Fabry–Perot cascade interferometer for temperature measurement of Si microstructures

Silicon MEMS micromirrors face critical thermal challenges from high optical loads, requiring accurate temperature validation for reliable design. Finite element thermal models are hindered by parameter uncertainties, while standard non-contact measurement methods fail for thin silicon structures. We present a novel optical technique, to our knowledge, using coherence-tuned Fabry–Perot interferometry to accurately measure the micromirror plate temperature. By employing two sequential interferometers with an incoherent source, we selectively isolate the temperature-dependent refractive index change in the mirror plate, excluding parasitic reflections from the underlying substrate. The method achieves temperature uncertainty on the order of ±2 ∘ C across the 40°C–200°C range when calibrated against a thermistor. This approach enables thermal characterization of MEMS devices where conventional contact-based methods are impractical.