Reflective optical record carrier

Claim 1

A record carrier containing information which is readable by a beam of radiation, said record carrier comprising a disc-shaped, radiation-transmitting substrate having a pair of planar surfaces on opposite sides thereof, a non-transmissive, radiation reflecting optical structure on one of said planar surfaces of said substrate, said optical structure comprising a plurality of adjacent, circular tracks extending about the center of said substrate and defining turns of a spiral or concentric circles spaced from each other in the radial direction, each circular track having a plurality of depressions in said one surface of said substrate, said depressions being spaced apart in the track direction by intermediate areas, and a reflective layer extending over said intermediate areas and said depressions so that upon illumination by a convergent beam of radiation which is projected on and enters through the other of said planar surfaces and which passes through said substrate and is focussed on said optical structure to a spot of a size of the order of the smallest detail of said optical structure, the radiation is modulated by said depressions and intermediate areas in accordance with the sequence thereof and the modulated radiation is reflected by said reflective layer towards and exists through said other planar surface, said substrate defining a substantially rigid support for said optical structure and having a thickness such that in the plane of said other surface, which forms the entrance and exit faces for the radiation, the diameter of the beam is sufficiently larger than the diameter of said spot so that dust particles, scratches and the like on said other surface, do not interfere with readout of information by the convergent beam focussed to said spot on said optical structure, and an additional layer secured to the side of said substrate remote from said other surface, said optical structure being disposed between said substrate and said additional layer so that it is protected from damage during handling.

Claim 7

An apparatus for reading information stored on a record carrier having a disk-shaped radiation transmitting substrate with a pair of parallel, planar surfaces on opposite sides thereof and a non-transmissive, radiation reflecting optical structure disposed on one of said planar surfaces, said optical structure comprising a plurality of adjacent, circular tracks extending about the center of the substrate and defining turns of a spiral or concentric circles spaced from each other in the radial direction, each circular track having a plurality of depressions spaced apart by intermediate areas in the track direction, said apparatus comprising means for supporting the record carrier for rotation about the center of the substrate in a plane parallel to the plane of said one surface, means positioned on the side of said substrate remote from said optical structure for producing a beam of radiation which is projected onto the other surface of said substrate so that the radiation passes through said substrate and is incident on said reflective optical structure, an objective system for focusing said beam to a spot on said optical structure so that the radiation is modulated by said optical structure in accordance with information stored thereby and the modulated radiation is reflected by said optical structure back through said other surface and passes through said objective system, said substrate having a thickness such that in the plane of said other surface the diameter of the beam is sufficiently larger than the diameter of said spot so that dust particles, scratches and the like on said other surface do not interfere with readout of information by the beam focussed to said spot on said optical structure, radiation-sensitive means for converting the modulated radiation into an electrical signal, said radiation sensitive means being disposed in the path of the modulated radiation reflected by the optical structure, and means for deriving from the radiation a signal indicative of a deviation of the plane of the optical structure from the plane at which the radiation is focused by said objective system for correcting the focusing.

Claim 8

An apparatus for reading information stored on a record carrier having a disk-shaped radiation transmitting substrate with a pair of parallel, planar surfaces on opposite sides thereof and a non-transmissive, radiation reflecting optical structure disposed on one of said planar surfaces, said optical structure comprising a plurality of adjacent, circular tracks extending about the center of the substrate and defining turns of a spiral or concentric circles spaced from each other in the radial direction, each circular track having a plurality of depressions spaced apart by intermediate areas in the track direction, said apparatus comprising means for supporting the record carrier for rotation about the center of the substrate in a plane parallel to the plane of said one surface, means positioned on the side of said substrate remote from said optical structure for producing a beam of radiation which is projected onto the other surface of said substrate so that the radiation passes through said substrate and is incident on said reflective optical structure, an objective system for focusing said beam to a spot on said optical structure so that the radiation is modulated by said optical structure in accordance with information stored thereby and the modulated radiation is reflected by said optical structure back through said other surface and passes through said objective system, said substrate having a thickness such that in the plane of said other surface the diameter of the beam is sufficiently larger than the diameter of said spot so that dust particles, scratches and the like on said other surface do not interfere with readout of information by the beam focussed to said spot on said optical structure, radiation-sensitive means for converting the modulated radiation into an electrical signal, said radiation sensitive means being disposed in the path of the modulated radiation reflected by the optical structure, and means for deriving from the radiation a signal indicative of a deviation of the plane of the optical structure from the plane at which the radiation is focused by said objective system for correcting the focusing.