Research on Vector Bending SPR Sensor Based on V-Groove Fiber

Bending curvature measurement and bending direction identification are very important in the field of mechanical engineering. This study aimed to realize the high sensitivity direction recognition and curvature sensing based on SPR mechanism by a V-groove fiber SPR vector bending sensor. By CO
₂
laser, multiple evenly spaced V-grooves were fabricated on the step multimode fiber. The V-groove fiber coupled the core mode to the cladding mode. By rotatably coating 50nm gold film on the cladding behind the V-groove area, and splicing with a multimode fiber with larger diameter to receive the light with SPR signal, the fiber SPR sensor was realized. When the sensing probe was concave inward, the V-groove was squeezed, the angle became smaller, and the excited cladding mode changed with it, resulting in the increase of SPR incident angle, the resonance valley blue shifted, and the sensitivity of curvature sensing wavelength is −5.98nm/m
⁻¹
. Similarly, when the sensing probe was convex outward, the angle became larger, resulting in the decrease of SPR incident angle, the resonance valley red shifted, and the sensitivity of curvature sensing wavelength is 1.42nm/m
⁻¹
. The proposed V-groove fiber SPR sensor realized the bending curvature measurement and bending direction identification. The manufacturing method is simple and the sensitivity is high, which opens up a new way for application of the SPR technology in bending measurement.