Analysis of Signal to Noise Ratio in Magneto-Optical Disk Using a Polarization Simulator

Magneto-optical (M-0) disk is an erasable and large capacity memory which has been actively developed by many companies in the world. One of the most serious problem in developing M-0 disk is to guarantee the signal to noise (SN) ratio . In the M-0 disk, Kerr effect is utilized to reproduce the recorded data on the disk. However, Kerr effect is usually so small that the SN ratio is considerably small comparing with that of the write-once optical disk. Moreover, the SN ratio decreases in association with the retardation of disk substrate because of the degradation of the polarization state of the laser beam. Consequently, a precise analysis of the SN ratio taking retardation of disk substrate into account is significantly important for designing M-0 disk system. In this paper, retardation of the policarbonate substrate is precisely investigated and quantitative relations between the SN ratio and the retardation of disk substrate are particularly studied by the polarization simulator which traces polarization state of the laser beam.