JP2604353B2 - Spot position error detection system for optical pickup - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spot position error detection system for an optical pickup that performs recording, reproduction, and the like using light.

(Prior Art) FIG. 4 shows a basic optical system of an optical pickup device including a conventional spot position error detection system. Light emitted from the laser light source 20 is focused on a recording medium 25 via a collimating lens 21, a polarizing beam splitter 22, a quarter-wave plate 23, and a focusing lens 24. Light reflected from the medium is split by a simple isolator composed of a quarter-wave plate and a polarizing beam splitter. Part of the reflected light is a half mirror 26
Light splitting photodetector 10 for detecting track errors
The rest enters the two-part photodetector 10 for focus error detection via the converging lens 2 and the knife edge 11.

The error detection system of this optical pickup includes a converging lens 2,
It comprises a photodetector 10, a nail edge 11, and a half mirror 26. The track error is detected by the push-pull method for detecting the deviation of the far field, and the focus error is detected by the knife edge method.

(Problems to be Solved by the Invention) The sensitivity of error detection can be sufficiently obtained by the above-described optical system. However, in this system, reflected light from a medium is divided by a half mirror, so that two photodetectors are used. It is necessary, and it is difficult to reduce the size of the optical system.

For playback-only devices such as compact discs, one 6
An error is detected using a split photodetector. A spot on the recording medium is divided into three by placing a diffraction grating between the collimating lens and the polarizing beam splitter. The center spot is located on the track, and the front and rear spots are located at the left and right track edge positions. In the detection system, as shown in FIG. 5, the center beam is converged on the center of the six-segment photodetector 1 through the converging lens 2 and the cylindrical lens 27, and the focus error is detected by the astigmatism method. Do.
The remaining two beams respectively enter the two surrounding photodetectors and perform track error detection. However, in the astigmatism method, since the detection is performed in the far field as compared with the case where the knife edge method detects the light at the light condensing point, there is a problem that a track error is largely wrapped around the focus area. Further, this system has a problem that an error signal cannot be stably detected by a device that performs recording as well as reproduction only. In addition, there is a system in which a focus error is detected by a critical angle method using a four-divided photodetector and a track error is detected by a push-pull method. However, there remains a problem that a track error largely wraps around to a focus error.

An object of the present invention is to provide a spot position error detection system capable of detecting a focus error and a track error with one photodetector without causing the above-described problems.

(Means for Solving the Problems) A spot position error detection system for an optical pickup according to the present invention comprises a converging lens, an optical path splitter disposed immediately before or immediately after the converging lens, and two parallel splitting lines. A six-segment photodetector having a two-segment photodetector unit and two independent photodetectors is arranged so that the optical axes thereof coincide with each other, and the converging lens and the optical path splitter radially divide the circular beam into four beams. And the divided diagonal areas are symmetrically arranged with respect to the optical disk track direction, and the components of the diagonal areas are respectively collected by two independent photodetectors of the photodetector. It has a function of emitting light and condensing the remaining two components of the pair of diagonal regions on the dividing lines of the two bisected photodetectors.

(Operation) FIG. 1 shows a basic configuration of an error detection system according to the present invention. A
The light beam is split into four areas by an optical path splitter 3 having four areas divided into 〜D. Of these, area A
The light transmitted through (6) and the area C (8) are condensed on the dividing lines of the two two-part light detecting units 4 by slightly changing the optical path to the left and right. The focus error is detected by this beam. This principle is basically equivalent to detection by a knife edge method using a wedge-shaped knife edge 11 as shown in FIG. The detection characteristics of the knife edge are almost the same as those of the conventional linear type. Area B
The light transmitted through (7) and the area D (9) is converged on the light detection unit 5 by largely changing the optical path to the left and right, and the track error is detected by the push-pull method. In the present invention, since the knife edge method is substantially used, the wraparound of the track error caused by the focus error detection by the astigmatism method or the critical angle method of the related art to the focus error can be sufficiently suppressed, and the detector can be used with one or more detectors. A small system can be configured by itself.

The photodetector used in the present invention has the same configuration as the six-segment detector of FIG. 5 which has already been used in the past, and it is not necessary to develop a new detector.

The operation of the optical path splitter is the same even after the converging lens.

(Embodiment) As shown in FIG. 1, the configuration is such that a light splitter 3, a converging lens 2, and a six-split photodetector 1 are arranged with respect to the optical axis of incident light.
The light detector has a light receiving surface at a focal position of incident light transmitted through the converging lens.

As a photodetector, a 6-division detector for a compact disk shown in FIG. 5 is used. 130 μm from the optical axis to the center of the two-segment light detector, and 6 μm from the outer light detector to the center
00 μm. The focal length of the converging lens is 20 mm. The optical path splitter is formed by combining four fan-shaped prisms whose front and rear planes shown in FIG. 3A have a certain angle. When BK-7 glass is used as the material, the angles between the front and rear surfaces are as follows. Regions A and C are formed at 0.7 degrees in opposite directions, and regions B and D are formed at 3.4 degrees in opposite directions. A spot can be formed on a desired light detection unit. As the optical path splitter, one using the diffracted light of the hologram element in FIG. 3B, one combining four reflecting mirrors having different angles in FIG. 3C can be used. Further, the prism can be formed as one body with the converging lens.

(Effects of the Invention) According to the present invention, it is possible to obtain a spot position error detection system for an optical pickup device that can easily perform highly sensitive error detection with a single photodetector.

[Brief description of the drawings]

1 is a diagram showing a basic configuration of the present invention, FIG. 2 is a diagram showing a focus error detection method, FIG. 3 is a diagram showing a configuration of an optical path splitter, and FIG. 4 is a diagram showing a configuration of a conventional optical pickup device. FIG. 5 is a diagram showing a configuration of a conventional error detection system. In the figure, 1... 6-segmented photodetector, 2... Convergent lens 3... Optical path splitter, 4... 2-segmented photodetection unit 5. , 8... Area C, 9... Area D 10... Two-split photodetector, 11... Knife edge 20... Laser light source 21... Collimating lens 22... Polarizing beam splitter 23. Wave plate 24: condensing lens, 25: recording medium 26, half mirror, 27: cylindrical lens.

Claims (1)

(57) [Claims] 1. A convergent lens, an optical path splitter disposed immediately before or immediately after the convergent lens, a split photodetector unit having two parallel split lines, and two independent photodetectors. A split-type photodetector is arranged with the optical axis aligned, and the converging lens and the optical path splitter divide the circular beam radially into four components, and the set of diagonal areas is an optical disc. The components of the diagonal area are arranged symmetrically with respect to the track direction, and condensed on two independent photodetectors of the photodetector, respectively, and the two components of the remaining set of diagonal areas are combined with the two components. A spot position error detection system for an optical pickup, comprising a function of condensing light on split lines of two split photodetectors.