Highly sensitive refractive index sensor based on novel Mach–Zehnder interferometer with multimode fiber–thin core fiber–multimode fiber structure

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A highly sensitive refractive index (RI) sensors based on a fiber in-line Mach–Zehnder interferometer (MZI) with a multimode fiber–thin core fiber–multimode fiber (MMF–TCF–MMF) structure was proposed and demonstrated. This MZI has shown a good interference visibility as high as 16 dB in air. Experimentally, the sensor exhibited high RI sensitivity, with a max sensitivity of up to 453.99 nm/RIU in the RI range of 1.3330–1.3904. Furthermore, the dependences of RI sensitivity and TCF length were also analyzed. In addition, the proposed sensor has the advantages of simplicity of fabrication, low cost, compact size, and high sensitivity, which are beyond what conventional RI sensors can offer.