Displacement sensor based on cross-coupling method for high resolution and sensitivity using polymer optical fiber

Most displacement sensors offer high resolution but suffer from limited sensitivity and measurement range. Typically, increasing the range results in a reduction in both resolution and sensitivity. This study presents a novel displacement sensor based on a spiral-structured polymer optical fiber that operates through intensity modulation via bend-induced coupling. Controlled spiral bending generates radiative loss, which is coupled by strategically positioned secondary fibers. The sensor comprises two segments: a spiral-shaped primary fiber that generates controlled radiative losses through macro-bending, and a vertically movable secondary fiber that couples the radiated optical power to quantify displacement. A custom 3D-printed experimental platform with a guiding groove was developed to ensure precise alignment and minimize axial motion. Experimental results demonstrate a displacement measurement range of up to 20 mm, with high sensitivity of 3.26μW/mm, resolution (30.67 nm), excellent repeatability, and stable response. The proposed sensor provides a compact, cost-effective, and flexible solution for distributed displacement monitoring in various applications.