Silicon Compatible Fabry-Perot Optical Filter for mid-IR Microspectrometer Applications

Summary: The design and modeling of two arrays of Fabry-Perot types of IR optical interference filters for micro-spectrometers is described. The materials used are PolySi and SiO2 only. The design is complicated by the rapidly increasing extinction coefficient for SiO2 beyond 2 μm wavelengths, however it is shown that having relatively thin layers it can be used up to 8 μm wavelengths. A 7 layer Fabry-Perot filter, including substrate, is designed using layers thicknesses in between 200 and 400 nm for fabrication in a sputter system. The first filter is designed for maximum range and can be tuned to 13 different channels between 2.2 and 3.5 μm, by changing the thickness of middle SiO2 layer. A second design is optimized for resolution and is composed of 11 layers to yield 20 passband channels between 2.2 and 2.86 μm