Tracking and reading system for an optical medium and medium for use therewith

Claim 1

A tracking and reading system for an optical medium, said system comprising: an optical disk comprising: s substrate with a central axis; a guide track formed on said substrate and spiraling outward from a position relatively close to said central axis of said disk to a position relatively close to an outer edge of said disk; and a pair of information tracks, with one information track being formed on either side of said spiraling guide track and not flanked by another guide track; and apparatus for reading and tracking the optical disk, comprising: means directing each different one of only a pair of focussed polarized light beams to said disk surface; means for positioning each beam to continuously nominally illuminate a different one of said flanking information tracks and at least part of the intermediate guide track; and means, responsive to a portion of each of said pair of beams being reflected from said surface, for simultaneously detecting amplitudes of both phase components of a reflected beam from each different one of said flanking information tracks to recover separate amplitude signals V 11 and V 12 for a first one of said flanking information tracks and separate amplitude signals V r1 and V r2 for a second one of said flanking information tracks, for simultaneously providing continuous position information, as a difference of each track amplitude signal sum (i.e. (V 11 +V 12 )-(V rl +V r2 )) of the light beams relative to of flanking information tracks to cause each of said beams to track substantially the center of the information track on which that beam is directed, and for providing, as a first difference signal (V 11 -V 12 ) for the first track and as a second difference signal (V r1 -V r2 ) for the second track, information data simultaneously from both of said two flanking information tracks.