A novel method for simultaneous measurement of temperature and strain based on EFPI/FBG

A modified intensity demodulation method for fiber optic Fabry-Perot cavity and fiber Bragg grating combined sensing system is proposed, through which the cross-sensing error can be reduced effectively and high sensing speed can be realized at the same time. The system is based on an Extrinsic Fabry-Perot Interferometer for strain sensing, and a fiber Bragg grating for temperature sensing. Three-wavelength digital phase demodulation method and passive linear filtering demodulation method are adopted for the demodulation of F-P cavity length and fiber Bragg grating central wavelength, respectively. Meanwhile temperature varied from 25 degrees C to 105 degrees C under constant pressure, the demodulation accuracy of strain after correction is +/- 0.6 mu epsilon, which is improved by 2 times than the direct demodulation result. The demodulation accuracy of temperature is 1.4 degrees C after correction, with pressure ranging from 0 to 10 MPa at constant temperature. Temperature demodulation error is decreased to 1/3 of its original value. Strain sensing accuracy after correction was +/- 1 mu epsilon. Experimental studies show that the proposed sensing system has a more compact size and higher measurement accuracy than the previous ones.