Partial response precoding for parallel readout optical memories

The data density that can be resolved in optical memories is limited by the inherently bandlimited nature of optical systems. In this paper, we show how a precoding technique used in serial communications, Partial Response (PR) precoding, can be applied to a parallel readout optical system to pre-compensate for the spatial data broadening that occurs as result of this bandlimiting. We examine the performance of 1+D PR precoding, a particular form of PR precoding, in an unapodized coherent imaging system. However, this technique can also be applied to other readout systems. A factor of 15 improvement in average worst case contrast ratio and a factor of 11 improvement in average contrast ratio were measured experimentally. Approximately 50% more area would be needed to achieve the same contrast ratio in a system without precoding. PR precoding was also found to be robust to defocusing and slight tilts, and can be used with a broad range of detector sizes.