JPH02205755A - Apparatus and method for measuring double refraction - Google Patents

Abstract

PURPOSE:To make it possible to measure the double refraction values of a double refraction member at many points in a short time highly accurately by inserting the double refraction member between a first polarizing plate and a second polarizing plate, inputting a bundle of rays into the second polarizing plate from the first polarizing plate, and moving the bundle of rays in the specified direction relatively. CONSTITUTION:A double refraction member 4 can be inserted between a first polarizing plate 1 and a second polarizing plate 2 which are set in a pattern wherein the polarizing directions are orthogonally intersected in a measuring apparatus 10. A bundle of rays in a radial pattern having the equal distribution of amounts of light is generated in concave lenses 7 and inputted into the second polarizing plate 2 from the first polarizing plate 1. A plurality of the concave lenses 7 are continuously arranged in the specified direction along the member 4. The incident light path of the incident bundle of rays 16 is switched to the side of the lenses 7 with a rotary mirror 17. The bundle of rays 16 is vertically inputted into the lenses 7 with correcting prisms 18. In this way, the bundle of rays is sequentially moved for every neighboring measuring point. The amount of the light after the light has been transmitted through the polarizing plate 2 is measured for every measuring point with a photoelectric transducer element train 12.

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.

Here, the birefringence value includes an in-plane birefringence value for a light ray that is perpendicularly incident on the surface of the birefringent member, and a thickness direction birefringence value for a light ray that is obliquely incident on the surface of the birefringent member.

The conventional method for measuring in-plane birefringence is called the Senarmont method, and is as follows: First, collimated laser light is transmitted through a polarizing plate to create linearly polarized light in the same direction as the polarizing direction of the polarizing plate. Linearly polarized light is transmitted at 45 degrees to the optical axis of the disk in the 0th order.

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 at this time. However, when this elliptically polarized light is then transmitted through a 174-wave plate, the plane of polarization is rotated and it 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, the in-plane birefringence value can be measured by making a light beam perpendicularly incident on the surface of the birefringent member and measuring the rotation angle with an analyzer.

In addition, the conventional method for measuring birefringence in the thickness direction is to make a light beam that is tilted at a certain angle with respect to the normal to the surface of the birefringent member enter the birefringent material all around, and to measure the maximum and minimum values of the birefringence obtained. The birefringence value in the thickness direction can be measured by substituting the angle of incidence into a complex retardation calculation formula.

[Lesson 1 that the invention attempts to solve! l! However, the conventional method for measuring in-plane birefringence 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) It is difficult to complete measurements in a short time for a large number of measurement points on a birefringent member.

Further, the method of measuring the birefringence value in the thickness direction using the conventional retardation calculation formula has the following problems (1) and (2).

■A large number of birefringence values at oblique incidence are measured, and more complex calculations are required, and the measurement time is long.

(2) It is difficult to complete measurements in a short time for a large number of measurement points on a birefringent member.

In addition, regardless of the measurement method using the conventional Senarmont method or the measurement method using the retardation calculation formula,
It is not possible to simultaneously measure both the in-plane birefringence value and the thickness direction birefringence value in one measurement operation.

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 simultaneously measure both the in-plane birefringence value and the thickness direction birefringence value by one measurement operation.

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. A bundle of light rays that can enter the radial bundle and have an equal light intensity distribution is incident from the first polarizing plate toward the second polarizing plate, and is relatively moved in a specific direction along the birefringent member, so that the rays constituting the radial bundle of rays are The birefringent member is configured to include an optical system that can measure the amount of light after passing through the second polarizing plate for each angle of incidence with respect to a certain measurement point of the birefringent member.

According to the second aspect of the present invention, a birefringent member can be inserted between a first polarizing plate and a second polarizing plate whose polarization directions are set to be orthogonal to each other, and a birefringent member can be inserted between a first polarizing plate and a second polarizing plate whose polarization directions are set to be orthogonal. The light rays constituting the radial ray bundle are made incident from one polarizing plate toward the second polarizing plate, and are relatively moved in a specific direction along the birefringent member, for each incident angle with respect to a certain measurement point of the birefringent member. An optical system that can measure the amount of light after passing through the second polarizing plate is configured, and the correlation between the measured value of the amount of light and the birefringence value for each angle of incidence in the optical system is determined in advance, and the object to be measured this time is The measurement point of the birefringent member can be determined from the above-mentioned light amount measurement value for each incident angle and the above-mentioned correlation about the measurement point of the birefringence member measured with the above-mentioned optical system in which the birefringence member is installed. This method is designed to calculate the birefringence value for .

The present invention according to claim 3 provides that the correlation between the light quantity measurement value and the birefringence value for each predetermined incident angle in the optical system is determined using the in-plane birefringence value and the thickness direction birefringence value as parameters, and this time The value of the birefringent member can be determined from the above-mentioned light intensity measurement value for each incident angle and the above-mentioned correlation at a certain measurement point of the birefringent member measured by the above-mentioned optical system in which the birefringent member as the measurement object is inserted. The in-plane birefringence value and the thickness-direction birefringence value for a measurement point are determined.

According to a fourth aspect of the present invention, both the radial ray bundle and the birefringent member are moved, and their moving directions are perpendicular to each other.

[Action] 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 a light source, first and second polarizing plates, and a light receiving device, a radial bundle of rays is incident from the first polarizing plate, and the birefringent member of the rays constituting this bundle of rays is The birefringence value of the birefringent member can be measured by a simple operation of measuring the amount of light after passing through the second polarizing plate for each incident angle with respect to a certain measurement point. 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).

■Since the correlation between the measured light amount and birefringence value for each incident angle was determined using the in-plane birefringence value and the thickness direction birefringence value as parameters, the measured light amount distribution for each incident angle, which is the measurement result, is compatible. By searching for the parameters,
Both the in-plane birefringence value and the thickness direction birefringence value can be measured simultaneously by one measurement operation.

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

■Measurement of the birefringence value, pronation birefringence value, and thickness direction birefringence value at each measurement point of the birefringent member into which the radial beam flux is incident is performed based on the movement path of the beam beam and the birefringence value that are orthogonal to each other. The birefringent member is sequentially moved to a plurality of measuring points determined on both sides of the movement path, and the birefringence values at multiple points within the plane of the birefringent member (for example, multiple points in the radial direction and circumferential direction of a magneto-optical disk) or within the plane are measured. Birefringence value and thickness direction birefringence value 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)
, (C), and (D).

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 the birefringent member 4 is inserted between the polarizing plates 2, the 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 is further transmitted to the second polarizing plate 2. 2
The light passes through 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.

Furthermore, when the incident light on the surface of the birefringent member 4 is incident obliquely than from the perpendicular direction, the amount of leaked light 6 and the birefringence value of the birefringent member 4 become larger, and the larger the incident angle Amount of leaked light 6 and birefringent member 4
The birefringence value increases (see FIG. 2(C)). The change in birefringence value due to the difference in incidence angle is determined by the in-plane birefringence value and the thickness direction birefringence value.

That is, in the present invention, the concave lens 7 as shown in FIG. The angles of incidence of each of the rays constituting the radial ray bundle on the birefringent member 4 are made different, and the changes in the amount of leaked light 6 corresponding to the rays with different angles of incidence are measured at each measurement point of the birefringent member 4. Memorize. As a result of this,
As shown in FIG. 2(D), at a certain measurement point of the birefringent member 4, it is possible to read the change in the light amount of the leaked light 6 corresponding to each of the above-mentioned rays, and as a result, the birefringence value for each incident angle and the in-plane This means that the birefringence value and the thickness direction birefringence value can be measured.

That is, as in the present invention as set forth in claim 2, (1) the correlation between the measured value of the light amount of the leaked light 6 and the birefringence value for each of the incident angles in the optical system consisting of the polarizing plate 1.2 is determined in advance. If it is determined, the light intensity measurement value for each incident angle at a certain measurement point of the birefringent member 4 measured by the optical system in which the birefringent member 4 to be measured this time is measured and the above correlation. From this, the birefringence value for each incident angle for the measurement point of the birefringent member 4 can be determined.

Further, as in the present invention as set forth in claim 3, (2) the correlation between the light quantity measurement value and the birefringence value at each predetermined incident angle in the optical system is determined by the in-plane birefringence value and the thickness direction birefringence value. is determined as a parameter, and the birefringence can be calculated from the above-mentioned light intensity measurement value for each incident angle and the above-mentioned correlation at a certain measurement point of the birefringent member 4 measured with the above-mentioned optical system in which the birefringent member 4 is installed this time. The in-plane birefringence value and the thickness direction birefringence value for the measurement point of the member 4 can be determined.

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 an optical disk, 7 is a concave lens as a light source, and 12 is a light receiving device. 13 is a rotation axis,
14 is a chuck, 15 is a motor, 16 is an incident beam bundle, 1
7 is a rotating mirror, and 18 is a correction prism.

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 measure the radial light intensity distribution generated by the concave lens 7. An equal flux of rays is transferred from the first polarizing plate 1 to the second polarizing plate 2.
second polarization of the light rays for each incident angle with respect to a certain measurement point of the birefringence member 4 of the light rays constituting the radial ray bundle; The amount of light after passing through the plate 2 can be measured by the photoelectric conversion element array 12.

Furthermore, the birefringence measuring device 10 arranges a plurality of concave lenses 7 in succession in a specific direction along the birefringence member 4 (for example, in the same radial direction of the magneto-optical disk), and rotates the rotating mirror 17 to change the incident optical path between adjacent concave lenses. The incident light beam 16 switched to the side of 7 is further made perpendicularly incident on the concave lens 7 by the correction prism 18, so that the concave lens 7
The radial light beam generated by the birefringent member 4 is relatively moved in the above-mentioned specific direction,
The adjacent measurement points are sequentially moved.

At this time, the photoelectric conversion elements constituting the photoelectric conversion element array 12 are arranged in a line corresponding to each of the continuously arranged fully concave lenses 7, and the incident angle of the light rays constituting the radial bundle of rays is Each time, the amount of light after passing through the second polarizing plate 2 is measured by the photoelectric conversion element array 12 at each measurement point of the birefringent member 4 and is stored in memory. As a result, as shown in FIG. 2(D), the birefringence measuring device 10 detects leakage light rays corresponding to each of the rays constituted by the radial ray bundle at a certain measurement point of the birefringence member 4. It is possible to read the change in the amount of light, and in turn, it is possible to measure the birefringence value for each incident angle, as well as the in-plane birefringence value and the thickness direction birefringence value.

At this time, in the birefringence measuring device 10, the polarizing plate 1
．． 2. The correlation between the measured light amount and the birefringence value for each angle of incidence in the optical system composed of the concave lens 7 and the photoelectric conversion element array 12 is determined in advance, for example, as shown in FIG. 3. Furthermore, this correlation is determined as a parameter for the in-plane birefringence value and the thickness direction birefringence value. The correlation shown in Figure 3 is the in-plane birefringence value Δn, y=23 nm,
The thickness direction birefringence value Δn = 354 ns is used as a parameter.

This correlation is based on birefringence for which the birefringence value for each incident angle, in-plane birefringence value, and thickness direction birefringence value are known using a conventional birefringence measurement method such as the Senarmont method. A photoelectric conversion element in which a member is inserted between a first polarizing plate 1 and a second polarizing plate 2, and the amount of leakage light 6 (see Fig. 2) transmitted through the second polarizing plate 2 at each incident angle is calculated. It is determined by measuring column 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, when the birefringence member 4 as the object of measurement is inserted into the optical system of the birefringence measurement device lo, the amount of leakage light 6 transmitted through the second polarizing plate 2 at each incident angle at a certain measurement point. From the correlation between this light amount measurement value and the above-mentioned FIG. You can find the value.

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 also moved in a direction perpendicular to the continuous arrangement direction of the concave lenses 7 (for example, in the circumferential direction of the magneto-optical disk). Repeating the light intensity measurement by the photoelectric conversion element array 12 at each point in the moving direction, at this time,
The switching speed at which the incident light beam 16 is moved in the direction of continuous arrangement of the concave lenses 7 by the rotation of the rotating mirror 17 is set to be considerably higher than the rotational speed of the rotating shaft 13. Thereby, for example, the birefringence value, in-plane birefringence value, and thickness direction birefringence value at each point in the circumferential direction of the magneto-optical disk can be continuously measured.

The birefringence measuring bag W10 collects the data of the light amount measurement value obtained for each measurement point of the birefringence member 4 at the position of the measurement point (for example, the radial direction and circumferential direction position of the magneto-optical disk).
The above-mentioned birefringence value, as well as the in-plane birefringence value and the thickness direction birefringence value can be determined by data processing by a microcomputer. Thereby, for example, the birefringence value, in-plane birefringence value, and thickness direction 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.

■Concave lens 7 and first and second polarizing plates 1.2 as light sources
Using an optical system configured with a photoelectric conversion element array 12, a radial light beam is incident from the first polarizing plate 1, and the light beams constituting this light beam are directed to a certain measurement point of the birefringent member 4. 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 for each incident angle. Therefore, using a simple device,
Birefringence values can be measured in a short time.

■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.

■Since the correlation between the measured light amount and birefringence value for each incident angle was determined using the in-plane birefringence value and the thickness direction birefringence value as parameters, the measured light amount distribution for each incident angle, which is the measurement result, is compatible. By searching for the parameters,
Both the in-plane birefringence value and the thickness direction birefringence value can be measured simultaneously by one measurement operation.

(2) Measurement of the birefringence value, in-plane birefringence value, and thickness direction birefringence value for each measurement point of the birefringent member 4 into which the radial light beam is incident is carried out along the movement path of the light beam and the birefringence value that are perpendicular to each other. The birefringence member 4 is sequentially moved to a plurality of measurement points determined on both sides of the movement path, and the birefringence values at multiple points in the plane of the birefringence member 4 (for example, multiple points in the radial direction and circumferential direction of the magneto-optical disk) are measured. Alternatively, the in-plane birefringence value and the thickness direction birefringence value can be measured in a short time.

In carrying out the present invention, a light source having a single wavelength, an equal output distribution, and a collimated light source is used.

In addition, it is desirable that the radiation range angle of the radial bundle of rays generated by a concave lens is 30 degrees. Setting the range to 30 degrees makes the difference in birefringence noticeable, and if the range is larger than this, the difference in birefringence will increase. This is because the refraction becomes too large, making it difficult to measure, or the desired light does not pass through in the correct amount due to reflection by the birefringent member, which may lead to inconveniences.

[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, both the in-plane birefringence value and the thickness direction birefringence value can be measured simultaneously by one measurement operation.

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... Birefringent member, 7... Concave lens (light source), 12... Photoelectric conversion element array, 13... Rotation axis , 17...Rotating mirror 18...Correction prism Patent applicant: Sekisui Chemical Co., Ltd. Representative Hiroshi 1) Kaoru Figure 2 (A) Figure 2 (B) Figure 2 (C) Yan Figure 2 ( D)

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 a radial beam having an equal light intensity distribution is incident from the first polarizing plate toward the second polarizing plate, and the birefringent member is relatively moved in a specific direction along the birefringent member. and the second of the rays constituting the radial ray bundle for each incident angle with respect to a certain measurement point of the birefringent member.
A birefringence measurement device that includes an optical system that can measure the amount of light after it passes through a polarizing plate. (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 a radial beam having an equal light intensity distribution is incident from the first polarizing plate toward the second polarizing plate, and the birefringent member is relatively moved in a specific direction along the birefringent member. and the second of the rays constituting the radial ray bundle for each incident angle with respect to a certain measurement point of the birefringent member.
An optical system capable of measuring the amount of light after passing through a polarizing plate is configured, and the correlation between the measured value of the amount of light and the birefringence value for each angle of incidence in the optical system is determined in advance, and the birefringence member as the object of measurement is determined in advance. The birefringence value for the measurement point of the birefringent member is determined from the above-mentioned light intensity measurement value for each incident angle and the above correlation, measured by the optical system containing the birefringence member at the measurement point. A method of measuring birefringence to determine the (3) The correlation between the light quantity measurement value and the birefringence value for each predetermined incident angle in the optical system is determined using the in-plane birefringence value and the thickness direction birefringence value as parameters, and the birefringent member as the measurement target this time The in-plane birefringence at the measuring point of the birefringent member is calculated from the above-mentioned light amount measurement value for each incident angle and the above correlation at a certain measuring point of the birefringent member measured by the optical system in which the birefringent member is loaded. 3. The method for measuring birefringence according to claim 2, wherein a refraction value and a thickness direction birefringence value are determined. (4) The birefringence measuring method according to claim 2 or 3, wherein both the radial light beam and the birefringence member are moved, and the directions of movement thereof are orthogonal to each other.