Ultrasensitive refractive index sensor based on Cascaded tilted fiber Bragg grating

An ultrasensitive refractive index sensor based on cascaded tilted fiber Bragg grating (CTFBG) is proposed and simulated. On the basis of TFBG theory, CTFBG is theoretically deduced by the transmission matrix method. The spectral characteristics of CTFBG under different surrounding refractive indexes are simulated and analyzed. The results show that the small changes of surrounding refractive index has little effect on the core mode, but has great influence on the cladding mode. The high-order cladding mode near 1557.67nm is extremely sensitive to the surrounding refractive index, and when the surrounding refractive index increases from 1.44322 to 1.44330, the sensitivity of CTFBG refractive index sensor is 9.39×10⁵ dB/RIU, which is nearly double that of TFBG.