Yutaka Kashihara

Experimental Study of High-Density Rewritable Optical Disk Using a Blue-Laser Diode

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.

Combined adaptive controlled PRML signal processing for high-density optical disk

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.

New write shift compensation method modified for optical disk systems to which partial response maximum likelihood (PRML) detection is applied

A new write shift compensation method is proposed in this paper. The method is suitable for an optical disk system which adopts partial response maximum likelihood (PRML) detection, and it can optimize adaptive controlled writing pulses even under severe inter-symbol interference (ISI) conditions to reduce detection errors. This advantage is attributable to the use of the Euclidean distance as the estimation index of the mark edge shift error. The effect is confirmed by the experimental results for blue laser systems.

A new method of evaluating signal quality for systems to which partial response and maximum likelihood is applied

The partial response and maximum likelihood (PRML) detection method is promising as a detection scheme for next-generation optical disk systems. For application of the PRML detection, a new value is required in order to evaluate signal quality instead of jitter, which is used in current optical disk systems. For this requirement, we developed a new evaluation method that is based on the principle of the PRML detection. This evaluation value is defined as the occurrence probability of miss-detection in the PRML detection. We evaluated the proposed method using a simulated waveform and an experimental waveform for two systems. Each system consists of a phase change disk with cover layer thickness of 0.6 mm and 0.1 mm, a blue laser with wavelength of 409 nm and 407 nm and an objective lens with numerical aperture of 0.65 and 0.85, respectively. As a result, we confirmed the validity of the proposed method for each system.

Simulation study for high- density optical disk system

A newly developed simulator indicates that adopting (1,7)RLL code and PRML method leads to a 29.5GB system.

Measure to evaluate readout signal quality for the system using PRML

A Partial Response Signal-to-Noise Ratio (PRSNR) and a Simulated bit Error Rate (SbER) are introduced as measures to evaluate a signal quality for a system using PRML. PRSNR is a measure to evaluate S/N and linearity, and SbER is a measure instead of bER. The signal quality from various points of view is clarified by these indexes. PRSNR and SbER are applied to HD DVD.

Combined Adaptive Controlled Partial Response and Maximum Likelihood Signal Processing for High-Density Optical Disks

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.

A new method to evaluate signal quality for systems to which PRML is applied

The partial response and maximum likelihood (PRML) method is promising as the detection scheme for next-generation optical disk systems. PRML detection requires a new value to evaluate signal quality instead of jitter, which is used in the current optical disk systems. For this requirement, some evaluation methods have been proposed. However, any evaluation methods for practical use has not been reported. In this paper, we propose a new method to evaluate the signal quality for systems to which PRML detection is applied. We compare the evaluation value of the proposal method with measured channel bit error rate (bER), and confirmed the validity of the new method.

Experimental study of 30 GB/side rewritable optical disk using a blue-laser diode

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.

A new write shift compensation method modified for optical systems to which PRML detection is applied

A new write shift compensation method modified for optical disk systems to which PRML detection is applied is developed. The compensation method achieves optimization of all writing pulses adaptively. The compensation parameters are calculated to minimize the probability of detection errors. The experimental results certify that the ch.bER is improved using this method.