Simultaneous measurement of temperature and strain based on all-fiber Fabry-Perot sensor

An all-fiber Fabry-Perot (FP) interferometer (FPI) sensor which can simultaneously measure strain and temperature is proposed and experimentally demonstrated. The FPI sensor is composed of a cascaded-cavity structure with a hollow-core tube fiber cavity and a standard single-mode fiber (SMF) cavity. Different cross section areas and thermal-optic coefficients of the two cavities make them differently sensitive to temperature and strain. The individual interference spectrum based on the air cavity or silica cavity can be extracted by band-pass filtering the spectrum of the sensor in frequency domain. The temperature and strain sensitivity of each cavity are obtained by tracing the wavelength shifts of the interference spectra. Furthermore, the temperature-strain cross-talk is eliminated by solving a cofficient matrix equation composed by the temperature and strain sensitivities of the two FP cavities. The strain sensitivities of two FP cavities achieved are 1.173 nm/με and 1.86 nm/με. The temperature sensitivities of two FP cavities are 0.00574 nm/°C and 0.00549 nm/°C. The advantages of the proposed sensor including simultaneous measurement of temperature and strain, no temperature-strain cross-talk, simple fabrication, and all-fiber structure make it appropriate for the real sensing applications.