Abstract

Page-access optical memories are being investigated for the next generation of digital storage due to their potential for simultaneously achieving high capacity, fast transfer rates, and short access times. Examples of such memories are systems based on volume holography[1], two photon 3D recording[2], and spectral hole burning[3]. A common feature of these systems is that data is input using a spatial light modulator (SLM) and the output signal is imaged onto a CCD array. A typical arrangement for a digital volume holographic memory is shown in Fig. 1. To meet the capacity and transfer rate goals of a commercial system, page sizes on the order of one million pixels are required. The need to image pixel-to-pixel from the SLM to the CCD array over such a large page imposes tight tolerances on the optical design. Deviations from ideal imaging typically result in degraded performance. In future systems, signal processing methods will be required to overcome the limitations of the optical components. We describe a technique for data detection in page-acces memories that extends the well-known method of sequence detection from digital communications to two dimensions. The technique, which we term Decision Feedback Viterbi Algorithm (DF-VA) Detection improves the bit-error-rate (BER) performance of systems without ideal optics. Use of such a detection scheme can allow the use of less expensive, lower-complexity imaging optics, or, alternatively, can lead to higher information density per data page.

© 1996 Optical Society of America