Photorefractive volume holographic memory systems: approaches, limitations, and requirements

Volume holographic memory systems provide a compact method by which data can be stored with high density and rapid accessibility. In these systems, for example, wavelength, angle, and phase multiplexing approaches have been utilized for the addressing of data pages. We analyze, in general, practical limitations in such systems due to cross-talk effects, beam depleting and material heating absorption effects, and multiplexing approaches. For example, beam depletion during the writing and reading of holograms in a volume holographic memory will cause the envelope of the diffracted beams to not be rect-like as simple cross-talk theories rely on, and material heating will act to detune, smear, and redirect beams during readout. We also characterize the photon-limited information throughput rates during recall from these systems. Finally, we demonstrate advances in our sparse-wavelength angle-multiplexed volume holographic memory system, achieving the storage of 2,000 holographic pages, each with approximately 2.35 million bits each, utilizing 400 angles (over a 3 degree external tuning span) and five wavelengths (over a 56 nanometer span) in a 1.86 cubic centimeter volume of lithium niobate.