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 turn 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 mum and 0.0987 mum, respectively. These parameters correspond to a capacity of 30 GB/side. In the 0.65 NA optical disk system, they are 0.37 mum and 0.155 mum, respectively, corresponding to a capacity of 15 GB/side. A bottom channel bit error rate (ch:bER) of less than 5.0 x 10(-5) can be obtained in these systems, and it is confirmed experimentally that the ch.bER remains below 1.0 x 10(-4) up to 1000 cross-write cycles.

The partial response and maximum likelihood (PRML) signal processing method is effective for fabricating high-density optical disks because it allows inter-symbol interference in decoding. However, some deterioration factors, namely impulse response fluctuations and signal level fluctuations, still exist even though PRML signal processing is adopted. A combined adaptive controlled PRML signal processing method is proposed to surmount the problem of these two deterioration factors simultaneously. The key points of the combined adaptive controlled PRML signal processing are that the gain of the Viterbi decoder is unity and the expected signal takes into account the reference levels controlled in the adaptive controlled Viterbi decoder. The effectiveness of such processing is confirmed using simulated reproduced signals and actual reproduced signals. The characteristics in terms of the tangential tilt of the disk and the signal asymmetry are ameliorated by adopting the combined adaptive controlled PRML signal processing method.

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 μm and a track pitch of 0.29 μm. These experimental results certify the feasibility of a rewritable optical disk with a capacity of 30 GB/side.

The combined adaptive controlled PRML signal processing was newly developed. The new method is a combination of the adaptive controlled FIR filter and the adaptive controlled Viterbi decoder. The adaptive controlled Viterbi decoder was operated under the condition that the Viterbi decoder is controlled such that the unity gain is kept. We report the simulation results, which are evaluated using signal asymmetry margin and tangential tilt margin to verify the effectiveness of this method expanding the margins. The combined adaptive controlled PRML signal processor is effective for these signal tolerances. Furthermore, the experimental results confirm the simulated effectiveness for expanding the tangential tilt margin. Consequently, a new method of combined adaptive controlled PRML signal processing is effective in reducing the deteriorations of data detection for high-density optical disk.

This paper presents a rewritable optical disk with a capacity of 30 GB/side intended for the next generation of rewritable optical disks. The experimental results have shown that this optical disk has wide tilt margin and is a prospective candidate for supplanting VCR in the HDTV era.

The possibility of an optical disk capacity of 28GB/side is studied. The read-write characteristics of a phase-change optical disk are examined using a thin cover layer, a blue laser diode, high NA objective lens and the PRML method. The wide tilt margins of high-density recording are achieved.

A new focusing error detection method using ±first-order diffracted beams of a holographic optical element (HOE) is proposed. We fabricate the proposed HOE and measured the focus offset between a land a groove. According to the measurement results, the focus offset of the proposed HOE was smaller than that of an astigmatic focusing error detection.