Evaluation of Pixel-scale Tunable Fabry-Perot Filters for Optical Imaging

The Fabry-Perot interferometer (FPI) is a well-developed and widely used tool to control and measure wavelengths of light. In optical imaging applications, there is often a need for systems with compact, integrated, and widely tunable spectral filtering capabilities. We evaluate the performance of a novel tunable MEMS (Micro-Electro-Mechanical System) Fabry-Perot (FP) filter device intended to be monolithically integrated over each pixel of a focal plane array. This array of individually tunable FPIs have been designed to operate across the visible light spec-trum from 400-750 nm. This design can give rise to a new line of compact spectrometers with fewer moving parts and the ability to perform customizable filtering schemes at the hardware level. The original design was modeled, simulated, and fabricated but not tested and evalu-ated. We perform optical testing on the fabricated devices to measure the spectral resolution and wavelength tunability of these FP etalons. We collect the transmission spectrum through the FP etalons to evaluate their quality, finesse, and free spectral range. We then attempt to thermally actuate the expansion mechanisms in the FP cavity to validate tunability across the visible spectrum. The simulated design materials set was modified to create a more practical device for fabrication in a standard CMOS/MEMS foundry. Unfortunately, metal thin film stress and step coverage issues resulted in device heater failures, preventing actuation. This FP filter array design proves to be a viable manufacturing design for an imaging focal plane with individually tunable pixels. However, it will require more optimization and extensive electrical, optical, thermal, and mechanical testing when integrated with a detector array