Multi-parameter sensor based on femtosecond laser pulses inscribed EFBG

In this paper, we presented a multiparameter sensor for temperature, refractive index or bending based on eccentric fiber Bragg gratings (EFBGs). The EFBG was prepared in SMF-28 single-mode fiber by 800nm femtosecond laser point-by-point writing method. The cladding mode resonances were significantly enhanced by refractive index modulation asymmetry and exhibit sensitivity to surrounding refractive indices and bending. When the temperature increases, the Bragg wavelength increase linearly with temperature and the temperature sensitivity is 14.4 pm/°C. As the refractive index of the surrounding medium increases, the cutoff wavelength of EFBG cladding mode resonance shifts red with the sensitivity of 649.29nm/RIU. When the EFBG is bent, the coupling strength of the cladding mode gradually decreases from the lower order mode and the sensitivity is -0.36dB/m^-1 when the bending direction is 180° from the grating offset surface. With this well-conditioned system, temperature and RI(bending) can be determined independently with high sensitivity.