Nobuyoshi Tsuboi

Single‐beam overwriting with melt‐erasing process in an InSbTe phase‐change optical disk

Single‐beam overwriting with melt‐erasing process was made in a 5.25‐in.‐diam phase‐change optical disk using an In22Sb37Te41 recording film. In the overwriting between 2 and 3 MHz signals at the linear velocity of 3–11 m/s, a carrier to noise ratio (C/N) more than 46 dB and an erasability less than −35 dB could be obtained. This high erasability was found to be due to the melt‐erasing process. This disk presents highly erasable overwriting and long data retention time supported by an activation energy of 2.3 eV and a temperature of 230 °C for crystallization of the amorphized part.

Optical head with optical beam control using acoustic wave device

An optical head is disclosed, in which a plate-shaped optical wave guide comprises an optical system including a collimator lens, a beam splitter and an objective lens; a laser light source for emitting a laser light in the form of a light beam which is to be impinged on an optical recording medium; and electro-acoustic transducers are disposed between the beam splitter and the objective lens, the transducers being adapted to be driven by the outer electrical signal for producing surface acoustic waves in the optical wave guide, thereby establishing a condensation and rarefaction distribution in refractive index in the optical wave guide which distribution influences the direction of transmission and the degree of focusing of the light beam passing therethrough so that regulation of the tracking and the focal length can be effected without any mechanical movements.

Three‐dimensional analysis of overwritable phase‐change optical disks

Three‐dimensional computer calculations which analyze time‐transient behavior of heat conduction and phase‐change kinetics in an InSbTe overwritable disk were made. To improve the calculation accuracy, thermal conductivities of thin‐film materials and critical cooling rate for crystallizing the recording film were estimated. For realization of high‐performance overwrite, it was found that the cooling conditions of writing and erasing processes should be controlled to match the critical cooling rate in a given linear velocity range. This could be achieved by optimal design of the disk structure.

Overwritable phase-change optical disk using an In3SbTe2 ternary compound

By employing transmission electron microscopy and thermal ana1yis, we examined overwrite repeatability of optical disks using In-Sb-Te alloys, which have high C/N ratio and excellent overwrite modulation characteristics. The overwrite repeatability of more than 105 was achieved by using an In3SbTe2 single-phase ternary compound and heat-flow balanced disk structure.

40 dB OVERWRITE -MODULATION PHASE- CHANGE OPTICAL DISK USING In -Sb -Te ALLOY

A single-beam overwrite was achieved by an In-Sb-Te phase-change optical disk. The carrier to noise (C/N) ratio of more than 50 dB and the overwrite modulation of -40 dB were obtained for overwriting frequencies of 2 MHz and 3 MHz using a low power laser diode of 30 The high C/N ratio and the excellent overwrite modulation were due to the large reflectivity difference between the written and erased phases and the use of suitable write/erase power.