Using volume holograms to search digital databases

Abstract

Holographic data storage offers the potential for simultaneous search of an entire database by performing multiple optical correlations between stored data pages and a search argument [1,2]. This content-addressable retrieval produces one analog correlation score for each stored volume hologram. We have previously developed fuzzy encoding techniques for this fast parallel search, and holographically searched a small database with high fidelity [2]. We recently showed that such systems can be configured to produce true inner-products, and proposed an architecture in which massively-parallel searches could be implemented [3]. However, the speed advantage over conventional electronic search provided by parallelism [2] brings with it the possibility of erroneous search results, since these analog correlation scores are subject to various noise sources. We show that the fidelity of such an optical search depends not only on the usual holographic storage signal-to-noise factors (such as readout power, diffraction efficiency, and readout speed), but also on the particular database query being made. In effect, the presence of non-matching database records with nearly the same correlation score as the targeted matching records reduces the speed advantage of the parallel search. Thus for any given fidelity target, the performance improvement offered by a content-addressable holographic storage can vary from query to query even within the same database.