Optimization of Pit Depth for Concurrent Read Only Memory–Random Access Memory Optical Disk

Abstract

We have studied a concurrent read only memory–random access memory (ROM–RAM) optical disk system without laser feedback by optimizing pit depth. When the pit depth was 47 nm (optical depth about 1/11 λ) and the pit width 0.45 µm, about 8% jitter in both pit and magneto-optical (MO) signals was obtained with a 785 nm wavelength laser diode and 0.55 NA objective lens by employing magnetic-field-modulation (MFM) MO recording. Both pit data and MO data were recorded with eight to fourteen modulation (EFM) code with a minimum mark length of 0.83 µm and a track pitch of 1.6 µm and thus the areal density is comparable to 1.3 GB for φ120 mm single sided disk. By the optimization of the pit depth, sufficient system margins for practical use were obtained without laser feed back for the simultaneous reproduction of both pit and MO signals.