Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Patent
1993-09-21
1996-11-19
Nguyen, Viet Q.
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
369100, 369110, 369109, 369113, G11B 1110
Patent
active
055770185
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/JP93/00158 filed Feb. 8, 1993.
TECHNICAL FIELD
The present invention relates to a phase changing apparatus such as a phase delay type prism, combination optical rotating plate, etc. and to an optical pickup apparatus used for an optical disk device using the phase changing apparatus more particularly relates to an optical pickup apparatus for a magneto-optic storage device suitable for reproduction of information recorded in a magneto-optic recording medium (MO) and a phase difference generation apparatus used in this optical pickup apparatus etc.
BACKGROUND ART
In an optical pickup apparatus used for a magneto-optic storage device for reproducing information recorded in a magneto-optic recording medium, for example, a magneto-optic disk, a linear polarized laser beam is irradiated on a recording surface of the magneto-optic disk, and the information recorded as a magnetization direction on the recording surface is converted to a rotation of the polarization plane by the electrooptic Kerr effect or the Faraday effect, which are interactions between light and magnetization, and then detected.
Such an optical pickup apparatus for a magneto-optic storage device differs from an optical pickup apparatus which reproduces information from a compact disk (CD) such as an optical disk used only for reproduction, a write-once optical disk, a phase change type optical disk, etc., that is, an optical pickup apparatus for an optical recording and reproduction apparatus which detects the change of the amount of reflection light based on the presence/absence of pits.
In an optical system for a CD, as seen in a laser coupler, a reduction of size has been realized. However, in an optical system for an MO, it is technically difficult how to design that the reflection film of a beam splitter for splitting the MO signal can be used in the converged light, and thus the reduction of size as in the optical system for a CD has not yet been realized.
On the other hand, a polarization beam splitter has been known as an optical element which can exhibit desired characteristics even if it is placed in converged light, but it has been thought to be difficult to separate a MO signal using a polarization beam splitter. Nevertheless, several methods mentioned below have been known.
A conventional optical pickup apparatus for a magneto-optic storage device is constituted by for example a semiconductor laser; a collimate lens which collimates the light emitted from this semiconductor laser to a parallel beam; an objective lens which converges the emitted light collimated to the parallel beam by this collimate lens and irradiates the same on the recording surface of the magneto-optic disk; a polarization beam splitter which is arranged between the semiconductor laser and the objective lens and separates a part of the reflection light reflected at the recording surface of the magneto-optic disk (hereinafter referred to as the first polarization beam splitter); a light detector which detects a part of the reflection light split by this first polarization beam splitter; a photoelectric conversion element which detects the level of the light transmitted through this light detector (hereinafter referred to as a detector), etc. The emitted light from the semiconductor laser is converged and irradiated on the recording surface of the magneto-optic disk, a part of the reflection light reflected at this recording surface is split, and the level of the component having a predetermined polarization plane in a part of the split reflection light, that is, a predetermined light vibration plane is detected, and the information recorded in the magneto-optic disk is detected from that component.
As the above-mentioned light detector, a "sheet analyzer" has been generally used, but a sheet analyzer has a low "extinction rate", and therefore has a problem in that the S/N (signal to noise ratio) is low. This type of optical pickup apparatus for a magneto-optic storage device is not used much at all at present.
Therefore, a
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Horimai Hideyoshi
Saito Kimihiro
Seo Katsuhiro
Toyota Kiyoshi
Kananen Ronald P.
Nguyen Viet Q.
Sony Corporation
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