New Optical Erasable Medium Using Tellurium Suboxide Thin Film

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Abstract
A suboxide thin film of TeOx ( x is smaller than the stoich.Lometric value ) containing a small amount of additives of such metals and semimetals as Sn and Ge has been found to have the property of showing a reversible change in its optical constants when the film was exposed in turn to two diode laser spots with different sizes, and this property can be utilized for an erasable disc. For recording, a TeOx thin film deposited on a PMMA substrate is irradiated by a diffraction limited laser spot, 0.8 pm in dia., modulated in response to an input electrical signal. This causes a micro-sized area of the film to be suddenly heated and rapidly quenched, resulting in a decrease in optical reflectivity. This recorded bit can be erased at real time by the irradiation of a diffused laser spot to an elliptical shape, 1 x 10 pm, by which the bit recovers its optical properties. An optical head having the two laser beams, one for recording/playback and one for erasing, has been developed. Real time erasing and recording at the same time has been achieved for a video signal. In excess of a million record/erase cycles have been demonstrated with no significant degradation in playback signal quality or erasability. Carrier-to-noise ratio, C/N, was more than 55 dB at 5 MHz, 30 kHz bandwidth.

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