Oblon, Spivak, McClelland, Maier & Neustadt, P.C.
Optical phase-change disc
 An optical phase-change disc comprises a substrate having thereon a spiral groove or concentric grooves for guiding a focused light beam, and a layer structure including a recording layer and protective layers sandwiching therebetween the recording layer. The groove has wobble for recording ATIP (absolute time information) or ADIP (address information). The following relationship between the groove width GW, beam diameter R.sub.0 and wobble amplitude a.sub.w : EQU 0.25.ltoreq.GW/R.sub.0 .ltoreq.0.45 or 0.65.ltoreq.GW/R.sub.0 ; and EQU 0.03.ltoreq.a.sub.w /GW.ltoreq.0.08 hold for preventing distortion of the groove caused by repeated overwriting operation to improve reliability of the optical disc. 
Mitsubishi Chemical Corporation
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Masaaki Takashi Hideyuki Michikazu Ken-Ichi Masae Haruo Hironobu
Mizuno Ohno Kubo Horie Takada Kubo Kunitomo Mizuno