JPH02284044A - Measurement instrument for double refraction - Google Patents

Abstract

PURPOSE:To accurately measure double refraction in a driving state by providing respective means for disk rotation, a analyzer constant-angle rotation synchronized with above disk rotation, and photodetector output sampling at a specific position on a disk substrate. CONSTITUTION:This instrument is provided with a spindle motor 6 for driving the disk substrate 5 and its driving circuit 9, a rotation analyzer 7 and a driving circuit 10 for its stepping motor 7a, a timing generator 11 which controls them, a reference clock generator 12, a read amplifier 13 for amplifying the output of a photodetector 8, a sample hold circuit 14, and a signal processing circuit 15. Then the light of a light source 1 is reflected by the disk 5 which rotates at a constant rotating speed, passed through the analyzer 7 which rotates having a constant time difference from the disk and converted photoelectrically by the detector 8, and amplified by the amplifier 13, whose output is inputted to the circuit 14, so that the signal is held to the output of the same position of the substrate 5 with sample holding pulses in every spindle rotation at each set angle of the analyzer 7.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a birefringence measurement device for a disk substrate for recording information or on which information has already been recorded. The present invention relates to a birefringence measurement device capable of measuring birefringence in its peak state.

[Conventional technology]

Conventional methods for measuring birefringence include methods using an elliplymeter and methods using laser light as shown in FIGS. 5(a) and 5(b).

In FIG. 5, 1 is a laser light source of semiconductor laser light, 2 is a laser light source of semiconductor laser light;
is a collimator lens, 3 is a quarter-wave plate, 4 is a polarizer,
5 is a disk substrate which is the object to be measured, 7 is a rotating analyzer, 8
is a photodetector.

First, in method (a), the azimuth angle is 4 with respect to the object to be measured.
Linearly polarized light with a polarization direction of 5 degrees is irradiated, and the light that is transmitted or reflected by the object to be measured is used to produce elliptically polarized light using a phase difference using a quarter-wave plate. Circularly polarized light is irradiated onto the object to be measured, creating elliptically polarized light due to the phase difference.This elliptically polarized light is passed through an analyzer consisting of a Glan-Thompson prism, etc. that rotates around the optical axis, and a photodetector is used while the analyzer makes one revolution. The extinction ratio is measured from the maximum and minimum values of the output, and the birefringence is calculated from the result.
“Measurement and evaluation technology for optical discs” supervised by Takahiro Kubo (S 63
．． 4.26) Described in detail in Japan Industrial Technology Center No. 2m.

The media used in optical discs and the like that optically read and/or read information are rotating at high speed inside a shell, and especially in positive link substrates, the centrifugal force of the rotation of the disc is This causes elongation, so the birefringence value measured with the disk Eli54N stationary and the value when the disk rotates? Since the value does not match the value of 3I refraction, the effect of birefringence during disk rotation cannot be predicted unless birefringence is actually measured during disk rotation. Furthermore, even if the disc substrate is rotated, there is no means to synchronize its rotation with the rotation of the analyzer, so even though it is unknown whether the birefringence distribution within the disc substrate is constant, - Only the average of the circumference can be measured, making it impossible to accurately measure birefringence.

[Problem to be solved by the invention]

The present invention solves the drawback of the conventional measuring device as described above that it cannot measure the influence of birefringence when the disk substrate is actually rotated, and provides a birefringence measuring device that can obtain highly accurate birefringence data. intended to provide.

[Means to solve the problem]

The present invention measures the birefringence of a disk substrate placed on a drive device under the same conditions as when it is actually used, and the rotation speed of the spindle of the disk drive device is kept constant (10 to 10). 40Hz),
Every time the spindle rotates once, for example, 5 sync pulses are extracted from the spindle motor drive circuit, and the rotating analyzer is set at a certain angle θ (0<θ≦60
°) Rotate in synchronization with the spindle, sample the output of the photodetector at the same position on the disk substrate, hold this sampling output while the disk substrate rotates once, and collect the photodetector for one rotation of the rotating analyzer. The outputs are combined, the extinction ratio is measured from the signals, and the value of birefringence is calculated.

〔Example〕

FIG. 1 shows an embodiment of the present invention, which includes a laser light source 1 such as a semiconductor laser or a He-Ne laser, a collimator lens 2, a quarter-wave plate 3, a disk substrate 5, a rotating analyzer 7, and a photodetector. The optical system components such as 8 are the same as those of the conventional device shown in FIG.
This device differs from the conventional device in that it includes a control circuit for controlling the step motor 7a of the rotary analyzer 7.

The control circuit includes outputs of a spindle motor drive circuit 9, a drive circuit 10 for driving a rotating analyzer, a timing pulse generator 11 that controls the motor drive circuit 9 and the drive circuit 10, a reference clock generator 12, and a photodetector 8. It is comprised of a read amplifier 13 for amplifying the signal, a sample hold circuit 14, a signal processing circuit 15, and the like.

Next, the operation of the embodiment of the present invention will be explained.

Light emitted from a laser light source 1 (semiconductor laser) is circularly polarized by a quarter-wave plate 3 and enters a disk substrate 5.

On the other hand, the disk substrate 5 is attached to a spindle 6, and the spindle 6 is controlled to have a constant rotation speed by a rotation speed control pulse from a reference table generator 12. The light flux transmitted or reflected by the disk substrate 5 is guided to a rotating analyzer 7. The zero-rotation residue photon 7 is driven by a step motor 7a. Step motor 7a
The timing for driving the spindle motor 6 is determined by the 5 sync pulse (spindle motor 6
(one pulse is output for each round of the motor) or a step motor drive pulse having a constant time difference (td) with the 5 sync pulse generated by the timing pulse generator 11. The light that has passed through the rotating analyzer 7 is photoelectrically converted by a photodetector 8 and further amplified by a read amplifier 13. The output of the read amplifier 13 is input to the sample hold amplifier 14 and is processed by the sample hold pulse from the timing pulse generator 11.
At each set angle of the rotating analyzer 7, the output is held at the same position on the disk substrate 5 for each spindle rotation. The sample hold pulse lags behind the 5sync pulse by an arbitrary time Δt (0≦Δt<t,) and Δt
t can be set freely.

Fig. 2 shows an example of the timing pulse output by the timing pulse generator 311. t is the time for the spindle 6 to make one revolution, t is the time difference between the sync pulse and the step motor drive pulse, and Δt is the 5 sync pulse and sample hold. This is the time difference from the pulse.

FIG. 3 shows examples of output waveforms of the read amplifier 13 and sample-hold amplifier 14. (a) is the read amplifier output, and (b) is the sample and hold amplifier output. (a
In ), the output fluctuates while the spindle 6 makes one revolution, but in (b), the output at the same position on the disk substrate 5 is sampled.

FIG. 4 shows an example in which birefringence at a plurality of points on the same radius on the disk substrate 5 is simultaneously measured in the present invention. A plurality of (n) sample hold pulses are sent from the timing pulse generator (time difference Δt with the sync pulse,
~Δt, 1) and measure the birefringence at n points on the same radius of the disk substrate 5 at once using n sample-and-hold amplifiers.

Although not explained in the above embodiment, by making it possible to change the angle of incidence on the disk substrate 5, the most appropriate data regarding birefringence depending on the type of disk substrate 5 and the type of laser beam can be obtained. be able to.

〔Effect of the invention〕

As explained above, the present invention actually rotates the disk substrate, rotates the rotating analyzer at a certain angle in synchronization with the rotation speed, samples the photodetector output at a predetermined position on the disk substrate, and samples the photodetector output at a predetermined position on the disk substrate. Since the data for calculating the birefringence of the disk substrate is obtained from the sampling output, it is possible to accurately measure the birefringence at a specific position on the disk substrate when the disk substrate is actually written with data and driven for data reproduction. can.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the overall configuration of the embodiment of the present invention, FIG. 2 is a timing chart of control signals in the embodiment of the present invention, FIG. 3 is a waveform diagram of the signal system in the embodiment of the present invention, and FIG.
The figure is a schematic diagram showing the overall configuration of a modified example of the present invention, and FIG. 5 is an explanatory diagram showing an example of a conventional birefringence method. 1...... Laser light source, 5......
・Disk board, 6... Spindle motor, 7... Rotating analyzer, 8...
. . . Photodetector, 9 . . . Spindle motor drive circuit, 10 . . . Step motor drive circuit, 11 . . . Timing pulse generation. 14... Sample and hold amplifier. Congee diagram Condolence diagram Funeral diagram Funeral diagram Figure 5

Claims (3)

[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 a rotating analyzer, and the amount of light transmitted through the analyzer and incident on the photodetector changes. A birefringence measurement device for measuring the birefringence index of a disk substrate, comprising: a disk rotation means for rotating the disk substrate; an analyzer rotation means for rotating the analyzer by a certain angle in synchronization with rotation of the disk substrate; sampling means for sampling the photodetector output at a predetermined position on the substrate, and from the output of the sampling means corresponding to one rotation of the analyzer, the birefringence at a specific position on the disk substrate during rotation of the disk substrate is determined. A birefringence measurement device characterized by measuring birefringence. (2) The sampling means is a continuous sampling means that continuously samples the photodetector output at a plurality of points on the same circumference of the disk substrate, and the sampling means continuously samples the photodetector output at a plurality of points on the same circumference of the disk substrate, and the sampling means continuously samples the photodetector output at a plurality of points on the same circumference of the disk substrate, and the sampling means continuously samples the photodetector output at a plurality of points on the same circumference of the disk substrate, and the sampling means continuously samples the photodetector output at a plurality of points on the same circumference of the disk substrate. 2. The birefringence measuring device according to claim 1, wherein the birefringence of a plurality of specific positions on the disk substrate is simultaneously measured from the sampling output for each point. (3) Claims (1) and (2) further comprising an incident angle changing means for changing the incident angle of linearly polarized light or circularly polarized light incident on the disk substrate to the disk substrate.
) The birefringence measuring device described in ).