Pit Shape At Overwriting Of Thermal Magneto-Optical Recording

ABSTRACT The pit shape in magnetic field modulation recording is obtained from temperature profile which is calculated by using three dimensional thermal diffusion equations considering the movement of laser spot. The pit edge shape changes more elliptically with increasing disk velocity. The calculated frequency response does not degrade so much as the pit edge shape changes. The influence of disk velocity to the frequency response is less than that of recorded pit duty. These calculation method is useful for obtaining the recording characteristics of read-write channel, when various parameters are changed, without experiments. 1. INTRODUCTION In MO(magneto-optical) disk system, some overwriting techniques have bee^ proposed previously. The magnetic field modulation method is the most promising method. ' In this overwriting method, the shape of the pit is similar to crescent. The width of the pit is decided by laser spot radius, and the length of that is decided by switching time of magnetic field.The pit formations in optical disk were studied by the calculation of the temperature profile during light-induced recording process. The pit shape can be obtained from the calculated temperature profile on recording layer in MO disk, because the pit formation process is simpler than ablative recording. The playback signal from the pit shape is calculated using the Fourier transformation. The calculated playback signal from these pit shape agreed with the experimental results. Therefore, these calculation method is useful for obtaining the recording characteristics of read-write channel, when various parameters are changed, without experiments.This paper describes the basic overwriting characteristics by experiments and calculations. The influence of the pit shape to a frequency response of the playback signal and the residual pre-recorded signal are reported.