Fibre axial strain sensor based on a microwave photonic filter with dual-passband

A fibre axial strain sensor based on a phase modulated microwave photonics filter (MPF) with dual-passband is proposed and experimentally demonstrated. According to the phase-modulation to intensity-modulation (PM-IM) conversion in the MPF, dual-passband can be generated by utilizing two cascaded fibre Bragg grating Fabry-Perot (FBG-FP) filters. The fibre axial strain will change the wavelength of the FBG-FP, and resulting in the frequency variation in the passband. Thus, with one FBG-FP serving as the sensing element and the other acting as the reference element, a highly sensitive strain sensor can be realized simply by monitoring the frequency difference variation between the two passbands. The result shows that the passband frequency changes linearly in response to the strain with a sensitivity of 1.40x10(8)Hz/epsilon. The sensor reveals the advantages of highly sensitive, small hysteresis and good stability, providing great potential for practical applications.