Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
1998-04-09
2001-01-23
Hindi, Nabil (Department: 2753)
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
C369S112040
Reexamination Certificate
active
06178151
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical head which can be used for an optical disk apparatus performing reproduction and/or recording of data through use of a laser beam, and performs reading and/or recording of a signal, and also to a method for producing the same.
2. Description of the Related Art
Recently, optical disk media have been practically used as high-capacity data files. Realization of optical disk media having a higher capacity has been desired in order to widen the range of applications thereof. Regarding a recording density of an optical disk apparatus, the partial response technology has put to practical use a recording density of about 0.3 &mgr;m/bit for a linear density direction and a recording density of about 1.2 &mgr;m/track for a track direction.
An improvement in the recording density of the optical disk apparatus can be realized by a reduction in the size of a light spot formed on an optical disk medium by a light beam which is converged by an optical head. Such a size of the light spot formed by the optical head is generally determined by a wavelength of a light source and an aperture of a converging lens. Accordingly, various systems in which the size of the light spot is reduced through an improvement in these parameters in order to improve the recording density of the optical disk apparatus have been proposed.
In one of these proposed systems, such as that disclosed in Japanese Laid-Open Publication No. 5-135401 and U.S. Pat. No. 5,590,110, light reflected from the optical disk medium is converged again using a lens, and only the light in a central portion of the converged light beam is separated and detected by being passed through a pinhole region of a pinhole filter. Such a system enables a signal to be reproduced with a resolution higher than an original resolution determined by the wavelength of the light source and the aperture of the converging lens employed in the optical system, thereby making possible the realization of a high-density optical disk apparatus.
In the following, this system is referred to simply as “optical head super-resolution reproducing system.”
In the optical head super-resolution reproducing system according to the conventional technology, it is necessary that the pinhole region of the pinhole filter be aligned with the central portion of the converged light beam with high precision on the order of a micron. In this case, the alignment in the focal length direction from the lens can be realized easily to some extent by arranging the pinhole filter at a design-based, prescribed position. However, in order to obtain sufficient functioning of the optical head super-resolution reproducing system, it is necessary that the converged light beam precisely pass through the minute pinhole region of the pinhole filter. This requires that the pinhole filter be precisely two-dimensionally aligned in a plane which is spaced from the lens by a focal length and is perpendicular to an optical axis (this plane may be referred to as “focal length plane” in the following).
In reality, however, it is impossible to achieve a sufficient level of precision in such alignment of the pinhole region (especially, the two-dimensional alignment in the focal length plane). Consequently, it is extremely difficult to put the optical head super-resolution reproducing system into practical use.
SUMMARY OF THE INVENTION
An optical head of the present invention includes: a light source; a photodetector for generating a prescribed signal based on light which the photodetector receives; a converging optical system for converging a light beam emitted from the light source to be incident upon a prescribed reflective member; and a reproducing optical system for guiding reflected light from the prescribed reflective member to the photodetector. The reproducing optical system is configured for converging light on a prescribed converging point, and a filter having a light transmissive region for allowing light in the vicinity of a center of the converged light to selectively pass therethrough is provided in the vicinity of the converging point. The light transmissive region of the filter is formed by light which has passed through at least a part of the reproducing optical system and has been converged.
The prescribed reflective member may be an optical disk medium. Furthermore, the optical disk medium may be a magneto-optical disk medium.
In one embodiment of the invention, the optical head has an optical arrangement of a finite luminous flux system.
Preferably, the light transmissive region of the filter may be formed by the reflected light which has passed through the reproducing optical system and has been converged.
In one embodiment of the invention, the reproducing optical system includes a converging lens for converging the reflected light, and the filter is provided on a surface opposing a lens-forming surface of the converging lens.
In another embodiment of the invention, a film made of a material which has a higher refractive index than the converging lens is formed between the surface opposing the lens-forming surface of the converging lens and the filter.
In one embodiment of the invention, the filter is formed using a film made of a material which has a melting point of about 500° C. or lower. For example, the film may be a Te—C film.
Alternatively, the filter may be formed using a film of a dye whose transmittance reversibly changes in accordance with optical energy of irradiated light. For example, the dye may be a photon mode photochromic dye.
In one embodiment of the invention, the light transmissive region of the filter is provided at a position which is offset from a converging point obtained in the case where an optical axis of the reproducing optical system and the filter are arranged so as to be perpendicular to each other.
The light source, the converging optical system and the reproducing optical system may be integrally structured.
Another aspect of the present invention provides a method for producing an optical head, which includes: a light source; a photodetector for generating a prescribed signal based on light which the photodetector receives; a converging optical system for converging a light beam emitted from the light source to be incident upon a prescribed reflective member; and a reproducing optical system for guiding reflected light from the prescribed reflective member to the photodetector. The method includes the steps of: configuring the reproducing optical system so as to converge light on a prescribed converging point; providing a film made of a prescribed material in the vicinity of the converging point; and irradiating the film made of a prescribed material with light which has passed through at least a part of the reproducing optical system and has been converged to form a filter having a light transmissive region for allowing light in the vicinity of a center of the converged light to selectively pass therethrough.
In one embodiment of the invention, the method further includes the step of increasing an amount of the reflected light which is guided from the prescribed reflective member to the reproducing optical system. For example, the step of increasing an amount of the reflected light may include the step of changing a polarization state of the reflected light.
The prescribed reflective member may be an optical disk medium. Furthermore, the optical disk medium may be a magneto-optical disk medium.
In one embodiment of the invention, an optical arrangement of a finite luminous flux system is provided.
In one embodiment of the invention, the film made of a prescribed material is provided on a surface opposing a lens-forming surface of a converging lens which is included in the reproducing optical system and converges the reflected light.
In another embodiment of the invention, the method further includes the step of forming a film made of a material which has a higher refractive index than the converging lens between the surface opposing the lens-forming surfa
Birukawa Masahiro
Hino Yasumori
Miyatake Norio
Nakamura Tadashi
Hindi Nabil
Matsushita Electric - Industrial Co., Ltd.
Renner , Otto, Boisselle & Sklar, LLP
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