Showing papers by "Ignacio Moreno published in 2002"

Convergent optical correlator alignment based on frequency filtering

Abstract: The convergent correlator is widely used but it presents the drawback of the alignment requirements: fine focusing of the input scene Fourier transform on the filter plane, filter centering, scaling the scene Fourier transform to match the filter size, and azimuth matching of the filter with the input scene. We propose a set of tests to obtain a precise alignment of the convergent correlator. These methods are based on frequency filtering properties and they are applicable either for amplitude input or for phase-encoded input. The tests we present allow us to fulfill all the alignment requirements. The theory on which these tests are based is explained. The experimental results obtained during the alignment procedure are presented. We show some additional verifications of the correct alignment of the convergent correlator.

Optimization of the polychromatic discrimination capability in multichannel pattern recognition

Abstract: We present the improvement of color pattern recognition by the optimization of a new parameter, the polychromatic discrimination capability. We use the polychromatic correlation obtained as the addition of the three correlation intensities obtained with the RGB components of the input color scene and the corresponding components of the color target. The polychromatic discrimination capability is defined in this fused correlation plane. We propose a method to optimize this perfor- mance parameter, which represents a global criterion for the optimization of the polychromatic correlation. The approach involves the design of regions of support to be used with the matched phase-only filters to optimize the polychromatic discrimination. We present simulation results illustrating the improvements obtained after the optimization process. We also include experimental results obtained with an optical real-time cor- relator that uses two spatial light modulators. Experimental data confirm the numerical results and show the capacity of the proposed technique to improve color pattern recognition. © 2002 Society of Photo-Optical Instrumen-

Surface and optical characterization of yttrium hydride films deposited on regular glass to be used as switchable mirrors

Abstract: Yttrium and palladium thin films deposited on glass have been characterized by means of XPS depth profiling, SEM, energy-dispersive x-ray spectroscopy and ultraviolet-visible spectroscopy. These films allow optical windows of variable transparency to be obtained based on the formation of yttrium hydride by hydrogenation, with the palladium film working as a barrier against yttrium oxidation but being permeable to hydrogen. The transformation of yttrium into its hydride is concomitant with a metal-semiconducting transition that changes the physical properties of the material, especially its optical behaviour: the transmittance in the visible range goes from 0% for the metallic state to 30-70% for the hydrogenated state. In this work, the preparation conditions of optical windows using low-cost regular glass as substrate have been optimized, both regarding the deposition and the hydrogenation. Uniform films free of impurities, such as oxygen and carbon, have been obtained under ultrahigh vacuum conditions of ∼10 -7 Pa. Deposition has been performed by electron bombardment of the material, using palladium and yttrium of high purity.

Characterization of the liquid crystal display modulation. Optimization for some applications

Abstract: In this paper we revise recent results of our team in the optimization of twisted nematic liquid crystal displays to be used as spatial light modulators for image processing and diffractive optics. In general two kind of responses are desired for the mentioned applications: amplitude-only and phase-only modulations. However, it is not a trivial task to find the polarization configurations for which these responses are obtained. We show that a reverse-engineering approach is needed to optimize the liquid crystal display response. According to this reverse-engineering approach the modulation characteristics can be calibrated by evaluating the modulation response in a few polarization configurations. These results are used to fit the liquid crystal display behavior to a simplified physical model, which uses two modulation parameters. We demonstrate that the degree of accuracy of this model is very high, thus enabling the prediction of the modulation behavior of the display at other polarization configurations. Therefore, we can perform computer searches for the optimum orientation of the polarizing elements to obtain the required optical transmission. We demonstrate the need to use short wavelengths and the need to insert wave plates in front and behind the liquid crystal displays to obtain either amplitude-only or phase-only regime.