JPH03218440A - Birefringence measuring device - Google Patents

Abstract

PURPOSE:To simultaneously measure the direction and quantity of birefringence by providing a mechanism for rotating a transparent medium to be measured in accordance with the quantity of light receiving through a polarized light splitting means. CONSTITUTION:The linear polarized light emitted from a laser 11 is passed through the surface layer 13 of an optical card 12 as the transparent medium injected into the card 12 fixed to an optical card mount 14 and reflected. The polarization characteristic is changed in accordance with the birefringence quantity of the surface layer 13, and the light is then passed though a polarized beam splitter 15 and splitted into both polarized beams P and B which are received by polarized light detectors 18 and 19. The card 12 is rotated by a stepping motor 17 in accordance with the quantity of the former beam received. The direction of birefringence is measured from the angle of rotation, and the quantities of beams at their maximums received by the detectors 18 and 19 are then inputted to a computer 20 to calculate the birefringence quantity.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an apparatus for measuring birefringence of a surface transparent layer of polycarbonate or the like used in optical discs, optical cards, and the like.

BACKGROUND OF THE INVENTION In recent years, optical recording media such as optical disks and optical cards that can record large amounts of data have been attracting attention as an alternative to magnetic recording media. Such optical recording media are
In order to protect the recording surface from scratches and dust, it is covered with a transparent surface layer made of polycarbonate or other material with a thickness of several hundred microns to several millimeters. These transparent media such as polycarbonate are often made by injection molding to reduce costs.
Generally has birefringence. Therefore, in the production of optical recording media and the design of optical recording and reproducing devices, there is an increasing need to accurately measure the birefringence of such transparent media.

Conventionally, when measuring the birefringence of such a transparent medium, measurement has been carried out based on the deflection characteristics using a deflection beam meter.

The conventional birefringence measuring device is explained below. FIG. 7 is a configuration diagram of a conventional birefringence measuring device, in which 1 is a laser, 2 is an optical card, 3 is a surface layer of the optical card, 4 is a fixing table,
5 is a polarized beam splitter, 6 is an S polarization detector,
7 is a P polarization detector, and 8 is a meter.

The measurement method for the birefringence measuring device configured as described above will be explained below. First, take the light emitted from laser 1 to fixed base 4. The beam enters the measurement head of the light card 2 and is reflected at a certain angle. Although the light emitted from the laser 1 is linearly polarized, it undergoes birefringence when passing through the surface layer 3 of the optical card, so the light reflected by the optical card 3 becomes elliptically polarized. Next, the angle of the fixing table 4 is adjusted so that this elliptically polarized light is incident on the polarized beam splitter 5.

As shown in FIG. 8, the elliptically polarized light emitted from the surface layer of the optical card is split into S-polarized light and P-polarized light by a polarized beam splitter 5, and the amount of light is detected by an S-polarized light detector 6 and a P-polarized light detector 7, respectively.

Also, when the respective received light amounts PA, P■ are converted into electrical signals and inputted to the calculator 8, the summer meter 8 receives the PA, P. The amount of birefringence (phase difference) φ of the surface layer 4 of the optical card is determined by the following calculation formula, and the amount of birefringence of the surface layer 4 of the optical card is measured.

Problems to be Solved by the Invention However, in the conventional configuration described above, the optical card to be measured remains fixed to a fixed stand, so only the amount of birefringence, which originally has vector characteristics of direction and amount, can be measured. Can not. Therefore, it is only possible to measure the amount of birefringence in transparent media whose direction of birefringence varies uniformly, and it is not possible to measure the amount of birefringence in transparent media where the direction of birefringence does not vary, such as polycarbonate made by injection molding. I had an issue.

The present invention solves the above-mentioned conventional problems, and allows simultaneous measurement of the direction and amount of birefringence even in transparent media where the variation in the direction of birefringence is not uniform. The object of the present invention is to provide a J refraction measuring device.

Means for Solving the Problems In order to achieve this object, the birefringence measurement device of the present invention has the following features:
It is characterized by having a mechanism for rotating a transparent medium to be measured with respect to the polarization separation means, and configured to rotate the transparent medium in accordance with the amount of light that passes through the polarization separation means and is received by the light reception means. It is something.

Function: With this configuration, the direction of birefringence of the transparent medium can be matched with the polarization direction of the light emitting means, and the direction and amount of birefringence of the transparent medium can be measured simultaneously.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings.

The first part shows a configuration diagram of a birefringence measurement apparatus according to a first embodiment of the present invention.

In FIG. 1, numeral 11 indicates a laser which is a light emitting means, and the laser 11 emits linearly polarized light. This linearly polarized light passes through the surface layer 13 of the optical card 12, which is a transparent medium, and enters the optical card 12 mounted on the optical card mount l4. As shown in FIG. 2, the optical card mounting base 14 is
The rotary table 15, which is composed of a rotary table 22 and a fixed table 16, and an optical card l2 is attached to the fixed table 16 by a stenting motor 17, is configured to rotate around the axis of the stevening motor 17. There is. An angle scale indicating the rotation angle of the rotary table 22 is attached to the circular fixed table l6. Emitted from laser l1 and optical card l2
The incident light is incident on the rotation center of the optical card mount l5, is reflected by the optical card 12, and is then incident on the polarized beam splitter 15 through the surface layer 13 of the optical card. . The light incident on the polarized beam splitter 15 is divided into S-polarized light, that is, reflected light, and P-polarized light, that is, transmitted light, depending on the polarization characteristics, and enters the light receiving means of the S-polarized light detector 18 and the P-polarized light detector 19, respectively. The amount of light received by each detector 18, 19 is input to the calculator 20 as an electrical signal. Also, the amount of light received by the S-polarized light detector 18 is
The signal is input as an electric signal to the motor control circuit 21 and is configured to drive the stenobing motor 17.

The operation of measuring the direction and amount of birefringence of the surface layer 13 of an optical card using the birefringence measurement apparatus configured as described above will be described.

The light emitted from the laser 11 is linearly polarized light, which enters the optical card 12 through the surface layer 13 of the optical card, is reflected by the optical card l2, and returns to the surface layer l3 of the optical card.
As shown in FIG. 8, when the light is emitted through the optical cart, the polarization characteristics change by an amount corresponding to the amount of birefringence of the surface layer with respect to the direction of birefringence of the surface layer l3 of the optical cart, and the light becomes elliptically polarized light. Become.

After this elliptically polarized light passes through the polarized beam splitter 15, it is separated into an S-polarized light component and a P-polarized light component.
The S-polarized light component and the p-polarized light component in FIG.
The light is received by

The amount of light received by the S-polarized light detector 18 is input as an electrical signal to the motor control circuit 21, and the stevening motor 17 is driven according to the amount of light received by the S-polarized light detector 18, thereby rotating the optical card 12. That is, as shown in FIG. 3, the output of the S-polarized light detector 18 at the position after the pulse is applied to the stenobing motor l7 becomes smaller than the output before the pulse is applied until the output of the S-polarized light detector 18 reaches the minimum value. Apply a positive or negative pulse signal to
When the difference between the output of the S-polarized light detector 18 at the position before the pulse application and the output after the pulse application reaches Ov, the rotation of the stenobing motor 17 is stopped. The stenoping motor 17 generates positive pulses in the direction of the arrow in FIG.
Each is rotated by a negative pulse.

At this time, the direction of birefringence of the surface layer 13 of the optical card is aligned with the direction of deflection of the laser 11, as shown in FIG. That is, the amount of birefringence experienced by the linearly polarized light emitted by the laser 11 decreases as the direction of birefringence of the surface layer 13 of the optical card approaches the polarization direction of the laser beam, and when they completely match, the birefringence is no longer experienced. . At this time, the amount of light received by the S-polarized light detector 18 shows a minimum value. At this time, by reading the angle scale on the fixing base 16 of the optical card mounting base 14, the surface layer l2 of the optical card can be determined.
It is possible to measure the direction of birefringence of.

After measuring the direction, the polarity of the motor control circuit 2l is switched, and as shown in FIG. A positive or negative pulse is applied so that the output of the S-polarized light detector l8 at the position becomes larger than the output before application.

3 When the amount of light received by the polarization detector l8 increases,
As before, the optical cart mount 14 stops.

At this time, the amount of light received by the 3-polarization detector 18 and the p-polarization detector 19 is determined by P. & and P, the calculator 20
When input as an electrical signal, the calculator 20 calculates the amount of birefringence φ by calculating 1+a P, P.

At this time, as shown in FIG. 6, the linearly polarized light incident on the surface layer of the optical card is inclined at 45 degrees with respect to the direction of birefringence of the surface layer l3 of the optical card, and φ in the above calculation is It accurately represents the amount of birefringence of the layer.

Note that in this example, the light emitted from the laser was incident on the transparent medium before passing through the deflection beam subunit; however, the light emitted from the laser was incident on the transparent medium after passing through the deflection beam subunit, and then passed through the mirror. Alternatively, the reflected light may be incident on the deflection beam converter again. Also,
The surface layer of the optical cart was used as the transparent medium, but a combination of a transparent medium and a mirror may also be used. Of course, only a transparent medium can be used to allow the light emitted from the laser to pass through the transparent medium only once and be deflected without being reflected. It may also be configured such that the light enters the beam splinter and the transmitted light and reflected light of the deflected beam splitter are received by respective detectors.

Effects of the Invention As described above, the present invention rotates a transparent medium according to the amount of reflected light from a deflection beam splinter.
The direction and amount of birefringence of a transparent medium can be measured simultaneously.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a birefringence measuring device according to the first embodiment of the present invention, FIG. 2 is a perspective view of the configuration of an optical card mount in the same device, and FIGS. 3 and 5 are stamping diagrams in the same device. A characteristic diagram showing the pulse applied to the motor, Figure 4 is a theoretical diagram showing the state of biasing, which measures the direction of birefringence.
Fig. 6 is a theoretical diagram showing the state of polarization when determining the amount of birefringence, Fig. 7 is a configuration diagram of a conventional birefringence measurement device, and Fig. 8
The figure is a theoretical diagram showing how linearly polarized light changes to elliptically polarized light due to birefringence of a transparent medium. 11...Laser, l3...Surface layer of optical card, l5 Deflection beam splinter, 16...
・Fixed stand, 18...S polarization detector, l9
...P polarization detector 22 ... Rotating table.

Claims (1)

[Claims] a light emitting means, a polarized light separating means, a light receiving means, and the light emitted from the light emitting means is incident on a transparent medium, and the light transmitted through the transparent medium and the polarized light separating means is received by the light receiving means according to the amount of light. , means for rotating the transparent medium relative to the polarization separation means.