JPS62245951A - Disk measuring instrument - Google Patents

Abstract

PURPOSE:To simplify the constitution of an instrument and to reduce its cost by splitting light transmitted through a desk, and photodetecting the split light beams and finding the value of the double refraction. CONSTITUTION:Light from a light source 11 passes through an objective 14 and is transmitted through the disk 3 and converged on a specific convergence point 10. Then, the light becomes parallel light through an objective 15 and is split by a beam splitter 17 into parallel beams. One light beam split by the beam splitter 17 is incident on the 1st photodetecting element 18, and the other light beam is incident on the 2nd photodetecting element 19. The output signal st of the element 18 and the output signal sr of the element 19 are inputted to an arithmetic circuit 22 through amplifiers 20 and 21. The value of double refraction of the disk is calculated by the circuit 22 from the two input signals, so the double refraction is measured in a short time not only in the radial and tangential directions of the disk 3, but also in the optical-axis direction. This measurement system eliminates the need for an automatic focusing mechanism and does not require any swing and tilt mechanism, etc., unlike a system wherein the parallel light is made incident slantingly on the disk, so the constitution is simple and the cost is reducible.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a measuring device for a disc that optically records and reproduces information.

[Summary of the invention]

In the present invention, light emitted from a light source is converged outside the disk, and a value related to the birefringence of the disk is calculated by receiving the light that has passed through the disk.

[Conventional technology]

In recent years, disks that optically record and reproduce information, such as compact disks, optical video disks, and optical disks, have become popular. When reproducing information from such a disc,
It is necessary to irradiate the disk with light such as a laser beam and read changes in the reflected or transmitted light. Therefore, if there is a change in birefringence, for example, in the substrate that constitutes the disk, the amount of returned light will decrease and the S/N of the reproduced signal will deteriorate. Therefore, it is necessary to use a disk with as little change in birefringence as possible.

Conventionally, such changes in birefringence have been measured by irradiating the disk with parallel light.

[Problem that the invention seeks to solve]

Since conventional disk measuring devices use parallel light in this way, they have the disadvantage that they cannot measure changes in birefringence, especially in the optical axis direction. Furthermore, since birefringence has directionality, it is necessary to change the direction of light irradiation in order to measure changes in the radial and tangential directions of the disk, which not only makes the device complicated and expensive. However, it also had the disadvantage of taking a long time to measure.

[Means for solving problems]

A light source, an objective lens that converges the light emitted from the light source to a predetermined convergence point, a turntable that supports the disc at a position apart from the convergence point, and a light source that is emitted from the light source and irradiated onto the disc via the objective lens. , a beam splitter that splits the light transmitted through the disk into at least two parts;
A first light receiving element receives one of the lights split by the beam splitter, a second light receiving element receives the other light, and a disc is detected from the output of the first light receiving element and the output of the second light receiving element. and an arithmetic circuit that calculates a value related to birefringence.

[Effect]

Light emitted from a light source is irradiated onto a rotating disk so as to converge near the recording surface of the disk. The light transmitted through the disk is split by a beam splitter, and a value related to birefringence is calculated from the output of a light receiving element that receives the split light.

〔Example〕

FIG. 1 is a block diagram of a disc measuring device according to the present invention. In the figure, reference numeral 1 denotes a motor, which rotates a turntable 2. As shown in FIG. A disk 3 is placed on the turntable 2 and clamped by a clamper 4 at a predetermined pressure. Therefore, the disc 3 is supported by the turntable 2.
be rotated.

Divergent light emitted from a light source 11 such as a semiconductor laser is made into parallel light by a collimator lens 12, and is input to a wavelength plate 13 such as a quarter-wave plate. The light emitted from the light source 11 is linearly polarized light, but it is turned into circularly polarized light by the wavelength plate 13.

This light is converged to a convergence point 10 by an objective lens 14,
The light that has passed through the convergence point 1o diverges from there. The disk 3 is arranged to rotate at a position spaced apart from the convergence point 10. In other words, the objective lens 14 converges the light near the recording surface of the disc 3 (it may be in a so-called defocused state); in this respect, it is designed to converge the light onto the disc in a normal information recording/reproducing device. It's very different from what it is.

This also means that a so-called focus servo device is not necessary.

The light irradiated onto the disk 3 through the objective lens 14 and transmitted through the disk 3 is converted into parallel light again by the objective lens 15. This parallel light is incident on a wavelength plate 16 such as a quarter-wave plate, and is returned to linearly polarized light. This linearly polarized light is split, and a component whose polarization plane matches the human plane of the polarizing beam splitter 17 passes through the beam splitter 17 and enters the light receiving element 18, and a component that does not match is reflected by the beam splitter 17 and is received. incident on element 19. The output signal St of the light receiving element 18 and the output signal Sr of the light receiving element 19 are each amplified by an amplifier 20.
is input. The calculation circuit 22 calculates a value related to birefringence from two input signals.

That is, the value of the signal St/(Sr+St) is determined.

A signal corresponding to this calculated value is input to the comparator circuit 23,
It is compared with a predetermined reference value set in advance.

The comparison result is input to the determination circuit 26.

- A signal corresponding to the force calculation value is further input to the calculation circuit 24. The arithmetic circuit 24 differentiates this calculated value and outputs a signal corresponding to the differentiated value to the comparator circuit 25. The comparison circuit 25 compares the signal corresponding to this differential value with a predetermined reference value set in advance.

The comparison result is output to the determination circuit 26. 'The judgment circuit 26 determines that the disc 3 passes when the calculated value is less than the reference value and the differential value is also less than the reference value, and rejects the disc 3 when either or both of them are greater than the reference value. , pass/fail is displayed on the display device 27.

The division value being less than or equal to the reference value means that the absolute amount of birefringence is less than or equal to the predetermined value. However, even if the absolute value is satisfied, if the time variation is large, it will adversely affect the S/N of the reproduced signal. Therefore, the differential value is also measured, and the disk (substrate) 3 is passed only when the hourly variation is also less than a predetermined reference value. For this reason, the disk is rotated as will be described later.

Birefringence has directionality, but since the light incident on the disk 3 is not parallel light but convergent light by the objective lens 14, measurement in the optical axis direction is possible. Furthermore, since the light incident on the disk 3 is not linearly polarized but circularly polarized by the wave plate 13, 1llI! of the radial and tangential directions of the disk 3! ! It becomes possible to If birefringence exists, circularly polarized light becomes elliptically polarized light, so measurement is possible in principle even if the wavelength plate 16 on the light receiving section 28 side is omitted. However, if it is omitted, the measurement sensitivity will decrease, so it is preferable to include it.

In addition, when the light receiving section 28 is fixed, the light receiving section 28 (wave plate 16
The measurement value is affected by the orientation of the beam splitter 17) and the in-plane azimuth of the birefringence anisotropy axis of the disk 3 cannot be measured.

Therefore, the light receiving section 28 (wave plate 16 and beam spiriter 1)
7 azimuth) by motor 29 or hand mJ
Rotate degrees. Then, the worst value (maximum value) of the division value and differential value obtained by rotation is taken as the measured value of the disk 3.

Further, in order to measure the birefringence of the entire disk 3, the light emitting section 30 and the light receiving section 28 are integrally transported in the radial direction of the disk 3 by means not shown. Disk 3 is CL
When the disc is a V-disc, the radial position of the light emitting section 30 (light receiving section 28) is detected by a position detection circuit 31 made of, for example, a potentiometer, and a signal corresponding to the position is sent to the drive circuit 33 via the switch 32. is input.

As a result, the drive circuit 33 controls the motor 1 and the light emitting unit 30
The closer to the outer periphery of disk 3, the slower the rotation becomes.
so that the linear velocity of is approximately constant.

Further, in the case of a CAV disc, the switch 32 is switched to the reference signal generation circuit 34 side, and the reference signal generation circuit 34
The disk 3 is rotated at a substantially constant angular velocity in response to the reference signal outputted by the disk 4. In this way, the disk 3 is rotated at approximately the same speed as the speed at which information is recorded and reproduced. Even when the light emitting part 3° is moved in the radial direction, the worst value among the division value and differential value obtained at that time is used as the criterion for pass/fail.

The characteristics of each component of this device will vary depending on the desired measurement accuracy, but as the light source 1, for example, a semiconductor laser with a wavelength of 830 nm can be used. The smaller the error, the better. Further, it is preferable to use a material having as good linear polarization as possible. The objective lens 14 is preferably the same as that used in a pickup for recording and reproducing information on the disk 3, and for example, one having a numerical aperture (NA) of 0.5 to 0.55 can be used. . The diameter of the beam on the disk 3 is, for example, 1 mm to 2 mm. The numerical aperture of the objective lens 15 is greater than or equal to the numerical aperture of the objective lens 14 (for example, 0
．． 6) is preferable.

It is preferable that the retardation error of the wave plates 13, 16 and the extinction ratio of the beam splitter 17 are small.

Further, if the clamping force of the clamper 4 is too strong, birefringence will increase, so it is set to a predetermined value (the same value as in the information recording/reproducing apparatus).

Because of the relationship between the relative angle between the polarization direction and the anisotropy axis direction, it is extremely difficult to detect all effects in circularly polarized light from measurements using linearly polarized light. It is possible to estimate the impact. Therefore, the present invention can also be applied to measurement of magneto-optical disks.

Note that when measuring the value at a predetermined point, the disk 3 may be stopped without rotating. Also, if necessary, the outputs of the arithmetic circuits 22 and 24 can be used as they are,
Measured values at each radial position may be stored in correspondence with the output of the position detection circuit 31.

〔effect〕

As described above, the present invention includes a light source and an objective lens that converges the light emitted from the light source to a predetermined convergence point.

A turntable that supports the disc at a position spaced from the convergence point, and at least two lights that are emitted from a light source, irradiated onto the disc via an objective lens, and transmitted through the disc.
a beam splitter that splits the light into two; a first light receiving element that receives one of the lights split by the beam splitter;
Since the second light receiving element that receives the other light and the arithmetic circuit that calculates the value of birefringence of the disc from the output of the first light receiving element and the output of the second light receiving element are provided, Birefringence not only in the radial and tangential directions of the disk but also in the optical axis direction can be measured in a short time. In addition, there is no backtalk effect on the light source, so stable measurements can be made. Furthermore, there is no need for an autofocus mechanism, compared to methods that make parallel light incident on the disc obliquely.

Since the lifting mechanism etc. is not required, the configuration is simplified,
Cost can be reduced.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a disc measuring device according to the present invention. 1... Motor 2... Turntable 3... Disk 4... Clamper 10... Convergence point 11... Light source 12... Collimator lens 13... Wave plate 14.15... Objective lens 16...Wave plate 17...Beam splitter 18.19...Light receiving element 22...Arithmetic circuit 23...Comparison circuit 24...Arithmetic circuit 25...Comparison circuit 26... Judgment circuit 27...Display device 28...Light receiving section 29...Motor 30...Light emitting section 31...Position detection circuit 33...Drive circuit 34...Reference signal generation circuit or higher

Claims (1)

[Claims] a light source, an objective lens that converges the light emitted from the light source to a predetermined convergence point, a turntable that supports a disk at a position apart from the convergence point; a beam splitter that splits the light irradiated onto the disk and transmitted through the disk into at least two; a first light-receiving element that receives one of the lights split by the beam splitter; and a first light-receiving element that receives the other light. Disk measurement characterized by comprising a second light receiving element that receives light, and an arithmetic circuit that calculates a value related to birefringence of the disc from the output of the first light receiving element and the output of the second light receiving element. Device.