Coding Techniques to Reduce Material Saturation in Holographic Data Storage.

摘要

Holographic data storage (HDS) is an emerging data storage technology that has received attention due to a high theoretical data capacity, fast readout times, and a potentially long lifetime of the recording materials. The work presented in this thesis was undertaken to solve one of the technical impediments preventing the widespread use of HDS, the occurrence of large concentrations of power in recorded holograms. Such peak values of optical power cause the medium to saturate during the recording process. As a result, the most significant portions of the hologram are not recorded accurately, and on readout, saturated recordings are not reconstructed correctly.;This thesis presents a two-step coding technique that decreases the likelihood and severity of peaks in encoded holograms. In the first step, sparsity, the proportion of OFF-pixels in the array, is increased, which decreases the total power in the encoded array. In the second step, phase masks are used to alter the phase of ON-pixels to decrease periodic content in the data array. This reduces the likelihood of an encoded array containing large peak values at any point in the Fourier domain.;Analysis is presented for the sparsity encoding which demonstrates the worst-case sparsity for certain system parameters. The performance of both the sparsity encoding and phase masking procedure are tested with numerical simulations. The results of these simulations indicate that these encoding techniques effectively inhibit the occurrence of large intensity peaks the holograms of encoded arrays.;In the implementation of HDS considered in this thesis, data is organized into an array of pixels using hybrid ternary modulation that contains an OFF-pixel and two different ON-pixels that are differentiated by their phase terms. The Fourier transform of this data array is created optically and the image of the Fourier transform is recorded holographically.