We consider M-ary signaling in page-oriented holographic storage systems that multiplex pages using three methods: conventional angular multiplexing throughout the volume, localized recording, and a combination of angular multiplexing within localized recording. We study the mutual information transfer, which is increasingly easy to achieve in practice, between the recorded and recovered data, and use it to assess the storage density in these systems. We use the existing holographic channel model for the dominant Rician noise case for deriving the mutual information bound on the capacity and examine the interplay between the storage density and the number of recorded pages within the medium. We quantify through information-theoretical analysis that it is possible to obtain considerably higher storage capacities using gated localized holography than what can be achieved in conventional volume holography with angular multiplexing by appropriately optimizing the number of intensity levels for a given material constant and signal-to-noise ratio.
We present a class of spectrometers that work based on diffractive properties of spherical beam volume holograms. The hologram in these spectrometers is recorded by a plane wave and a spherical beam and acts as a spectral diversity filter (SDF), which maps different input wavelengths into different locations in the output plane. The experimental results demonstrate that the spherical beam volume holograms have the capability of separation different wavelength channels of a collimated incident beam. For the analysis of the spherical beam volume hologram, a new theoretical method is introduced and used. It is shown that the experimental results are in good agreement with the theoretical study. Using these results, we demonstrate a Fourier-transform volume holographic spectrometer formed by a Fourier-transform lens, a spherical beam volume hologram, and a CCD. We show that this spectrometer can operate well under spatially incoherent light illumination without using any spatial filter (i.e., slit) in the input. We finally introduce a new implementation of a spectrometer for diffuse source spectroscopy by using only a volume hologram, recorded by two spherical beams, and a CCD. The proposed spectrometer is very compact, inexpensive, less sensitive to optical alignment, and has potentially high throughput that can be widely used in biological and environmental sensing applications.
We present a new technique for optical correlation using gated holographic recording by which the holograms are localized in separate slices along the recording medium. We compare the performance of localized holographic correlators (LHCs) with that of the conventional correlators using normal volume holography. Crosstalk, shift invariance, and the capacities of the LHC and of the conventional method are examined. We show that the proposed method has better performance and distinctive advantages over the conventional method. These advantages include selective recording and erasure for dynamic pattern modification, extendable capacity, and compactness.
We explain and compare two different methods (two-step and two-center recording) for gated holographic recording in lithium niobate crystals. We first compare the holographic recording performance of the two schemes based on the experimental results published in the literature. Then, we use a general model to compare the essential physics of the two methods theoretically, and we show that two-center recording has better performance in low light intensities. Global optimization of two-center recording as well as a unique feature of gated holography (i.e., localized recording) for new applications will also be discussed.