Low-Cost High-Resolution Multipoint Displacement Sensor Using POF Based on Coupled Bend Loss

This study presents a novel multipoint displacement sensor based on a spiral-structured utilizing polymer optical fiber. The work is based on the intensity modulation through bend-induced coupling. Controlled spiral bending generates radiation loss, which is coupled through strategically positioned secondary fibers. The sensor comprises two segments, namely a primary fiber configured in a spiral bend and a vertically positioned secondary fiber that made movable for displacement measurement. Two distinct configurations were developed for simultaneous multipoint sensing: (1) cascaded spiral units connected in series for sequential displacement detection, and (2) a single spiral unit with multiple receiver fibers. The sensing behavior was characterized across various parameters, including bend radius, fiber diameter, and displacement direction. Experimental results demonstrated a displacement sensing range of up to 14 mm and resolution about 4.345 μm, with the sensor exhibiting high sensitivity (2.301 μW/mm), repeatability, and a stable response. Notably, the independent coupling mechanism in both configurations eliminates the need for signal decoupling, simplifying design and enhancing scalability. The proposed sensor offers a compact, cost-effective, and flexible solution for distributed displacement monitoring.