Arash Karbaschi

Compact Fourier-transform volume holographic spectrometer for diffuse source spectroscopy

We present a new idea for diffuse source spectroscopy using a Fourier-transform volume holographic spectrometer formed by a Fourier-transform lens, a volume hologram, and a CCD. We show that this spectrometer can operate well under spatially incoherent light illumination. Furthermore, this spectrometer is less bulky, less sensitive to input alignment, and potentially more appropriate for implementation of highly sensitive spectrometers than conventional spectrometers.

Spherical beam holograms for spectroscopic applications: Modeling and implementation

A new approach for analyzing spherical beam holograms is presented and tested. This method describes the diffraction effect in spherical beam holograms and its application in spectroscopy. The theoretical results are verified by experiments.

Qualitative demonstration of spectral diversity filtering using spherical beam volume holograms.

We investigate the feasibility of designing spectral diversity filters using spherical beam volume holograms. Our experimental results qualitatively show the separation of the information of different incident wavelength channels using spherical beam volume holograms. The major trade-off in using these holograms is between the degree of spatial spectral diversity and the number of allowed spatial modes (or the divergence angle) of the incident beam.

Role of recording geometry in the performance of spectral diversity filters with spherical beam volume holograms

We present experimental demonstrations of spectral diversity filters with spherical beam volume holograms for multimodal multiplex spectroscopy. Major properties of filters under diffuse-light illumination are discussed. The comparisons of spectral diversity between the transmission geometry holograms and the reflection geometry holograms are also studied. The results show that there is a trade-off between the degree of the spatial coherence of the source and the spectral diversity of the filter. We also conclude that the reflection geometry holograms have better spectral diversity and less sensitivity to the spatial coherence of the source.

Gated holography: materials, techniques, and applications

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.

GEN04-2: M-ary, Binary, and Space-Volume Multiplexing Trade-offs for Holographic Channels

In this paper, we consider the tradeoffs of binary and M-ary signaling in page-oriented holographic storage systems that multiplex pages using two methods: conventional angle multiplexing throughout the volume and 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 trade-offs in these systems. We use the transmission model developed by Heanue, Bashaw, and Hesselink [7] for deriving the mutual information bound on capacity and examine the interplay between the storage density and the number of recorded pages within the medium. This result is useful for deciding the number of recorded pages and the desired level of a multi-level modulation code for maximizing the storage density in a volume holographic memory. We analyze our results for localized and angle multiplexed recording and compare the performance in these two cases.

Optical correlation using gated localized holography

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 perfor- mance of localized holographic correlators LHCs with that of the con- ventional 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.

Volumetric storage limits and space-volume multiplexing trade-offs for holographic channels

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.

Dynamic optical correlation using localized holography

A new technique for optical correlation using gated holographic recording is demonstrated. Several persistent holograms are localized within separate slices as close as 33 microm apart along the crystal. Individual holograms can be dynamically erased and rerecorded with no need to refresh all other recorded holograms. Experimental results showing the correlation capability, cross talk, shift invariance, and dynamicity of the localized holographic correlator demonstrate unique performance and capabilities for these correlators.

Implementation of spectral diversity filters using spherical beam volume holograms

We present experimental demonstrations of spectral diversity filters using spherical beam volume holograms. Major properties of filters under collimated and diffuse light will be presented. We also show rotation multiplexing can improve the spectral diversity.