Optical record carrier and apparatus for reading it
AssigneeU.S. Philips Corporation
InventorJan G. Dil
Life of this patent
Estimating the term…
Abstract
A record carrier is described in which information is recorded in an optically readable information structure comprising trackwise arranged information areas; as well as an apparatus for reading said record carrier. By arranging the adjacent information track portions on different slopes the track spacing can be reduced without increasing crosstalk.
Claims22
A record carrier containing information stored in a form readable by a beam of radiation, said carrier comprising a substrate and at least one elongated track on a surface of said substrate, said track having at least two longitudinally extending surface portions, a first and second plurality of information areas adapted to produce a detectable change in a beam of radiation when illuminated by the beam, said information areas of said first plurality being disposed on one of said surface portions and spaced from each other in the longitudinal direction of said track to define a first information track and said information areas of said second plurality being disposed on the other of said surface portions and spaced from each other in the longitudinal direction of said track to define a second information track, said surface portions being inclined in different directions with respect to a line normal to said surface of said substrate and the longitudinal axis of said track so that when one of said first and second information tracks is illuminated by a read beam of radiation, the radiation incident on said one information track is deflected thereby in a first direction and radiation of the read beam incident on the other of said first and second information tracks is deflected thereby in a second direction which is different from said first direction thereby reducing crosstalk between said first and second information tracks.
An apparatus for reading information stored on a record carrier having a substrate and an elongated groove formed therein, the groove having at least two longitudinal extending surfaces, and a plurality of spaced apart information areas formed in each of said surfaces, said information areas on each surface defining an information track containing information to be read, said apparatus comprising means for producing two radiation beam components, an objective for focussing radiation from said producing means to a read spot on an information track to be read and a radiation sensitive detector for converting radiation, which has been modulated by the information areas, into an electrical signal, the axes of said two beam components making an angle with respect to each other which is substantially equal to or greater than 1/2 arcsin (NA/n), where N.A. is the numerical aperture of said objective, and n is the refractive index of a medium adjacent said information tracks.
Dependencies are inferred from the claim text.