Recording medium and optical pickup device

Details Recording medium and optical pickup device Recording medium and optical pickup device

1999-10-21

2001-07-17

Tran, Thang V. (Department: 2651)

Dynamic information storage or retrieval

Storage medium structure

Optical track structure

C369S275300

Reexamination Certificate

active

06262966

ABSTRACT:

TECHNICAL FIELD
The present invention relates generally to a recording medium and an optical pickup device, and more particularly to a recording medium having a recording density twice a recording density of a compact disk and an optical pickup device reproducing information from the recording medium.
BACKGROUND ART
Optical disks, such as CD-ROM (Compact Disk-Read Only Memory), from which information can be read by semiconductor lasers and about 1.2 mm in thickness, have been available. For the reproduction of information from such an optical disk, a focusing servo control and a tracking servo control are performed on an objective lens and a pit string on a signal recording surface are irradiated with laser beams in an optical pickup device. Recently, higher densification has been achieved for recording animation lasting for a long time period.
For example, a DVD (Digital Video Disk) standard has been proposed. According to this standard, a DVD is formed as an optical disk recording information of 4.7 G bytes per one surface and having the same diameter with a CD-ROM, that is, 12 cm. By joining DVDs together back to back, each 0.6 mm in thickness, information of 9.4 G bytes can be recorded on one optical disk. Further, a double density CD that has a recording density twice the recording density of a CD and a CD-&agr; that has a recording density three times the recording density of the CD are under development. Still further, an LD (Laser Disk) and a MUSE-LD (Multiple Sub-Nyquist Sampling Encoding-Laser Disk) recording a MUSE signal have been proposed.
Among these various optical disks, double density CDs, that are of the same diameter and thickness as CDs and hence attract attention as optical disks satisfying the requirement of high densification and requirements of players at the same time, are expected to be utilized as optical disks for karaoke or games, for example. If the double density CDs are to be employed as such, it is desirable to achieve high densification while maintaining the thickness of the double density CD same with CDs, that is 1.2 mm, to ensure the compatibility with the existing optical disks.
In the variety of currently available optical disks, various values are employed for a wavelength of a semiconductor laser employed in an optical pickup device, a numerical aperture of an objective lens, a track pitch and a minimum pit length of the recording medium. In the double density CD, the optimization of reproduction characteristic has not been considered in view of an actual setting of values such as the wavelength of the semiconductor laser, the numerical aperture of the objective lens, the track pitch, and the minimum pit length.
Hence, an object of the present invention is to provide a recording medium having favorable reproduction characteristics and an optical pickup device for the same.
DISCLOSURE OF THE INVENTION
According to one aspect of the present invention, a recording medium for an optical pickup device having a laser with a wavelength of &lgr;&mgr;m and an objective lens with a numerical aperture of NA includes a track with TP &mgr;m pitch where the expression 0.7<TP/(&lgr;/NA)<0.8 is satisfied.
On the other hand, an optical pickup device for a recording medium having a track with TP &mgr;m pitch includes a laser and an objective lens. The laser has a wavelength of &lgr;&mgr;m. The objective lens focuses beams from the laser and has a numerical aperture of NA where the expression 0.7<TP/(&lgr;/NA)<0.8 is satisfied.
Because of the above relation of wavelength &lgr;&mgr;m of the laser, the numerical aperture NA of the objective lens, and the track pitch TP &mgr;m, crosstalk and jitter can be suppressed and a tracking error signal at a sufficient level can be obtained. Thus, the reproduction characteristics are improved.
According to another aspect of the present invention, a recording medium for an optical pickup device having a laser with a wavelength of &lgr;&mgr;m and an objective lens having a numerical aperture of NA, has a track having a minimum pit length L &mgr;m, wherein an expression 0.40<L/(&lgr;/NA)<0.45 is satisfied.
On the other hand, an optical pickup device for a recording medium having a track with a minimum pit length L &mgr;m includes a laser and an objective lens. The laser has a wavelength of &lgr;&mgr;m. The objective lens focuses a beam from the laser and has a numerical aperture of NA, where an expression 0.40<L/(&lgr;/NA)<0.45 is satisfied.
Because of the above described relation of the minimum pit length L &mgr;m, the wavelength &lgr;&mgr;m of the laser, and the numerical aperture NA of the objective lens, jitter can be suppressed and a sufficient modulation ratio can be obtained. Thus, the reproduction characteristics are improved.
In addition, as far as track pitch TP &mgr;m satisfies the relation 0.7<TP/(&lgr;/NA)<0.8 or the minimum pit length L pm satisfies the relation 0.40<L/(&lgr;/NA)<0.45, various semiconductor lasers and objective lenses can be employed. As a result, the design of the optical pickup device is facilitated.


REFERENCES:
patent: 5422874 (1995-06-01), Birukawa et al.
patent: 5477527 (1995-12-01), Tsuchiya et al.
patent: 5659534 (1997-08-01), Terasaki et al.
patent: 5673250 (1997-09-01), Mieda et al.
patent: 5828648 (1998-10-01), Takasu et al.
patent: 5905699 (1999-05-01), Ishibashi
patent: 0 553 541 (1993-08-01), None
patent: 8-87747 (1996-04-01), None
patent: 9-147421 (1997-06-01), None
Patent Abstracts of Japan; vol. 1996, No. 11, Nov. 29, 1996 & JP 08 180492 A (Sharp Corp), Jul. 12, 1996 *abstract*.

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