Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Patent
1996-11-04
1998-09-08
Huber, Paul W.
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
369124, G11B 700
Patent
active
058055584
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
This application is a 371 of PCT/JP/00190 filed Jan. 31, 1996.
1. Technical Field
This invention relates to a light signal detection circuit for optically reproducing signals recorded on an optical recording medium which takes disc shape or tape shape, etc., and more particularly to a light signal detection circuit preferable when applied to reproduction of signals recorded on a magneto-optical disc magneto-optically recorded, or an optical disc recorded by phase pits or change of reflection factor.
2. Background Art
Initially, the optical disc for the magneto-optical disc will be described below.
In the magneto-optical disc, recording signals are recorded by perpendicularly magnetizing the magnetic film in an upper direction or in a lower direction in accordance with recording signals. Reproduction of the magneto-optical disc is carried out by irradiating linearly polarized laser beams onto the disc. With respect to a reflected light of linearly polarized laser beams irradiated onto the magneto-optical disc, its plane of polarization is rotated in dependency upon the fact that the direction of magnetization is changed upwardly or downwardly by the so-called Kerr effect. In the optical system for the magneto-optical disc, change (fluctuation) of the plane of polarization of reflected light is converted into change of light intensity by light detection element, e.g., polarization beam splitter, etc. Photo-detector detects such change of the light intensity as light current.
For the photo-detector, photo-diode, e.g., PIN photo-diode or avalanche photo-diode, etc. is used. By allowing this light current to be passed through current/voltage converter, reproduction signal is obtained.
Explanation will be given in more practical sense. Since a reflected light from the magneto-optical disc is such that since quantity of rotation of the plane of polarization is extremely small, common mode (in-phase) noise component is canceled so that S/N ratio can be improved. The reflected light from the magneto-optical disc is caused to undergo rotation of the plane of polarization, e.g., by half wave plate thereafter to convert change of plane of polarization into light intensity modulated two light beams which are opposite to each other in phase through a light detection element. Changes of light intensity of these light beams are respectively detected by photo-detectors to obtain a magneto-optical reproduction signal by differential component (difference).
A more practical example of a conventional circuit configuration for such a magneto-optical signal reproduction will be described with reference to FIG. 1.
Two light beams which have been intensity-modulated in the state opposite to each other in phase are incident to photo-diodes 80, 81 shown in FIG. 1. As a result, electron (positive) hole pairs are produced in proportion to incident light quantity so that current is caused to flow. Thus, two current signals modulated in the state opposite to each other in phase are respectively taken out from the anode sides (or the cathode sides). In taking out detection output currents from these photo-diodes 80, 81, in order to improve the response speed or the lineality, inverse biases are respectively applied to the terminals to reduce capacity between electrodes.
Output currents from the photo-diodes 80, 81 are respectively passed through capacitors 82, 83 so that DC component is eliminated, and are then converted into voltage signals by current/voltage converters 84, 85. The current/voltage converters 84, 85 respectively output voltage signals of phases opposite to each other to the inverting terminal (-) and the non-inverting terminal (+) of a differential amplifier 86. The differential amplifier 86 removes common mode (in-phase) noise component of the delivered signal to take out a differential (difference) component to thereby obtain a reproduction signal.
The detection technology for light signal by the differential detection system will now be described as the related technology. Initially, FIG. 2 shows a conve
REFERENCES:
patent: 4691308 (1987-09-01), Takagi et al.
patent: 4785167 (1988-11-01), Madrid
patent: 5265085 (1993-11-01), Jaquette et al.
patent: 5295129 (1994-03-01), Lee
Huber Paul W.
Kananen Ronald P.
Sony Corporation
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