JPH0414629A - Optical pickup device - Google Patents

Abstract

PURPOSE:To realize the pickup device in which information is accurately recorded and reproduced by forming a 2nd converged spot having an astigmatism on a disk and correcting a spot generated by a reflected light. CONSTITUTION:A luminous flux 2 from a laser light source 1 is collected on a disk 5 via an aperture 3 and an objective lens 4 to form a spot 8. Since the disk 5 is driven by a driving mechanism, the converged spot 8 scans a group 6 on the disk 5 continuously and the distribution of the reflectance onto the spot 8 is asymmetrical and asymmetry is caused in the intensity distribution on a far field of the reflected luminous flux 10. On the other hand, a 2nd converged spot 17 bridges over the group 6 and a land 7 thereby not causing the asymmetricity. Thus, an offset of a radial error signal is corrected by a spot moving signal generated from the reflected light from the 2nd spot 17 to attain accurate information recording and reproduction.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to an optical pickup device for optically recording and reproducing information on a disk.

[Prior Art] Fig. 4 is a configuration diagram showing a conventional optical pickup device, in which (1) is a laser light source, (2) is a radiation beam from the laser light source (1), and (3) is a radiation beam. (2) is an aperture that restricts the spread of light, (4) is an objective lens that focuses the emitted light beam (2) onto the disk (5), and (6) is a track-shaped engraved on the disk (5). Information is recorded or reproduced on the group (6) by an optical or magnetic method. (7) is a land formed between groups (6), (8) is a focused spot formed on group (6), and (9) is a reflected light beam from disk (5). (10) and a beam splitter for separating the emitted beam (2), (11) is a two-split photodetector placed in the far field on the reflected beam (10), and (12) is a photodetector. (11) Each detector (
11a), a differential amplifier that amplifies the differential output from (llb), (13) is an output terminal for the radial error signal output from the differential amplifier (12), and (14) is a photodetector (1
1) The spot formed above, (15) is the objective lens drive mechanism.

Next, the operation will be explained. The emitted light flux (2) from the laser light source (1) is restricted by the diaphragm (3) and then focused by the objective lens (4) onto the group (6) on the disk (5), forming a focused spot ( 8).

This focused spot (8) is modulated by the recorded information on the disk (5), becomes a reflected light beam (10), enters the objective lens (4) again, passes through the beam splitter (9), and is reflected. A photodetector (11) placed in the far field above the light beam (10) converts it into an electrical signal. The boundary line (0) of this photodetector (11) is the reflected light flux (10)
lies on the straight line containing the chief ray of .

The focused spot (8) constantly scans the group (6) on the disk (5) because the disk (5) is rotationally driven by a drive mechanism (not shown). However, if the focused spot (8) deviates from the group (6) due to eccentricity of the disk (5), and a positional shift occurs between the group (6) and the focused spot (8), Since the size of the focused spot (8) is smaller than the width of the group (6) on the disk (5), the reflected light beam (1
0), there is asymmetry in the intensity distribution on the far field.

For this reason, each detector (11a) of the photodetector (11),
(llb) is amplified by a differential amplifier (12) to generate a radial error signal proportional to the relative positional deviation between the focused spot (8) and the group (6). This radial error signal causes the objective lens drive mechanism (1
5) and drive the objective lens (4),
The positional deviation between the group (6) and the focused spot (8) has been corrected. At this time, since the diaphragm (3) is built into the objective lens drive mechanism (15), the objective lens (4)
It moves with the movement of.

[Problems to be Solved by the Invention] Since the conventional optical pickup device is configured as described above, the diaphragm moves as the objective lens (4) moves, and the chief ray of the reflected light flux also moves. Become. For this reason,
The spot (14) on the photodetector (11) moves, the principal ray of the reflected light beam deviates from above the boundary line (0) on the photodetector (11), and an offset occurs in the radial error signal.
There was a problem in that it was impossible to accurately position the focused spot (8) on the group (6), making it extremely difficult to reproduce and record information.

The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide an optical pickup device in which no offset occurs in the radial error signal even if the objective lens moves.

[Means for Solving the Problems] An optical pickup device according to the present invention includes a first optical system that forms a first focused spot on a disk, and a first optical system that forms a first focused spot on a disk, and a a second optical system that forms a second spot having a convergent line perpendicular to the track direction on the disk and has astigmatism; and a first optical system that generates a radial error signal by the reflected light beam from the first condensed spot. a photodetector and a first signal generation circuit; a second photodetector and a second signal generation circuit that generates a spot movement amount signal from the reflected light beam from the second focused spot; and the spot movement amount. and a correction surface path for correcting the offset of the radial error signal using the signal.

[Operation] The optical pickup device of this invention forms a focused spot with astigmatism on the disk, and corrects the offset of the radial error signal using a spot movement amount signal generated by the reflected light beam from this focused spot. By doing so, it is possible to accurately record and reproduce information.

[Example 1] An example of the present invention will be described below with reference to the drawings. 1st
In the figure, (1) is a laser light source, and (2) is a laser light source (
1), (3) is the diaphragm that limits the spread of the radiant beam (2), and (4) is the radiant beam (2) from the disk (
5) Objective lens (6) for condensing light onto the disk (5) is a group carved into a track shape, and information is recorded on this group (6) by an optical or magnetic method. or played. (7) is a land formed between groups (6), and (8) is a first focused spot (9) formed on group (6) from a disk (5). Reflected luminous flux (10) and emitted luminous flux (2)
(11) is a first photodetector placed in the far field on the reflected beam (10), (12) is a first photodetector (11
), the differential amplifier (13) amplifies the output difference from each detector (11a), (11b), and the differential amplifier (12
) is the output terminal for the radial error signal output from (1
4) is a spot formed on the first photodetector (11), and (15) is an objective lens drive mechanism, which have the same structure as the conventional apparatus shown in FIG. 4 above.

(16) is a second beam splitter that makes the radiation beam (2) transmitted through the first beam splitter (9) enter the objective lens (4), and (17) is the second beam splitter (1
A second focused spot is formed on the disk (5) by the emitted light beam reflected by 6), and this second focused spot (17) is reflected by the second beam splitter (16). Since the reflected light flux is incident on the objective lens (4) with an image height, a spot with astigmatism whose convergence direction is in the radial direction is formed. (18) is a second photodetector divided into two that receives the reflected light beam from the second condensing spot (17). In this embodiment, the objective lens (4) and the first beam splitter (9) constitute the first optical system, and the objective lens (4) and the second beam splitter (16) constitute the second optical system. is formed.

FIG. 2 is a diagram showing the shapes of the first and second focusing spots (8) and (17) formed on the disk (5) and the relationship between the image focusing spots.

FIG. 3 shows a processing circuit that processes detection signals from the first and second photodetectors (11) and (18).
is each detector (l) of the first photodetector (11) divided into two.
(20) is a first differential amplifier that amplifies the output difference from (1g) and (llb), and (20) is a second photodetector that is divided into two (
a second differential amplifier that amplifies the output difference output from each of the detectors (18a) and (18b) of 18) by the spot (19) formed thereon; (21) is a correction circuit; This correction circuit (21) is connected to the first differential amplifier (1
2) to the radial error signal (22) output from the second
A correction signal (23) indicating the spot movement amount outputted from the differential amplifier (20) of
).

Next, the operation of the above embodiment will be explained. Laser light source (
The emitted light flux (2) from 1) is restricted by the diaphragm (3) and then focused by the objective lens (4) onto the group (5) on the disk (5).
6) The light is focused on and forms a focused spot (8).

This focused spot (8) is modulated by the recorded information on the disk (5), becomes a reflected beam (10), enters the objective lens again, passes through the first beam splitter (9), and is reflected. A first photodetector (11) placed in the far field above the light beam (10) converts it into an electrical signal. The boundary line (0) of this first photodetector (11) is on a straight line that includes the chief ray of the reflected light beam (10).

The focused spot (8) constantly scans the group (6) on the disk (5) because the disk (5) is rotationally driven by a drive mechanism (not shown). However, due to the eccentricity of the disk (5), the condensed spot (8
) leaves group (6) and moves to the boundary between land (7) and group (6).

At this time, the reflectance distribution on the condensed spot (8) becomes asymmetric, so that the intensity distribution on the far field of the reflected light beam (1o) becomes asymmetric. Therefore, the output difference between each detector (11a) and (llb) of the first photodetector (11) is amplified by the differential amplifier (12), and the focused spot (8
) and group (6) is generated.

However, when the objective lens (4) is driven by the objective lens drive mechanism (15) using this radial error signal, since the aperture (3) is fixed to the objective lens (4), as the objective lens (4) moves, , the reflected light beam (10) moves, and the first point on the far field of this reflected light beam (1o) moves.
The spot (14) on the photodetector (11) also moves, causing an offset in the radial error signal.

On the other hand, the second focused spot (16) is a spot with focused lines in the radial direction, and includes groups (6) and lands (7).
), and the second focused spot (
16) moves on the disk (5), asymmetry is unlikely to occur in the far-field pattern of the reflected light beam from the second focused spot (16).

Therefore, the second differential amplifier (21) amplified by the second differential amplifier (21)
Each detector (18a) of the photodetector (18), (18
The differential output in b) does not depend on the position of the second focused spot (16) on the disk (5). However, this differential output is proportional to the movement of the spot (19) on the second photodetector (18) and becomes a signal (23) indicating the amount of spot movement.

The signal (23) indicating this spot movement amount is transmitted to each detector (11a) of the first photodetector (11), (l
The radial error signal (2 lb) generated by the differential output of
2) is added to the correction circuit (21). Therefore, the offset of the radial error signal (22) that occurs with the movement of the spot (14) on the first photodetector (11) is caused by the movement of the spot output from the second differential amplifier (20). The output terminal (24) outputs a radial error signal whose offset has been corrected by the signal (23) indicating the amount.
) can be obtained.

FIG. 4 shows another configuration example for generating the second focused spot (17), and the same parts as in FIG. 1 are given the same reference numerals and redundant explanation will be omitted. In Figure 4, (25
) is a prism, which prism (25) is arranged in the radiation beam (2). The radiation beam (2) that has passed through this prism (25) enters the objective lens (4) with an image height, so astigmatism occurs and the disc (5)
) to form a spot with astigmatism.

Note that the processing circuit shown in FIG. 3 can be used as is for processing the detection signal from the second photodetector (18) shown in FIG. Further, in this embodiment, a second optical system is formed by an objective lens (4), a beam splitter (9), and a prism (25).

[Effects of the Invention] As described above, according to the present invention, a second focused spot having astigmatism is formed on the disk, and a spot movement amount signal generated by the reflected light beam from this focused spot is used. Since the structure is configured to correct the offset of the radial error signal, there is no offset in the radial error signal even if the objective lens moves, resulting in an optical pickup device that can accurately record and reproduce information. .

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an optical pickup device according to the present invention, FIG. 2 is a diagram showing the relationship between the first and second focused spots formed on the disk, and FIG. 3 is a diagram showing the relationship between the first and second light detection spots. FIG. 4 is a block diagram of a processing circuit for processing detection signals from a conventional device. FIG. FIG. 6 is a diagram showing a condensed spot formed on a disk, and FIG. 7 is a block diagram of a processing circuit for processing detection signals from a photodetector. In the figure, (1) is a laser light source, (2) is a radiation beam,
(3) is an aperture, (4) is an objective lens, (5) is a disk, (8) is a first focal spot, (9) is a first beam splitter, and (11) is a first photodetector. , (12) is the first differential amplifier, (15) is the objective lens drive mechanism, (1
6) is the second beam splitter, (17) is the second focusing spot, (18) is the second photodetector, (20) is the second
(21) is a correction circuit, (22) is a radial error signal, and (23) is a spot movement amount signal. In addition, in the figures, the same reference numerals indicate the same or corresponding parts. Agent Patent Attorney Yoshi 1) Kenji (2 others) 1 Mochisa 0 sudden analysis of the invention of 10 Tsukuyaku: Figure 4 Diagram 1. 2f) Concentrating Subo/Site Sekif Book (2) Figure 2

Claims (1)

[Claims] The radiation beam from the laser light source is focused onto the disk and the first
a first optical system that forms a condensed spot; and a first optical system that receives a reflected light beam from the first condensed spot, and whose boundary line is parallel to the direction of the track carved on the disk in the received light beam. a first photodetector divided into two parts as shown in FIG. a second optical system that forms a second focused spot having astigmatism and a radio field perpendicular to the track direction on the disk in front or behind the first focused spot; and the second focused spot. A second photodetector divided into two parts receives the reflected light flux from a second signal generation circuit that generates a spot movement amount signal shown in the table; a correction circuit that corrects the offset of the radial error signal using the spot movement amount signal; , an optical system drive mechanism that drives a second optical system.