Super-Resolution Optical Disc with High Readout Stability Using a Zinc Oxide Thin Film

We report a new super-resolution read-only-memory (ROM) disc with high readout stability using a zinc oxide (ZnO) thin film. A ZnO film utilized in our experiment showed a change in optical constant depending on temperature. By applying this characteristic to a ROM disc, we obtained a linear bit density two times higher than that of conventional ROM discs in our experimental optical pickup system with a 408-nm-wavelength laser and a 0.65-numerical-aperture (NA) objective lens. The readout stability was improved by employing a Si film. A high readout cyclability of more than 1.0×105 was obtained. Moreover, the super-resolution readout function was confirmed in another optical pickup system with a 408-nm-wavelength laser and a 0.85-NA objective lens.