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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.

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