Novel optical elements made from porous Si

It is shown that porous silicon in various geometries and morphologies can be used for novel optical elements by combining theoretical insights with suitable porous structures and some pre- and post-processing of the silicon. The paper restricts itself to light propagation in the pore direction, using a theory utilizing specific variants of waveguide modes matched to the element investigated. A short introduction into the theoretical and pore etching background is followed by detailed theoretical and experimental results to the following novel optical elements: environmentally stable optical components from mesoporous silicon, long-wave pass filters, macroporous silicon UV filters, polarization components for the UV range, retroreflection suppression plate, omnidirectional IR and visible wavelengths filters. Either new components are presented, mostly with first experimental results, or the state-of-the-art for previously discussed elements is considerably improved upon. An integral part of the paper is the use of various kinds of pore wall coatings or special pore geometries, which are needed to meet demanding requirements.