A Fiber-optic Mach-Zehnder Liquid Refractive Index Sensor Based On A Spindle-shaped Air Cavity

Fiber optic sensors have advantages which traditional sensors don't have.It has become a research hotspot in the field of sensing.The refractive index optical fiber sensor mainly includes fiber plasmon resonance type,light-emphasizing type and interference type.There are four main types of Mach-Zehnder refractive index optical fiber sensor structure,which are dislocation welding type,fusion tapering type,fiber bubble type and core mismatch type.The sensitivity of the sensor can be improved by tapering the optical fiber.Common taper methods include chemical grinding,grinding and fusion tapering.In this paper,a fiber Mach-Zehnder refractive index sensor based on a spindle-type air cavity is designed,which is fabricated by fusing single-mode fiber and photonic crystal fiber.Using FDTD Solutions simulation software to study the influence of tapering zone cladding thickness,air cavity shape and tapering zone length on the sensing performance of optical fiber refractive index sensor.Optimizing the structure of the sensor based on this.The transmission of optical signals in the sensor with cladding thickness of 1.15?m and 8?m was analyzed.The relationship between the valley wavelength of the sensor and the environmental refractive index is simulated and studied,and the refractive index sensitivity of the sensor under different environmental refractive indexes is obtained.Among them,for the cladding thickness of 1.15?m,When the environmental refractive index is 1.4-1.42,the refractive index sensitivity is as high as 3133.3nm/RIU;The temperature crosstalk characteristics are simulated,and it is found that the temperature sensitivity is only 0.039nm/?.Using COMSOL Multiphysics simulation software to simulate and analyze the effective refractive index and optical field distribution of the tapered zone cladding and air cavity.It is found that as the environmental refractive index increases,the effective refractive index of the air cavity remains unchanged,and the effective refractive index of the cladding increases.The manufacturing method and experimental system of the fiber Mach-Zehnder refractive index sensor based on the spindle-type air cavity are introduced.Three refractive index sensors with different tapering lengths and cladding thicknesses were fabricated,the cladding thickness was 7.4?m-11?m.Set up an experimental system to conduct a refractive index sensing characteristic experiment on them.The highest refractive index sensitivity of the three sensors are 130.96nm/RIU,226.67nm/RIU and 333.33nm/RIU,respectively.The experimental results show that as the thickness of the cladding in the tapered zone decreases,the refractive index sensitivity gradually increases.