Biomedical subjects

Demetri Psaltis

Publications and source records attributed to Demetri Psaltis.

5 recordsLinked to original sources

PubMed2003

Dispersion and nonlinearity compensation by spectral phase conjugation.

We propose the use of spectral phase conjugation to compensate for dispersion of all orders, self-phase modulation, and self-steepening of an optical pulse in a fiber. Although this method cannot compensate for loss and intrapulse Raman scattering, it is superior to the previously suggested midway temporal phase conjugation method if high-order dispersion is a main source of distortion. The reshaping performance of our proposed scheme and a combined temporal and spectral phase conjugation scheme in the presence of uncompensated effects is studied numerically.

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PubMed2003

Comparison of transmission and the 90-degree holographic recording geometry.

We compare the system performances of two holographic recording geometries using iron-doped lithium niobate: the 90-degree and transmission geometry. We find that transmission geometry is better because the attainable dynamic range (M/#) is much higher. The only drawback of transmission geometry is the buildup of fanning, particularly during readout. Material solutions that reduce fanning such as doubly-doped photerefractive crystals make transmission geometry the clear winner.

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PubMed2003

Folded shift multiplexing.

Shift multiplexing is a holographic recording method that uses a spherical reference wave. We extend the principle to a thin slab of holographic material that acts as a waveguide. Total internal reflection folds the reference spherical beam in one dimension. We demonstrate that the shift selectivity with the folded spherical beam is independent of the slab thickness but depends instead on the numerical aperture of the coupled spherical wave. A shift selectivity of 0.5 microm has been achieved with a 1-mm-thick LiNbO3 crystal and 50 high-definition data pages are recorded with this method.

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PubMed2002

Coherent optical information systems.

Coherent optical beams are used to communicate, store, and process information in a growing number of applications. The availability of coherent laser sources is of critical importance for the realization of such optical information systems. An incoherent source randomly populates the available temporal and spatial channels of the optical system, making it difficult to represent information. Coherent laser sources provide a stable carrier on which to encode information, making it possible to realize powerful information-processing techniques such as wavelength division multiplexing in fiber networks, gated holographic imaging, and three-dimensional optical data storage.

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PubMed1997

Network Synthesis through Data-Driven Growth and Decay.

AN ALGORITHM FOR ADDITION AND DELETION (ADDEL) OF RESOURCES DURING LEARNING IS DEVELOPED TO ACHIEVE TWO GOALS: (1) to find feed-forward multilayer networks that are as small as possible, (2) to find an appropriate structure for such small networks. These goals are accomplished by operating alternately between an adding phase and a deleting phase while learning the given input-output associations. The adding phase develops a crude structure by filling in resources (connections, units and layers) at a virtual multilayer network with a maximum of L possible layers. The deleting phase then removes any unnecessary connections to obtain a refined structure. The additions and deletions are done based on a sensitivity measure and a corresponding probability rule so that only the synapses which are most effective in reducing the output error are preserved. A generalization error estimated from a validation set is used to control the alternation between the two learning phases and the termination of learning. Simulations, including handwritten digit recognition, demonstrate that the algorithm is effective in finding an appropriate network structure for a small network which can generalize well. The algorithm is used to investigate when the size of a network is important for generalization. Copyright 1997 Elsevier Science Ltd.

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