All-chalcogenide Tunable Infrared Filter
Dielectric mirrors are simple one dimensional photonic structures made using quarter wave stacks (QWS). It was recently shown that QWSs fabricated with high contrast index materials may possess full photonic band gaps (PBG) resulting in omnidirectional reflection. This opens up the possibility of making infrared mirror or filter design at desired wavelengths by piling suitable dielectric materials and controlling their layer thicknesses.
Here, we present an infrared filter fabricated by thermal evaporation using only chalcogenide glasses. Based on the optical characterization of infrared transparent chalcogenide glasses, an omnidirectional filter is designed and simulated using the transfer matrix method (TMM). Accordingly, stacks of As2S3 and GAST are vacuum evaporated on a tilted silicon substrate. The slanted geometry gives graded layer thickness along the substrate length, resulting in a position dependent omnidirectional photonic band gap whose center shifts from 1.5 µm to 4 µm along the substrate.
These infrared filters are now being integrated into a portable infrared spectrometer, where thermal blackbody source will be used as source and the infrared spectrum will be sensed with a micro-machined bolometer array. Potential applications include disposable chemical and biological sensors.
H. Esat Kondakcı, Mecit Yaman, Ozlem Koylu, Aykutlu Dana, Mehmet Bayındır
All-chalcogenide glass omnidirectional photonic band gap variable infrared filters, Applied Physics Letters, volume 94, page 111110 (2009) 
