COMPLETELY ERASABLE PHASE-CHANGE OPTICAL DISK

A phase change optical disk using a new quaternary system of Ag-In-Sb- Te as the active layer will be reported. With this disk, "complete era sure" of the recorded signal has been achieved. A carrier-to-noise rat io of 47 dB and an erase ratio of -47 dB were obtained in the two-pass writing-erasing mode with a linear velocity of 7 m/s and a writing po wer of 11 mW. In the one-pass overwriting mode, a carrier-to-noise rat io greater than 40 dB was obtained and this recorded signal was also c ompletely erased. The peak power and the bias power for the overwritin g were 10 mW and 5 mW, respectively. The facts that the widths of the written marks are narrow and that no large crystalline grains are obse rved in the periphery of the written marks are considered to be the ma jor causes for the high erasability. We also found that the existence of fine crystalline particles in the initialized active layer can be c onsidered to be of great advantage to high sensitivity.