Apparatus for optically reading a record carrier with two types of information areas
AssigneeU.S. Philips Corporation
InventorJosephus J. M. Braat
Life of this patent
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Abstract
A record carrier is described which has an optically readable information structure in which information areas of adjacent information track portions have different phase depths, and an apparatus for reading said record carrier. By a suitable choice of the phase depths and by an electronic phase shift of the signals supplied by the read detectors, cross-talk between adjacent tracks can substantially be eliminated.
Claims16
An apparatus for reading information from a record carrier containing information areas of a first type having a first phase depth and information areas of a second type having a second phase depth which is different from said first phase depth, the information areas being arranged in a plurality of generally parallel tracks and being spaced from each other in the track direction, said apparatus comprising means for producing a read beam of radiation, means for focussing said read beam to a read spot on said record carrier, means for producing relative movement between said record carrier and said beam so that said read spot scans a given track and the radiation is modulated in accordance with information stored thereby due to variations in the phase of the radiation produced by the information areas, at least two radiation sensitive detectors each having an output for supplying an electrical output signal corresponding to radiation incident thereon, said detectors being disposed in the path of the modulated radiation coming from the record carrier, with a respective one of said detectors being disposed on each side of a line which is effectively transverse to the direction of the tracks, means for combining said output signals of said detectors so as to produce a further signal representative of the information being read, and means for coupling said output of each detector to said combining means, said coupling means including means for introducing a predetermined, constant phase shift into at least one of said output signals.
An apparatus for reading information from a record carrier containing information areas of a first type having a first phase depth and information areas of a second type having a second phase depth which is different from said first phase depth, the information areas being arranged in a plurality of generally parallel tracks and being spaced from each other in the track direction, said apparatus comprising means for producing a read beam of radiation, means for focussing said read beam to a read spot on said record carrier, means for producing relative movement between said record carrier and said beam so that said read spot scans a given track and the radiation is modulated in accordance with information stored thereby due to variations in the phase of the radiation produced by the information areas, at least two radiation sensitive detectors each having an output for supplying an electrical output signal corresponding to radiation incident thereon, said detectors being disposed in the path of the modulated radiation coming from the record carrier, with a respective one of said detectors being disposed on each side of a line which is effectively transverse to the direction of the tracks, means for adding said output signals, said adding means supplying a sum signal representative of the sum of said output signals, means for coupling said output of each detector to said adding means, said coupling means including means for introducing a predetermined, constant phase shift into at least one of said output signals, means for subtracting said output signals from each other, said subtracting means supplying a difference signal representative of the difference between said output signals, and switching means coupled to said subtracting and adding means, said switching means having an output for supplying one of said sum and difference signals in dependence on which one of the two types of information areas is being scanned by said spot.
Dependencies are inferred from the claim text.