Analysis of read-out signals in land/groove recording of a phase-change optical disc

We have analyzed the read-out signal obtained from a phase-change optical disc. The marks were recorded both on land tracks and in groove tracks with the focused laser beam of a wavelength of 685nm and a numerical aperture (NA) of 0.6 Characteristics of the read-out signal of marks recorded both on land tracks and in groove tracks were understood by considering the land/groove configuration of the substrate, the reflectance difference and the phase difference between amorphous and crystalline states of a recording layer. By comparing the measured carrier levels obtained from the land and groove tracks with the simulation results based on the diffraction theory, we found that the measured carrier level difference between land and groove recordings resulted mainly from the effects of groove geometry and the phase difference which was estimated to be 20 degrees for our sample disc. For this work, the groove geometry of the substrate and mark sizes were precisely estimated from transmission electron microscopy (TEM) micrographs.