Fiber Mach-Zehnder interferometer based on concatenated down- and up-tapers for refractive index sensing applications

We report a novel fiber Mach-Zehnder interferometer based on concatenated down- and up-tapers simply fabricated by arc discharging and fusion splicing. High-quality interference spectra with a maximum attenuation peak depth beyond 20 dB were obtained. Experimental results show that the RI sensitivity of the MZI with a length of 52 mm reaches −82.8 nm/RIU for a RI range of 1.333–1.3869, which is nearly 5 times higher than that of the conventional MZI based on two down-tapers, and 12 times higher than that of MZI based on two up-tapers. The temperature cross sensitivity is discussed and the influence can be eliminated by simultaneous measurement of RI and temperature using different sensitivities of different attenuation wavelength peaks. Such MZIs with low-cost and ease of fabrication will find various sensing applications.