Optical recording medium having a track pitch less than the wave

Details Optical recording medium having a track pitch less than the wave Optical recording medium having a track pitch less than the wave

1997-11-14

2000-01-11

Cabeca, John W.

Dynamic information storage or retrieval

Specific detail of information handling portion of system

Radiation beam modification of or by storage medium

369 4423, 369109, 369118, 3692754, G11B 7135, G11B 709

Patent

active

060143606

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention relates to an optical head and an optical recording apparatus which perform a processing such as recording or regeneration onto or from an optical recording medium such as a digital video disk (DVD) or a compact disk (CD).


BACKGROUND TECHNOLOGY OF THE INVENTION

A commercially available optical disk at present such as a compact disk (CD) has a disk substrate thickness of 1.2 mm, and a pitch of 1.6 .mu.m of a track for recording information. For the purpose of playing back such a CD, an optical head provided with a semiconductor laser emitting a laser beam having a wavelength of 0.78 .mu.m and an objective lens having a numerical aperture (NA) of 0.45 is employed. Regenerating methods commonly used for processing an information signal derived by an optical head from a CD include waveform equalization based on a transversal equalizer or the like and a method based on digitization.
An optical disk having a recording density higher than that of a CD has recently been standardized to serve as an optical recording medium. The standardized specifications for a digital disk (DVD), one of the high-recording-density optical disks set forth a disk substrate thickness of 0.6 mm and a track pitch of 0.74 .mu.m, and for this DVD, use is now considered of an optical head which irradiates a laser beam having a wavelength of 0.65 .mu.m or 0.635 .mu.m through an objective lens having a numerical aperture of 0.6. There is proposed an optical recording apparatus capable of processing optical disks of a plurality of specifications including not only an optical disk having a high recording density such as a DVD, but also conventional CDs.
However, a write-once type CD (CD-R) used as commonly as a CD at present cannot be employed in an optical recording apparatus playing back a DVD by the use of a laser beam of a short wavelength for DVD and capable also of playing back a CD. The CD-R is used for production of a slight quantity of CD-ROMs, data backup or trial manufacture of CDs, and is a dye-based optical recording medium having a high wavelength selectivity near the wavelength (0.78 .mu.m) of a laser beam for a CD. In the proximity of the standard wavelength (0.65 .mu.m), the reflectivity is too low to be practicable. Specifications for wavelengths of a laser beam used for recording or regeneration on or from an optical disk are usually determined by taking account of the track pitch. For a CD, for example, the ratio of the light source wavelength (0.78 .mu.m) to the track pitch (1.6 .mu.m) is 0.49, and for a DVD, the ratio of the light source wavelength (0.65 .mu.m) to the track pitch (0.74 .mu.m) is 0.88. All standards use a laser beam having a wavelength far shorter than the track pitch. In an optical recording apparatus using a laser beam having a short wavelength in conformity to these standards, therefore, regeneration is made possible for DVD and a read-only CD by using a two-focus hologram so as to condense the laser beam onto a CD and DVD having different disk thicknesses, whereas compatibility with a CD-R cannot be ensured in this case. Consequently, it is still necessary to use a separate optical recording apparatus based on a laser beam having a longer wavelength for the purpose of accomplishing recording or regeneration of a CD-R.
The present invention has therefore an object to provide an optical head and an optical recording apparatus which permit recording or regeneration in a group of a CD of any specifications for a DVD, a read-only CD and a CD-R. It is also an object of the invention to provide an optical head and an optical recording apparatus capable of processing a currently commercially available CD-R as well as a DVD permitting high-density recording with a single unit of head or apparatus. Another object of the invention is to provide an optical head and an optical recording apparatus which ensure compatibility of a digital video disk (DVD) and a next-generation high-density optical disk with a currently commercially available CD and a conventional write-

REFERENCES:
patent: 4665512 (1987-05-01), Ando
patent: 5121378 (1992-06-01), Hirose et al.
patent: 5450376 (1995-09-01), Matsumura et al.
patent: 5600620 (1997-02-01), Ohguri
patent: 5625613 (1997-04-01), Kato et al.
patent: 5689495 (1997-11-01), Tsuchiya et al.
patent: 5701286 (1997-12-01), Sato
patent: 5796683 (1998-08-01), Sumi et al.

Affiliated with

Also associated with

Rating

Optical recording medium having a track pitch less than the wave does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Optical recording medium having a track pitch less than the wave, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical recording medium having a track pitch less than the wave will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-1467511