JPS58118036A - Reproducing system of optical recording medium - Google Patents

Abstract

PURPOSE:To minimize an error of relative position between a recording information track of an optical recording medium and a light spot to be focused, by detecting and compensating the relative position error between the information track and the light spot. CONSTITUTION:A pupil 4 which functions like a phase element that gives a 1/2 change to the light waveguide through its half region is provided at the side of a light source of an objective lens 2. A light spot having an intensity distribution of a double top type is focused on the surface of an optical recording medium 3, and reflected beams r1 and r2 are separated from each other by a polarized beam splitter 7. These separated beams are received by photodetecting elements 81 and 82. As a result, a relative position error can be detected from the difference signal between the elements 81 and 82. Thus the tracking servo control is possible to make a light spot always follow up the shift of an information track with a method which controls the angle of revolution of a rotary mirror based on the above-mentioned difference signal. At the same time, the splitter 7 is turned into a Wallastone prism or the like which has a high ratio of extinction with the above-mentioned method. Then a photomagnetic recording medium can be reproduced by the difference signal between the elements 81 and 82.

Description

Detailed Description of the Invention The present invention relates to an optical recording medium in which light from a light source is focused by an objective lens onto the surface of the optical recording medium on which +1 information is optically recorded, and the reflected light is used for reproduction. This relates to the playback method.

In this type of system, an important issue is to minimize the relative positional error between the recording information track of the medium and the focused light spot.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a reproducing method for an optical recording medium that can detect and correct the above-mentioned relative position error with a simple configuration.

The invention will now be described in detail in conjunction with the drawings.

Figure 1 is an explanatory diagram showing an optical system that focuses linearly polarized light from a light source onto the surface of a recording medium. The light is reflected by the objective lens 2 and focused onto the recording medium 3, but the relative position error (hereinafter simply referred to as relative position 1if-+A) between this focused light spot and the recording information track of the recording medium
A pupil 4 is provided on the light source side of the objective lens 2 as a means for detecting the difference. As shown in detail in FIG. 2, this pupil 4 has a circular aperture 5 formed therein.
The shaded portion 6 in FIG. 2 is a 1/2 wavelength retarder that changes the phase of light by 1/2 wavelength.

Therefore, the light spot focused on the recording medium 6'' is the 6th one.
It has a two-peak intensity distribution as shown in Figure (α), and its image is as shown in Figure 6(b). The two sub-points in Fig. 6) P, , P2U: The planes of polarization are orthogonal due to the presence of the 1/2 wavelength phase shifter B.

Therefore, as shown in FIG. 4, when the reflected light from the recording medium 3 is guided to the polarizing beam splitter 7 and its optical axis is set appropriately, the reflected light r from the sub spot P1 is transmitted to the light receiving element 8. The reflected light r2 from the sub-spots P and P can respectively flow to the light-receiving element 82.

Now, as shown in FIG. 5, when the center of the light spot on the medium is shifted in one direction from the center of the information recording track 9 of the medium, the reflected light from the sub-spots p, , p, subject to change. For example, when transmissive information bits are recorded, the reflected light from sub-spot P1 decreases.

Therefore, it is possible to know the difference signal between the light receiving element 8I and the light receiving element 82, the relative position error, and the direction of the error. Based on this signal, for example, the rotating mirror 1 in FIG.
By controlling the rotation angle θ, it becomes possible to perform tracking servo in which the light spot always follows the movement of the information track.

The above-described 1/2 wavelength retarder can be easily formed by depositing a birefringent material using a mask while controlling the film thickness. Further, as this retarder, one as shown in FIGS. 6 and 7 may be used, and the shaded portion 10.11 in the figure is a 1/2 wavelength retarder.

As described above, according to the present invention, a pupil whose half area is a retarder that changes the wavelength of light by 1/2 wavelength is provided on the light source side of the objective lens, and two peaks are distributed on the medium surface. The light spot of the intensity distribution of the mold is focused, and the reflected light is separated by a polarizing beam head.

Since both of the separated lights are received by the respective light receiving elements (6), it is possible to detect the relative position error from the difference signal between the two light receiving elements. Then, by controlling the rotation angle of the rotating mirror based on this difference signal, it is possible to perform tracking servo in which the light spot always follows the movement of the information track.

In addition, in this method, if the polarizing beam splitter is made of a material with a high extinction ratio such as a Wollaston prism, the difference signal between the two light receiving elements can be used for another purpose, such as reproducing the magneto-optical recording medium. .

[Brief explanation of the drawing]

The drawings show an embodiment of the optical recording medium reproducing method according to the present invention. Fig. 1 is an explanatory diagram of an optical system that focuses linearly polarized light from a light source onto the surface of a recording medium, and Fig. 2 shows an explanatory diagram of an optical system that focuses linearly polarized light from a light source onto the surface of a recording medium. An explanatory diagram of the formed 1/2 wavelength retarder, FIG. 6 ((Z) is an intensity distribution diagram of the focused light spot, and FIG. 3(b) is an explanatory diagram of the image formed by the light spot. , Figure 4 is a scatter diagram of the optical system that guides the reflected light of the light spot to two light receiving elements, Figure 5
The figure is an explanatory diagram showing one example of the relative position error (4) difference, and FIGS. 6 and 7 are explanatory diagrams each showing other examples of the 172-wavelength retarder. In the figure, 1 is a rotating mirror, 2 is an objective lens, 6 is an optical recording medium,
4 is a pupil, 5 is an aperture, 6, 10.11 is a 172 wavelength phase shifter, 7 is a polarizing beam splitter, 81j82 is a light receiving element,
9 is an information recording track. Patent Applicant Fujitsu Limited Agent Patent Attorney Gobe Tamamushi (6 others) Figure 1 Figure 2 (α) Figure 3 (b) 1' χ Gate P-Figure 4 Figure 5 Figure 6 Figure 7 209

Claims (1)

[Claims] 1゜ Between the light source and an objective lens that focuses light from the light source onto the surface of an optical recording medium on which information is optically recorded,
A pupil whose half area is a phase shifter that changes the phase of light by 1/2 wavelength is provided to focus a light spot with a two-peak intensity distribution on the optical recording medium, and to collect the reflected light from the medium. is separated by a polarizing beam splitter, each of the separated lights is received by a light receiving element, and the difference signal is used to detect the relative position error between the recorded information track of the medium and the light spot. Features a playback method for optical recording media. 2. A reproducing system for an optical recording medium according to claim 1, in which the polarizing beam splitter is made of a material having a high extinction ratio such as a Wollaston prism, thereby making it possible to reproduce signals from a magneto-optical recording medium.