Gray-Scale Data Pages for Digital Holographic Data Storage

Abstract

Many of the attractive features of holographic data storage — such as high capacity, high density, and fast readout — are due to the use of large pixellated data pages, which are recorded into a photosensitive material as volume holograms [1–3]. It is often claimed that each hologram can store as many bits of digital data as there are pixels in the data page. To this end, most of the work performed in the field has used binary encoding, where pixels take one of two distinct states — ON(bright) and OFF (dark), corresponding to binary 1 and 0 — to encode one bit of information. Preceding chapters have shown that the coding introduced to maintain acceptable bit-error-rate (BER) comes with an unavoidable overhead cost, resulting in somewhat less than one bit per pixel. In this chapter, we discuss the use of gray-scale: recording and detecting more than two brightness levels per pixel, leading to more than one bit of data per pixel.