Optical engineering of parallel optical data storage
Volume holographic data storage uses the superposition of image holograms in a suitable medium to pursue large storage capacity and high readout rates. The holographic method of structuring the medium with data, and subsequent readout of those data structures, relies on an optical system with two distinct paths. The object path is typically a 4F system relaying a high space-bandwidth-product object to an image plane with the storage medium placed near the Fourier plane. Optical system parallelism, measured by space-bandwidth-produce, promotes both storage capacity and readout rate. The reference path is typically a relay with the field stop placed near the center of the storage material. We will consider how the properties of the object path optical system affect the storage capacity and readout rate. We will demonstrate that the object beam 4F system can be optimized for the particular requirements of volume holographic storage, and that relatively simple optical systems can provide high parallelism. We will also consider the optical parallelism possible for standard optical disk storage, and how these results compare to volume holographic storage. Finally, we will consider how the optical system of the reference path affects the storage capacity. We find that modifications to the reference beam, or apodization, can substantially mitigate the effects of interpage crosstalk, a fundamental noise source in volume holographic storage.
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