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.
Compact and efficient spectrometers are of great interest for biological and environmental sensing. In this paper, we
describe a new class of spectrometers that work based on diffractive properties of spherical beam volume holograms
(SBVHs) and cylindrical beam volume holograms (CBVHs). The hologram in these spectrometers acts as a spectral
diversity filter (SDF) that maps different input wavelengths onto different locations in the output plane. The main
properties of these holographic SDFs and new techniques for removing the ambiguity between incident wavelength (or
the input channel) and incident angle (or the input spatial mode) are discussed. By using CBVHs, we show that the
spectral mapping of the input beam can be obtained in one direction and the beam can be independently modified in the
perpendicular direction. Using this unique property, we demonstrate a spectral wrapping technique to considerably
increase the operation spectral range of spectrometers, without sacrificing their resolution. Finally, it is also shown that
by combining CBVHs with a Fabry-Perot interferometer, a true two-dimensional spatial-spectral mapping can be
formed, and an ultra-high resolution of 0.2 nm with large spectral bandwidth is demonstrated for this tandem
A simple, inexpensive, and efficient stabilized holographic recording setup is described which precludes the destructive fringe movement encountered in long-lasting holographic exposures. Utilizing a straightforward methodology, stability greater than /25 (recording wavelength =532 nm) for holographic recording sessions longer than 6 h can be achieved. Due to the software basis of this design, in the LabVIEW platform, the functionality of expensive hardware components is provided in software. Moreover, this setup is modularly designed and can be easily replicated for multiple labs, with the need only of the following hardware components: a piezo-shifting mirror, a computer, a data-acquisition card, and a photodetector.
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.
The detailed performance of two-center holographic recording is theoretically studied. We present here a systematic method for global optimization of two-center holographic recording, and apply the method to lithium niobate crystals doped with iron and manganese (LiNbO<sub>3</sub>:Fe:Mn). Both the dynamic range (M/#) and sensitivity (S) are considered, and the optimum design parameters for LiNbO<sub>3</sub>:Fe:Mn crystals are predicted. To perform optimization, we use both an analytic approach and a complete numerical approach. The light absorption in the crystal is also considered. We show that the optimum design parameters for maximizing the M/# are different from those for maximizing S.
We present an RC-model approach for understanding and analysis of holographic storage in photorefractive materials. In this model the resistor, capacitor and the current source are completely defined based on material parameters and light intensities. The model has good accuracy for the practical applications. It can also be used to understand and improve the properties of photorefractive materials for holographic recording. One interesting application of the model is the qualitative analysis of two-center recording. We also discuss this application in detail.