Record carrier with an optically readable trackwise-arranged information structure

Claim 1

A record carrier for storing information comprising a substrate having thereon an optically readable information structure comprised of a plurality of generally parallel, spaced apart elongated information tracks containing information stored along the length thereof, which information is retrieved by a read beam of radiation which is directed onto the track to be read and is modulated in accordance with information stored in that track as the read beam traverses the length of the track to be read, said tracks being arranged in at least two juxtaposed groups each containing a plurality of said tracks, the spacing between tracks in at least contiguous portions of adjacent groups varying from group to group such that when said structure is scanned by a spot of radiation spanning a plurality of said tracks and moving relative to the record carrier in a direction transverse to the longitudinal direction of said tracks, the variation in the spacing between tracks produces a detectable change in the radiation comming from the record carrier as the spot moves from one to the other of said groups.

Claim 7

An apparatus for reading information stored in a record carrier having an optically detectable structure comprising a plurality of generally parallel, spaced apart elongated tracks in which the information is stored, the spacing between said tracks in at least portions of said optical structure varying with an amplitude of variations smaller than the average distance between the tracks, said apparatus comprising a radiation source for producing a read beam of radiation, a radiation sensitive detection system, an objective system for passing said read beam via the record carrier to said detection system, said detection system converting radiation of the said beam which has been modulated by the information structure into an electrical signal, means for supplying at least one address beam of radiation, means for forming, from radiation of each address beam, an address spot of a size such that address spot spans a number of tracks which approximately equals the quotient of the average distance between tracks and the amplitude of the variation of the distance between tracks, and two auxiliary detectors associated with each address beam, said auxiliary detectors being disposed in the path of the radiation of the associated address beam which is diffracted in a first order by the information structure in a direction transverse to the track direction.

Claim 8

An apparatus for reading information stored in a record carrier having an optically detectable structure comprising a plurality of generally parallel, spaced apart elongated tracks in which the information is stored, the spacing between said tracks in at least portions of said optical structure varying with an amplitude of variations smaller than the average distance between the tracks, said apparatus comprising a radiation source for producing a read beam of radiation, a radiation sensitive detection system, an objective system for passing said read beam via the record carrier to said detection system, said detection system converting radiation of the said beam which has been modulated by the information structure into an electrical signal, means for supplying at least one address beam of radiation, means for forming, from radiation of each address beam, an address spot of a size such that address spot spans a number of tracks which approximately equals the quotient of the average distance between tracks and the amplitude of the variation of the distance between tracks, and two auxiliary detectors associated with each address beam, said auxiliary detectors being disposed in the path of the radiation of the associated address beam which is diffracted in a first order by the information structure in a direction transverse to the track direction.

Claim 16

The apparatus according to claims 12 or 13 wherein said supplying means includes a plate having two areas with Fresnel rings disposed in the path of radiation produced by said auxiliary radiation source so as to produce two of said address beams from the radiation produced by said auxiliary source.