Dispersive turning point effect based microfiber wide range water temperature sensor

In the processes of industrial wastewater recycling and treatment, chemical plants typically employ physical-chemical or biological treatment methods, with temperature recognized as a key factor influencing the efficiency of industrial wastewater treatment. The temperature measurement range for industrial wastewater typically falls around 25 - 60 degrees C. Based on the interference peak shift and temperature variation's linear relationship, we propose a microfiber structure for temperature monitoring in water environments such as industrial wastewater. The dispersion turning point produced by the difference in the effective group refractive index between the odd and even supermodels is utilized by this structure. The sensing system is encapsulated in a liquid solution, effectively eliminating interference from other stray modes and significantly improving sensing characteristics. Theoretical and experimental studies were conducted on microfiber with different waist diameters, showing good agreement between the two. The findings show that the dispersion turning point is wavelength -dependent and rises with the refractive index of the surrounding medium. Therefore, the ideal waist diameter for maximal sensitivity exists at a constant wavelength and refractive index of the surrounding medium. By optimizing sensor parameters, the sensor achieved a refractive index sensitivity of 7008.325 nm/RIU near the dispersion turning point. For temperature sensing, the sensor exhibited a high sensitivity of -0.911 nm/degrees C in the temperature range of 25 - 60 degrees C for wastewater treatment, demonstrating excellent repeatability and stability. Due to its simple structure, fast response time, straightforward detection scheme, and miniaturization, this sensor holds great potential for widespread applications in the field of temperature monitoring in water environments, especially in industrial wastewater.