Fiber-optic multimode interferometric curvature sensor based on small-inner-diameter hollow core fiber

A highly sensitive fiber-optic curvature sensor based on single mode fiber (SMF) and hollow core fiber (HCF) in an SMF-HCF-SMF multimode interferometric (MMI) structure is proposed. The sensor can be simply manufactured by fusing a short section of small-inner-diameter HCF between two SMFs. As the inner diameter of the HCF is smaller than the core diameters of the SMFs, multiple guiding modes can be excited directly in the sidewall of the HCF without any additional structures. Curvature can then be measured by monitoring the transmission spectrum shift caused by the bending-sensitive MMI effect. Experiments show that a high sensitivity of similar to 19.88 nm/m(-1) can be achieved in a curvature range of 0.48-1.52 m(-1). The sensor also has low-temperature sensitivity.