JPH045545A - Double refraction index measuring instrument - Google Patents

Abstract

PURPOSE:To accurately measure double refraction at a specific position on a disk substrate in its rotation by rotating the disk substrate and measuring the double refraction index at the time of the rotation of the disk substrate. CONSTITUTION:Light emitted by a laser light source 8 is polarized circularly and made incident on the disk substrate 7. The disk substrate 7, on the other, is fitted on a spindle motor 6, which is brought PLL control with rotating speed control pulses generated by dividing the frequency of pulses from a reference clock generator 1 by a frequency divider 2. The luminous flux reflected by the disk substrate 7 is guided to a rotary analyzer 13. The rotary analyzer 13 is driven by a motor brought under PLL control with rotating speed control pulses generated by dividing the frequency of the pulses from the reference clock generator 1 by a frequency divider 3. The output of a photodetector 15 is inputted to a sampling hold circuit 17. This holding is timed at the constant position on the disk substrate 7 and a signal processing circuit 18 calculates the double refraction index.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a birefringence measurement device for a transparent disk substrate, and in particular to a birefringence measuring device that can measure birefringence when the disk substrate is rotating at high speed. This invention relates to a rate measuring device.

[Conventional technology]

Conventionally, a birefringence measuring device as shown in FIG. 4 has been devised. In the figure, 25 is a laser light source such as a semiconductor laser, 26 is a lens, 27 is a wavelength plate, 28 is a polarizer, and 29
30 is a rotating analyzer; 31 is an object to be measured such as a disk substrate;
is a photodetector.

First, in the method shown in FIG. 2(a), linearly polarized light having a polarization direction such that the azimuth angle is 45 degrees is irradiated onto the measured object 29, and the light transmitted or reflected from the measured object 29 is divided into 1/4. The wavelength plate 27 produces elliptically polarized light due to the phase difference.

In addition, in the method shown in FIG. 3B, circularly polarized light is irradiated onto the object 29 to be measured, and elliptically polarized light is created due to a phase difference. This elliptically polarized light is passed through an analyzer 30 consisting of a Glan-Thompson prism or the like that rotates around the optical axis, and the extinction ratio is measured from the maximum and minimum values of the photodetector output during one revolution of the analyzer 30. Calculate the refractive index. Regarding the above, Takahiro Kubo supervised "Measurement and evaluation technology for optical discs" (1988, 3)
) Japan Industrial Technology Center, No. 24H.

Media used such as optical disks on which information is written and/or read out optically rotate at high speeds, especially in plastic disk substrates, due to the centrifugal force of the rotation of the disk substrate. Causes elongation. Therefore, the birefringence value measured when the disk substrate is stationary does not match the birefringence value when the disk rotates, and unless the birefringence is actually measured when the disk rotates, the birefringence value when the disk rotates cannot be measured. Impact cannot be predicted.

Furthermore, the disk substrate has a slight distribution of birefringence in the circumferential direction, and even if the disk substrate is rotated, there is no means to synchronize its rotation with the rotation of the analyzer, so only the average of the circumference of the disk substrate is present. It is not possible to measure birefringence accurately.

Also, when measuring birefringence using focused light, if the disk substrate is not rotated, the recording film will be damaged by the heat from the focused light, making it impossible to measure accurately with the recording film attached. I have this problem.

[Problem to be solved by the invention]

The purpose of the present invention is to solve the drawback of conventional measuring devices that birefringence cannot be accurately measured when the disk substrate is rotating, and also to make it possible to measure birefringence with a recording film attached. It is something to do.

[Means to solve the problem]

In order to achieve the above object, the present invention directly injects polarized light or circularly polarized light into the disk substrate to be measured, guides the reflected light from the disk substrate to an analyzer, rotates the analyzer, and transmits the light through the analyzer. A birefringence measurement device that measures the birefringence of a disk substrate from changes in the amount of light incident on a photodetector, which includes means for rotating the disk substrate and measures the birefringence as the disk substrate rotates. It is characterized by being configured as follows.

[Effect]

The present invention measures the birefringence of a disk substrate under the same conditions as when the disk is mounted in a drive device and actually used. That is, the reference clock is used to keep the rotational speed of the spindle for the disk substrate constant, and the same reference clock is used to keep the rotational speed of the analyzer constant. At this time, the ratio of the respective rotational speeds is set so as not to be an integral multiple of each other's rotational speed. When the ratio of the rotation speeds of the spindle and the analyzer is set to n:m, the analyzer rotates m/n each time the spindle rotates once. At this time, data is sampled, and the ellipticity at that position of the disk can be measured from the measured values of n photodetector outputs sampled when the spindle rotates n times. Then, the value of birefringence is calculated from that value.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing a first embodiment of the present invention, in which 1 is a reference clock generator, 2 is a frequency divider (1), and 3 is a frequency divider (2).
), 4 is a frequency divider (3), 5 is a spindle drive circuit, 6 is a spindle motor, 7 is a disk substrate, 8 is a laser light source, 9 is a quarter wavelength plate, 10 is a polarizing prism, 11 is a diaphragm lens, 12 is a rotating analyzer drive circuit, 13 is a rotating analyzer, 14 is a lens, 15 is a photodetector, 16 is an amplifier,
17 is a sampling hold circuit, and 18 is a signal processing circuit.

As shown in the figure, light emitted from a laser light source 8 such as a semiconductor laser or a HeNe laser is made into circularly polarized light by a quarter-wave plate 9 or the like, and then enters a disk substrate 7 .

On the other hand, this disk substrate 7 is attached to a spindle motor 6, and the spindle motor 6 divides the pulses from the reference clock generator 1 into 1/2 by a frequency divider (1) 2.
PLL control is performed to keep the rotation speed constant using rotation speed control pulses divided by m.

The light beam reflected from the disk substrate 7 is guided to a rotating analyzer 13. Similarly to the spindle motor 6, the rotating analyzer 13 also converts pulses from the reference clock generator 1 into a frequency divider (2) 3.
The motor is driven by a PLL-controlled motor so that the rotational speed is constant using a rotational speed control pulse whose frequency is divided by 1/n. This frequency division ratio n:m is set so that it is not a multiple of any other integral number.

On the other hand, the output of the photodetector 15 is converted into voltage and amplified by an amplifier 16, and then introduced into a sampling and holding circuit 17. This hold timing is performed once at a fixed position on the disk substrate 7 for every rotation of the spindle motor 6, and is sent to the signal processing circuit 18. Then, the birefringence is calculated in the signal processing circuit 18 from the hold signal of the spindle n-rotating bone.

FIG. 2 is a diagram showing a second embodiment of the present invention.

In this embodiment, a pulse signal from an encoder attached to the spindle motor 6 is used as the clock signal for the rotating analyzer 13.

FIG. 3 shows a specific example of the configuration of the signal processing circuit. In the figure, 19 is a peak hold circuit (11 and 20 are peak hold circuits (2), 21 is an amplifier, 22 is an inverting circuit, 23 is a divider, and 24 is an AD converter).

In the peak hold circuit (1) 19 shown in the figure, Vmax(
long axis of the ellipse), peak hold circuit (2) at 20■l
Find 1lin-Vvaax. Birefringence δ at this time
is calculated as Vggax +V+++in. Actually Vmax − VIIlin /
Vmax + Vmin are A/D converted and transferred to the host computer for calculation to determine the birefringence.

〔Effect of the invention〕

As explained above, the disk substrate is attached to the spindle motor and rotated at the same number of rotations as when rotated by the drive device, and the rotating analyzer is rotated at a different number of rotations from the spindle in synchronization with the rotation of the spindle motor. By installing a sample and hold circuit between the read amplifier and the signal processing circuit that calculates birefringence from the extinction ratio of elliptically polarized light, birefringence at a specific position on the disk substrate as it rotates can be accurately measured. can.

[Brief explanation of drawings]

1 and 2 are block diagrams of a birefringence measuring device according to each embodiment of the present invention, FIG. 3 is a block diagram of a signal processing circuit used in the measuring device, and FIG. 4 (al,
bl is a principle diagram of a conventional birefringence measuring device. 1... Reference clock generator, 2... Frequency divider (1),
3... Frequency divider (2), 4... Frequency divider (3), 5...
・Spindle drive circuit, 6... spindle motor, 1
2... Rotating analyzer drive circuit, 13... Rotating analyzer,
15... Photodetector, 16... Amplifier, 17... Sampling hold circuit, 18... Signal processing circuit, 1
9... Peak hold circuit (1), 20... Peak hold circuit (2), 21... Amplifier, 22... Inverting circuit, 23... Divider. Diagram

Claims (7)

[Claims] (1) Linearly polarized or circularly polarized light is incident on the disk substrate to be measured, the transmitted light or reflected light from the disk substrate is guided to an analyzer, the analyzer is rotated, and the light is transmitted through the analyzer and detected as a photodetector. A birefringence measurement device for measuring the birefringence of a disk substrate from changes in the amount of light incident on the disk, characterized by having means for rotating the disk substrate and measuring the birefringence while rotating the disk substrate. Birefringence measuring device. (2) The birefringence measuring device according to claim (1), characterized in that the rotation of the analyzer is synchronized with the rotation of the spindle using an encoder signal of a spindle motor that rotates the disk substrate as a clock. (3) The birefringence measuring device according to claim (1), characterized in that the rotation of the analyzer is synchronized with the rotation of the spindle using the same clock as that of a spindle motor that rotates the disk substrate. (4) In claim (2) or claim (3),
A birefringence measuring device characterized in that the rotational speed of the spindle and the rotational speed of the analyzer are not integral multiples of each other's rotational speed. (5) In claim (4), the output of the photodetector at a certain position on the disk substrate is sampled at at least four points when the angle of the analyzer is different, and the ellipticity is measured from the result, A birefringence measuring device characterized by measuring birefringence at a specific position on a substrate. (6) In claim (5), the photodetector outputs at a plurality of points on the same circumference of the disk substrate are continuously sampled, the ellipticity is measured for each point, and the ellipticity of the disk substrate is measured. A birefringence measuring device characterized by simultaneously measuring birefringence at a plurality of specific positions. (7) A birefringence measuring device according to claim (6), characterized in that it has an automatic focus control means and a tracking follow-up control means.