| The pH value is an important indicator to measure the strength of acids and alkalis of a solution,which is of great significance in biology,medicine and aquaculture.Traditional methods for measuring pH include pH test paper measurement,chemical titration and so on.These methods have high accuracy,but they cannot be used for online monitoring.At present,fiber optical sensors have been extensively studied due to their small size and high sensitivity.Therefore,this paper combines the requirements for pH measurement and the advantages of optical fiber sensors to design and fabricate two fiber optic pH sensors with different structures.Firstly,a fiber-optic pH sensor based on a extrinsic Fabry-Perot interference is designed.The volume swelling rate of the material in the Fabry-Perot cavity material changes with the pH value of the solution,and the property of the corresponding hydrogel materials are studied.The relationship between the interference fringe characteristics of the sensor and the pH value of the solution is numerically analyzed with simulation software,which demonstrates the correlation between the interference spectrum and the pH value.Secondly,based on the simulation results,a new type of fiber optic pH sensor based on Fabry-Perot interference is fabricated.The calcium alginate gel is used as the pH-sensitive membrane and the material of the Fabry-Perot cavity.The feasibility and correctness of the design and simulation are verified through experiments,and the sensitivity,stability and time response of the sensor are tested by experiments.Finally,a fiber optic pH sensor based on the Mach-Zehnder interference is fabricated.The best connection method of two segments of single-mode fiber and endless single mode photonic crystal fiber composing this structure is researched and realized.The length and diameter of the sensing area of the sensor and the size of the welding point are optimized,and the sensitive membrane material for pH sensing is studied. |
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