Magnetooptic direct overwrite using a resonant bias coil

A method is introduced for achieving direct (single-pass) overwrite in magnetooptical disk systems. In this method, a sinusoidal magnetic bias field is efficiently generated by incorporating the bias coil in a parallel resonant LC circuit. Magnetooptic domains of either sign can be written by timing laser pulses to coincide with either positive or negative peaks of the field. Continuous domains of variable length are written by overlapping the domains generated by successive laser pulses. Using a bias field with a fixed frequency of 4.5 MHz, carriers at various lower frequencies were written on a TbFe disk with 47-dB carrier-to-noise ratio. Direct overwrite resulted in erasure of old carriers by at least 34 dB. Suitable run-length-limited coding schemes are discussed, and a novel code type, called (d, k)-even 0, is introduced.<
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