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US 4,450,553 AGranted
Multilayer information disc
AssigneeU.S. Philips Corporation
InventorsPeter L. Holster, Johannes M. Wittkamper
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AssigneeU.S. Philips Corporation
InventorsPeter L. Holster, Johannes M. Wittkamper
Estimating the term…
The invention relates to a multilayer information disc, in particular a video disc, which is read by laser light. The disc comprises at least two radiation-reflecting optical structures each having a relief-like information track of regions situated alternately at a higher and a lower level which is read in reflection and on the basis of phase differences. Each of the optical structures is covered with a reflection layer at least one of which partially transmits the reading radiation so that upon reading the other optical structure or structures, the radiation passes through the structure provided with the partially transmitting reflection layer. The coefficients of reflection of the various reflective layers are preferably matched to each other in a manner such that upon reading the same amount of light returns from each optical structure. A suitable material for the partially reflective layer is a dielectric which has no light absorption.
A multilayered record containing information in optically readable form, said record comprising a planar member of a material substantially transparent to radiation with which the information is to be read, an optical structure extending over at least a portion of each of two opposite surfaces of said planar member, said optical structures each having a plurality of planar information areas arranged in an information track and disposed in a first plane generally parallel to the plane of said planar member, said information areas being spaced from each other in the track direction by regions spaced from said first plane in a direction perpendicular thereto and being adapted to be read by a beam of radiation from a source positioned on one side of said planar member, and a first and second reflective layer covering the entire optical structure on said one side of said planar member and the entire optical structure on the other side of said planar member, respectively, at least said first reflective layer being partially transmissive to said radiation whereby the optical structure on said other side is read by radiation which passes through said first reflective layer and is incident onto said optical structure on said other side, the information recorded on said optical structure on said other side being derived from the portion of the radiation reflected by said second reflective layer.
A multilayered optically readable information record comprising a planar member of a material substantially transparent to radiation with which said record is to be read, an optical structure extending over at least a portion of each of two opposite surfaces of said planar member, said optical structures each having a plurality of information areas adapted to be read by a beam of radiation from a source positioned on one side of said planar member, and a first and second reflective layer covering the optical structure on said one side of said planar member and the optical structure on the other side of said planar member, respectively, at least said first reflective layer being partially transmissive to said radiation whereby the optical structure further from the radiation source is read by radiation passing through said first reflective layer, said first and second reflective layers having mutually different coefficients of reflection such that approximately equal amounts of radiation incident on said record is returned from each of said optical structures during reading.
Dependencies are inferred from the claim text.