Space-variant image processing with volume holography

Abstract

In this work we explore the application of volume effects given by holographic optical elements (HOEs) to image processing operations. Bragg diffraction, exhibited by HOEs, modifies the impulse response of an imaging system, facilitating spatial filtering operations with no need for a physical Fourier plane. Both the holographic recording material we use and the specific HOE we design are important parameters. In the present communication we report our last results using a polyvinyl alcohol/acrylamide (PVA/AA) photopolymer. This compound combines good optical properties, ease of fabrication, and self-development capability. We are able to produce layers as thick as 1 millimeter (mm) with a diffraction efficiency higher than 80%. Using layers with a thickness of 0.1 mm and 1 mm we have recorded both holographic diffraction gratings and holographic lenses. When using the holographic gratings we can obtain image edge enhancement as demonstrated in previous works. As a novelty, in this work we show that when using the holographic lenses we obtain a space-variant image edge enhancement. We analyse the properties of this space-variant operation in terms of the reconstruction geometry and the local grating structure exhibited by the lens across its aperture.