Thin Injection-Molded Substrate for High Density Recording Phase-Change Rewritable Optical Disk

Abstract

A thin disk substrate was examined for use as a high-density recording optical disk. An injection-molded polycarbonate thin disk substrate of 0.6 mm thickness showed birefringence under 60 nm and small tilt angle under 5 mrad. The track pitch was 1.0 µm and the diameter was 86 mm. The laser source was visible light at wavelength 680 nm, and the numerical aperture ( NA ) of the optical head was as large as 0.6. This new high-density disk and drive system had the characteristics of wide tilt angle tolerance, equivalent to conventional thick substrates of 1.2 mm, and high-density small mark length of 0.52 µm, giving a carrier-to-noise ( C / N ) ratio beyond 48 dB. We found that for new high-density disk generation, thin disk substrates were suitable.