Biomedical subjects

Joseph Shamir

Publications and source records attributed to Joseph Shamir.

7 recordsLinked to original sources

PubMed2006

Paradigms for bit-oriented holographic information storage.

One of the difficulties encountered during the many years of research on holographic information storage was the lack of an easy theoretical way to assess proposed paradigms. I exploit the fact that for bit-oriented holographic storage, Gaussian beams are usually involved. For this case I show that the reconstructed wave can be represented as a superposition of simple Gaussian beams, regardless of the exact recording condition, and a virtual source for this wave can be determined. This theoretical result is used to explore several holographic storage architectures, in particular thick volume holograms and layered volume holograms. Simulation results demonstrate the power of the method, show good correspondence with earlier experimental studies, and provide clues for further developments.

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PubMed2006

Simple online recognition of optical data strings based on conservative optical logic.

Optical packet switching relies on the ability of a system to recognize header information on an optical signal. Unless the headers are very short with large Hamming distances, optical correlation fails and optical logic becomes attractive because it can handle long headers with Hamming distances as low as 1. Unfortunately, the only optical logic gates fast enough to keep up with current communication speeds involve semiconductor optical amplifiers and do not lend themselves to the incorporation of large numbers of elements for header recognition and would consume a lot of power as well. The ideal system would operate at any bandwidth with no power consumption. We describe how to design and build such a system by using passive optical logic. This too leads to practical problems that we discuss. We show theoretically various ways to use optical interferometric logic for reliable recognition of long data streams such as headers in optical communication. In addition, we demonstrate one particularly simple experimental approach using interferometric coinc gates.

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PubMed2006

Laser-mode selection by a combination of biprism-like reflectors with narrow amplitude masks.

In recent work the laser mode selectivity induced separately by a biprism-like reflector and by an absorbing strip was investigated by numerical analysis. It was shown that each of these elements in an otherwise conventional resonator was suitable to cause the laser to oscillate preferentially on the first odd mode that contains a line singularity, which is a useful dark beam (i.e., a laser beam with a dark central region) for high-resolution metrological applications. We study the combined effect of these two mode-selecting elements and show that the unified analysis leads to much better performance than could be expected from a simple superposition of the performance with each element alone. The results indicate that the mode selectivity can be enhanced by at least a factor of 3 compared with that of laser resonators with biprism-like reflectors alone. Thus a laser equipped with such a combined element will oscillate on a pure first-order mode with high power efficiency. Moreover, calculations show that the resultant dark beam, focused for metrological applications, has a significantly improved shape compared with the dark beam obtained by external modulation of a fundamental Gaussian beam.

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PubMed2006

Achieving stabilization in interferometric logic operations.

Interferometric systems with amplitude beam splitters can implement reversible operations that, on detection, become Boolean operators. Being passive, they consume no energy, do not limit the operating bandwidth, and have negligible latency. Unfortunately, conventional interferometric systems are notoriously sensitive to uncontrolled disturbances. Here the use of polarization in a common-path interferometric logic gate with and without polarization beam splitters is explored as an attractive alternative to overcome those difficulties. Two of three device configurations considered offer significant stability and lower drive modulator voltage as advantages over the previous systems. The first experimental tests of such a system are reported. Common-path interferometry lends itself to even more stability and robustness by compatibility with no-air-gap, solid optics.

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PubMed2005

Two regions of mode selection in resonators with biprismlike elements.

A resonator structure in which one reflector is replaced by a biprismlike reflecting surface is investigated theoretically. It is shown that such a modification leads to two regions of parameters, each with different regimes of mode selection. The first region has an improved laser power output because of the nearly flat-top mode shape. In the second region the biprism is inverted, with the result that the main oscillating mode can be the first odd mode. The line singularity contained in such a mode is one example of singular beams that are employed in various fields, such as micromanipulators and advanced high-resolution metrology.

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PubMed2004

Tunable, oblique incidence resonant grating filter for telecommunications.

We have designed a tunable, oblique-incidence resonant grating filter that covers the C band as an add-drop device for incident TE-polarized light. We tune the filter by tilting a microelectromechanical systems platform onto which the filter is attached. The fabrication tolerances as well as the role of finite incident-beam size and limited device size were addressed. The maximum achievable efficiency of a finite-area device as well as a scaling law that relates the resonance peak width and the minimum device size is derived. In good agreement with simulations, measurements indicate a negligible change in shape of the resonance peak from 1526 nm at a 45 degrees angle of incidence to 1573 nm at a 53 degrees angle with a full width at half-maximum of 0.4 nm. In this range the shift of the peak wavelength is linear with respect to changes in the angle of incidence.

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PubMed2002

Generalized Bragg selectivity in volume holography.

The diffraction efficiency of holographically recorded volume gratings was extensively studied, and it can be accurately predicted as long as the recording wave fronts are simple. The derivation of the diffraction efficiency when complicated wavefronts or images are involved is much more tedious and less explored. In this work we derive operator expressions that can be used to analyze these processes regardless of the shape of the wavefront and the nature of the optical systems through which they propagate. The compact expressions derived are directly applicable to the analysis of volume holographic processes, and the deterioration of the holographic reconstruction quality is derived as a function of the deviations from the recording parameters. The generalized results obtained reduce to the conventional Bragg effect for plane wave recording and reconstruction. Previously unexplored phenomena are discussed and demonstrated through some simple, and practically useful paradigms, including hologram recording and reconstruction in the Fresnel, Fourier transform, and image plane regions, as well as recording with plane and spherical waves. Some prior experimental results are also interpreted mathematically. In subsequent publications the analysis will be explored further to facilitate its application to more complicated architectures.

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