Compact Fiber-Optic Sensor for Simultaneous Force Measurement and Depth Profiling

This study presents a compact sensor for simultaneous force measurement and depth profiling. We have developed a fiber-optic sensor structure capable of integrating common-path optical coherence tomography (CP-OCT) and Fabry–Pérot Interferometry (FPI) within a single unit. The proposed FPI-OCT sensor, with an outer diameter of 0.25 mm, is encased in a 0.41 mm hypodermic tube. Analytical models were developed for efficient beam path optimization and signal interpretation, where multiple common-path references yielded distinct interferometric signals. The sensor has a sufficiently high sampling rate of 780 Hz for both CP-OCT and FPI signal processing using parallel computing. The fabricated sensor achieved a measurable force range of approximately 5 N with a resolution of 0.119 mN, and a depth sensing range of 3.6 mm with an axial resolution of 6.0 ${\mu }$m. Furthermore, injection experiments with multilayered phantoms and ex vivo porcine eyes demonstrated that the sensor could simultaneously measure force and depth profiles, providing enriched information during the tasks.