Design of High-sensitivity π-PS-LPFG sensor based on SDOR for simultaneous measurement of SRI and temperature

In this paper, a pi-phase-shifted long-period fiber grating (pi-PS-LPFG) sensor structure operating near phase-match turning point (PMTP) is proposed, which is able to simultaneously detect surrounding refractive index (SRI) and temperature. First, the parameters of film, grating period and grating length are designed by theoretical simulations. Then, a pi-phase-shift is introduced to make the single peak of the 25th cladding mode disappear, and two loss peaks are formed in both sides of the original single peak. When the external environment changes, the distance between the center wavelengths of the two loss peaks changes, while a single peak is formed again at the wavelength of the original 25th cladding mode with the change of intensity. Finally, the wavelength spacing of dual-peak and the intensity of the 25th cladding mode resonance peak with SRI and temperature are analyzed, and the results show a good fitting. The simulation results show that the SRI sensitivities based on wavelength modulation and intensity modulation are 9093.3 nm/RIU and -2870 dB/RIU respectively, and the temperature sensitivities based on wavelength modulation and intensity modulation are -0.3 nm/celcius and 0.217 dB/celcius respectively. Compared with other wavelength and intensity modulation based dual-parameter LPFG sensors, the SRI and temperature sensitivities of our proposed sensor structure are at least 10 times and 2 times higher than that of those LPFG sensors that have been reported. Its low fabrication cost, simple configuration, good fitting and high sensitivity make this sensor have potential applications in multi-parameter measurement.