Enlarge-Tapered, Micro-Air Channeled Cavity for Refractive Index Sensing in SMF

We report a compact, highly sensitive all SMF refractive index (RI) sensor based on a waist enlarged tapered (WET) fiber probe with a micro-air cavity (MAC) located at the tip. The fabrication of WET probe has been accomplished using a commercial splicer machine and the MAC has been realized using ultrashort pulsed laser based micromachining. The WET fiber section facilitates excitation of cladding modes while the MAC in conjunction with the curved tip, provides a convenient platform for achieving core mode as well as cladding mode interference within the probe. The probe, with an optimized WET fiber section, exhibited maximum refractive index (RI) sensitivity of 123.7 nm/RIU with a negligible temperature sensitivity of 15.34 pm/°C.