Sensitivity-enhanced distributed hydrostatic pressure sensor based on BOTDA in single-mode fiber with double-layer polymer coatings

A sensitivity-enhanced distributed hydrostatic pressure sensor based on Brillouin optical time domain analysis (BOTDA) technique is theoretically proposed and experimentally demonstrated, where double-layer polymer coatings are used on the single-mode fibers (SMF) to enhance the hydrostatic pressure sensitivity. The pressure-induced strain model of multilayer coated fibers based on Lame formula is established to analyze the enhancement mechanism of pressure sensitivity of Brillouin frequency shift (BFS). Simulation results show that BFS pressure sensitivity can be enhanced with increasing of outer coating radius or decreasing of outer coating Young's modulus and Poisson's ratio. Four types of optical fibers are designed including single-coated and double-coated fibers to verify theoretical results, where the outer coating radius of double-coated fibers are 450 μm, 1000 μm and 1500 μm, respectively. Experimental results show that the BFS pressure sensitivity are -0.75 MHz/MPa, -1.65 MHz/MPa, -2.66 MHz/MPa and -3.61 MHz/MPa in the range of 0-30 MPa after temperature compensation for above four kinds of fibers, respectively. The maximum pressure sensitivity is measured about 5 times higher than single-coated SMF, and the maximum measurement error of pressure sensing system is less than 0.09 MPa with a spatial resolution of 1.5 m.