SOURCES OF NOISE IN ERASABLE OPTICAL DISK DATA-STORAGE

Noise sources in the readback signal for phase-change and magneto-opti cal disks at red, green, and blue wavelengths are examined, and a simp le model is presented to explain the observed noise spectra. For phase -change disks the media noise, which corresponds to similar to 0.4% fl uctuation in the disk's amplitude reflection coefficient, is the limit ing performance factor for the conventional detection scheme. In magne to-optical media the depolarization noise, whose fluctuations are simi lar to 0.05% of the disk's reflection coefficient, is the major contri butor to the media noise in the differential detection scheme. In phas e-change optical disks the main sources of noise are the roughness of the groove profiles and the graininess of the polycrystalline recordin g layer. In nongrooved regions of the disk the media noise measured wi th green light is found to be nearly the same as that obtained with th e red light. In magneto-optical disks the scattering of light hom the rough groove profiles, as well as media inhomogeneities, gives rise to depolarization. Measurements on nongrooved regions of a magneto-optic al disk indicate that the media noise obtained with the green light is somewhat higher than that obtained with the red light. (C) 1998 Optic al Society of America.