14 May 2007 Extending the tuning range of SWIR microspectrometers
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We have developed a microspectrometer based on monolithic integration of a Fabry-Perot optical filter directly with a HgxCd1-xTe-based infrared detector. The tunable Fabry-Perot is created by a parallel plate MEMS fabricated from two dielectric mirror stacks separated by an initial air gap of 1.4 μm. We have measured linewidths as low as 55 nm, switching times of 40 μs and a tuning range of 380 nm. However this tuning corresponds to only 42% of the desired tuning range, from 1.6-2.5 μm (900 nm). The tuning range is limited by a process called "snap down" which occurs when the MEMS is drive by a voltage source. It can be shown that for a parallel plate snap down occurs at 1/3 the initial gap; complete tuning across the SWIR band requires a physical deflection of at least 60% of the gap. We have developed a modified actuator design which allows 60% tuning of the moveable mirror. Further, the method minimizes actuation-induced stress gradients which can lead to substantial bowing of the mirror and subsequently broad optical linewidths. We will compare the results of our current microspectrometer with our new extended tuning designs. These designs are based on Coventorware and analytical mechanical models combined with optical models for the Fabry- Perot.
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Jason S. Milne, Jason S. Milne, Adrian J. Keating, Adrian J. Keating, Jarek Antoszewski, Jarek Antoszewski, John M. Dell, John M. Dell, Charles A. Musca, Charles A. Musca, Lorenzo Faraone, Lorenzo Faraone, "Extending the tuning range of SWIR microspectrometers", Proc. SPIE 6542, Infrared Technology and Applications XXXIII, 65420M (14 May 2007); doi: 10.1117/12.718972; https://doi.org/10.1117/12.718972

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