JPS60147941A - Optical information reproducing device - Google Patents

Abstract

PURPOSE:To suppress the crosstalk between spots and to attain ease of light collection to a light detecting face by providing a condenser lens by which astigmatism is given to a reflected laser light spot on the photodetecting face and where the interval between the spots on the photodetecting face is spread more than the interval on a recording medium. CONSTITUTION:The emitted light from a light source 1 is separated into three luminous fluxes by a diffractive grating 3 and three optical spots 14 are produced on a disc 12 via a half prism 4, a collimate lens 7, a reflection prism 9 and an objective 10. The reflected luminous flux goes reverse, it is reflected on a half prism 4, expanded by a concave lens 17, astigmatism is formed to a cylindrical concave lens 40 and the result is led to a photodetector 19a. The cylindrical concave lens 40 is arranged so that the direction of the center line has an angle of 45 deg. with the direction of a split line of a 4-split photodetector 19a, and when the focus of the condenser lens 10 to the disc 12 is matched, the luminous flux on the photodetector 19a is round, the interval between spots is remote and the crosstalk is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an optical information reproducing device, and more particularly to an information track tracking device and an automatic focusing device.

[Prior art]

A conventional device of this type is shown in FIG.

In the figure, to is a light source such as a semiconductor laser.

(2: is the output beam emitted from the light source (1). I3) is the output beam + 21 ft3 A diffraction grating that separates the beam into a single beam, (4) is a half prism that separates the irradiation beam (51) and the reflected beam (61). .

(7) is a collimating lens that converts the irradiation light beam (51 into a parallel light beam (8), +9) is a parallel light beam, and a reflecting prism that reflects the beam (8) in an orthogonal direction; This is an objective lens that focuses light as a light spot α on the information track (131).
is placed near the focus of objective lens 4.

Also, the light spot a41 is actually three light spots (1
It consists of 4a), (14b), and (14c). In addition, the information truck (131 is the pit (I9 and land Qe)
It becomes more. Further, the disk +121 is rotated by a motor (not shown). Also disk 1I7J
The luminous flux reflected by the objective lens +1Q,
It passes through the collimating lens (7) and passes through the half prism (4).
) is bent in an almost orthogonal direction and becomes a reflected light beam (6). The background is a concave lens that reduces and expands the reflected light flux +61 UJ convergence angle, or a cylindrical convex lens that causes astigmatism in the light flux that passes through the concave lens, +I! I is a photodetector and piezoelectric (19a).

(19b) and (19c).

The central photodetector (19a) is divided into four parts, and the cylindrical convex lens is arranged with the lens center line inclined by 45 degrees with respect to the dividing line.

(20a), (20b), and (20c) are photodetectors (19a), respectively.

(19b) and (190) are the light fluxes above. I2υ is a photodetector (19b).

A differential amplifier that differentially amplifies the output of (19c), @ is the output of the differential amplifier QI), @ is the four-split photodetector (19a) with the diagonally arranged photodetectors common to each other. , *
A differential amplifier that differentially amplifies the output of the two detectors, (■) is the output of the differential amplifier +21, (C) is a 4-split detector (1Sa)
(7) is the output in the adder, which is the signal output reproduced from the disk (12).

Next, the operation will be explained. The reproduction information read by (14a) is taken out as an electrical signal from the output f, and is then subjected to information processing.

It is converted into a TV signal, audio signal, etc.

Normally, the center of rotation of the disk l12 does not coincide with the center of the disk due to installation error or the like. As a result, track deviation occurs due to rotation. The correction method will be described below. Light source (1
) The emitted light (2) is separated into three beams by a nine-diffraction grating (3) and then emitted in three directions, resulting in three light spots (20a), (20b), (20c) on the disk U7J.
The light is focused on. At this time, the position of the nine diffraction gratings in the rotational direction is adjusted and set so that the arrangement of the three optical slits is slightly oblique with respect to the information track +131. At this time,
The outputs of the photodetectors (19a), (19b), and (19c) are as follows.

The track deviation is as shown in FIG. 2.

At that time, the differential amplifier output with respect to the track deviation becomes as shown in FIG. This output is used as the objective and lens (11
If an application is applied to a tracking actuator (not shown) that moves in the X direction so as to form a negative feedback ring system,
The optical spora (20a) can be constantly focused on the center of the information track.

Also, the dike surface is not normally flat, but wobbles due to rotation. Next, the correction method will be described.

The reflected light flux is magnified by a concave lens 1171, astigmatism is formed by a cylindrical convex lens ag, and is guided to a photodetector (1!J).As shown in FIG. The direction of one circle differs by 90 degrees depending on the direction of the shift.At this time, the differential amplifier output +241 with respect to the focus shift changes as shown in FIG.

Therefore, the focusing actuator that moves the condenser lens in the optical axis direction Y is operated by the output, and the focal shift of the condenser lens can be constantly corrected by a known method.

Since the conventional device is constructed as described above, it has the following drawbacks. That is, as shown in FIG. 6, if there is no cylindrical convex lens U, the light spot will be (20a),
(30b) and (30c), but the distance between the lens center line and the light spot is narrowed in the entrance direction by the cylindrical convex lens, and the light spot becomes (20a).

(20b) , (20 The disadvantage is that the crosstalk characteristics between However, there was also the drawback that productivity deteriorated.

In addition, the photodetector size remains the same and the concave lens (17
If we increase the magnification by 1, the focal length of the concave lens (171) must be made smaller, and the curvature of the lens becomes larger.
This method had the disadvantage that the number of sheets that could be polished at a time was reduced, which increased costs, and that the placement accuracy of the concave lens ([71] became stricter.

[Summary of the invention]

This invention was made in order to eliminate the drawbacks of the conventional ones such as 9 and above, and it is designed so that one reflected laser beam spot causes astigmatism on the photodetection surface and between the reflected laser beam spots on the photodetection surface. Crosstalk between the nine reflected laser beam spots is suppressed by providing a lens between the record carrier and the detection surface that focuses the light onto the photodetection surface so that the distance between the two is wider than the distance between the laser beam spots on the record carrier. In addition, we aim to provide an optical information reproducing device that facilitates focusing of light onto a light detection surface.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. In the figure, +41 is a cylindrical concave lens, which is arranged so that the direction of the center line of the lens makes an angle of 45° with the direction of the dividing line of the 4-split photodetector (19a). The 4-split photodetector (19a) detects when the condensing lens H is focused on the disk aa.
) is placed at such a position that the luminous flux above is rounded.

The light flux on the 4-split photodetector (19a) changes as shown in FIG. 4 depending on the position of the disk O2, as in the case of the conventional device, and a curve corresponding to the focus line as shown in FIG. 5 is obtained. From the differential amplifier outputs of the photodetectors (19b) and (19c), the output characteristics with respect to the track deviation shown in FIG. 3 can be obtained, and the optical spoiler (14a) can be controlled so as to focus on the center of the information track.

FIG. 8 shows the effect on the light spot spacing when a cylindrical concave lens is inserted. The cylindrical concave lens widens the distance between the lens center line and the light spot in the A direction, making the light spot (2 ob).

As shown in (20a) and (20c), the distance between the light spots becomes wider. Therefore, the distance between the light spots (20a) and (2ob) and between the light spots (20a) and (20c) can be increased.

In addition to the above embodiments, as shown in Figure @9, the light source (1) such as a semiconductor laser is used as three light sources (la), (1b),
(lc), and one diffraction grating (3) may be omitted. Further, in the first embodiment, the present invention is applied to an optical information reproducing device, but as shown in FIG. 10, the present invention may also be applied to a recording device that modulates a light source such as a high-power semiconductor laser to enable direct writing.

〔Effect of the invention〕

As described above, according to the present invention, the spot interval on the photodetector becomes large, making it easy to adjust the precision of the arrangement of the photodetector, and also facilitate the precision adjustment of the optical system in the optical axis direction.

[Brief explanation of the drawing]

Figure 1 is a schematic configuration diagram of a conventional example, Figures 2 and 3 are output signal waveform diagrams of the photodetector and differential amplifier in response to track deviation signals, and Figure 4 shows the state of the laser beam spot when the focus is out of focus. FIG. FIG. 5 is a diagram of the output signal waveform of the differential amplifier in response to the defocus signal, FIG. 6 is a plan view of the main part showing the state between the laser beam spots reflected by the cylindrical convex lens, and FIG. 1 is the optical system according to an embodiment of the present invention. Fig. 8 is a plan view of the mounting part showing the state between the reflected laser beam spots by the cylindrical concave lens, Figs. 9 and 10.
The figure is a configuration diagram showing another embodiment of the present invention. In the figure, fil is a light source, (4) is a Nof prism,
(The power is collimating lens, (cur6 reflective prism, (
11% is the objective lens; Agent Masuo Oiwa Figure 1 Figure 2 Figure 3 Figure 4 (a) (41-) (C) Figure 8 Figure 10

Claims (1)

[Claims] (t)? A laser light source device that irradiates the information recording bits of a record carrier with J number of laser light spots, a concave lens that expands the interval between the plurality of reflected laser light spots from the record carrier, and a concave lens that receives the light that has passed through the concave lens. In a device equipped with a photodetector that outputs a deviation correction signal of the laser beam spot irradiation position from the pit row due to the difference in light intensity between the spots, one reflected laser beam spot becomes an astigmatism on the photodetection surface of the photodetector. A cylindrical concave lens is provided between the concave lens and the detection surface to focus the light onto the photodetection surface so as to cause aberration and widen the interval between the reflected laser beam spots on the photodetection surface. Optical information reproducing device. (2) The optical information reproducing device according to claim 1, wherein the laser light source device 1 is configured to obtain a plurality of laser light spots from a laser beam passing through a diffraction grating. 131. The optical information reproducing device according to claim 1 or 2, wherein the laser light source device is configured to obtain a plurality of laser beam spots using a plurality of semiconductor laser devices. (4) The optical information according to any one of claims 1 to 3, wherein the photodetector is composed of six light receiving elements that receive three laser beam spots. playback device.