| 摘要 |
PROBLEM TO BE SOLVED: To improve a recording and reproducing characteristic by forming a groove and a land in helical form on a substrate and forming prepits while leaving one part of the inner peripheral side or the outer peripheral side of the land, thereby obtaining a stable preformat signal to reproduce prepit information correctly. SOLUTION: A groove 2 and a land 3 and prepits 4 are formed on a substrate 1. The prepit 4 is formed while leaving one part of the land 3 without making it to be in a ladder shape having a form connecting adjacent grooves with each other. Since the cross-sectional shape of the prepit 4 becomes asymmetric with respect to the center T2 of the track of the groove 2, it generates a preformat signal in a push-pull signal. When a track pitch is defined as Tp, the groove width Wp of the prepit 4 is regulated within a specific range of 0.45 μm<=Wp<=(Tp-0.1). Moreover, the preformat signal is prevented from leaking into an RF signal and the push-pull signal by regulating the length Lp of the prepit 4 within a specified range of 0.4 μm<=Lp<=1.0 μm. |
