Abstract
Spatial optical Fourier filtering is a widespread technique for in situ image or light field processing. However, conventional fixed absorbing patterns or mechanical irises only allow an inflexible, very restricted control. Thus, we present two electrochromic spatial filters with ring-shaped or directional segments, which can be individually addressed and continuously tuned in transmission resulting in up to 512 different filtering states. For realization of the electrochromic devices, we overcome technical obstacles to realize seamless, gap-free electrochromic segments. We describe this novel fabrication process and demonstrate the successful application in an optical Fourier transform set-up.
Highlights
In Fourier optics the electric field distribution of an object is described as superposition of plane waves with certain spatial frequency components k[1]
For realization of the electrochromic devices, we overcome technical obstacles to realize seamless, gap-free electrochromic segments. We describe this novel fabrication process and demonstrate the successful application in an optical Fourier transform set-up
In this so called 2f Fourier transform set-up, spatial frequency filtering is performed by blocking certain frequency components in the back focal plane
Summary
In Fourier optics the electric field distribution of an object is described as superposition of plane waves with certain spatial frequency components k[1]. The combination of EC molecules with high coloration efficiency and conductive nanoparticles enabled excellent switching times of less than 1 s with at least 90 % Michelson contrast over the entire optical spectral range [19] Using this optimized material composition, we present a microfabricated tunable EC iris for low pass, band pass and high pass filtering and EC azimuthal sector devices for directional spatial Fourier processing. We avoided the insulating gap between adjacent EC segments that deteriorates imaging contrast of the devices [10] by covering the segmented transparent control electrodes by means of a homogeneous nanoparticle layer carrying the EC molecules This reduced the impact of the misalignment of the cathodic coloring (viologen/TiO2) and anodic colouring (TPB/ATO) electrode
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