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Optical Data Storage

Each bit in the volume of the polymer disk (left) is a micro-hologram written by the interference of two counter-propagating foci. During readout, the top (reference) focus holographically reconstructs the bottom (object) beam if a bit is present.
Traditional optical data storage uses a laser to read and write spots on a spinning disk made of one to four layers. Capacity is limited to several hundred gigabytes. Extending this to terabyte capacity requires using the full 3D volume of the disk. Diffusive photopolymers are an attractive material for this application due to their low cost, ease of processing and high sensitivity. Unfortuntely, "blobs" of refractive index written by a focused laser in the photopolymer volume cannot be efficiently read back out in the traditional reflection geometry. An alternative is to write "micro-holograms" with two counter-propagating laser foci. The interference pattern writes a micron-scale Bragg reflector. Each such micro-hologram encodes a single bit and can be rapidy read by a focused laser as the disk rotates.

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