Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Patent
1996-06-28
1999-04-20
Tran, Thang V.
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
369110, 369 4423, 369 4437, G11B 700
Patent
active
058963600
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to an optical pickup device and an optical disc driving apparatus adapted for employing a variety of optical discs, such as a play-only optical disc, a recordable phase-change optical disc or a magneto-optical disc.
BACKGROUND ART
As optical discs for recording/reproducing the information by irradiation of a laser beam, a magneto-optical disc, a variety of write-once optical discs, a digital audio discs, such as a so-called compact disc or an optical video disc, have been put to practical use.
Of these optical discs, the compact disc or the optical video disc is a play-only disc, and is comprised of a transparent substrate, in which data pits corresponding to information signals are formed as recesses, and a reflective layer formed on the transparent substrate.
As the transparent substrate, a disc-shaped substrate, formed by injection molding a resin, such as polycarbonate, is predominantly employed, since the cost may be lowered especially in case of mass production. On concentric or spirally extending track(s) of the transparent substrate, there are formed data pits as recesses. The reflective layer is layered on the surface of the transparent substrate carrying the data pits. In general, an Al reflective film is used because it has high reflectance and good thermal conductivity.
With the above-described play-only optical disc, the difference in the amount of reflected light between the pits and mirrors, that is disc portions devoid of the pits, on laser light irradiation from the transparent substrate, is detected, and a bit pattern on the track(s) is accordingly reproduced.
For correctly reproducing error-free signals by the above technique, laser light spots need to be radiated correctly on a track on which a bit pattern to be read out is formed. To this end, the optical disc driving apparatus performs tracking servo of the optical pickup device. Among optical disc systems for scanning the concentric or spirally extending track(s) with the laser light beam for recording/reproducing various sorts of data, there are known a CLV system for rotationally driving the optical disc at a constant linear velocity (CLV) for recording/reproducing data, and a CAV system for rotationally driving the optical disc at a constant angular velocity (CAV) for recording/reproducing data. There are also known a continuous servo system in which tracking control is done using a continuous pre-groove formed along the track, and a sample-servo system in which tracking control is done using servo areas provided discretely on the track(s).
A conventional optical pickup device for a magneto-optical disc is configured as shown for example in FIG. 1. During reproduction or recording, a laser beam as an outgoing light beam of a P-polarized component is radiated from a laser diode 1. This outgoing light is collimated by a collimator lens 2 so as to be shaped by a shaping prism 3 to fall on an S-polarizing beam splitter 4.
The S-polarizing beam splitter 4 has a light polarization beam splitter film 4a having characteristics of reflecting the S-polarized light component having the direction of polarization perpendicular to the P-polarized light component and reflecting and transmitting 50% of the P-polarized light and the remaining 50% thereof, respectively. Thus, one-half of the outgoing light of the P-polarized light, incident on the S-polarizing light beam splitter 4, is reflected, while the remaining one-half thereof is transmitted. The outgoing light transmitted through the S-polarizing beam splitter 4 is reflected by a 45.degree.-mirror 5 and thence radiated via an objective lens 6 on a magneto-optical disc 7.
During recording, data is supplied via an input terminal 8 on a magnetic head 9. This drives the magnetic head 9 responsive to the data for.generating a magnetic field corresponding to the data. This magnetic field is impressed on an area of the magneto-optical disc 7 irradiated with the laser beam for recording data thereon.
A reflected light beam is produced by the magneto-optical
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Sony Corporation
Tran Thang V.
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