BUSINESS SYSTEMS ANALYSIS AND DESIGN

Business Systems Analysis and Design

Abstract

We implement a new modulation scheme for inputting digital data pages for content-addressable holographic data storage. This scheme, which is a modification of the hybrid ternary modulation (HTM) scheme, exploits the advantages of both pure phase modulation and hybrid ternary modulation. The technique of using binary phase data pages with equal number of 0 and p using twisted-nematic liquid crystal spatial light modulator reduces strong dc component and produces a more homogeneous spectral distribution at the recording plane. This technique should facilitate better recording of all spatial frequencies, and thus improve the discrimination capability of a content-addressable memory. In HTM, there are three states to represent binary bits, whereas in the proposed code, we use the two bright states with a difference of p for coding the binary data. The third state, which is a dark state, is used to code the undesired regions of the spatial light modulator (SLM) while performing a search operation using a small search argument. We also introduce a new balanced modulation code which is a modified version of the 8:12 modulation code to address the coding subtleties associated with phase-based data pages. The proposed technique enhances the discrimination capability of content search using small search arguments, thereby giving better results in associative recall in a holographic memory system, with very low number of false hits compared to the existing schemes. A comparative study is presented of discrimination ratio and SNR for the different modulation schemes.

Business Systems Analysis and Design

1. Introduction

Volume holographic datastorage has wide potential as a promising datastorage technology due to its exceptional features like high capacities, high storage density, and high data transfer rates, etc. One of the unique features of holographic datastorage is its content-addressability. Volume holographic memories allow searching of all their contents in a single step by performing multiple optical correlations between stored data pages and a search argument. A holographic data bank consisting of N multiplexed data pages, when illuminated by a search argument S, reconstructs simultaneously all the reference beams used to multiplex the data pages. The amount of power diffracted into each output beam is proportional to the correlation between the input page and the stored data page. This property of content-addressability can be exploited for fast content search operations in a database. Earlier works in this area have clearly demonstrated the strong potential and wide applications of this technique in a practical binary database environment, which cannot be provided by the current datastorage technologies that are serially addressed. Most of the current technologies for querying through a database are time-consuming and not suitable for real-time application.

Although the results of a content-addressable holographic memory are promising, studies have highlighted the system drawbacks, which lead to false hits and mismatches while performing search operations and . While performing a search operation in content-addressable memory, the search argument is multiplied with all the stored data pages and the incident beam will be diffracted into all the reference ...