Coding and signal processing for a magneto-optic resonant bias coil overwrite experiment

Abstract

A magnetooptic direct overwrite experiment using the resonant bias coil technique has been carried out. The technique requires even-numbered transitions to be written on even-numbered clock cycles and odd-numbered transitions to be written on odd-numbered clock cycles. This constraint is met by double-spaced run-length-limited (d,k,2) codes where the number of consecutive zeros is even. By exploiting the polarity of the transitions, a detection window that is double the size of the code bit period is possible. The authors describe a detection circuit that achieves the enlarged detection window and present a phase detector which is particularly simple to implement. Channel bit-error-rate measurements have been carried out employing a rate 1/3 (2,8,2) code. Error rates of 10-8 were achieved for recording densities up to 33 kb/in. The results demonstrate the expected excellent immunity of the direct overwrite scheme to bloom.