Large-aperture Fabry-Perot filters based on silicon/silicon carbonitride distributed Bragg reflectors for the near-infrared
This contribution presents silicon carbonitride as a new low refractive index material for integration together with silicon in suspended distributed Bragg reflector membranes. We show how its benign mechanical stress properties can be used to fabricate inherently flat mirror membranes of up to 5 mm diameter. Due to the large refractive index contrast to silicon such mirror membranes exhibit high reflectance over a wide spectral range. Using these mirrors, we demonstrate a proof of concept for a large aperture Fabry-Perot filter with narrow bandwidth that could help miniaturize hyperspectral imaging sensors.
CO/sub 2//H/sub 2/O gas sensor using a tunable Fabry-Perot filter with wide wavelength range
An electrostatically driven tunable MEMS Fabry-Perot filter (FPF) with wide wavelength range from 2.5 /spl mu/m to 4.5 /spl mu/m has been developed for non-dispersive infrared (NDIR) CO/sub 2//H/sub 2/O gas sensors. The electrostatic discharge (ESD) test and the long-term repetition-stability test were carried out for the FPF and no remarkable change of FPF performance was observed in either test. An NDIR system was equipped with the FPF, and the principle of the gas sensing method was confirmed. The resolutions defined by standard deviation are about 13 ppm for CO/sub 2/ of 2000 ppm and 0.35 g/m/sup 3/ for H/sub 2/O Of 22.5 g/m/sup 3/.
Lead Salt Resonant Cavity Enhanced Detector with MEMS Mirror
We describe a tunable resonant cavity enhanced detector (RCED) for the mid-infrared employing narrow gap lead-chalcogenide (IV-VI) layers on a Si substrate. The device consists of an epitaxial Bragg reflector layer, a thin p-n+ heterojunction with PbSrTe as detecting layer and a micro-electro-mechanical system (MEMS) micromirror as second mirror. Despite the thin absorber layer the sensitivity is even higher than for a conventional detector. Tunability is achieved by changing the cavity length with a vertically movable MEMS mirror. The device may be used as miniature infrared spectrometer to cover the spectral range from 30 μm.