Thomson-csf

Pierre Berthet

Claude Bricot

Jean-Louis Gerard

Michel Audoin

Jean L Gerard

Bruno Mertz

A process and device for focussing a light energy beam on a data carrier comprising sites fromed of virgin areas free from any data recording provided along tracks and serving as reference plane for said focussing. In a preferred variation, these areas are preceded by flags associated with a specific code. Control is achieved by measuring the deviation between the plane of focussing of a beam into a spot scanning the tracks and the reference plane formed by the surface of the virgin areas. Between two passages of these areas of the measurements are stored. The focussing error signal is obtained by filtering these measurements.

Process and system for optical recording and reading on a mobile data

The process makes it possible to generate on the basis of discrete preetching elements or flags, the radial tracking error and/or focusing error signals. The flags comprise portions displaced with respect to the mean axis of the tracks to be followed. According to a first variant, each track comprises portions displaced on either side of the axis. According to a second variant the flags comprise portions alternately displaced to one and then the other side thereof. In response to the passages of these portions, windows are generated and the pulses supplied by the photodetectors of the interaction of these portions on the focused scan beam are compared between successive windows.

Process and optical device for generating signals controlling the

A process and device for focussing a light energy beam on a data carrier comprising sites formed of virgin areas free from any data recording provided along tracks and serving as reference plane for said focussing. In a preferred variation, these areas are preceded by flags associated with a specific code. Control is achieved by measuring the deviation between the plane of focussing of a beam into a spot scanning the tracks and the reference plane formed by the surface of the virgin areas. Between two passages of these areas the measurements are stored. The focussing error signal is obtained by filtering these measurements.

The angular velocity of an information element contained in the precut track of an information carrier disk is controlled by means of a concentric circular ring located internally with respect to the precut track and constituted by mark zones uniformly spaced in angular sectors. A light beam is projected onto the circular ring and the emergent beam is modulated as a function of the mark zones and blank zones which form the circular ring. Errors arising from eccentric displacement of the track can thus be corrected and the rate of travel of information can be controlled in relation to the reading or recording light beam.

Information carrier disk with angular coding means and a system for

A mobile pre-etched data carrier is provided in which the pre-etching is formed by a succession of discrete non continuous elements materializing the mean axis of the tracks. The spatial distribution of these discrete elements may be uniform or not. In a first embodiment, each discrete element is formed by a smooth track section. In a second embodiment, each discrete element comprises several sections defining a particular code. In other preferred variations of the invention, each element comprises, besides a portion centered on the mean axis of the tracks, one or more portions offset with respect to the axis. Finally, each of the pre-etchings may itself be preceded by an additional pre-etching element used for the purpose of synchronization. The tracking device comprises photodetector means, measuring circuits comprising sampler-inhibitors or storage integrator circuits and sampling circuits. A radial tracking error is formed from the evolution of the signals detected during successive passages.

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Paris, France

Pierre Berthet