High-sensitivity Simultaneous Demodulation of Multi-parameters in Polarization-maintaining Fibers Based on Brillouin Dynamic Gratings
Distributed Brillouin fiber sensing technology enables continuous spatial measurement of parameters such as temperature and pressure,offering advantages over traditional point sensors in terms of wide range,long distance,and high capacity.Civil structures and large machinery inevitably face lateral pressures due to their own weight and external impacts during construction and use,necessitating reliable and efficient sensors for these forces.Additionally,temperature is a crucial physical parameter that often needs to be measured simultaneously with pressure.The use of Brillouin frequency shift in fiber optic distributed sensing for temperature or pressure is common,but its sensitivity to both parameters simultaneously complicates the measurement of multiple variables at once.Hence,this paper introduces a simultaneous demodulation method for temperature,fast-axis pressure,and slow-axis pressure.The numerical simulation and emulation were performed using the wave optics and solid mechanics modules within the COMSOL Multiphysics finite element analysis software.After setting the boundary conditions,pressure was applied to the photonic crystal fiber,and its deformation under pressure was calculated.The effective refractive index of the fiber was calculated using the wave optics module.By substituting into formulas,the birefringence frequency shift,Brillouin frequency shift,and Brillouin linewidth resulting from deformation were obtained.Demodulation was then employed to acquire the specific values of these three variables.To validate the reliability of the demodulation results,lateral pressure is applied to both the fast and slow axes,while simultaneously altering the temperature.Using the birefringence frequency shift,Brillouin frequency shift,and Brillouin line width at 0 MPa and 0 ℃ as reference values,simulations determined the variations in these parameters under different pressures or temperatures.These variations are then substituted into formulas to calculate △P1',△P2',and △T.By comparing these calculated values with the actual applied values of △P1,△P2,and △T,the corresponding error values can be ascertained.The results indicate that the three parameters can be simultaneously demodulated with demodulation errors within 1 MPa and 1 ℃.The mean errors for fast-axis pressure,slow-axis pressure,and temperature were 0.21 MPa,0.31 MPa,and 0.30 ℃,respectively,with standard deviations of 0.15 MPa,0.21 MPa,and 0.21 ℃,respectively.When lateral pressures of 0 to 30 MPa and temperatures of 0 to 100 ℃ were applied,the pressure sensitivity in the fast-axis direction of the photonic crystal fiber was approximately-1.961 GHz/MPa,the pressure sensitivity in the slow-axis direction was about 1.356 GHz/MPa,and its temperature sensitivity was around 0.105 MHz/℃.Compared with the current optimal structure of the photonic crystal fiber,the pressure sensitivity is improved by-957 MHz/MPa.This paper presents a highly sensitive polarization-maintaining photonic crystal fiber that enables simultaneous demodulation of temperature,fast axis pressure,and slow axis pressure.Due to the sensitivity of the polarization-maintaining fiber to temperature,fast axis pressure,and slow axis pressure,this technology can be applied to the detection of high-precision fiber optic gyroscope rings.The proposed sensor and demodulation method offer significant reference value for the distributed monitoring of temperature and pressure in different directions during the construction and use of civil structures and large machinery.
Fiber optic sensingBrillouin dynamic gratingsFinite element methodPhotonic crystal fiberSimultaneous demodulation
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维普
