions are orthogonal to each other.
A birefringent member can be inserted between the polarizing plate and the collimated light beam is made perpendicularly incident from the first polarizing plate to the second polarizing plate, and the amount of light after passing through the second polarizing plate is calculated. A birefringence measurement device that includes an optical system that can perform measurements. (2) A first polarizing plate and a second polarizing plate whose polarization directions are orthogonal to each other.
A birefringent member can be inserted between the polarizing plate and the collimated light beam is made perpendicularly incident from the first polarizing plate to the second polarizing plate, and the amount of light after passing through the second polarizing plate is calculated. An optical system capable of measurement is configured, a correlation between the light amount measurement value and the birefringence value in the optical system is determined in advance, and the birefringence value measured by the optical system in which the birefringence member to be measured is inserted is determined in advance. A birefringence measuring method for determining a birefringence value at a certain measuring point of the birefringent member from the above-mentioned light intensity measurement value and the above-mentioned correlation for the certain measuring point of the refractive member. (3) A laser diode array in which a plurality of laser diodes are arranged in a line is used as the light amount of the optical system, and a plurality of photoelectric conversion elements are arranged in a line so as to correspond to the laser diode array as the light receiving device of the optical system. 3. The birefringence measurement method according to claim 2, wherein the light amount is simultaneously measured at a plurality of measurement points of the birefringence member using a photoelectric conversion element array. (4) The birefringence member is moved relative to the line-shaped beam flux emitted by the laser diode array in a direction perpendicular to the line-shaped beam, and the simultaneous measurement operation of the light amount at a plurality of measurement points of the birefringence member is performed. 4. The method for measuring birefringence according to claim 3, wherein the birefringence measurement method is carried out continuously within the plane of the member.