Patent ID: 6229783
Filing Date: 2001-05-08
Classification: G11B

Abstract:
An optical recording device, comprising:a recording medium with a first recording level and a second recording level superimposed on the first recording level;a light source configured to illuminate said first and second recording levels, the second recording level being illuminated through the first recording level;a receiving circuit configured to receive light reflected by the first recording level and by the second recording level, said receiving circuit comprising:at least two photoreceivers,a first channel configured to measure the difference of signals supplied by said at least two photoreceivers, anda second channel configured to measure the sum of the signals supplied by said at least two photoreceivers,wherein the receiving circuit is configured to read the first recording level based on a phase modulation of a beam reflected by said first recording level, the first channel supplying a differential signal restoring information recorded in said first recording level,wherein the receiving circuit is configured to read the second recording level based on an intensity modulation of a beam reflected by said second recording level, the second channel supplying a sum signal restoring information recorded in said second recording level,wherein said first recording level comprises a first active film configured to have amorphous areas and crystalline areas, said first recording level being configured to produce a phase difference between an optical beam reflected by said amorphous areas and an optical beam reflected by said crystalline areas, andwherein said second recording level comprises a second active layer configured to have first areas and second areas, said second recording level being configured to produce an intensity difference between an optical beam reflected by said first areas and an optical beam reflected by said second areas.