Dynamic information storage or retrieval – Storage medium structure – Optical track structure
Patent
1997-08-21
2000-07-18
Dinh, Tan
Dynamic information storage or retrieval
Storage medium structure
Optical track structure
369 94, G11B 724
Patent
active
060916974
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
FIELD OF INVENTION
The invention relates to an optical information recording/reading medium and more particularly to a medium making it possible to record information items in various planes through the thickness of the medium.
DISCUSSION OF BACKGROUND
Systems are known in the art which make it possible to record through the thickness of a material, in various strata, various series of information items (see for example French Patent 90 07284). This art is aimed at increasing the storage capacities of optical systems.
Currently used optical media take the form of discs rotating about an axis and the information items. are recorded on the disc in the form of concentric or spiral tracks. In thickness-wise recording various planes (or strata) inside the discs are intended to each contain information tracks.
Recording and reading in the various planes of the disc is carried out with the aid of a laser beam and an optic for focusing this beam. This optic must be able to form focusing spots at various depths beneath the surface of the disc. The focusing optic can also be displaced radially with respect to the disc so as to carry out the recording and reading of the various tracks of each plane of the disc.
When recording information, an optical recording stylus is used which includes for example an optic which can be displaced vertically with respect to the surface of the disc.
To do this, an optic is used which has a very low depth of field so that focusing is effective only in a very limited depth zone.
Several information strata are superimposed in this way by making provision for means for displacing the focal plane of the reading or writing optic in such a way as to allow focusing on a stratum (plane) chosen from several stacked strata.
The optic is also radially displaceable with respect to the axis of the disc. In this way, the whole useful surface of the disc can be scanned by the laser recording beam, for each of the information strata.
In a know technique, in order to adjust the focusing of the beam and allow the focusing point to follow a particular track in a stratum of the disc, guidance information elements are provided at the surface of the disc or on a principal face of the recording layer. When recording or reading, the optic is firstly focused on these information elements so as to effect focusing adjustment and tracking, and then the optic is displaced by a specified distance so that focusing takes place in the stratum to be recorded or to be read. The drawback of such a system lies in the fact that the optic exhibits inertia such that the displacement of the optic is not immediate. The time taken to displace the optic from the surface of the disc to the stratum to be recorded or to be read results in a decrease in the density of information contained in each stratum. Furthermore, the displacements have to be strictly identical from one usage to another usage.
According to another technique, it is possible to provide for a first beam which is focused onto a reference surface of the disc and at least one second beam which is focused through the thickness of the disc. The reference surface then includes guidance and focusing information items and the first beam is used for the focusing and guidance of the system. The second beam is locked to the first beam and serves for the recording or the reading through the thickness of the disc. The drawback of such a system is that the reproducibility of the positions of the focusings of the two beams is uncertain. For example, the angles of incidence of the beams on the disc can vary, which implies that from one usage to another there should be no relative inclination of the disc with respect to the optical head which emits the beams (tilt) in order to avoid parallax errors.
The objective of the invention is to solve these problems.
SUMMARY OF THE INVENTION
The invention therefore relates to an optical information recording/reading medium including at least one transparent layer making it possible to record or read in
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Huignard Jean-Pierre
Le Carvennec Fran.cedilla.ois
Puech Claude
"Thomson-CSF"
Dinh Tan
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