High temperature and strain dual-parameters fiber sensing based on intermodal interference and femtosecond laser fabricated fiber Bragg grating

Abstract

In this paper, the sensor was proposed by combination of grapefruit photonic crystal fiber (GPCF) and femtosecond laser fabricated fiber Bragg grating (FBG) based on Sagnac interferometer. The GPCF was sandwiched between two single-mode fibers (SMFS) to form a SMF-GPCF-SMF structure, which was based on intermodal interference. The FBG with a central wavelength of 1535.32 nm was inscribed through polyimide coating and cladding by the femtosecond laser point-by-point inscribing method. The spectrum drift data of sensing structure were collected and the dual-parameters matrix of temperature-strain was constructed to realize the simultaneous measurement of temperature and strain. The experimental results showed that the linear range of the strain measurement was from 0 με to 2,000 με at different temperature, the wavelength of FBG and GPCF was red drift and blue drift, respectively, the average strain sensitivity at different temperature was 1.25 pm/με and −2.05 pm/με, all the linearity R2 are higher than 0.999, and has the high repeatability. The linear range of temperature measurement was from 20 °C to 450 °C, the wavelength of FBG and GPCF was red drift and blue drift, respectively, the temperature sensitivity of FBG and GPCF was 15.17 pm °C−1 and −8.87 pm °C−1, the linearity was 0.99983 and 0.99989, respectively.