Dynamic information storage or retrieval – Storage medium structure – Optical track structure
Patent
1992-09-09
1995-01-24
Dzierzynski, Paul M.
Dynamic information storage or retrieval
Storage medium structure
Optical track structure
3692751, 369200, G11B 7013
Patent
active
053847644
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to an optical data storage medium and to methods for recording and reading data on/from such medium.
More specifically, a concept is described for optical storage of information on data carriers such as fiches, cards or tape.
The data carrier's surface is completely or partly covered with focusing microstructures adjacent to a layer which is able to change its optical properties when exposed to intense light. (In the following, this layer will for simplicity in most cases be referred to as the "burn-film". This expression does not imply any particular embodiment of the layer, which can be of the reversible or the irreversible type, as discussed below.) During recording of data, local changes are created in the layer by having the microstructures focusing the light, thus obtaining a high light intensity on the layer. During reading of data, the optical microstructures may operate as an active optical component assisting the reading equipment.
By using e.g. transparent microspheres (typical diameter: 1 to 100 .mu.m) as focusing elements disposed over an optically absorbing film, a tight focusing and a high data storage capacity can be achieved without the complexity and the expenses that otherwise would be required for a recording and reading system which focuses directly on the light absorbing layer. Using oblique illumination through the microspheres, possibilities arise for storage of a high number of data bits at each microsphere position, as well as for hierarchically built data bases, in certain cases combined with data protection. Easy prerecording on mass produced data carriers becomes possible. During reading of data the microspheres function as auxiliary optics, which makes it possible e.g. to read large blocks of data without the use of a laser.
Storage of data by means of laser beams which produce local change of the optical properties of a thin film on a planar substrate are well known, for example from SPIE vol. 329 (1982), SPIE vol. 490 (1984) , SPIE vol. 695 (1986), SPIE vol. 899 (1988), SPIE vol. 1078 (1989). The change in optical properties can be reversible, whereby the stored data can be deleted and replaced by new data.
Alternatively, the change in optical properties can be irreversible, whereby it becomes impossible to delete and/or rerecord new data. Storage media of the latter type are often referred to as WORM (Write Once Read Many Times) media.
A usual method of preparation of WORM media consists of depositing on the substrate, which is a plastic disc, a thin film of a low melting point metal such as Te. During data storage each bit is represented by the physical status of the specific film area assigned for the storage of said bit (one elementary data storage cell with its address), i.e. whether that area has been irreversibly changed due to exposure to light or whether it is unchanged. According to present knowledge, all practical optical data storage systems are so far based on reflection from the burn-film. The irreversible change consists in such a case of an increase or a decrease of the reflectivity of each cell when a focused laser beam heats the burn-film. In the film is thereby created a hole through which the light can pass, or the film is smoothened so that its reflectivity increases. Several other processes can be used, e.g. local deformation of the substrate which influences the reflectivity. Reading is most commonly performed by examining the reflectivity of each cell by means of a focused laser beam scanning the surface of the data carrier systematically. This laser beam is too weak to influence the reflectivity.
From NO patent application 86.4041 (=DE 35 36 739)a data storage medium of the optical type is known, which medium is equipped with focusing optical structures integrated in the medium together with and on top of a material the optical properties of which can be changed by irradiation with light. This known data carrier is however only adapted for storage of visible data, i.e. images which are visual
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Dyno Particles A.S.
Dzierzynski Paul M.
Wong Don
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