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

Abstract

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 μm. 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.