Two-dimensional partial response maximum likelihood with constant-weight constraint for holographic data storage

The areal density of holographic memory can be increased by decreasing the aperture size of the optical system; however, this causes the deterioration of a reproduced image due to the elimination of the high-frequency components of the image. We have developed two-dimensional partial response maximum likelihood (2D PRML), which is based on the previously proposed "decision feedback Viterbi algorithm" and added the new idea of the "constant-weight constraint (CW constraint)" and the "amplitude PR method". We have confirmed the improvement in error rate using 2D PRML compared with the conventional differential detection method in a high-density holographic memory system by simulation.