Holographic optical elements for Bragg image processing

Abstract

In this work we analyse the very specific properties offered by volume holography when applied to image processing with no Fourier plane. Bragg diffraction, exhibited by holographic optical elements (HOEs), modifies the impulse response of an imaging system, facilitating spatial filtering operations with no need for a physical Fourier plane (Bragg processing). We show both experimental and simulated results with holographic phase gratings and with holographic lenses generated on a polyvinyl alcohol/acrylamide (PVA/AA) photopolymer. We determine which are the significant parameters to model the performance of the HOEs for Bragg filtering: orientation and bandwidth of the passband of the filter. We relate these spatial filtering parameters with their corresponding counterparts in volume holography. We also show how the local variation of these parameters is responsible for space-variance properties of the HOE when applied in Bragg processing. We have also analysed the impulse response characteristics of the Bragg filter together with the effects of the limited aperture of the imaging system.