Fabry-Perot Interferometer Curvature Sensor Based on Microwave Photonic Filter Technique

In this letter, we propose and experimentally demonstrate an approach to performing high-resolution and temperature-insensitive idea of a Fabry-Perot interferometer (FPI) curvature sensor utilizing microwave photonic filter (MPF) technique. A section of the capillary fiber is spliced between a single-mode fiber and a core-less fiber to form the air-gap FPI. The bending deformation of the FPI leads to changes in the fringe visibility (V) and free spectral range (FSR) of the interference pattern, which are converted into the changes in peak power and central frequency of the corresponding MPF. Consequently, the bending curvature can be recovered by tracking the frequency shift or the magnitude change. The experimental results show that the peak of the MPF decreases non-linearly with the increased curvature and a second-degree polynomial curve is fitted to predict the relationship. Compared with the fringe visibility change in optical domain, the peak power change of the MPF is enhanced by ~5 times. Meanwhile, the wavelength shift has a linear relationship with the curvature, and the sensitivity of 19.5 pm/m−1 is achieved in the curvature range of 3.3065-9.0552 m<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\mathrm {-1}}$ </tex-math></inline-formula> with a resolution of 1.026 m−1. The central frequency shifts linearly with the increase of curvature, and the sensitivity is 0.86 MHz/m<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\mathrm {-1}}$ </tex-math></inline-formula> with a resolution of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.16\times 10 ^{-3}$ </tex-math></inline-formula>m−1, which is much larger than that obtained by tracking the wavelength shift.