High-density phase-change optical disk system possessing read/write compatibility with 90 mm magneto-optical disks

High-density recording characteristics of phase-change optical disks were studied using 2-7 pulse-position-modulation (ppm) in-groove recording. Carrier-to-noise-ratio (CNR) was over 50 dB at a mark length of 0.60 μm and the crosstalk at the track pitch of 1.10 μm was less than -30 dB. In addition, a 256 MB 90 mm overwritable PC optical disk system having read/write compatibility with the ISO 128 MB MO disk has been developed based on the acquired results. The drive is based on the 90 mm MO drive at a wavelength of 780 nm and NA of 0.53. The user capacity of 256 MB was achieved using a mark length of 0.63 μm, track pitch of 1.25 μm, 2-7 ppm in-groove recording, and MCAV with 10 zones. The number of sectors per track was varied from 31 to 49.