JPS63205830A - Optical pickup - Google Patents

Abstract

PURPOSE:To obtain a stable servo control signal and light information signal by forming one face of a concave lens which magnifies the reflected light from a disk and spots the same onto a photodetector to an aspherical face. CONSTITUTION:Light from a semiconductor laser 1 is condensed by an objective lens 3 onto the disk 4 and the reflected light thereof is detected through lenses 13, 16 by a photodetector 7. The one face of the concave lens 13 which magnifies the light spot on the element is formed to the aspherical face. Mapping directions 8, 9 of tracks and the virtual line perpendicular thereto in a spot diagram on the element 7 can be decreased in spherical aberration by the aspherical concave lens 13 and, therefore, said lines coincide with division lines 10a, 10b. The stable servo control signal and light information signal from which the false focus error by a tracking error and disk distortion is eliminated are thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical pickup that optically reads information by projecting a light spot onto an information trunk on which high-density signals are recorded on a disk.

Conventional technology In the optical path that guides the reflected light from the disk to the photodetector, (1) the spot diameter on the photodetector is enlarged to facilitate adjustment within a plane perpendicular to the optical axis of the photodetector; .

(2) An optical system using a 3-beam system, with the main beam (
The distance between the (O-dimensional) and sub-beam (1-dimensional) on the light receiving element is widened.

(3) Semiconductor laser and photodetector are beam splitters
(Half mirror) is provided with adjustment means to maintain a conjugate relationship.

For this purpose, concave lenses have been commonly used.

Figure 6 shows a conventional general one-beam optical system, in which 1 is a semiconductor laser, 2 is a nof mirror,
3 is an objective lens, 4 is a disk, 6 is a concave lens, θ is a cylindrical lens, and 7 is a light receiving element.

The concave lens used in the optical system has conventionally been a biconcave lens with spherical surfaces on both sides (Fig. 6a) or a plano-concave lens with a spherical surface on one side (Fig. 6b), and the purpose is as described above. By using the concave lens, spherical aberration occurs on the light receiving element.

Problems to be Solved by the Invention FIG. 7 is a spot diagram on the light receiving element 7 in the optical system shown in FIG. 6, where 8 indicates the mapping direction of the track (bit string) on the disk on the light receiving element T; 9 is the mapping direction of the virtual line perpendicular to the track on the light receiving element 7; 10
&, 10b is a dividing line of the light receiving element.

In FIG. 7, the track mapping direction 8 does not coincide with the dividing line 102L due to the spherical aberration of the concave lens 5, and the farther it goes to the periphery of the spot, the further away from the dividing line 10&.

This not only causes tracking errors when the phase difference method is used as the tracking servo system, but also causes problems when the defect enters if there is a defect 11 such as a scratch on the surface of the disk 4 as shown in Figure 8. The defect mappings 12 & , 12b on the light-receiving element 7 are as shown in FIG. This has the drawback of causing focus errors and deteriorating signal reproducing ability (hereinafter referred to as playability).

Means for Solving All Problems The present invention provides an optical pickup with stable servo and playability by making at least one surface of the concave lens aspherical.

Function The present invention uses a concave lens with the above configuration and suppresses spherical aberration as much as possible to make the track mapping on the light receiving element coincide with the dividing line of the light receiving element, thereby eliminating tracking errors and false focus errors due to disk defects. As a result, stable servo control signals and original information signals can be obtained, and playability can be improved.

Embodiment FIG. 1 shows an optical pink-up optical system according to an embodiment of the present invention, and 13 is an aspherical concave lens having an aspherical surface on one side and a spherical surface on the other side. The other details are the same as in Figure 6.

The operation of the original pickup configured as described above will be explained below.

FIG. 2 is a spot diagram on the light receiving element 7 in the optical system shown in FIG. 1, and 8 and 9 are the mapping directions of a track and a virtual line perpendicular to the track, respectively. These mapping directions are determined by the dividing line 1 of the light-receiving element because the spherical aberration can be made very small by the aspherical concave lens 13.
02L and IQb are in very good agreement.

In the original pickup configured as described above, no tracking error occurs even if the phase difference method is used as the tracking servo method.

Furthermore, even for a disk with a defect 11 as shown in FIG. 8, the defect mappings 122L and 12b on the light receiving element T when the defect enters are as shown in FIG. Since B is mainly C+D, focus errors hardly occur.

Fig. 4 shows a half mirror 14 using a parallel flat plate, but in addition to tilting the concave lens 13 to correct coma aberration, which is conventionally known, it is possible to make the concave lens 13 an aspherical lens. , a spot 7) diagram and track mapping similar to that shown in FIG. 2 can be obtained.

As described above, according to this embodiment, the track mapping on the light-receiving element can be made to match the dividing line of the light-receiving element very well, and stable servo characteristics and improved playability can be realized.

Effects of the Invention As described above, the present invention makes at least one surface of the concave lens provided in the optical path from the disk to the light receiving element aspherical, thereby changing the track mapping on the light receiving element to the dividing line of the light receiving element. It is possible to obtain stable servo control signals and optical information signals, and to realize an optical pickup with excellent playability.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of an optical pickup optical system according to an embodiment of the present invention, Fig. 2 is a spot diagram on the light receiving element of the optical system shown in Fig. 1, and Fig. 3 is a spot diagram on the light receiving element when entering a defect. FIG. 4, which is a plan view of the defect mapping, is a configuration diagram of an optical system in a second embodiment of the present invention. 6th
The figure is a block diagram showing the optical system of a conventional optical big amplifier.
The figure is a sectional view showing the shape of the concave lens of the optical system shown in Fig. 6, Fig. 7 is a spot diagram on the light receiving element in the optical system shown in Fig. 6, and Fig. 8 is a plan view of a disk having a defect. FIG. 9 is a plan view of a defect mapping on the light receiving element when the disk of FIG. 8 enters a defect. DESCRIPTION OF SYMBOLS 1... Semiconductor laser, 2... Half mirror 13... Objective lens, 4... Disk, 6... Lindrical lens, 7...
. . . Light receiving element, 8 . . . Track mapping direction, 9 . . . Mapping direction of a virtual line perpendicular to the track,
1 ON, 1 ob... Division 1 of light receiving element
．． 13...Aspherical concave lens, 14...
Half Mirror 0 Name of agent: Patent attorney Toshio Nakao and 1 other person/
-4-4#L, -Day 2-" Half mirror 3 - Objective lens 4 - Disc 6 - Cylindrical square lens 7 - Notch element 13 - Non-X1.fI concave lens Fig. 1 Fig. 2 0a Fig. 3 10a 12b Figure 4 Figure 5 Figure 6 (C1) tbJ Figure 7

Claims (1)

[Claims] An objective lens that focuses the light emitted from the semiconductor laser onto the disk, a light receiving element that receives the modulated reflected light from the disk, and a light spot on the light receiving element in the optical path from the disk to the light receiving element. 1. An optical pickup comprising: a concave lens for magnification; at least one surface of the concave lens has an aspherical shape.