We propose a novel refractive index (RI) sensor based on a fiber Mach-Zehnder interferometer formed by large lateral offset fusion splicing between two abrupt tapers. The cladding modes are efficiently excited by transmitted light in the large misalignment junctions. The RI sensitivity of the sensor to surrounding RI change is measured, and the sensitivity of 100 nm/RIU is obtained, which is three to six times higher than that of fiber structures with only a pair of tapers or two offset junctions. Moreover, the sensor is made by a low-cost fabrication method. Thus, the proposed structure is beneficial to the RI sensing applications.
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