High-sensitivity distributed static pressure sensor based on Brillouin dynamic grating

Abstract

Brillouin dynamic gratings (BDGs) has been, in recent years, addressed using a polarization-maintaining fiber with many prominent advantages and proved that the BDGs have a profound high sensitivity to fiber birefringence changes. When the two parallel polarized counter-propagating pump waves with a frequency offset of fiber Brillouin frequency shift, and the orthogonally polarized probe pulse wave satisfied with the phase-matching condition, the BDGs would be excited through stimulated Brillouin scattering and read, while the optical frequency difference between the pump and probe waves is determined by the birefringence. The birefringence-induced frequency shift (BireFS) associated with the impact of external environment may be affected by local static pressure. Though the measurement of the BireFS changes along the fiber, one can realize a distributed fiber static pressure sensing. In our presentation, a temperature-insensitive distributed static pressure sensor based on BDGs is proposed and experimentally demonstrated for the first time, to the best of our knowledge. The measurement principle is to interrogate the static-pressure-induced fiber birefringence changes through generating and mapping the BDGs in the fiber under test (FUT). The experimental setup adopted two pump waves to excite a BDG and a short probe pulse to read the Brillouin grating spectrum associated with the birefringence with a spatial resolution of 20 cm. The sensing technique features a distributed measurement, temperature-insensitivity and high sensitivity to the static pressure. The distributed transverse load measurement experiment is conducted in an temperature-insensitive elliptical-core polarization-maintaining fiber with a measurement accuracy as high as 0.8 × 10−3 N/mm; and the distributed hydrostatic pressure measurement experiment is also performed in a thin-diameter pure silica polarization-maintaining photonic crystal fiber with a measurement accuracy as high as 0.025MPa with a character of temperature compensation.