Research On Composite Interferometric Sensor Based On Thin-core Fiber

Optical fibers have numerous potential applications in the field of sensing due to their special properties like electromagnetic immunity,portability,remote sensing capability and corrosive resistance.Compared to traditional sensor networks,fiber-based sensors have significant advantages in remote sensing,structural health monitoring,and security,especially for interference-based fiber optic sensors that have been used to sense various physical and chemical parameters such as refractive index(RI),temperature,strain,curvature and pH.The basic theory used in this paper is the principle of inter-mode interference.Combining with the existing Mach-Zehnder fiber-optic sensors,three new composite interference sensing structures have been fabricated using the cascade of microstructure(spherical structure,taper structure and offset-core structure)and thin-core fiber(TCF).The main contents and research achievement of this paper are as follows:1.Based on the composite interference theory,a composite interference sensing structure based on a spherical structure cascaded TCF is proposed,in which the spherical structure acts as a coupler,and the middle part acts as the sensing area.The output of the sensing structure is the interference spectrum formed by the superposition of two interferences.Through the simulation analysis of the spherical structure,it is proved that the spherical structure has a spectroscopic effect.The temperature and RI sensitivity of the sensing structure are simulated and experimentally studied.The simulation results are consistent with the experimental conclusions.The temperature sensitivities of the experimental results are 0.046nm/°C and 0.048nm/°C in the temperature range of 25~70°C,and the RI sensitivities are 52.679nm/RIU and-39.803nm/RIU in the RI range of 1.3330~1.3797.2.A composite interference sensing structure based on a down-taper structure cascaded TCF is designed,in which the down-taper structure acts as a coupler,and the middle part acts as the sensing area.The output of the sensing structure is the interference spectrum formed by the superposition of two interferences.Through the simulation analysis of the down-taper structure,it is proved that the down-taper structure has a spectroscopic effect.The temperature and RI sensitivity of the sensing structure are simulated and experimentally studied.The simulation results are consistent with the experimental conclusions.The temperature sensitivities are 0.065nm/°C and 0.053nm/°C in the temperature range of 25~70°C,and the RI sensitivities are-30.29nm/RIU and-79.335 nm/RIU in the RI range of 1.3562~1.3786.3.A composite interference sensing structure based on offset-core structure cascaded TCF is designed,in which the offset-core structure acts as a coupler,and the middle part acts as the sensing area.The output of the sensing structure is the interference spectrum formed by the superposition of two interferences.The temperature and RI sensitivity of the sensing structure are simulated and experimentally studied.The simulation results are consistent with the experimental results.The temperature sensitivities of the experimental results are 0.069nm/°C and 0.034nm/°C in the temperature range of 35~75°C.The RI sensitivities in the RI range of 1.34 to 1.36 are-26.6nm/RIU and 61.5nm/RIU.According to the principle of multi-parameter measurement,the above sensors can be used for simultaneous measurement of temperature and RI.