This paper describes the use of strain stiffening infixed-fixed beam actuators to extend the tuning range of microelectromechanical-systems-based Fabry–Perot filters. The measuredwavelength tuning range of 1.615–2.425 μm is the largestreported for such a filter. Curvature in the movable mirror wascorrected using a low-power oxygen plasma to controllably alterthe stress gradient in the mirror. After curvature correction, thelinewidth of a filter was 52 nm, close to the theoretical minimumfor our mirror design. As a proof of concept, a filter was bondedto a broadband infrared detector, realizing a wavelength-tunableinfrared detector. All measured data have been compared to theoreticalmodels of the optics and mechanics of the filters, withexcellent agreement between theory and measurement demonstratedin all cases. Finally, the Young’s modulus and stress ofthe actuator materials were extracted directly from the measuredvoltage–displacement curves, demonstrating a novel technique formaterial property measurement.