Optical pick-up device

Details Optical pick-up device Optical pick-up device

1998-08-27

2000-12-12

Hindi, Nabil

Dynamic information storage or retrieval

Specific detail of information handling portion of system

Radiation beam modification of or by storage medium

369 4424, 369110, 369 94, G11B 700

Patent

active

061607835

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention relates to an optical pick-up device, and more specifically to an optical pick-up device capable of recording on and/or playback of optical disks each having a transparent substrate of a different thickness.


DESCRIPTION OF THE BACKGROUND ART

A type of optical pick-up devices currently provided employs semiconductor laser to read information recorded on optical disks, such as compact disk (CD) and compact disk-read only memory (CD-ROM). This optical pick-up device irradiates a train of pits on a signal recording surface with laser beam while applying focusing servo and tracking servo controls to an objective lens for pick-up to reproduce audio, video and data signals and the like.
In recent years, optical disks of higher density have been developed to record moving pictures for a long period of time. For example, a digital video disk (DVD) standard has been proposed for recording approximately 5 G bytes of information on one side of an optical disk the diameter of which is the same as that of CD-ROM, i.e. 12 cm.
According to this standard, the transparent substrate of the DVD has a thickness of approximately 0.6 mm.
Optical lens for pick-up is designed taking into consideration the thickness of the transparent substrate of the optical disk to be played back and the wavelength of the semiconductor laser used. Thus, an optical disk the transparent substrate of which is not as designed in thickness cannot be played back since a laser beam is not focused on the signal recording surface of the optical disk.
For example, an objective lens designed for a DVD with a transparent substrate of 0.6 mm in thickness cannot focus a laser beam on the signal recording surface of a CD with a transparent substrate of 1.2 mm in thickness so that the CD cannot be played back.
Therefore the present invention contemplates an optical pick-up device capable of employing the optical activity of liquid crystal to record on and/or playback of optical disks each having a transparent substrate of a different thickness and also capable of reducing loss of laser beam due to the liquid crystal.


DISCLOSURE OF THE INVENTION

An optical pick-up device according to the present invention provides recording on and/or playback of a first optical disk having a transparent substrate of a first thickness and a second optical disk having a transparent substrate of a second thickness greater than the first thickness, and includes a laser, rotation means, an objective lens, and a polarizer. The laser produces a laser beam having a predetermined polarization direction. The rotation means rotates the polarization direction of the laser beam by approximately 90.degree. in recording on or playback of the first or second optical disk. The objective lens focuses the laser beam on the signal recording surface of the first or second optical disk. The polarizer blocks the perimeter of the laser beam in recording on or playback of the second optical disk. The rotation means includes a first transparent electrode, a second transparent electrode, a first rubbing film, a second rubbing film, and liquid crystal. The first transparent electrode is located at the incident side of a laser beam. The second transparent electrode is located at the emissive side of the laser beam and opposite to the first transparent electrode. The first rubbing film is formed on an inner surface of the first transparent electrode and has a first rubbing direction approximately parallel or perpendicular to the polarization direction of the laser beam. The second rubbing film is formed on an inner surface of the second transparent electrode and has a second rubbing direction approximately perpendicular to the first rubbing direction. The liquid crystal is interposed between the first and second rubbing films.
With this optical pick-up device, a laser beam having its polarization direction rotated by liquid crystal by approximately 90.degree. can change the effective numerical aperture of the objective lens to allow recording on and/or playb

REFERENCES:
patent: 5930219 (1999-07-01), Kim

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