Multilevel Signal Processing Technique for a 30 Gbit/inch2 Phase-Change Optical Disk System

Abstract

We developed a multilevel recording technique and a Viterbi decoding technique for increasing the recording density of a phase-change optical disk. In this multilevel recording technique, each mark recorded on the disk changes its edge position in four steps according to four-level data. Since two consecutive mark edges are reproduced simultaneously, their reproduced signal takes seven levels. We devised a Viterbi decoder with reference matrices in order to improve data detection performance by compensating the nonlinearity of this multilevel signal. We evaluated the error rate performance of this optical disk system by computer simulation. The Viterbi decoder with the reference matrices showed superior performance, and had an improved noise margin which is 3.5 dB higher than that of a conventional Viterbi decoder. By employing the multilevel recording technique and the Viterbi decoding technique, we confirmed the feasibility of the phase-change optical disk system with a recording density of 30 Gbit/inch2.