<title>Chromatically compensated multichannel optical correlators</title>

Abstract

The scope of this work is the compensation of the chromatic dispersion inherent to free-space light propagation, both in the Fraunhofer and in the Fresnel diffraction region. The cornerstone of our procedure lies in achieving, in a first- order approximation, the incoherent superposition of the monochromatic versions of the selected diffraction pattern in a single plane and with the same scale for all the wavelengths of the incident light. Our novel optical configurations with achromatic properties for the field diffracted by a screen are formed by a proper combination of a small number of conventional diffractive and refractive lenses, providing an achromatic real image of the diffraction pattern of interest. The residual chromatic aberrations in every case are low even when the spectrum of the incident light spreads over the whole visible region. The resulting achromatic hybrid (diffractive- refractive) systems are applied, in a second stage, for implementing several achromatic diffraction-based applications with white light, like wavelength-independent spatial- frequency filtering, achromatic pattern recognition, white- light array generation, and to designing a totally-incoherent optical processor that is able to perform color processing operations under natural illumination (both spatially and temporally incoherent).