High sensitivity fiber optic SPR strain sensor based on asymmetric groove structure

The recent proposed fiber surface plasmon resonance (SPR) strain sensors all use microstructure excited cladding modes to achieve SPR strain sensing. The superposition of multiple cladding modes results in the broadening of the SPR resonance valley, causing a decrease in sensitivity. This article proposes an ultrasensitivity fiber SPR strain sensor based on an asymmetric groove structure (AGS). Different depths of grooves are fabricated on both sides of the single-mode fiber, and the core of the groove area is slightly bent by heating under a hydrogen-oxygen flame. A 50 nm gold film is coated at the bottom of the deeper groove to form the SPR sensing area, and the fiber is restored by coating UV curing adhesive. The bending core of the single-mode fiber effectively reduces the number of SPR optical modes and provides an SPR incidence angle. When subjected to strain, the change in the bending degree of the fiber core leads to a change in the SPR incidence angle, achieving high-sensitivity strain sensing. The experimental results indicate that the maximum strain sensitivity of the sensor can reach 117.01 pm/<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \varepsilon $ </tex-math></inline-formula>. This sensor has the advantages of high sensitivity and low fabrication cost and has potential application prospects in the field of fiber optic strain sensing.