Phase-change optical disks compatible with a two-wavelength laser beam

Three types of multiple-layer structure are proposed for a two-wavelength-compatible phase-change optical disk that uses an 830-nm beam for writing and erasing and a 670-nm beam for reading. Each disk with an optimized structure exhibits high-enough carrier-to-noise and erasing ratios at 830 nm and 670 nm for practical use. One of the disks has a lower erasing ratio at 670 nm than at 830 nm for the same erased marks. This difference is explained by optical characteristics that stem from the multiple-layer structure of the disks.