Abstract
Miniaturized Mach–Zehnder interferometer (MZI) is constructed using sharply tapered photonic crystal fiber (PCF) for highly sensitive ambient refractive index (RI) measurement. The sensor is fabricated by fusion splicing a small stub of PCF between standard single-mode fibers with fully collapsed air holes of the PCF in a splicing region. The influence of sharp tapering of the PCF is then studied using two different hydrogen flame diameters of 1 and 3.5 mm at the tip. Tiny flame geometry enables the sharp tapering of the PCF for a short fiber length and provides higher RI sensitivity. It appears that sharp tapering has a greater impact on RI sensitivity enhancement compared with decrease in taper waist diameter. The MZI with the taper waist diameter of $65~\mu \text{m}$ and the length of 3.8 mm offers an RI sensitivity of 334.03, 673.91, and 1426.70 nm/RIU within the RI range of 1.3327–1.3634, 1.3634–1.3917, and 1.3917–1.4204, respectively.
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