Substrate noise in optical data-storage systems

Noise in optical disk readout has been examined for different polarizations of the incident beam. The disks studied are bare grooved glass substrates, having different groove shapes or differing jaggedness in the sidewalls. We perform measurements for the electric field of the incident laser beam parallel to the track and perpendicular to the track using both differential magneto-optical and conventional phasechange readout schemes. The incident beam of light is focused on the grooved surface of the (bare) substrate either through the substrate or directly from the air. Experiments reveal that the noise level is dependent on the state of polarization, the nature of the track (i.e., land or groove), and the medium of incidence. Surface roughness and sidewall jaggedness are two dominant contributors to the media noise in these substrates.