Optical data recording using radiation of different characteristics

Claim 1

An optical data storage member, prior to recording information thereon, comprising an optically-recordable surface having a plurality of tracks in which information may be recorded in analogue or digital form, the tracks being of a first type in which the material constituting the track is heat sensitive, and is sensitive to radiation of a first predetermined characteristic but not to radiation of a second predetermined characteristic, and a second type in which the material thereof is also heat sensitive but is sensitive to radiation of said second predetermined characteristic, but not to radiation of said first predetermined characteristc, said material constituting each of said tracks constituting means for changing state in response to heating to alter reading characteristics when irradiated by one of said predetermined types of radiation but not when irradiated by the other of said predetermined type of radiation; wherein tracks of the first type alternate across the surface of the optical data storage member with tracks of the second type, whereby the information may be recorded by irradiating the first and second tracks with radiation respectively of the first and second characteristics so that spaces between adjacent tracks are not required to prevent cross-talk; said member being of circular form and wherein the tracks are disposed concentrically about the centre of the circular form which constitutes a disk; said tracks of said first type being constituted by a surface carrying a plurality of closely spaced grooves arranged in a first direction, and wherein the tracks of said second type are constituted by a surface carrying a plurality of closely spaced grooves arranged in a second direction, said first and second directions being mutually substantially orthogonal; said tracks of said first type carrying radial grooves, and said tracks of said second type carrying concentric grooves; and said adjacent tracks being optically distinguishable from one another by virtue of their response to polarized radiation constituting said predetermined types of radiation.