Study On The Optical Fiber Interferometric Sensors Based On Phase Modulation

With the development of science and technology,sensors are playing an increasingly important role in various industries.Optical fiber sensors have been widely used in aerospace,biomedical,environmental monitoring and other fields due to their unique advantages such as high sensitivity,strong anti-interference ability,high stability,fast measurement speed,and large information capacity,which have become hot research topics in the field of sensing.This article first introduces the working principle and development history of optical fiber sensors,the classification of optical fiber sensors,and the principles of different modulation methods.Then,briefly analyze the mode theory of optical fiber.Based on Maxwell's equations,the waveguide equations and Helmholtz equations of electromagnetic waves,and the analytical solution expressions of modes propagating in optical fibers are introduced.The traditional phase modulation method is described,and a new phase modulation method is proposed to measure the refractive index.The simulation method of optical fiber sensors,the finite difference time domain method and simulation software FDTD Solutions are introduced.Next,focusing on the research of optical fiber interferometric sensors,two common fiber sensor structures are targeted:Mach-Zehnder interferometer and single-mode-multimode-single-mode structure based on mode interference.And use the new phase modulation method to measure the refractive index of the external environment,make an analysis of the dependence of resolution error and processing error on each parameter.The sensitivity of the refractive index sensor based on Mach-Zehnder interferometer can reach 2e4/RIU.The sensitivity of the single-mode-multimode-single-mode structure based on mode interference reaches 3e4/RIU.The new method of phase modulation can obtain measurement results without external calibration,and can obtain the dispersion relationship of the refractive index of the external environment,which greatly reduces the magnitude of the error and greatly improves the sensitivity.Finally,we summarized and prospected optical fiber sensor based on phase modulation proposed in this paper.