2D and 3D Equalizers for Page-Oriented Optical Memories

Abstract

In this study we investigate the use of 2D and 3D equalizers to suppress intersymbol interference (ISI) in 2D parallel channels. The techniques demonstrated here are best suited for parallel implementation and can be used for any page-oriented readout application including increasing the data density achievable in volume optical memories or increasing the number of links achievable in free-space optical interconnects. Page-oriented optical memories are currently being investigated for their potential as high data-rate, high capacity storage devices,1-3 however the cost-effectiveness of such devices is limited by their requirements for high resolution in the optical system and severe alignment tolerances on the 2D detector array. Various techniques have been used in an attempt to reduce the amount of ISI generated by optical aberrations and misalignment including the use of guard bands around each bit and also reduced fill-factor detectors,2,3 however such techniques have the undesirable result of also reducing the signal intensity of each bit. An alternative approach is to remove the crosstalk electronically after detection. Serial equalizers have been used for years in communications and storage channels as a method of reducing ISI in a temporal bit stream.4 Limited 2D equalizers have also been demonstrated to reduce inter-track interference in high density optical disc recordings with multiple-beam readout heads.5-7 The use of partial-response maximum-likelihood (PRML) detection has been demonstrated to reduce the effects of crosstalk in page-oriented memories, however the complexity of PRML detectors increases rapidly as the number of spatial dimensions and the number of possible states increases.8 In this paper we propose the design of 2D and 3D equalizers suitable for page-access optical memories and investigate the performance of both linear and decision feedback implementations.