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A few mode fiber curvature sensor based on two spherical-shape structures modal interferometer

In order to improve the equilibrium between fiber sensor performance and cost, a curvature sensor based on Few Mode Fiber(FMF) is proposed. A length of FMF is spliced with waist enlarge between two Single mode Fibers(SMFs) to form two spherical- shape structure. Fiber core mode interfere with clad mode due to the excite and couple function of spherical-shape structure, respectively. The phase difference between the cladding and core regions of the fiber changes with the external strain increase, and then the interference spectrum changes. Two sensors with different length of FMF are fabricated, and the transmission spectrum are obtained. The result shows the optical power at certain wavelength is increasing with the curvature increasing. When the curvature range is 0~0.42m-1 and the FMF is 5.7cm, the curvature sensitivity can be 11.22dB/m-1. When the FMF is 5.9cm, the curvature sensitivity can be climbed to 14.08dB/m-1.