Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Patent
1985-02-11
1987-10-27
Psitos, Aristotelis M.
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
369108, 369110, 369275, 365124, G11B 700, G11B 370
Patent
active
047034696
DESCRIPTION:
BRIEF SUMMARY
This invention relates to optical data storage and, more particularly, is concerned with (i) a method of recording data on an optical storage member, e.g. a disk; (ii) an optical storage member suitable for such recording; and (iii) an optical storage member carrying recorded information.
There are now a variety of optical data storage systems described in the literature and a limited number of these have been reduced to commercial practice. The term "optical" is used herein to denote radiation whose wavelength lies within the near ultra-violet, the visible range and in the near infra-red range. The optical storage members used are generally disks, and the term "disk" will be used hereinafter to denote an optical storage member regardless of its shape. Currently in all optical disks, information is recorded in tracks with unrecorded bands, known as "guard bands", between them. These guard bands are necessary to prevent cross-talk or interference between adjacent tracks on the optical disk. Typically, a data track of about one micron width will be separated from an adjacent data track by a guard band of about 0.6 micron in width. The dedication of a considerable area of the disk surface to such guard bands means that the information packing density is reduced to a significant extent.
We have now devised a technique whereby the function of a guard band in preventing cross-talk between adjacent tracks of information can be maintained while allowing the recording of information or control data in the guard band zones.
According to the present invention, there is provided an optical data storage member carrying optically-readable information in one or more tracks on the surface of the optical data storge member, wherein adjacent tracks are separated by a guard band carrying information or control data which is recorded so as to be optically distinguishable from the information carried in said track or tracks. In such an optical storage member, there is no need for empty guard bands; accordingly adjacent tracks can be of the same or closely similar width. Despite this equivalence, it will be convenient hereinafter to continue to refer to track as either main data tracks or guard bands.
There are several ways in which information or control data can be recorded in the guard bands of an optical storage member (e.g. a disk) while maintaining that information or control data in a state which is optically distinguishable from the information carried in the main data tracks. Two important ways of achieving this result rely upon differences in wavelength sensitivity or sensitivity to polarisation state between the material constituting the guard bands and that constituting the main data tracks.
According to a second aspect of the present invention, there is provided an optical data storage member comprising an optically-recordable surface having a track or tracks thereon which is or are sensitive to radiation of a first predetermined characteristic and, between said tracks, a second zone or zones of optically-recordable material which is sensitive to radiation of a second predetermined characteristic.
According to a third aspect of the invention, there is provided a method of recording information on an optical storage member, which comprises irradiating a first, pre-selected area of the member with radiation of a first, predetermined characteristic the intensity of which radiation is modulated in analogue or digital form to represent a first set of information; and recording a second area of the member which is contiguous with said first area with radiation of a second, predetermined characteristic the intensity of which radiation is modulated in analogue or digital form to represent a second set of information.
Advantageously, the first and second optical characteristics are either the wavelength of the radiation or its polarisation state.
For effective use of the present invention, the optical data storage medium should have a surface (prior to recording information thereon) which is strongly absorbant of the radiat
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Gardner Keith
Longman Robert J.
Pettigrew Robert M.
Plasmon Data Systems, P.V.
Psitos Aristotelis M.
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