Large-Range and High-Sensitivity Displacement Sensing Based on Extrinsic Fabry–Perot Interferometer Assisted Microwave Photonic Filter

Displacement is a pivotal physical parameter, and advancements in displacement sensor technology have enabled the creation of a diverse array of physical and mechanical sensors through seamless integration with mechanical transducers. In this study, we introduce a displacement sensing technique leveraging an extrinsic Fabry-Perot interferometer (EFPI) assisted microwave photonic filter. By translating displacement-induced variations in the EFPI’s optical reflection into peak frequency shifts within its frequency response, we achieve large-dynamic-range displacement measurements with outstanding signal quality and demodulation ease. Proof-of-concept demonstrations showcase a substantial 5 mm range with a remarkable sensitivity of 1.148 GHz/mm, achieved using a basic single-mode fiber-based EFPI with a movable external mirror. Besides, nm-scale displacement monitoring is experimentally validated through a phase-measurement approach. Notably, the sensitivity and dynamic range can be tailored by adjusting the microwave photonic filter system’s parameter, i.e., the dispersion parameter of the dispersive element in the system. Furthermore, we introduce a strategy to enhance the dynamic range further by employing a virtual frequency down-conversion technique with an additional interferometer. This proposed technique opens avenues for developing a series of high-sensitivity and broad operating-range physical and mechanical sensors based on a simplified EFPI measurement configuration.