Toshiaki Iwanaga

High track density magneto-optical recording using a crosstalk canceler

High track density magneto-optical recording, using a crosstalk canceller which eliminates crosstalk from two adjacent tracks, has been developed. By this recording method, both land area and groove area can be used for data storage tracks, and twice the track density, cornpared with the conventional method, has been achieved. Applying this crosstalk canceller also realizes intersymbol interference compensation.

Multi-Beam Optical Disk Drive for High Data Transfer Rate Systems

A multi-beam optical disk drive, which improves the data transfer rate for magneto-optical disk systems, has been developed. The optical head employs an image rotator for tracing several tracks simultaneously. Four-channel parallel read/write operation has been achieved, and a digital video recording system with a data transfer rate of 22 Mbps has been realized. Real-time data verification at a linear velocity of 33 m/s has been demonstrated. Double track density recording, using a crosstalk canceler, has also been accomplished, and a 5.1×10-5 bit error rate has been obtained.

High Speed Accessing using Split Optical Head

High speed accessing using a split optical head with a linear actuator is presented. A new optical head, which can detect and compensate for the displacement between the optical axis and the optical head moving part, was developed for the linear actuator. The moving part weight for this disk drive is less than 30g. The 21 msec average coarse seeking time can be realized.

High-Density Land/Groove Recording for Digital Video File System

High-density land/groove recording technology for magnetooptical (MO) disks, using a high-speed crosstalk canceller which eliminates crosstalk from adjacent tracks, has been developed. A 0.50 µm/bit linear density with a 0.8 µm track pitch has been confirmed with a bit error rate (BER) less than 10-5. A digital video file system using this technology has also been developed. As a result, the authors confirmed the validity for the high-density land/groove recording technology in realizing larger capacity for digital video file systems.

High-density land/groove recording using PRML technology

High density land/groove recording, using partial response maximum likelihood (PRML) technology, which corrects errors in the readout signal for exploiting readout channel characteristics, has been developed. By this detection method, both land area and groove area can be used for data storage tracks without a crosstalk cancellation technique. Applying this method with a red laser, 8 times the storage capacity, compared with the conventional method, has been achieved.

Tracking Servo For Small Size Optical Disk System.

This paper describes a tracking servo system developed for a small size optical disk system. In this tracking servo system, new techniques, such as two stage servo system and tracking error integration memory, are applied for improving track access time and data transfer rate. The two stage tracking servo system has a unique position detector, which outputs a lens position error signal relative to the optical head. Using this detecting signal, the objective lens and the optical head are controlled co-operatively. Therefore direct track access from the current track to the target track is achieved without lens vibration. Also, average track access time is reduced. The tracking error integration memory integrates track error signal synchronized with disk rotation. This memory output signal is equivalent to track eccentricity after several disk rotations. Therefore, a tracking servo system with this tracking error integration memory can achive highly accurate track following even under highspeed disk rotation and large track eccentricity. As a result, disk rotation speed can be upped and data transfer rate can be improved.

Signal-to-Noise Ratio in a Partial-Response Maximum-Likelihood Detection

In this paper we describe a derivation of general expression of signal-to-noise ratio (SNR) in a partial-response maximum-likelihood (PRML) detection system. Because of media noise, as well as difference of transfer function between target PR and the actual channel, the noise at the Viterbi detector is no longer white but colored. The conventional expression of SNR is not appropriate for evaluating signal quality for the colored noise. We have shown how to calculate the variance of the colored noise in the PRML system. The derived SNR can be easily calculated using hardware and is very useful for evaluating signal quality under high-density recording conditions where jitter cannot be accurately measured. We have confirmed that the bit error rate (bER) predicted by the SNR correlates well with the actual bER, regardless of bit density.

Optimization of Write Strategy in a Partial-Response-Maximum-Likelihood System for High-Density Recording

It is difficult to optimize the write strategy by conventional methods in high-density recording systems with very severe intersymbol interference. We have proposed a new method using the index accounting for the linearity of the channel, which is very important in the partial-response-maximum-likelihood detection scheme. It has been confirmed that the minimum bit error rate can be obtained when the linearity of the channel becomes maximum. We have shown the feasibility of a recording capacity of over 20 GB with 120-mm-diameter phase-change media using the blue-violet laser diode with an objective lens whose numerical aperture is 0.65.

Optimization of write strategy in a PRML system for high density recording

Recently, there has been much research on high density recording using an NA = 0.85 objective lens . The use of PRML (partial response-maximum-likelihood) is an efficient way to handle inter-symbol interference (ISI) that degrades the bit-error-rate at a very high recording density. We have shown that the recording capacity of about 32 GB is achieved with the use of PR channel with a constraint length of 5, i.e., PR (12221) and Viterbi detection in the NA = 0.85 system. This paper describes the method for optimizing a write strategy in the PRML system. We have confirmed that the write strategy can be optimized in terms of a linearity of the channel. It has been found that the recording density near the optical cut-off frequency can be achieved by using the optimized write strategy and PRML.

High-Density Recording Using Mark Length Recording Method for Magnetooptical Disk

Mark length recording for a magnetooptical (MO) disk has two serious problems, thermal interaction and intersymbol interference. In order to resolve these problems, read-write compensation methods, the pulse train write compensation method, readout waveform equalization, and second-order differential pulse detection method, have been developed. Using mark length recording with effective read-write compensation, it has been confirmed that the (1, 7)RLL (Run Length Limited) code is a higher recording code than the (2, 7)RLL code for magnetooptical recording. A 0.5 µm/bit minimum bit recording length, using the (1, 7)RLL code for mark length recording, has also been achieved.