Patent ID: 7619962
Filing Date: 2009-11-17
Classification: G11B

Abstract:
1. An optical disc comprising: a first substrate having a thickness of 0.6 mm±30 μm, with a first recording layer formed thereon, the first recording layer having a string of first data pits formed concentrically or spirally in compliance with DVD-ROM specifications, the first data pits including 14T pits, T being a reference clock cycle; a first reflective film formed on the first recording layer, the first reflective film having a thickness in the range from 30 nm to 140 nm, the first substrate and the first reflective film having a relationship of 2.3≦Pw/Tf≦14 wherein Pw is a pit width of each 14T pit at a middle section of the 14T pit and Tf is a thickness of the first reflective film, the middle section being located between a top section and a bottom section of the 4T pit in a thickness direction of the first substrate, a distance from the top section to the middle section and another distance from the middle section to the bottom section being equal to each other; a second substrate having a thickness of 0.5 mm±30 μm and having a first surface and an opposing second surface, with a second recording layer formed on the first surface, the second recording layer having a string of second data pits formed concentrically or spirally in compliance with BD-ROM specifications; a second semi-transparent reflective film formed on the second recording layer, the first and second substrates being bonded to each other so that the first reflective film and the second surface of the second substrate face each other; and a transparent layer having a third surface and an opposing fourth surface, the transparent layer being formed over the second reflective film at the third surface, the fourth surface allowing a laser beam to pass therethrough in reproduction from at least either the first or the second data pits.