Relation between Groove Shape and Signal Quality in Magneto-Optical Disks

Abstract

The relation between groove profile and signal quality in magneto-optical disks was investigated theoretically and experimentally. First, the static characteristics of disks were measured using a micro-magneto-optical effect measurement apparatus. The Kerr rotation angle (θk), reflectivity (Ro) and coercive force in grooves 0.65 to 0.91 μm wide and 15 to 87 nm deep were similar to the values for the plane surface, except for a reduction in Ro due to groove diffraction effects. Then the carrier-to-noise ratio was examined using a magneto-optical disk drive, and the results compared with theoretical values. A decreased groove depth and increased width yielded good signal quality. As a result, high-quality magneto-optical signals in excess of 60 dB were obtained from a magneto-optical disk with grooves of depth 15 nm and width 0.8 μm, and with a four-layer structure medium consisting of A1N, GdTbFe, and Al.