Advanced Optical Fiber Sensors for Linear and Angular Displacement

Abstract

A thesis submitted in partial fulfillment for the degree of Doctor of Philosophy in the Bilbao School of Engineering UPV/EHU. Applied Photonics Group. February 2025. Industry 5.0 calls for photonic solutions that gather precise, real-time measurements under intense heat, vibration, and electromagnetic fields. Conventional electronics struggle here, often succumbing to interference or limited durability. This dissertation overcomes that gap by developing intensity-based optical fiber displacement sensors (OFDS) that measure linear and angular displacements with high accuracy, extended range, and minimal dead zones. This research closes the loop on OFDS design by uniting theoretical modeling, simulation, and hands-on fabrication. First, a brute-force methodology mapped a broad range of geometries, revealing surprising flexibility even under tight manufacturing tolerances. Next, a concise toy model distilled complex photonic interactions into three key equations—greatly reducing computational overhead while preserving sub-1% agreement with experiments. Building on these insights, we engineered tetra- and pentafurcated OFDS prototypes with extended linear ranges (up to 10.49 mm) minimal dead zones (2.50 mm) and high sensitivity (2.20 mm−1), validated experimentally at a mean square error of 0.25%. Finally, we introduced a heptafurcated optical fiber displacement angular and linear sensor (OFLADS), integrating concentric fiber rings for linear sensing with cross-arranged fibers for angular detection. This single, compact bundle simultaneously measures distance and tilt angles (±15º) without bulky optics or intricate alignment. Prototypes confirmed theoretical predictions, underscoring the viability of the sensor for demanding aero-engine applications. By merging rigorous modeling, efficient design strategies, and empirical testing, this dissertation surpasses state-of-the-art OFDS limitations and completes the circle from conceptual frameworks to fully operational, multi-parameter photonic sensors. The path ahead includes further miniaturization, broader angular detection, and integration with cutting-edge photonic platforms—solidifying OFDS as a key enabler of next-generation aerospace and industrial systems.