Nonadiabatically Tapered Microfiber Sensor With Ultrashort Waist

We investigated a nonadiabatically tapered microfiber refractive index sensor with an ultrashort waist length. Free spectral range (FSR) is one common issue in the interferometry-based sensors. Such sensors will not work properly once the resonant wavelengths shift over one cycle. It was found that the temperature and pulling speed are the crucial parameters to achieve a desired tapering profile. By setting a cooler tapering temperature and fast pulling speed, we successfully fabricated ultrashort microfibers with a waist length of only 2.4 mm and total length of 5.5 mm. The resulting FSR is ~80 nm and the maximum sensitivity achieved for such short microfiber is 25 667 nm/RIU.