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.
