A highly sensitive refractive index sensor based on super-structured long-period fiber grating

Fiber refractive index (RI) sensor shows superiority in various applications including biomedical detection and food chemistry. Herein, we propose and investigate a super-structured long-period fiber grating (SLPFG) for RI measurement with the high-sensitivity. This fiber structure is composed of periodically spliced no-core fibers (NCF) and single-mode fiber (SMF) according to a certain modulation function, which effectively excites the high order cladding mode and improves the sensitivity of RI. Experimental results show that the sensor has a high sensitivity of RI at 557.74 nm/RIU in the measurement range of 1.33-1.42. The total structural length of SLPFG is only 5.4 mm, which is beneficial for integrated applications. In addition, the sensor achieves good stability, repeatability and strong mechanical properties, which has broad application prospects in environmental monitoring, biochemical monitoring, medical diagnosis and other aspects.