Ultrasensitive long-period fiber grating refractive sensor with microcavities

We experimentally demonstrate an ultrasensitive refractive index (RI) sensor based on a single-mode fiber (SMF) and long-period fiber grating (LPFG) with periodic microcavities fabricated using a femtosecond laser. The presence of liquid within the microcavities induces a significant modulation in the refractive index, thereby exciting high-order cladding modes. The proposed sensor has obvious merits of easy fabrication and excellent reproducibility and exhibits an ultra-high RI sensitivity of - 11810 nm/RIU with high linearity within the range of 1.334-1.341 RIU. Additionally, it can function as a temperature sensor, presenting broad application prospects in the field of biochemistry.