Angle-of-incidence performance of random anti-reflection structures on curved surfaces.

Random anti-reflection structured surfaces (rARSS) have been reported to improve transmittance of optical-grade fused silica planar substrates to values greater than 99%. These textures are fabricated directly on the substrates using reactive-ion etching techniques, and often result in transmitted spectra with no measurable interference effects (fringes) for a wide range of wavelengths. The inductively coupled reactive-ion plasma (ICP-RIE) used in the fabrication process to etch the rARSS is anisotropic and thus well suited for planar components. The improvement in spectral transmission has been found to be independent of optical incidence angles for values from 0° to ±30°. Qualifying and quantifying the rARSS performance on curved substrates, such as convex lenses, is required to optimize the fabrication of the desired AR effect on optical-power elements. In this work, rARSS was fabricated on fused silica plano-convex lenses using a planar-substrate optimized ICP-RIE process to maximize optical transmission in the range from 500 to 1100 nm. Results are presented from optical transmission tests of rARSS lenses for both TE and TM incident polarizations at a wavelength of 633 nm and over a 70° full field of view. These results suggest optimization of the fabrication process to account for anisotropy is not required, mainly due to the wide angle-of-incidence AR tolerance performance of the rARSS lenses.

Four-plane space-variant Fresnel-transform optical processor with a random phase encoder.

We introduce a four-plane Fresnel-transform space-variant optical processor consisting of an input plane and two filter planes. One filter mask is programmable with a spatial light modulator. The second filter mask is a fixed random binary phase array with a known pseudorandom distribution of pixels. The order of the masks can be interchanged, giving different output characteristics. In one case the Horner efficiency of the correlator increases dramatically. In the other case the edge enhancement of the output image is removed. We discuss the theory for this general processor and its implementation with phase-only masks. We present experimental results when a binary magneto-optic spatial light modulator was used.