Research On Dual-parameter Optical Fiber Sensor Based On Cascaded Fabry-perot Interferometer

Two different types of dual-parameter optical fiber sensors are developed and fabricated in this paper,taking advantage of the Fabry-Perot Interferometer's(FPI)high sensitivity,compact size,and ease of integration.These optical fiber sensors effectively address the cross-sensitivity problem that occurs when optical fiber sensors are used in real-world applications.Furthermore,the fiber-optic Fabry-Perot interferometer's sensitivity enhancement method was studied,as well as related sensing experiments.The following are the key contents of this work:(1)The current state of research on fiber FPI and dual-parameter fiber sensors is summarized;beginning with multi-beam interference,the interference theory and sensing principle of fiber FPI are deduced,and two characteristics of fiber FPI output spectrum: free spectrum width and contrast are simulated and analyzed.(2)Designed and fabricated an optical fiber sensor that realizes dual-parameter measurement of refractive index and temperature.The structure is obtained by optical fiber FPI cascaded bending fiber interferometer,which has compact structure,simple process and low price.Through experiments,the refractive index response characteristics and temperature response characteristics are explored.The experimental results show that by establishing the refractive index temperature sensitivity matrix,the demodulation of the refractive index and temperature dual parameters can be achieved.The sensor has a refractive index sensitivity of 303.78 nm/RIU in the refractive index range of 1.3405 to 1.3800,and a linear fit of 0.997;temperature sensitivity in the temperature range of 40 ? to 80 ? can reach 0.202 nm/?.(3)Designed and fabricated an optical fiber sensor that realizes dual-parameter measurement of tensile force and temperature.The structure is obtained by optical fiber FPI cascaded fiber Bragg grating.The tensile force response characteristics and temperature response characteristics have been experimentally explored.The experimental data shows that the tensile sensitivity of FPI is 2.65 nm/N and the temperature sensitivity is 0.008 nm/?;the tensile sensitivity of FBG is 1.39 nm/N and the temperature sensitivity is 0.010 nm/?.(4)The sensitivity enhancement principle of the vernier effect is introduced,and the relationship between the free spectrum width of the vernier effect,the sensitivity magnification and the free spectrum width of two FPIs is derived.The optical vernier effect sensor is created by combining two FPI cascades with identical cavity lengths,and the tensile response characteristic of the envelope of the sensor's output spectrum is investigated experimentally.The results of the experiments show that the vernier effect will boost FPI's sensitivity by an order of magnitude,with a magnification of16.4 times.