Optical disc

Details Optical disc Optical disc

1996-07-01

1997-04-29

Hindi, Nabil

Dynamic information storage or retrieval

Storage medium structure

Optical track structure

G11B 700

Patent

active

056256205

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention relates to an optical disc in which tracking control, etc. is carried out by the sample servo system.


BACKGROUND ART

Hitherto, an optical disc for carrying out recording/reproduction of information by irradiation of laser beams, magneto-optical discs, various write-once type optical discs which are, digital audio discs so called compact discs, and optical video discs, etc. have been put into practical use.
The compact disc and/or the optical video disc among these optical discs are reproduction only optical discs, are ordinarily of a structure in which a reflection layer is formed on a transparent base (substrate) where data pits corresponding to information signals are formed in a recessed form.
As the transparent base, because cost can beheld down to a lower level particularly in the case where those bases are mass-produced, disc-shaped bases obtained by injection-molding resin such as polycarbonate, etc. are frequently used. Data pits are arranged and formed as a concave recessed form on tracks set in concentrical form or in spiral form of the transparent base.
Moreover, the reflection layer is stacked on the surface where data pits are formed of the transparent base. Aluminum reflection film is generally used because of its high reflection factor and good thermal conductivity.
In the reproduction only optical disc of such a configuration, a technique is employed to detect a difference between quantity of reflected light at the pit portion and that at the portion where no pit exist, i.e., the mirror portion when laser beams are irradiated from the transparent base side to reproduce the pit pattern on the tracks on the basis of the difference. In this case, in order to carry out precise signal reproduction free from error by such a technique, it is necessary that a laser beam spot is precisely irradiated onto the track where a pit pattern to be read out is formed. For this reason, in the optical disc drive, tracking servo of the optical pick-up is carried out.
As the optical disc system for scanning, by laser beams, tracks formed in a concentric form or in a spiral form to carry out recording/reproduction of various data, there are known the optical disc system of the CLV system for rotationally driving the optical disc at a constant linear velocity (CLV) to carry out recording/reproduction of data, and the optical disc system of the CAV system for rotationally driving the optical disc at a constant angular velocity (CAV) to carry out recording/reproduction of data.
Further, there are known, in terms of the servo system, optical discs of the continuous servo system to carry out tracking control, etc. by using pre-grooves continuously provided along the tracks, and optical discs of the sample servo system to carry out tracking control, etc. by making use of servo areas discretely provided on the tracks.
In the case of the optical discs of the sample servo system, respective tracks are divided into plural data areas, and two servo pits are respectively formed in the servo areas between the respective adjacent two data areas.
Respective two servo pits are formed as so called wobble pits by a geometrical concavity at positions respectively spaced by a 1/4 track width in a radial direction from a center line of the track by arrangement in wobble form in such a manner that the scanning line of the laser beam spot, i.e., the center line of the track is put therebetween before and after.
Tracking servo of the laser spot is carried out on the basis of servo pits arranged in a wobble form. Such servo pits are used for tracking servo as stated above, and are also utilized for generating a clock signal for the reproducing system. Accordingly, in the sample servo system, shape and/or position accuracy of the servo pit are very important for satisfactorily constituting the reproducing system.
Meanwhile, as the transparent base (substrate) of the optical disc, injection-molded bases are frequently used as described above. Such injection-molded base is made up, e.g., in a manner as des

REFERENCES:
patent: 5436770 (1995-07-01), Muto et al.
patent: 5533003 (1996-07-01), Kobayashi

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