Papers by arash karbaschi
A new technique for optical pattern recognition with two-center recording of persistent holograms... more A new technique for optical pattern recognition with two-center recording of persistent holograms in doubly doped LiNbO3:Fe:Mn crystal is presented, by which the holograms are localized in separate slices along the recording medium. The localized recording method has the distinctive advantage of selective recording and erasure of the individual holograms without affecting the entire holographic recording medium. This capability enables dynamic content modification of the optical pattern recognition systems. Also, the diffraction efficiency of localized holograms is much larger than that of the normal volume multiplexed holograms. It is theoretically shown that the localized holographic correlator (LHC) outperforms the conventional volume holographic correlators in terms of crosstalk, shift invariance, and capacity. The LHC is experimentally demonstrated. Several persistent holograms are localized within separate slices as close as 33 mum apart along the crystal. The excessive diffraction efficiency of the localized holograms is employed to enhance the LHC robustness through multiplexing several holograms per pattern within individual slices of the recording medium. A holographic data storage system based on two-center holographic recording in a doubly doped LiNbO3:Fe:Mn crystal is developed with angular multiplexing capability. The associated imaging system has been optimized for the pixel matching of pixelated bit patterns generated by a spatial light modulator (SLM) through the recording medium onto a camera. The initial multiplexed holograms show promising contrast of dark and bright pixels. With the optimized imaging system of the developed holographic memory, the implementation of a dynamic read/write data storage system with localized recording is envisioned. The large diffraction efficiency of the localized holograms enables multilevel (M-ary) data coding to improve the storage density of the system.
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International Journal of Gynecology & Obstetrics, 2005
ABSTRACT
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Optics Express, 2004
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Optics Letters, 2007
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We explain and compare two different methods (two-step and two-center recording) for gated hologr... more 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.
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Applied Optics, 2004
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Applied Optics, 2004
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We present a class of spectrometers that work based on diffractive properties of spherical beam v... more 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.
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Optics Letters, 2005
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Abstract In this paper, we consider the tradeoffs of binary and M-ary signaling in page-oriented ... more Abstract 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 ...
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We present experimental demonstrations of spectral diversity filters using spherical beam volume ... more 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.
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Optical Engineering, 2010
We consider M-ary signaling in page-oriented holographic storage systems that multiplex pages usi... more 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 ...
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Optics Letters, 2005
We present experimental demonstrations of spectral diversity filters with spherical beam volume h... more 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.
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Optical Engineering, 2005
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We propose a computationally efficient scheme to decode two-dimensional (2D) intersymbol interfer... more We propose a computationally efficient scheme to decode two-dimensional (2D) intersymbol interference (ISI) channel with M-ary input. The basic idea is to equalize the channel stage by stage. To begin with the stage with the highest signal power level, the BCJR algorithm is used to equalize each level by averaging the interference of the undecoded levels. Both the hard and soft decisions are passed to the next stages. The scheme hugely reduces the complexity of full-branch BCJR on the entire received page of data and makes the equalization applicable. Based on the statistic output of each stage the overall information rates are evaluated. Furthermore, the coding simulation results are presented. All of these results show the proposed scheme is a good candidate for decoding such M-ary 2D ISI channels.
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This work introduces the holographic correlators that use localized recording technique. The impl... more This work introduces the holographic correlators that use localized recording technique. The implementation of this method is based on a gated holographic recording technique such as two-center recording. A unique property of localized holographic correlators is the possibility of erasing and re-recording in each slice without affecting others. Therefore, dynamic modification of the patterns is possible. Moreover, by use of long crystals (5-10 cm), the capacity can be considerably increased. This is not possible in conventional holography due to adsorption of the recording and read-out beams through the crystal. Furthermore, the detector array contact the bottom surface of the crystal and no lens is required to collect and focus the diffracted correlation beams. This makes localized correlators a more compact system.
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Applied Physics B-lasers and Optics, 2008
We present a simple, very compact, and inexpensive spectrometer for diffuse source spectroscopy u... more We present a simple, very compact, and inexpensive spectrometer for diffuse source spectroscopy using only a volume hologram (recorded by two spherical beams) and a CCD camera (or a detector array). We show that this spectrometer can operate well under spatially incoherent light illumination. We also show that the resolution of this spectrometer can be optimized by proper selection of the location of the CCD camera (or the detector array). The results show the possibility of using optimized holographic optical elements as the integrated collimating, dispersive, and light-collective components of spectrometers.
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Papers by arash karbaschi