Sensitivity-Enhanced Fully Distributed LCFBG Sensor Based on Microwave–Photonic Interferometry

A sensitivity-enhanced high spatial resolution fully distributed linearly chirped fiber Bragg gratings (LCFBG) sensing method based on microwave photonic interferometry is proposed. The main idea of this work is that the LCFBG is interrogated by configuring a three-arm-MZI in the frequency domain to produce a Vernier effect to enhance the sensitivity. And by scanning wavelengths to determine the location information, distributed sensing with the high spatial resolution is achieved. Thanks to Microwave–photonic interferometry, the proposed sensor enjoys the advantages of high sensing resolution and high stability. A non-uniform distributed strain sensing experiment is performed for validation. Results show that a spatial resolution of
$\sim 2.4~\mu \text{m}$
is achieved within a length of 22.5 mm. Benefiting from the Vernier effect, the strain sensitivity is improved by ~22.9 times, and the strain resolution is increased to
$7.5 \times 10 ^{-6}\mu \varepsilon $
.