Fabry–Perot cavity-based contact force sensor with high precision and a broad operational range

A novel, compact, and robust contact force sensor based on a micro-length single-mode fiber (SMF) incorporated in a cleaved micro-air cavity (MAC) is proposed. The fabrication process involves splicing of the SMF with a hollow-core fiber (HCF) followed by cleaving of the MAC and insertion of a SMF into the MAC. The force sensing mechanism is based on the movement of the micro-SMF inside the cleaved MAC. The total length of the probe varies between 300 and 500 μm, making it bend proof. Due to the all-silica-based structure, the sensing capability of the probe is demonstrated for a low (0–1000 mN), as well as a high range of force (1–10 N) measurements. The optimized structure shows a maximum force sensitivity of 14.2 pm/mN with a negligible temperature dependence of 0.4 pm/°C. The performance of the sensor is verified using an FEM-based software. The proposed probe has a linear response, negligible hysteresis, and repeatability error, making it suitable for biomedical sensing and robotic applications.