Dynamic information storage or retrieval – Storage medium structure – Optical track structure
Reexamination Certificate
2001-07-03
2004-09-28
Dinh, Tan (Department: 2653)
Dynamic information storage or retrieval
Storage medium structure
Optical track structure
C369S275300
Reexamination Certificate
active
06798734
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an optical recording medium, particularly to a magneto-optical recording medium for recording, reproducing and erasing information with a laser beam and a magnetic field, and further to a surface reproduction type magneto-optical recording medium in which a recording film is directly irradiated with a laser beam without passing through a substrate, or a surface reproduction type phase-change recording medium for recording, reproducing and erasing information only with a laser beam.
BACKGROUND ART
Optical recording media are portable recording media in which large-capacity, high-density recording is possible, and demand therefor has rapidly increased as rewritable media for recording large-capacity files of computers or moving pictures, with recent development of multi-media systems.
In the optical recording medium, a multi-layer film containing a recording layer is generally formed on a transparent disk-shaped substrate made of a plastic resin or the like, recording or erasing is made by irradiation of a laser beam, and reproduction is conducted by reflected light of a laser. The optical recording media include rewritable erasable type ones such as magneto-optical recording media and phase-change recording media, and write once-type ones which are writable only once such as CD-Rs. As for the magneto—optical recording media, so-called light intensity modulation recording has hitherto been mainly employed, in which after erasing by application of a fixed magnetic field, a magnetic field fixed in the opposite direction is applied to conduct recording. Lately, however, a magnetic field modulation method has been noted, in which a magnetic field is modulated in accordance with a recording pattern while irradiating a laser beam, as a method capable of recording (direct overwriting) by one revolution, and capable of accurately recording even when the recording density becomes high. The phase-change recording media are possible in direct overwriting with light modulation recording, and reproducible with the same optical system as that of CDs or DVDS, which causes their recent significant growth. The write once-type CD-Rs are completely compatible with the CDs, so that they have been widely popularized.
Recording layers have hitherto been irradiated with lasers for recording and reproduction through substrates. As a means for increasing the recording density, the so-called near-field optical recording method has recently noted, in which method recording and reproduction are operated by an optical head brought near a recording film (Appl. Phys. Lett. 68, p.141 (1996)). In this recording method, a solid immersion lens (hereinafter referred to as SIL) head is used to minimize the laser beam spot size, thereby making it possible to reproduce a mark shorter than that of the former recording limit (~&lgr;/2NA, wherein NA indicates the numerical aperture of an objective lens) determined by the laser wavelength. (&lgr;) of a light source, resulting in the achievement of recording and reproduction with super high recording density. In this near-field optical recording, it is necessary that the optical head is brought near the recording medium (200 nm or less). Therefore, a method (surface reproduction type recording) is used in which recording layers are irradiated with laser beams directly without passing through substrates, unlike the conventional magneto-optical recording media in which recording films are irradiated through substrates. In this case, the use of a flying type slider head is proposed in order to bring the SIL head near the recording film.
In the optical recording medium, a track is generally formed in approximately concentric circle form or in approximately helical form, and divided into tens to hundreds of sectors. Each sector has a data recording region for recording data of a user himself and a header region for recording information for reproducing an address and so on of each sector (hereinafter referred to as header information).
In general, methods for recording header signals include a method of forming unevenness on a master plate by previously controlling the on/off of irradiation of a laser beam in a mastering process, and transferring it to a substrate by a molding process, thereby recording the signal (hereinafter referred to as pit format). Besides above, a method of forming only a reference signal showing the writing timing of a header signal in a header region in mastering and molding processes, leaving flat almost all portions succeeding to the header region, and recording the signal by the same system as that of recording data later (hereinafter referred to as soft format). In the pit format, a concave portion of the unevenness pattern constituting the header signal is referred to as a pit, and a convex portion thereof is referred to as a mark. In the case of the soft format, a reference signal indicating timing for writing a header signal is referred to as a timing pattern. In either case of the soft format or the pit format, a guide groove of a data writing region is referred to as a groove, and the other is referred to as a land.
As for the header signal, like CDs, address information and the like is generally recorded by the position or the length of a pit narrower in the width in a direction orthogonal to a track than the track width. Further, header information is reproduced by detecting a change in the amount of reflected light due to diffraction from a pit when a laser beam is irradiated.
Tracking is conducted by detecting diffracted light from a circumferentially continuous groove or a pit for a sample servo. In the case of the pit format, the header signal is detected by a change in the amount of light caused by an interference effect of reflected light on a pit portion and reflected light on a flat portion. On the other hand, in the case of the soft format, reading is carried out in the same manner as in the data recording region. However, in writing the header signal, detection of a timing signal is required, and a change in the amount of light caused by an interference effect of reflected light on a timing pit portion and reflected light on a flat portion are utilized therefor similarly with the pit format.
In an optical recording apparatus, the transfer of a laser beam between tracks apart from each other is called seek. The basic operation of recording/reproduction of the optical recording medium comprises allowing an optical head to seek to a desired track for recording/reproduction, and detecting the number of the desired track and the number of a sector, followed by recording/reproduction. Previously, the seek has been a system of calculating the radius value of a desired track, roughly moving an optical head, conducting a tracking operation at that place to detect the track number, detecting the difference between the track number and the number of the desired track, further minutely moving the optical head, and then conducting the tracking operation to detect the track number, which are repeated to reach the desired track.
Efforts have been made such as counting the number of tracks over which an optical head has passed during seeking in order to shorten the seeking time, or increasing the number of rotations of a medium in order to decrease the rotational latency. In recent years, attempts have been made to incorporate a gray code into a header, for example, as indicated in Unexamined Published Japanese Patent Application No. 6-259709. The track number has a different value for each track. However, when the gray code is used, the difference in the circumferential pit pattern arrangement between tracks adjacent to each other is always one minimum recording unit (wherein the minimum recording unit is a signal shortest in circumferential length, of signals formed in a header region by an unevenness pattern, and the length of all patterns is an integral multiple of this length). Accordingly, almost all pit pattern arrangements constituting pit patterns corresponding to the track numbers, parti
Asano Mutsumi
Futami Toru
Hiramatsu Shigeru
Kawara Yuji
Kawasaki Tatsuo
Dinh Tan
Sughrue & Mion, PLLC
Tosoh Corporation
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