Mitsuro Moriya

Tracking system for controlling the radial positioning of a transducer on a disc medium

A data track searching device capable of switching between two modes; one being the rough searching mode in which a transducer is displaced at a high velocity to a desired track and the other being the fine searching mode which follows the rough searching mode and in which the transducer is displaced at a relative low velocity and positioned over the proper or desired track. The operating point of a tracking element is shifted or deviated as a result of the high-velocity displacement of the transducer in the rough searching mode so that stable searching cannot be ensured. According to the present invention, therefore, the acceleration of the transducer in the rough searching mode is detected and a signal representative of the thus detected acceleration is applied to the tracking element so that the shift or deviation of the operating point of the tracking element can substantially made nil.

Study of phase-change erasable sample-servo optical disk with bit-capsule groove

Characteristics of the bit-capsule recording are studied. Every information bit is recorded on phase change erasable material in an enclosed bit-capsule using sample-servo technique. It is confirmed that the bit-capsule is effective on size-limited mark formation or low distortion recording, which is inevitable for high density recording.

Study of Pulse Erasing on Phase-Change Erasable (PCE) Sampled Servo Disc

An experimental study has been conducted on a phase-change erasable (PCE) sampled servo system. In the erase procedure, a pulse-modulated laser beam is irradiated on the PCE media. The result shows that media damage is less than in conventional continuous erasing.

Focus-error detection from far-field image flow

Features of a focus-error detection method from a far-field diffraction pattern are studied both theoretically and experimentally. An obtained focus-error signal, being a nonlinear function of focus error, has wide dynamic range of +/- 4 micrometers and enough signal-to-noise ratio for a stable focusing servo.

Single-beam overwrite optical disk memory using a phase-change medium

A single beam overwrite optical disk memory using a rewritable phase change medium has been developed for digital data storage. The overwrite function was realized by using the same simple optical head as that of write-once memory. An 86mm pregrooved disk has the large capacity of 280MB on both sides. A higher data transfer rate of 6Mbps was achieved. A split type optical head having a 9gr. moving portion realized 42ms seek time with low power consumption. Overwrite operation is done by making amorphous marks and crystallized (erased) area with single laser beam. As the read-out signal is obtained from the difference of their reflectivities in the same way as write-once media, the optical head has become simple and compact. The overwriting temperature of the active layer is much higher than the operating temperature. This optical disk memory can execute reliable write and read operations with a wide tolerance for the operating temperature. Rewritable media were evaluated under practical perating conditions and could be overwritten more than 100,000 cycles on the same physical sectors. Implementing effective defect management, the practical or logical cyclability of the optical disk memory was improved up to one million cycles.