Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Patent
1995-11-20
1998-11-10
Tran, Thang V.
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
369 4426, 369 4438, 369118, 369 13, G11B 700
Patent
active
058354697
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a system for optically recording and reproducing information, and more particularly to an improvement in the recording/reproduction density of an optical disk device that employs a disk-like medium.
BACKGROUND ART
At the present time, the surface density of commercially available optical disk devices is on the order of about 880 megabits per square inch. A surface density capable of being generally realized at the research and development level while overcoming the strict environmental conditions for using optical disk devices is said to be about three times as high as the surface density realized at the product level. In commercially available optical disk devices, a wavelength of 780 nm is used, the numerical aperture (NA) of the objective lens is 0.55, mark length recording is used as a recording system, and continuous servo is used as a servo system. "Standard ECMA-195" is a reference article by ECMA (European Computer Manufacturer Association) containing standards for data interchange on 130 mm optical disk cartridges.
An object of the present invention is to realize the highest density recording/reproducing characteristic of an optical disk while using constituent elements which are realizable at the present time. A recording density of 10 Gbit/in.sup.2 can be realized.
DISCLOSURE OF THE INVENTION
The gist of the present invention is summarized as follows. nm is used as a recording laser, and an SHG (Second Harmonic Generator) for oscillating the wavelength of 530 nm with an output equal to or higher than 15 mW is used as a reproducing light source. corrected for chromatic aberration for recording and reproducing wavelengths. no Larger than about one fourth of a spot size determined from the laser wavelength and the NA of the objective lens. Further, there is also used a medium which has a super-resolution characteristic using a difference in a temperature dependent magnetic characteristic among the layers of a multi-layer magnetic film. size on a disk surface can be made smaller than the spot size determined from the laser wavelength and the NA of the objective lens. Also, there is used a construction with which plural spots can be produced at the time of recording or reproducing. marks having the same circular form are arranged at lattice points of a two-dimensional lattice which extend in a track direction and in a track radius direction. two-dimensional lattice point is detected and the reproduction signals from respective marks are used to perform a signal processing, thereby detecting information. In this case, a light pulse is irradiated with a peak power larger than the power at the time of irradiation with ordinary DC light, and at a timing synchronous with the lattice point, and the reflected light is detected at a timing synchronous with the lattice point. recording clock signal and a reproducing clock signal are generated from buried pits which are discretely provided, and a tracking error signal is detected from wobbling marks.
The recording is made using a conventional high-output laser of 680 nm wavelength, which is capable of direct modulation. The spot size is on the order of 1.23 microns. Using an optical super-resolution effect and taking the efficiency of optical output into consideration, the spot size is reduced to 0.87 microns which is about 70% of 1.23 microns. This reduced spot is used to record a mark of 0.22 micron diameter in a medium in -which a mark equal to or smaller than one fourth of the recording spot can be formed. The construction of the medium is as follows. having a target form on the order of 0.22 microns are recorded beforehand. A recording spot is positioned on the buried mark layer by sample servo to generate a clock signal from the buried pits. In accordance with the generated clock signal, an information mark is recorded in a reproducing layer on the basis of whether or not the buried mark is to be magnetically transferred. The mark recorded in the reproducing layer provides a small mark which conform
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"Optical Components Replicated Optics", Philip Optics, Sep. 1994, pp. 1-28.
ECMA European Computer Manufacturers Association, "Standard ECMA-195", Data Intercharge on 130mm Optical Disk Cartridges--Capacity: 2 Gigabytes Per Cartridge., Sep. 1993.
Andoo Keikichi
Awano Hiroyuki
Komoda Osamu
Maeda Takeshi
Miyamoto Harukazu
Hitachi , Ltd.
Tran Thang V.
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