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The read-write characteristics of an optical disk utilizing a blue-laser diode are examined, applying land and groove recording and partial response and maximum likelihood (PRML) to two optical disk systems: 1) 0.85 numerical aperture (NA) optical disk system consisting of an objective lens with NA of 0.85 and a thin cover layer on a disk with a thickness of 0.1 mm and 2) 0.65 NA optical disk system consisting of an objective lens with NA of 0.65 and a 0.6-mm-thick disk substrate. In the 0.85 NA optical disk system, the track pitch and the data bit length employed for the experiment are 0.29 µm and 0.0987 µm, respectively. These parameters correspond to a capacity of 30 GB/side. In the 0.65 NA optical disk system, they are 0.37 µm and 0.155 µm, respectively, corresponding to a capacity of 15 GB/side. A bottom channel bit error rate (ch.bER) of less than 5.0×10-5 can be obtained in these systems, and it is confirmed experimentally that the ch.bER remains below 1.0×10-4 up to 1000 cross-write cycles.

The read-write characteristics of a land and groove disk have been examined using a blue-laser diode, high NA objective lens and the PRML method. The wide tilt and defocus margins have been obtained and no deterioration by CW has been observed at a data bit length of 0.0987 /spl mu/m and a track pitch of 0.29 /spl mu/m. These experimental results certify the feasibility of a rewritable optical disk with a capacity of 30 GB/side.

High-density recording capability of the five-layered phase-change disc has been examined from the viewpoints of optical simulation and disc performance. The optical simulation showed that the temperature rise in the amorphous state balanced that in the crystal state for the case when the thickness of the lower protective layer was adjusted from 70 nm to 120 nm. Carrier-to-noise ratio (CNR), overwriting erase ratio and jitter were measured by the optical recording system using a laser diode with a wavelength of 636 nm and an objective lens of 0.6 numerical aperture. Track-pitch was fixed at 0.6 µm and bit length was varied at a linear velocity of 6 m/s. CNR of 52 dB, overwriting erase ratio of more than 35 dB, and overwriting jitter of less than 10% were obtained on both land and groove at a bit length of 0.34 µm/bit.