JPS63263636A - Optical information reproducing device - Google Patents

Abstract

PURPOSE:To reduce influence due to the surface dirt of a transparent protection layer by dividing the photodetecting face of a photodetector for detecting a focus error into four quadrants and detecting a tracking error signal in accordance with a phase difference between the change of a total photodetecting variable included in 1st and 3rd quadrants and that included in 2nd and 4th quadrants. CONSTITUTION:Light beam radiated from a semiconductor laser 2 is converged into the surface of a recording medium 1 through the transparent protection layer after passed through a beam splitter 4 and a converging lens 3 and the reflected light beam is led into an electrophotodetector 6 to detect a tracking error signal. The detector 6 in said constitution is normally divided into photodetecting cells A-D so that a far-field pattern consisting of a minimum circle of confusion is formed on the center part, but when dirt such as a finger print exists on the transparent protection layer, light beam is dispersed and the far-field image 7 is expanded. Thereby, a tracking error signal is detected by the detector in accordance with the phase difference between the change of the total photodetecting variable of the cells A, C and auxiliary parts E, G which may be adopted in accordance with the degree of diffusion and that of the cells B, D and auxiliary parts F, H.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical information reproducing device that optically reads information from a recording medium, and particularly to detection of focus errors and tracking errors thereof.

2. Description of the Related Art In recent years, optical information reproducing devices that optically read information from recording media such as video disks and digital audio disks have been widely used. Information is recorded on information tracks with a minute width, and in order to reproduce the information from these tracks, precise focus control and tracking control are generally required. This is usually done using optical means. As a method for detecting the tracking error number, a method is already known in which the tracking error is detected from the phase difference between the signals output from the two parts of the photoelectric detector (hereinafter referred to as a phase difference method).

An example of an optical information reproducing apparatus using the conventional phase difference method described above will be described below with reference to the drawings.

FIG. 2 shows a block diagram of a conventional optical information reproducing device. In FIG. 2, ■ is a recording medium, and 2 is a semiconductor laser which is a light source. A converging lens 3 converges the light beam emitted by the semiconductor laser 2 onto the recording medium 1 . 4 is a beam splitter, 5 is a cylindrical lens, and 6 is a photoelectric detector.

This photoelectric detector 6 has four light-receiving cells A, B, C, and D, and a far-field image 7 is formed across these four light-emitting cells. 8 and 9 are current-voltage converters, which convert the sum of the output currents of light-receiving cell A and light-receiving cell C and light-receiving cell B.
and the sum of the output currents of the light-receiving cell D, respectively, are converted into voltages. 10 and 11 are waveform shapers that shape the waveforms of the outputs of the current-voltage converters 8 and 9, respectively, and 12 is a phase comparator that compares the phases of the outputs of the current-voltage converters 8 and 9. 13 is a low-pass filter, and phase comparator 12
A tracking error signal is output by extracting a low frequency component from the output. 14 is a tracking control circuit, which controls the tracking actuator 15 according to the tracking error signal.
is driven to displace the light spot on the recording medium. 1
6.17 is a low-pass filter that extracts low frequency components from the outputs of current-voltage converters 8 and 9, respectively. 18
A differential amplifier calculates the difference between the outputs of the low-pass filters 16 and 17 and outputs a focus error signal. A focus control circuit 19 drives a focus actuator 20 in accordance with a focus error signal to adjust focus. The operation of the optical information reproducing apparatus configured as described above will be explained below.

The irradiation light beam emitted by the semiconductor laser 2 passes through the beam splitter 4 and is focused by the converging lens 3 onto the recording surface of the recording medium 1 through the transparent protective layer, thereby forming a light spot. The reflected light from this light spot is condensed by a converging lens 3 to become a detection light beam, reflected by a beam splitter 4, and separated from the irradiation light beam. This separated irradiation light beam is given a sufficiently large astigmatism by the cylindrical lens 5,
A far-field image 7 of the circle of least confusion is formed on the photoelectric detector 6 . The photoelectric detector 6 is divided into four quadrants with the origin approximately at the center of the far-field image 7 by two straight lines that are substantially parallel to the moving direction of the information track and a direction perpendicular thereto, and one quadrant corresponds to each quadrant. and four light receiving cells A
, B, C and D are provided. A current-voltage converter 8 adds the currents output from the light-receiving cells A and C and converts the sum into a voltage. A current-voltage converter 9 adds the currents output from the light-receiving cells B and D and converts the sum into a voltage. Waveform shaping means 10 and 11 are current-voltage converters 8 and 9, respectively.
Shape the output signal from the . The phase comparator 12 compares the phases of the output signals whose waveforms have been shaped by these waveform shaping means 10 and 11, and outputs a phase difference signal corresponding to the phase difference. When the image of the information tracker mapped on the photoelectric detector 6 moves in the direction of arrow V in the figure, if there is no tracking error, there will be no phase difference, but if a tracking error occurs, the above phase difference will occur. It is already known that (For example, see Japanese Patent Laid-Open No. 52-93222).

Therefore, a tracking error signal can be obtained by removing the ripple component from the phase difference signal using the low-pass filter 6. (For example, JP-A-57-18
1433 Publication) Problems to be Solved by the Invention However, with the above configuration, if there is dirt or scratches on the surface of the transparent protective layer of the recording medium, noise is likely to be mixed into the tracking error, resulting in poor tracking control. It had the problem of stability.

In view of the above-mentioned problems, the present invention provides an optical information reproducing device in which even if the surface of the transparent protective layer of a recording medium is dirty, the adverse effect on tracking control is small.

Means for Solving the Problems In order to solve the above-mentioned problems, the optical information reproducing device of the present invention provides a core portion where a far-field image of a light spot on a recording medium is mainly formed, and a core portion around this core portion. and a photoelectric detector including an auxiliary portion located at the core portion, and the photoelectric detector is formed by a straight line substantially parallel to the moving direction of the information track and a straight line substantially perpendicular to the moving direction of the information track with the origin approximately at the center of the core portion. The light-receiving surface of the detector is divided into four quadrants, and a focus error is detected based on the amount of light received by the core portion, and the tracking control means is divided into four quadrants.
The tracking error is detected according to the phase difference between the change in the total amount of light received by the core portion and the auxiliary portion included in the quadrant and the change in the total amount of light received by the core portion and the auxiliary portion included in the second and fourth quadrants. It is composed of

According to the above-described structure, even if the detection light is scattered by dirt or scratches on the surface of the transparent protective layer of the recording medium, the scattered light is not incident on the core part of the photoelectric detector that detects focus errors. Since there is little noise, it is difficult for noise to be mixed into the focus error signal, and the two signals that detect tracking error based on the phase difference are output depending on the amount of light received by a wide area including the core and auxiliary parts of the photoelectric detector, so there is no deterioration. The tracking error can be detected with good darkness.

Example Below, regarding an optical information reproducing device according to an example of the present invention,
This will be explained with reference to the drawings.

FIG. 1 shows a block diagram of the main parts of an optical information reproducing apparatus according to a first embodiment of the present invention. In FIG. 1, 1 is a recording medium, 2 is a semiconductor laser as a light source, 3 is a converging lens, 4 is a beam splitter, 5 is a cylindrical lens, 8 and 9 are current-voltage converters, 10 and 11
is a waveform shaper, 12 is a phase comparator, 13 is a low-pass filter, 14 is a tracking control circuit, 15 is a tracking actuator, 16.17 is a low-pass filter, 18 is a differential amplifier, 19 is a focus control circuit, 20
is a focus actuator, which is the same as the conventional one.

The difference from the conventional example is that the photoelectric detector 30 is a light receiving cell A.

It has a core part consisting of B, C and D, and an auxiliary part consisting of light receiving cells E, F, G and H outside. When this photoelectric detector 30 is divided into four quadrants by two straight lines parallel to the direction in which the information track extends and the direction perpendicular to this mapping onto the photoelectric detector 30, the light receiving cells A and E are the first
- Light receiving cells B and F are arranged in the second quadrant, light receiving cells C and G are arranged in the third quadrant, and light receiving cells D and H are arranged in the fourth quadrant. Furthermore, 31 and 32 are high-pass filters that pass only the high frequency components included in the sum of the output currents from the light-receiving cells E and G and the sum of the output currents from the light-receiving cell F(!:)I, respectively. The current-voltage converter 8 converts the output current from the high-pass filter 31 and the sum of the output currents from the light-receiving cells A and C into a voltage, and the current-voltage converter 9 converts the output current from the high-pass filter 32 and the sum of the output currents from the light-receiving cells A and C into a voltage. Convert the sum of output currents from cells B and D to a voltage.

Regarding the optical information reproducing device configured as above,
The operation will be explained below.

The irradiation light beam emitted by the semiconductor laser 2 passes through the beam splitter 4 and is focused by the converging lens 3 onto the recording surface of the recording medium 1 through the transparent protective layer, thereby forming a light spot. The reflected light from this light spot is guided to the photoelectric detector 30 as in the conventional example, and the far-field image 7 of the circle of least confusion is usually placed at the core of the photoelectric detector 30 consisting of light receiving cells A, B, C, and D. form. The waveform shaping means 10.11, the phase comparator 12, the low-pass filter 13, the tracking control circuit 14, and the tracking actuator 15 constitute a tracking error detection means 35, and the far-field image 7
The tracking error can be detected from the phase difference between the change in the amount of light incident on the light-receiving cells A and B and the change in the amount of light incident on the light-receiving cells C and D, as in the conventional example.

However, there are fingerprints on the surface of the transparent protective layer of the recording medium 1.
If there is dirt or scratches on the recording surface, the light modulated on the recording surface and returned will be scattered by this surface, and the far-field image 7 on the photoelectric detector 30 will expand and become larger, and in some cases, the light receiving cell E
, F, G and H. Light receiving cell E.

Scattered light incident on F, G and H is transmitted to light receiving cell A, respectively.
, B, C, and D contain a large amount of scattered light. Therefore, in this embodiment, the light receiving cells A, C, E and G substantially included in the first quadrant and the third quadrant are
The tracking error is detected from the phase difference between the change in the total amount of light incident on the sensor and the change in the total amount of light incident on the light receiving cells B, D, F, and H included in the second and fourth quadrants. To enable such tracking error detection, the cutoff frequencies of the high-pass filters 31 and 32 are set so that most of the modulation components of the recording medium of the amount of light detected by the photoelectric detector 30 are passed.

On the other hand, the low-pass filters 16 and 17, the focus control circuit 19, which is a differential amplifier, and the focus actuator 20 constitute focus control means, and can perform focus control in the same manner as in the conventional example. In this case, the reflected light is scattered on the surface of the recording medium, and the light detected by the auxiliary portion of the photoelectric detector 30 tends to become noise in the focus error signal. Therefore, in this embodiment, the cutoff frequencies of the high-pass filters 31 and 32 are set so that low frequency components that adversely affect focus control are removed. In this way, the output signal corresponding to the amount of light received by the auxiliary part of the photoelectric detector 30 is transmitted through the high-pass filter 31.32 and the low-pass filter 16.17.
Since the focus error is completely removed by , the focus error can be detected in the same manner as in the conventional example. As mentioned above,
According to this embodiment, the focus error can be detected from the difference in level between the two signals that are the same as the two signals for which the tracking error is detected from the phase difference, so the circuit configuration is simplified.

A preferred set value of the cutoff frequency of the high-pass filters 31 and 32 as described above is, for example, 10 kHz to 200 kHz in the case of a compact disc (Philips registered trademark) player.

In the above embodiment, a method using astigmatism was used as a means for detecting focus error, but any method may be used as long as focus error can be detected from a far-field image whose size is controlled. There is no problem even if there is such a case, and the present invention is still effective.

As described above, according to this embodiment, the tracking error is substantially detected from the phase difference in the change in the amount of incident light between the two parts of the photoelectric detector, which has a wide light-receiving surface, and the focusing error is substantially detected by the photoelectric detector, which has a narrow light-receiving surface. Since the detection is performed using a detector, it is possible to reduce noise mixed into both the tracking error and the focus error.

Effects of the Invention As described above, the present invention condenses light from a light spot formed on a recording medium to form a far-field image of the light spot on a photoelectric detector. A straight line that includes a core portion where a far-field image is mainly formed and an auxiliary portion located around the core portion, and is substantially parallel to the direction in which the information track extends, with the origin approximately at the center of the core portion. The light-receiving surface of the photoelectric detector is divided into four quadrants by a straight line perpendicular to this, and the focus control means detects a focus error based on the amount of light received by the core portion, and the tracking control means divides the light-receiving surface into four quadrants. The tracking error is calculated according to the phase difference between the change in the total amount of light received by the core part and the auxiliary part included in the third quadrant and the change in the total amount of light received by the core part and the auxiliary part included in the second and fourth quadrants. By configuring to detect the detection light, it is possible to reduce noise mixed into the tracking error signal and the focus error signal even if the detection light is scattered by a fingerprint or the like on the readout surface of the recording medium.

Furthermore, astigmatism is introduced into the far-field image formed on the photoelectric detector, and the high-frequency components of the output signals from the auxiliary parts of these quadrants are added to the output signals from the core parts of the first and third quadrants. By configuring the focus error to be detected according to the difference from the signal obtained by adding , the tracking error and the focus error can be obtained from the same two signals, thereby simplifying the configuration.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG. 2 is a block diagram showing a conventional example. 2... Semiconductor laser, 3... Converging lens, 4... Beam splinter, 5...
・Cylindrical lens, 8°9...Current voltage converter, 3
0... Photoelectric detector, 31° 32... High pass filter, 35... Trafking error detection means, 36... Focus control means.

Claims (2)

[Claims] (1) A light source, a converging means for converging the luminous flux emitted from the light source onto a recording medium to form a light spot, and a converging means for converging the light beam emitted from the light source onto a recording medium, condensing the reflected light or transmitted light from the recording medium and directing the light beam onto the photoelectric detector. A light detection means that forms a far-field image of the light spot, and a focus that detects a focus error of the light spot from a signal output from the light detection means and controls the light spot to be in focus according to this focus error. The photoelectric detector comprises a control means, and a tracking control means for detecting a tracking error of the light spot from a signal output from the light detection means and controlling the position of the light spot according to the tracking error. , which includes a core portion where the far-field image is mainly formed and an auxiliary portion located around the core portion, and is substantially parallel to the direction in which the information track extends, with the origin approximately at the center of the core portion. When the light-receiving surface of this photoelectric detector is divided into four quadrants by a straight line and a straight line perpendicular to the same, the focus control means detects a focus error based on the amount of light received by the core portion, and the tracking control means detects a focus error based on the amount of light received by the core portion. Tracking according to the phase difference between changes in the total amount of light received by the core and auxiliary parts included in the 1st and 3rd quadrants and changes in the total amount of light received by the core and auxiliary parts included in the 2nd and 4th quadrants. An optical information reproducing device characterized by detecting errors. (2) The light detection means includes an astigmatism optical means that introduces astigmatism into the far-field image, and the focus control means is configured according to the amount of light received in the first and third quadrants of the core portion of the photoelectric detector. and the high-frequency components of the output signals output according to the amount of light received in the first and third quadrants of the auxiliary part, and the second and fourth quadrants of the core part. The focus is adjusted according to the difference between the output signal output according to the amount of light received in the auxiliary part and the high-frequency component of the output signal output according to the amount of light received in the second and fourth quadrants of the auxiliary part. The optical information reproducing device according to claim 1, wherein the optical information reproducing device detects an error.