A Mach-Zehnder interferometer based on tapered dual side hole fiber for refractive index sensing

An in-line fiber Mach-Zehnder interferometer (MZI) based on tapered dual side hole fiber (DSHF) is proposed and fabricated for refractive index measurement. The MZI is composed of a short piece of tapered DSHF which is sandwiched between two single mode fibers (SMFs). The DSHF is heated and tapered by using an oxy-hydrogen flame. At the taper zone, the core mode of the lead-in SMF is coupled to several cladding modes of the DSHF, and interference happened between the core and cladding modes of the DSHF. Due to the existence of the air hole at the tapered DSHF zone, the cladding modes can be much more easily stimulated than general SMF. The experiments indicated that the proposed sensor has a high refractive index sensitivity of 816.1 nm/RIU in the refractive index range of 1.333-1.379 with the tapered DSHF diameter of 33 μm. In addition, the sensor had a low temperature response of 19.9 pm/°C in the range from 30 to 110 °C. The proposed sensor is attractive for its high refractive index sensitivity, and easy fabrication, making it of potential value for refractive index measurements for chemical and biological sensing.