title: Gray-scale data pages for digital holographic data storage.
abstract: The prospects for gray-scale (or multilevel) digital holographic data storage are theoretically and experimentally investigated. A simple signal-to-noise ratio (SNR) partitioning argument shows that when SNR scales as 1 over the number of holograms squared, five gray levels (log(2) 5 bits/pixel) would be expected to result in a 15% capacity increase over binary data pages. However, the additional signal-dependent noise sources present in practical systems create a baseline SNR that reduces both the optimal number of gray levels and the resulting gain in capacity. To implement gray-scale recording experimentally, we adapt the predistortion technique previously developed for binary page-oriented memories [Opt. Lett. 23, 289 (1998)]. Several new block-based modulation codes for decoding gray-scale data pages are introduced. User capacity is evaluated by an experimental technique using LiNbO(3) :Fe in the 90 degrees geometry. Experimental results show that a balanced modulation code with three gray levels provides a 30% increase in capacity (as well as a 30% increase in readout rate) over local binary thresholding.
authors: IBM Almaden Research Center, 650 Harry Road, San Jose, California 95120, USA.
authors: G W
authors: GW
authors: Burr
authors: G
authors: G
authors: Barking
authors: H
authors: H
authors: Coufal
authors: J A
authors: JA
authors: Hoffnagle
authors: C M
authors: CM
authors: Jefferson
authors: M A
authors: MA
authors: Neifeld