JPH03221842A - Double refraction measuring instrument - Google Patents

Abstract

PURPOSE:To simultaneously measure the direction and the quantity of double refraction even concerning a transparent medium in which the variance of the directions of the double refraction is not uniform by constituting a device so that the double refraction quantity of a double refraction variable means may be changed in accordance with the received light quantity while the transparent medium which is a measured object is rotated with reference to an emitted light and polarized light separation means. CONSTITUTION:Linearly polarized light projected from a laser 11 passes the surface layer 13 of an optical card 12 which is the transparent medium and is reflected by the optical card 12 to pass through the surface layer 13 again. It becomes elliptically polarized light because its deflection characteristic is changed in accordance with the direction and the quantity of the double refraction of the layer 13 and is adjusted by a Babinet-Soleil compensator 23 so that the s-polarized light component may be maximum, then it becomes the linearly s-polarized light at a point where the double refraction direction of the surface layer 13 and the crystal axis of the compensator 23 coincide with each other. At such a time, the direction and the quantity of the double refraction of the surface layer 13 are measured based on the rotational angle of a turntable 22 and the crystal axis direction of the compensator 23 and based on the double refraction adjusting quantity known from the moving scale of a 2nd stepping motor 24 respectively.

Description

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

2. Description of the Related Art In recent years, optical recording media such as optical disks and optical cards capable of recording large amounts of data have been attracting attention as an alternative to magnetic recording media. Such optical recording media are
To protect the recording surface from scratches and dust, it is covered with a transparent surface layer 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 performed based on polarization characteristics using a polarization beam splitter.

A conventional birefringence measuring device will be explained below.

FIG. 6 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 polarization beam splitter, 6 is an S polarization detector, 7 is a p-polarized light detector, and 8 is a calculator.

The measuring method for the birefringence measuring device configured as described above will be explained below.

First, light emitted from a laser 1 is incident on a measurement point of an optical card 2 attached to a fixed base 4, 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.
The light reflected by becomes elliptically polarized light. Next, the angle of the fixing table 4 is adjusted so that this elliptically polarized light is incident on the polarizing beam splitter 5. As shown in FIG. 7, 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 polarization 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. or,
When each received light amount PA + pa is converted into an electric signal and inputted to the calculator 8, the calculator 8 calculates the amount of birefringence (phase difference) φ of the surface layer 4 of the optical card from P8 and PB using the formula: Then, 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 the fixed stand, so only the amount of birefringence, which originally has the characteristics of direction and quantity in hectors, is measured. Cannot be measured. 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 borino J-ponate made by injection molding. The problem was that it could not be used.

The present invention solves the above-mentioned conventional problems, and aims to provide a birefringence measurement device that simultaneously measures the direction and amount of birefringence even for transparent media in which the dispersion in the direction of birefringence is not uniform. purpose.

Means for Solving the Problems In order to achieve this object, the birefringence measurement device of the present invention has the following features:
It has a birefringence variable means that continuously varies the birefringence, and while rotating the transparent medium to be measured with respect to the light emitting means and the polarization separation means, the birefringence of the birefringence variable means is adjusted according to the amount of light from the light receiving means. It is characterized by being configured to change the amount.

Function: With this configuration, the direction and amount of birefringence of a transparent medium can be measured simultaneously, and the birefringence of a transparent medium in which the direction of birefringence does not vary uniformly can also be measured.

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

FIG. 1 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 directly polarized light passes through the surface layer 13 of the optical card, which is a transparent medium, and enters the optical card 12 mounted on the optical card mount 14 . As shown in FIG. 2, the optical card mounting base 14 is composed of a rotary base 22 and a fixed base 16. First stepping motor 1
It is configured to rotate around the 7 axis. The circular fixed base 16 is provided with an angle scale indicating the rotation angle of the rotary base 22.

The light emitted from the laser 11 and incident on the optical card 12 is incident on the rotation center of the optical card mount 14, and after being reflected by the optical card 12, the light is reflected on the surface layer 13 of the optical node J-card.
The beam passes through the Babinet-Soleil compensating plate 23, which is a birefringence variable means, and is incident on the polarization beam splitter 15, which is a polarization separation means. The Babinet Soleil correction plate 23 (hereinafter referred to as the correction plate) has two
By relatively shifting the two different birefringent plates A and B in the direction of arrow a, the amount of birefringence along the crystal axis direction shown by arrow a can be continuously varied. In this embodiment, the compensation plate 23 is moved in the direction of arrow a by the second stepping motor 24, and the amount of birefringence can be varied according to the amount of movement. Further, the crystal axis direction of the compensating plate 23 is at an angle of 45° with respect to the deflection direction in which the laser 11 emits light, as shown in FIG. The light incident on the polarization 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 the S-polarized light is received by the detector 18. The amount of light received by the detector 18 is input as an electrical signal to a motor control circuit 25, and the second stepping motor 24 is driven in accordance with the amount of received light.

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

The light emitted from the laser 11 is M-line polarized light, which enters the optical card 12 through the surface layer 13 of the optical card, is reflected by the optical card 12, and returns to the surface layer 13 of the optical card.
As shown in FIG. 7, when the light is emitted through the optical card, the polarization characteristics change depending on the amount of birefringence in the direction of birefringence of the surface layer 13 of the optical card, and the light becomes elliptically polarized light. When this elliptically polarized light passes through the compensating plate 23, it follows the crystal axis direction of the compensating plate 23,
The amount of birefringence along the crystal axis direction of the compensating plate 23 can be changed by the second stepping motor 24, so the compensating plate 23 absorbs the elliptically polarized light emitted from the optical card 12. In other words, the S reflected by the polarizing beam splitter 15
It is moved so that the polarization component becomes maximum. The fifth pulse is applied to drive the second stepping motor 24.
As shown in the figure. First, when a pulse is applied, the stepping motor 24 moves along the direction of arrow a in FIG. 3, depending on whether the pulse is positive or negative. Detector 1 after pulse application
Positive or negative pulses are continued to be applied so that the output of No. 8 is greater than the output before pulse application. When the second stepping motor 24 is stopped when the difference between the output of the detector 18 after the pulse is applied and the output before the pulse is applied, the detector 1
At 8, the S polarized light component received reaches its maximum.

While performing the above operations, the varnish chipping motor 17
When the surface layer 13 of the optical card is rotated by applying an input pulse as shown in FIG. As shown in Figure 4, the maximum value of this S-polarized light is
3 is rotated so that the direction of birefringence coincides with the crystal axis (arrow b) of the compensating plate 23, and the maximum value is reached.In other words, the linearly polarized light incident on the optical card 12 emitted from the laser 11 is reflected by the surface of the optical card. When it passes through the layer 13 and exits, it becomes elliptically polarized light, and is corrected by the correction plate 23 so that the S-polarized component becomes maximum as described above, and the direction of birefringence of the surface layer 13 of the optical card and the crystal axis of the correction plate 23 are corrected. The corrected light becomes linear S-polarized light when the The direction of birefringence of the surface layer 13 of the optical card can be measured. Also, at this time, since the amount of compensation by the compensation plate 23 corresponds to the amount of birefringence of the surface layer 13 of the optical card,
The scale indicating the movement of the second stepping motor 24 in FIG. 3 indicates the amount of birefringence compensation by the compensation plate 23, and the amount of birefringence can also be measured at the same time.

Note that in this example, the light emitted from the laser was incident on the transparent medium before passing through the polarizing heam splitter, but the light emitted from the laser was incident on the transparent medium after passing through the polarizing heam splitter, and the reflected light was reflected via a mirror. A configuration may also be adopted in which the light is incident on the polarizing beam splitter again. In addition, although we used the surface layer of the optical cart as a transparent medium, it is also possible to combine a transparent medium and a mirror, and of course, use only a transparent medium to allow the light emitted from the laser beam to pass through the transparent medium once and reflect it. It may also be configured such that the light is incident on a compensating plate and a polarizing beam splitter without causing the polarizing beam splitter, and the reflected light from the polarizing beam splitter is received by a detector.

Furthermore, although a polarizing heam splitter is used as the polarization separating means, a polarizing filter may also be used. Although the birefringence variable means is a Babineso I/I compensation plate, it may also be a Herec wavelength plate that can vary the amount of birefringence depending on the inclination.

Effects of the Invention 0 As described above, the present invention changes the direction of birefringence of a transparent medium by varying the birefringence of the birefringence variable means according to the amount of reflected light from a polarizing beam splitter while rotating the transparent medium. and quantity can be measured simultaneously.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram of a birefringence measurement device according to a 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 Fig. 3 is a Babinet Soleil compensation plate in the same device. Fig. 4 is a theoretical diagram showing the state of polarization when the direction of birefringence of the surface layer of the optical card is aligned with the crystal axis of the compensation plate, and Fig. 5 is a diagram showing the structure of the second stepping motor in the same device. A characteristic diagram showing applied pulses, FIG. 6 is a configuration diagram of a conventional birefringence measurement device, and FIG. 9 is a theoretical diagram showing how linearly polarized light changes into elliptically polarized light due to birefringence of a transparent medium. 11...Laser 13...Surface layer of optical card, 16...Fixing stand, 18...
Detector, 22... Turntable, 23...
... Babinet Soleil correction plate. 1

Claims (1)

[Claims] a light emitting means, a polarization separation means, a variable birefringence means for continuously varying birefringence, a light receiving means, the light emitted from the light emission means is incident on a transparent medium, and the transparent medium is connected to the polarization separation means. and means for rotating the birefringence variable means relative to the polarization separation means, and configured to change the amount of birefringence of the variable birefringence means in accordance with the amount of light received by the light receiving means through the polarization separation means.