Optical Fiber Surface Plasmon Resonance Torsion Sensor Based on Threaded Structure

Fiber optic surface plasmon resonance (SPR) sensors have achieved a large number of solutions for sensing physical quantities such as refractive index, micro displacement, curvature, strain, etc. However, there are few schemes for sensing torsional physical quantities. This article proposes an optical fiber SPR torsion sensor based on a threaded structure. A threaded structure that is prone to deformation during torsion is etched on the optical fiber. After the threaded area, an SPR sensing area is created. Clockwise rotation causes compression deformation in the threaded area, while counterclockwise rotation causes tensile deformation in the threaded area, resulting in a change in the optical transmission mode of the threaded area, changing the SPR incidence angle, causing the corresponding SPR resonance valley to move. Torsion sensing is achieved through the shift of the SPR resonance wavelength, and the torsion direction is determined by the shift direction of wavelength. The experiment indicates that the sensing probe has a clockwise twist sensitivity of 0.9088 nm/(rad/m) and a counterclockwise twist sensitivity of −0.8291 nm/(rad/m) within the detection range of −47.10 rad/nm to 47.10 rad/nm, providing a new scheme for directional detection of torsional physical quantities.