Simultaneous detection of SRI and temperature with a FM-LPFG sensor based on dual-peak resonance

A novel few-mode long-period fiber grating (FM-LPFG) sensor based on dual-peak resonance near the phase-match turning point (PMTP) for simultaneous detection of surrounding refractive index (SRI) and temperature is proposed. The dual-peak resonance near the PMTP of the FM-LPFG is analyzed based on the coupled-mode theory. The cladding modes of adjacent order exhibit dual-peak and single-peak resonances in the wavelength band 1450–1850 nm, respectively. And the response characteristics of different resonant peaks to temperature and SRI are discussed. Results of numerical simulations demonstrate that the SRI sensitivities corresponding to the distance between the dual peaks and single-peak transmissivity are 1114.28 nm/RIU and -685.42 dB/RIU, respectively, and the temperature sensitivities corresponding to the distance between the dual peaks and single-peak transmissivity are −0.27 nm/°C and 0.072 dB/°C. The different SRI and temperature sensitivities of those peaks help to sense multi-parameters.