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Modulation encoding and iterative detection for imaging page-oriented optical data storage

Various types of holographic and imaging volumetric page-oriented optical data storage (PODS) systems have great potential to provide data storage with larger capacity, faster access time, and higher transfer rates [1]. The usable data capacity is quantified by the code rate, or percentage of theoretical storage capacity that is actually useable for storing information at a minimum acceptable bit-error rate (BER). The BER is controlled by using a combination of channel coding (error-correcting coding or ECC) on the digital data, and a modulation coding procedure that formats the data for the physical storage medium. For a given coding scheme and level of signal processing, increasing the data packing density increases the code rate at the expense of lower BER due to the presence of spatial intersymbol interference (ISI), interpage interference (IPI) and noise. ISI and IPI are due to the point-spread function of the recording and readout optics. Some modulation codes [2] add redundant information to preserve the signal integrity and simplify the detection procedure. We describe a n iterative computational imaging technique that maintains a minimum required modulation coding BER (generally 10-3 or better) while improving the overall code rate and capacity of a page-oriented imaging optical data storage system