Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse... – Magnetic field and light beam
Patent
1993-12-28
1996-07-02
Epps, Georgia Y.
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
Magnetic field and light beam
365 122, 428694ML, G11B 1100, G11B 570
Patent
active
055329845
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a novel magneto-optical disk for exclusive use of reproduction and to reproducing method and reproducing apparatus thereof.
BACKGROUND ART
Efforts are being made to develop an optical recording/reproducing method satisfying various requirements including a high density, a large capacity, a high access speed, and a high recording and reproducing speed together with a recording apparatus, a reproducing apparatus and a record medium used therein.
Among many sorts of optical recording/reproducing methods, a magneto-optical recording/reproducing method is most attractive because of a unique advantage that information can be recorded and then erased, and new information can be again recorded, which process can be repeated many times.
A magneto-optical disk (record medium) used in the magneto-optical recording/reproducing method has a magnetic layer composed of a layer or multiple layers for record storage. The magnetic layer used to be horizontal magnetic layer or layers (which are magnetized in parallel with the surface of layer) early disks. Then developed were perpendicular magnetic layer or layers having a high record density and a high signal intensity. The latter is used for almost 100% of magnetic layers at present. Such a magnetic layer is made for example of amorphous GdFe, GdCo, GdFeCo, TbFe, TbCo, TbFeCo, etc. The perpendicular magnetic layer generally has concentric tracks or spiral track, on which information is recorded. There are two types of tracks, i.e., explicit track and implicit track.
[Explicit Track]
If a disk has the explicit track(s), there are spiral or concentric tracks for recording information on the disk when the disk is seen along the direction normal to the surface of disk. A groove for tracking and separation exists between two adjacent tracks. A portion between two grooves is called a land. Actually, the relation between lands and grooves on the front surface of disk is reverse to that on the back surface of disk. When the disk is seen in the same direction as the beam incident direction, the far side is called a land and the near side a groove. Since the perpendicular magnetic layer is formed over the entire surface of the disk to cover grooves and lands, either the groove portion or the land portion can be used as tracks. There is no specific size regulation between groove width and land width.
To form such lands and grooves, a substrate generally includes lands formed in spiral or concentric shape on the surface thereof and grooves formed between adjacent lands. A thin perpendicular magnetic layer is formed on such a substrate. Thus, the perpendicular magnetic layer has lands and grooves.
[Implicit Track]
A disk having implicit tracks has no apparent tracks. The tracks are conceptual. In this case, recording apparatus or reproducing apparatus will have a control system, by which a laser beam (spot thereof) emitted from an optical head or pickup is controlled relatively to run (track) on the disk in a spiral or concentric trace. The trace of the spot's running is the implicit track(s). Alternatively, marks as described below are scattered along a track, and a belt line connecting the scattered marks may be considered as the implicit track(s).
[Mark]
In this specification, either one of "upward" and "downward" to the surface of layer is defined as "A direction" and the other as "inverse A direction". It should be understood that an example of "predetermined direction" stated in the present invention is the "A direction". Information to be recorded is preliminarily binarized, and the information is recorded using two signals of mark (B.sub.1) having magnetization of "A direction" and mark (B.sub.0) having magnetization of "inverse A direction". These marks B.sub.1, B.sub.0 respectively correspond to either one and the other of digital signals of 1 and 0. The magnetization of a track about to be recorded is normally aligned in the "inverse A direction" by applying a strong external magnetic field before recording. The o
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Matsumoto Hiroyuki
Niwa Tatsuo
Dinh Tan
Epps Georgia Y.
Nikon Corporation
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