Theoretical analysis based on angle cascaded long period fiber grating for surrounding refractive index and temperature measurement

An angularly cascaded long period fiber grating (AC-LPFG) sensor for simultaneously measuring refractive index (SRI) and temperature in the surrounding environment has been proposed and theoretically demonstrated. The sensor consists of an un-tilted LPFG and a tilted LPFG with the same grating period, which has a transmission spectrum with typical three peaks. Our simulation results show that the simultaneous measuring of SRI and temperature can be achieved by monitoring the transmissivity in the middle peak and the wavelength distance of the two other peaks. For the transmissivity of the middle peak, the SRI and temperature sensitivities are –180.53 dB/RIU and 0.04 dB/℃, respectively. For the wavelength distance between the other two peaks, the SRI and temperature sensitivities are 604.55 nm/RIU and –0.19 nm/℃, respectively. From the perspective of intensity response, the maximum SRI of our sensor is 5 times higher than the cascaded LPFG-based sensors with dual-parameter ability.