JPS62145536A - Spot position error detecting system for optical pickup - Google Patents

Abstract

PURPOSE:To easily execute an error detection having the good sensitivity with one photodetector by having a 6-division type photodetector to provide two 2-division photodetecting parts and two independent photodetecting parts as a photodetector and arranging an optical path divider immediately before or immediately after a converging lens. CONSTITUTION:A converging lens 2, the optical path dividing device 3 arranged immediately before or immediately after the converging lens 2 and a 6-division type photodetector 1 having two 2-division photodetecting parts 4 and two independent optical detecting parts 5 are provided. To the optical axis of an incident light, the optical divider 3, the converging lens 2 and the 6-division photodetector 1 are arranged, and for the photodetector, the light receiving surface is provided at the focus position of the incident light to transmit the converging lens. As the photodetector, the 6-division detector for the compact disk is used, and as the optical path divider, the front and rear planes are formed by assembling four fan-shaped prisms having the constant angle. For the angle formed by the front and rear surfaces, when a BK-7 glass is used for the material, areas A and C form the inclination by 0.7 deg. respectively in the reverse direction, areas B and D form the inclination by 3.4 deg. respectively in the reverse direction, thereby forming a spot at the desired optical detecting part.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a spot position error detection system for a first pickup that performs recording, reproduction, etc. using light.

(Prior Art) FIG. 5 shows a basic optical system of an optical pickup device including a conventional spot position error detection system. The emitted light from the laser light source 20 is passed through a collimating lens 21, a polarizing beam splitter 22, a quarter wavelength plate 23, and a condensing lens 24.
The light is focused onto the recording medium 25 via the.

The light reflected from the medium is separated by a simple isolator consisting of a 174-wave plate and a polarizing beam splitter.

A part of the reflected light passes through the half mirror 26 and enters the two-split photodetector 10 for tracking error detection, and the rest passes through the converging lens 2 and knife lens 11 and enters the two-split photodetector 10 for focus error detection. do.

The error detection system of this optical pickup consists of a converging lens 2, a photodetector 10, a lens 11, and a half mirror 26. Track errors are detected using the push-pull method that detects far field deviation, and focus errors are detected using the knife method.

(Problem to be solved by the invention) Although sufficient sensitivity for error detection can be obtained with the above optical system,
In this system, since the reflected light from the medium is divided by a half mirror, two photodetectors are required, and it is difficult to miniaturize the optical system.

In a playback-only device such as a compact disc, a single six-segment photodetector is used to detect errors.

A diffraction grating is installed between the collimating lens and the polarizing beam splitter to divide the spot on the recording medium into three. The center spot is placed on the track, and the front and rear spots are placed at the left and right track edge positions.

As shown in Fig. 6, the detection system converges the central beam onto the central four-part part of the six-part photodetector 1 via the converging lens 2 and the cylindrical lens 27, and detects the focus error using the astigmatism method. Let's do it. The remaining two beams are incident on two peripheral photodetectors to perform tracking error detection. However, since the astigmatism method performs detection in the far field compared to the Naifezi method, which detects at a condensed point, there is a problem in that the tracking error is largely reflected in the focus error. Furthermore, this system has the problem that error signals cannot be stably detected in devices that are not only used for reproduction but also for recording. In addition to this, there is a system that uses a 4-split photodetector to detect track errors by pushing and pulling focus errors using the critical angle method, but there remains the problem that the track errors are largely reflected in the focus errors.

An object of the present invention is to provide a spot position error detection system that can detect focus errors and tracking errors with one photodetector without causing the above-mentioned problems.

(Means for solving the problem) The spot position error detection system of the present invention is an optical system in which a converging lens, an optical path splitter, and a photodetector are arranged on the optical axis. It has a 6-segment photodetector with a photodetector and two independent photodetectors, an optical path splitter is disposed immediately before or after the converging lens, and the optical path splitter and the converging lens form a circular beam. is divided radially into four components, and a pair of diagonal two components are divided into two components of the photodetector.
It is characterized by having a characteristic of condensing light onto the dividing line of the two-split photodetector, and condensing the remaining two diagonal components onto two independent photodetecting sections of the photodetector.

(Operation) FIG. 1 shows the basic configuration of the error detection system of the present invention. A-
The light beam is divided into four regions by the optical path splitter 3 having four regions divided into D. Of these, area A (6
) and the area C(8) are focused on the dividing lines of the two two-split photodetecting sections 4 by slightly changing their optical paths to the left and right. Focus error detection is performed using this beam. This principle is basically equivalent to detection by the knife method using a wedge-shaped knife 11 as shown in FIG.

The detection characteristics of the knife are almost the same as those of the conventionally used linear type. Area B (7) and area D (
The transmitted light beams 9) change their optical paths to the left and right and are respectively focused on the photodetecting section 5 to perform tracking error detection using the push-pull method. Since the present invention substantially uses the Naifezi method, it is possible to sufficiently suppress the track error that occurs in focus error detection using the astigmatism method or the critical angle method in the prior art, and to suppress the wraparound into the focus error, and only one detector is required. A small system can be constructed using

The photodetector used in the present invention has the same configuration as the conventional six-part detector shown in FIG. 6, and there is no need to develop a new detector.

As shown in Figure 3, the lower half of the beam is split into a knife; the upper half is used to detect focus errors due to
A method of dividing the optical path and bending the optical path for use in tracking error detection is also considered. However, this method has the disadvantage that the track error detection sensitivity is half of that of the conventional method, and it is also easily affected by recording bit edges.

Note that the optical path splitter has the same effect even after the converging lens.

(Example) As shown in Fig. 1, the configuration is such that a light splitter 3, a converging lens, and a 6-split photodetector 1 are arranged along the optical axis of the incident light. A light receiving surface is installed at the focal point of the incident light.

As the photodetector, a 6-segment detector for compact discs shown in FIG. 6 is used. The distance from the optical axis to the center of the two-split photodetector is 130 μm, and the distance to the center of the outer photodetector is 600 μm. The focal length of the converging lens is 20 mm. The optical path splitter is formed by combining four sector-shaped prisms whose front and rear planes have a constant angle as shown in FIG. 4(a). When BK-7 glass is used as the material, the angles formed by the front and rear surfaces are 0.7 degrees in areas A and C in opposite directions, and areas B and D are 3.4 degrees in opposite directions. By doing so, a spot can be formed at a desired photodetection section. As the optical path splitter, one that uses the diffracted light of the hologram element shown in FIG. 4(b), one that combines four reflecting mirrors with different angles as shown in FIG. 4(c), etc. can be used.

Further, the prism can also be formed integrally 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 a light and amplifier device that can easily perform highly sensitive error detection using a single photodetector.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the basic configuration of the present invention, FIG. 2 is a diagram showing a focus error detection method, FIG. 3 is a diagram showing another division method, and FIG. 4 is a diagram showing the configuration of an optical path splitter. FIG. 5 is a diagram showing the configuration of a conventional optical pickup device, and FIG. 6 is a diagram showing the configuration of a conventional error detection system. In the figure, 1... 6-segment photodetector 2..., converging lens 3...
... Optical path splitter 4 ... Two-split light detection section 5 ...
・Photodetection section 6...Area A7...Area B
8...Area C9...Area D10-2 split photodetector
11... Naifetsuji 20... Loser light source
210.・Collimating lens 22.4. Polarizing beam splitter 23...174 wavelength plate 24...Condensing lens 25...Recording medium 26...Half mirror 2
7... Cylindrical lens 71-1 Figure 2?2 Figure A'3 Opening 7i-4 Figure O 5 Figure O 6 Figure Cylindrical lens

Claims (1)

[Claims] A convergent lens, an optical path splitter placed immediately before or after the convergent lens, and a 6-split photodetector having two 2-split photodetectors and two independent photodetectors are aligned so that their optical axes are aligned. The converging lens and the optical path splitter split the circular beam radially into four components, and the diagonal set of two components are split into two two-split photodetectors of the photodetector. Spot position error detection for an optical pickup, characterized by having a function of condensing light onto a line and condensing the remaining two diagonal components onto two independent photodetecting parts of the photodetector. system.