JPS63249942A - Reproducing device for optical disk signal - Google Patents

Abstract

PURPOSE:To detect and reproduce information in a signal band of wide area without complicating the constitution of an optical system, by image-forming one of three spots deflected and separated by a wedge prism on an light receiving element in a central part, and two other spots on the linear segregated band of the light receiving element. CONSTITUTION:A pair of wedge prisms 17a and 17b are arranged so that their deflecting directions are set adversely at a position where first-order diffracted light on an optical path on which reflected light from an optical disk 16 advances to an optical detector 19 is distributed. The pair of wedge prisms 17a and 17b deflect and separate the reflected light from the disk to the three spots, and a convex lens 18 image-forms one of them on the light receiving element 20 in the center, and two other spots on the linear segregated bands of quartered light receiving elements. Therefore, it is possible to function the light receiving element 20 in the center as the one dedicated for detecting an RF signal, and the other light receiving elements 19a-19d as the ones dedicated for detecting control signals for focusing and tracking. In such a way, it is possible to design frequency band areas to the ones required for respective purpose without complicating the constitution of a circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION [2] Field of Industrial Application The present invention relates to an optical disc signal reproducing device for detecting and reproducing information recorded on an optical disc having a guide track.

2. Description of the Related Art Conventionally, in compact discs and the like, it has been common practice to extract a position control signal of a light spot and an information reproduction signal using a photodetector on the same plane in order to reduce the size of the optical system. For example, as shown in FIG. 5, a conventional device of this type includes a laser diode 1, a collimator lens 2,
a polarizing beam splitter 3, a λ/4 wavelength plate 4, an objective lens 6 facing the grooved disk 5, a condenser lens 7,
It has a photodetector 9 consisting of a cylindrical lens 8 and four-divided light receiving elements 9a, 9b, 9c, and gd, and the reflected light from the disk 5 is deflected by a polarizing beam splitter and transmitted through a condensing lens 7 and The light passes through the cylindrical lens 8 and becomes a single light spot and enters the photodetector 9. This light spot is a 3/, -7 light spot that serves both for information signal detection and control signal detection, and the total output sum of the four light receiving elements 98 to 9d becomes an information reproduction signal (hereinafter referred to as RF multiplied signal). The output difference between the four light receiving elements 9a to 9d becomes a control signal (focus error signal, tracking error signal).

Problems to be Solved by the Invention However, with such a configuration, if the signal band of data files etc. becomes wider and separates from the servo band, the signal amplification circuit etc. will require a wider band, which will result in an expensive circuit configuration. . In addition, since the light beam for the servo signal and the RF signal is common, there are problems such as error signal components (for example, tracking error signal components) are often mixed in as a noise factor in the RF multiplied signal. .

In order to avoid these problems, we have no choice but to use a half mirror to deflect and separate a portion of the light intensity, place a separate detector on an independent optical path, and use this separate detector to extract and output the R and F signals. However, this increases the optical system configuration and has the disadvantage that it cannot be simplified.

The present invention has been made in view of the above-mentioned problems, and can be applied to wide signal bands such as data files without complicating or enlarging the optical system configuration or complicating the amplifier circuit configuration. It is an object of the present invention to provide an optical disc signal reproducing device capable of detecting and reproducing certain information.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides a method for distributing first-order diffracted light due to the effect of the guide track of the optical disc on the optical path of the reflected light from the optical disc toward the photodetector. , a pair of wedge prisms for deflecting in a direction orthogonal to the diffraction direction are arranged so that the deflection directions are opposite;
A convex lens is placed behind it, and a photodetector consisting of a central light-receiving element and four light-receiving elements arranged along two orthogonal axes is placed at the focal point of the convex lens. It is prepared.

According to the above-described structure, the pair of wedge prisms directs the reflected light from the disk to the three spots 5.

The convex lens focuses one image on the central light-receiving element and the other two on the linear separation band of the four-divided light-receiving element, so that the RF of the central light-receiving element is It is possible to act as a detection element dedicated to signal detection, and to use the other four-divided light receiving element to detect focus and tracking control signals. In this way, the light beams for the RF signal and the focus and tracking control signals are incident on the five light-receiving elements arranged on the same plane.
There is no need to increase the size of the optical system, and since the light-receiving element for R and F signal detection and the light-receiving element for control signal detection are separate, the required frequencies can be adjusted for each without complicating the circuit configuration. Band can be designed. Furthermore, a high-quality signal without RF multiplied signals or error signal components can be obtained.

Embodiment FIG. 1 shows an embodiment of the present invention, in which 11 is a laser diode, 12 is a collimator lens, 6 to 1/13 is a polarizing beam splitter, 14 is a λ/4 wavelength plate, and 1 is a polarizing beam splitter.
5 is an objective lens, 16 is a grooved optical disk,
17a and 17b are a pair of wedge prisms, 18 is a convex lens, and 19 is a photodetector. A pair of wedge prisms 17a and 17b are placed on the surface of the polarizing beam splitter 13 facing the photodetector 19, that is, on the optical path on which the reflected light from the optical disk heads toward the photodetector 19, and on the effect of the guide track of the disk 6. At the position where the first-order diffracted light is distributed,
The orientation of each wedge is opposite to each other and parallel to the guide track. The photodetector] 9 is placed at the focal point of the convex lens 18.

As shown in FIG. 2, this photodetector 19 includes a central light-receiving element 9e and a light-receiving element 19a arranged around it and divided into four parts along two orthogonal axes.

It consists of 19b, 19C, and 19d. The central light-receiving element 19e is for detecting RF signals, and the other four light-receiving elements 193 to 19d are for detecting servo signals, and are each connected to a detection circuit (not shown). This 5-split photodetector 19 has three spots 20, 2], a, and 21b which are deflected and separated by wedges 7 and -7 and rhythms 17a and 17b.
0) at the center of the central light-receiving element, and the other two (2
1a, 21b) are arranged so as to form an image on the linear separation band of the light receiving element.

The operation of the optical disc signal reproducing apparatus having the above configuration will be explained.

The laser light from the laser diode 1 is converted into parallel light by the collimator lens 12, and then sent to the polarizing beam splitter 1.
3. The light is focused onto the optical disk 16 by the λ/4 wavelength plate 14 and the objective lens 15.

The reflected light from the optical disk 16 is deflected by the polarizing beam splitter 13, passes through the convex lens 18, and enters the photodetector 19. At this time, due to the diffraction of the guide track,
The light intensity distribution of the reflected light is as shown in FIGS. 3 and 4 on the exit surface of the polarizing beam splitter 13 to the photodetector 19. That is, in the same figure, 22 is O-order diffracted light, 23
The hatched portions indicated by a and 23b are the first-order diffracted light that appears when the optical spot on the disk deviates from the track center, and the intensity distribution changes depending on the depth, width, etc. of the guide track. As described above, the first-order diffracted light 23a.

At the position 23b, wedge prisms 17a, 171
) are in opposite directions (2 devices), so the reflected light that exits the polarizing beam splitter 13 is divided into three parts: a straight part in the center and parts that are deflected up and down on both sides.
Convex lens (two and three spots 20°212, 2
1b and enters the photodetector 19. central spora)
Reference numeral 20 mainly consists of 0th order diffracted light, which is used as light for RF signal detection by the light receiving element in the center of the photodetector 19).
19a. the other two spora) 21a,
21. b mainly consists of first-order diffracted light, and four light-receiving elements are used as error signal detection light)
The light is incident on the vertical separation strips 19a and 19d. Here, in FIG. 3, the width W of the wedge prisms 17a and 17b and the distance d between them are set so that the above-mentioned change in the first-order diffracted light can be sufficiently detected, and the amount of light for detecting the RF signal passing through the center is set such that the S/N etc. The optimum value is determined by taking into account the balance between the two.

9.\-) With the above configuration, the detection of the RF reproduction signal is performed independently by the central light receiving element 19a.

The position of the light spot is controlled by the other four light receiving elements)
19a and 19d. In other words, the focus error detection is the Knifezi method, and the theoretical formula is (19
a-1,9b)+(],9C-19d)=FE, and the tracking error detection is by push-pull method, (1,9a+1-9b)-(1,9C+19d)-
It is TE.

Effects of the Invention As is clear from the above explanation (2), the present invention provides a method of diffraction in the direction of diffraction on the optical path of the reflected light from the optical disc toward the photodetector, at the position where the first-order diffracted light is distributed due to the effect of the guide track of the disc. A pair of wedge prisms are arranged so that the deflection directions are opposite to each other, and a convex lens is placed behind the wedge prisms. 2 orthogonal
1 consisting of a light-receiving element divided into four parts along the axis.
0 ・, -7 By arranging the photodetector, the reflected light from the disk is deflected and separated into a central RF signal beam and two spot control beams on both sides, which are arranged in the same plane. The RF signal beam is incident on a photodetector, and the RF signal beam is incident on a central light receiving element dedicated to RF signal detection to output an information signal, and the other two spot control beams are
The control signal can be output by inputting it to a four-divided light-receiving element for control signal detection, and it is possible to obtain an RF multiplied signal in a high frequency band such as a data file while simplifying the optical system configuration and amplifier circuit configuration. This has the effect that it is possible to obtain high-quality R and F reproduced signals with few noise components.

[Brief explanation of drawings]

FIG. 1 is a schematic perspective view of an optical disc signal reproducing device according to an embodiment of the present invention, FIG. 2 is a plan view of a photodetector used in the above embodiment, and FIG. 3 is a diagram showing the light of the polarizing beam splitter in the above embodiment. FIG. 4 is a front view showing the surface facing the detector, FIG. 4 is a graph showing the light intensity 11 p// distribution on that surface, and FIG. 5 is a schematic perspective view of a conventional optical disc signal reproducing device. 11... Laser diode, 12... Collimator lens, 13... Polarizing beam splitter, 14...
2/4 wavelength plate, 15... objective lens, 16... optical disk, 17a, 17b... wedge prism,
18 - convex lens, 19... photodetector, 1.9a,
], 9e... Light receiving element.

Claims (1)

[Claims] On the optical path where the reflected light from the optical disk heads towards the photodetector, the direction of each wedge is in opposite directions and parallel to the guide track at the position where the first-order diffracted light is distributed due to the effect of the guide track of the disk. It has a pair of wedge prisms, a convex lens placed behind the prisms, and a photodetector placed at the focal point of the light reflected by the convex lenses. , and a light-receiving element arranged around the light-receiving element and divided into four by two orthogonal axes, and one of the three spots deflected and separated by the wedge prism is placed at the center of the central light-receiving element, and the other is placed at the center of the central light-receiving element. An optical disk signal reproducing device characterized in that two of the above are arranged so as to form an image on a linear separation band of a light receiving element.