Dynamic information storage or retrieval – Storage medium structure – Optical track structure
Patent
1995-06-05
1997-08-19
Tran, Thang V.
Dynamic information storage or retrieval
Storage medium structure
Optical track structure
369109, 3692754, 369103, G11B 700
Patent
active
056595360
ABSTRACT:
Disclosed is a system for the recording of data on optic disks. Presently used optic disks, which can be read with lasers working in wavelengths of the visible region (between 0.5 and 0.8 microns), have a maximum surface storage density of the order of one data bit per elementary zone having an area of about one square micrometer. Beyond this limit, the diffraction does not allow the neighboring zones to be distinguished. A means is proposed to considerably increase the storage capacities: in an elementary zone of a layer, an information bit is written not in the form of a point of absorption of a laser light but in the form of a diffraction grating with a determined pitch. Several diffraction gratings, having pitches different from one another, may be superimposed at the same position, enabling the recording, in one and the same zone, of several information bits. The diffraction gratings are made by a periodic local variation of the optic index of the layer. They are made by a high energy laser beam, out of a material with an index that may vary as a function of this energy. The reading is done by a frequency tunable laser that enables the detection, for different frequencies, of the presence or absence of diffraction gratings.
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Huignard Jean-Pierre
Lehureau Jean-Claude
Maillot Christian
Meunier Paul-Louis
Puech Claude
"Thomson-CSF"
Tran Thang V.
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