Compact gas cell integrated with a linear variable optical filter

A miniaturized methane (CH4) sensor based on nondispersiveinfrared absorption is realized in MEMS technology. A high level offunctional integration is achieved by using the resonance cavity of a linearvariable optical filter (LVOF) also as a gas absorption cell. For effectivedetection of methane at λ = 3.39 µm, an absorption path length of at least 5mm is required. Miniaturization therefore necessitates the use of highlyreflective mirrors and operation at the 15th-order mode with a resonatorcavity length of 25.4 µm. The conventional description of the LVOF interms of the Fabry-Perot resonator is inadequate for analyzing the opticalperformance at such demanding boundary conditions. We demonstrate thatan approach employing the Fizeau resonator is more appropriate.Furthermore, the design and fabrication in a CMOS-compatiblemicrofabrication technolog