Torsion sensor based on the modal interference pattern of helical side-hole fiber

A novel torsion sensor is proposed and demonstrated by detecting the modal interference pattern rotation of a helical sidehole fiber (HSHF). The HSHF is successfully fabricated by rotating and drawing a preform with side-hole drilling, which supports two modes. Based on modal coupling analysis, a single-mode fiber is precisely offset-spliced to one end of the HSHF to evenly excite the LP₀₁ and LP₁₁ modes. Subsequently, the fabricated sensor is subjected to torsion, and its torsion response is evaluated by analyzing the output modal interference pattern, which demonstrates a high linear correlation with the torsion angle. The torsion sensitivity is 0.946, allowing for accurate identification of the torsion angle.