Fumiaki Ueno

Phase-change optical disk with nitride interface layers

Two marked effects are obtained by forming a Ge-N interface layer on either side of Ge-Sb-Te recording layer. One effect is a suppression of atomic diffusion between Ge-Sb-Te layer and protective layers, ZnS-SiO2 representatively, which leads to a significant improvement in overwrite cyclability, and the other is the acceleration of crystallization process which leads to higher speed optical disks. A rapid-cooling type experimental disk with Ge-N layers on both sides of the Ge-Sb-Te recording layer proved to be capable of exceeding 105 cycle overwrites and a recording data rate 40 Mbps at linear velocity 12 m/s. The recording conditions: bit length 0.28 micrometer and track pitch 0.6 micrometer (L/G method) using laser source with a wavelength 658 nm and a numerical aperture 0.6 correspond to a capacity 4.7 GB/(phi) 120 mm.

V-grooved optical disc applied to HDTV signal recording

We have realized a V-grooved optical disc that achieves an increase in recording density over conventional optical discs. This report describes the results of our research : namely its fabrication process and optical read-out method. The features of the V-grooved optical disc system are: 1) high density with narrower track pitch 2) double transfer rate using two-channel simultaneous read-out 3) applicability to read out current CD The V-grooved optical disc is suitable for recording of a baseband HDTV signal because the signal requires a large volume and high transfer rate. 1 . HIGH DENSITY OPTICAL DISCS Optical discs such as Compact Discs (CD) or Video Discs are currently used as information media because they feature large volume high density and easy random access. Recording density reaches 1 bit per 1 um2. However downsizing of disc diameter and applicability to HDTV signals require even higher recording density. Since an optical disc system reads out signals by focusing a laser to the diffraction limit the foremost way to realize higher recording density is minimizing the laser spots focused on the discs shortening of semiconductor laser wavelength and designing of better objective lenses have been the important themes of recent research and development. The wavelength of semiconductor lasers used to read out CD is in the near-infrared around 78Oniu but mass production of G7Onm lasers has just been initiated. Research and development of Il-VI