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We report a novel method to enhance the modal interference pattern in an anti-resonant negative curvature hollow-core fiber (NCHCF), enabling in-fiber multimodal interferometer in a short (few mm) length. The enhanced interference provides well defined fringes suitable for sensing; and their application for mechanical sensing is demonstrated. An 8 mm length of NCHCF was exposed to periodic arcs from a conventional splicer, leading to periodic modulation of fiber parameters along the length of the fiber. This periodic modulation alters the interaction between interfering modal fields, causing enhanced modal overlap and a four-fold increase in the intensity variation of the interference pattern. The enhanced interference dips are observed to be sensitive, with a linear response, to external mechanical forces like curvature, while being insensitive to thermal crosstalk by virtue of the hollow core design.
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