DIRECT OVERWRITE MAGNETO-OPTICAL DISK AND HIGH DATA DENSITY RECORDING

Abstract

MO disks have the thermal response functions to laser heating. Those thermal response functions have finite, not zero, values of time constant (τ). Thermal interference between the heat which forms recording marks, accordingly, causes thermal build-up shifts of mark edges, leading edges and trailing edges. We report how to measure the thermal response functions. Direct overwrite (DOW) MO disks, as compared to current MO disks which have an Aluminum layer, have more suitable thermal response functions for high data density recording with mark edge recording. The Aluminum layer would cause a phenomenon of thermal echo with a larger τ. The thermal interference should be precompensated for, or made uniform (i. e. not dependent on the data pattern recorded on the disk), or made small enough, so that the thermal build-up shifts should not make narrow window margins in reproducing recorded data and discriminating the locus of mark edges. When a technique, the pattern dependent adjustment to timing of laser pulse edges precompensating for the thermal interference is applied for high data density (0.54 μm/bit) recording on the DOW-MO disk, the window margin is 21 % of the channel clock period, 15.9 nsec, at B.E.R. = 10-6.