Fabrication Of Fiber Fabry-Perot Interferometer And Study On Temperature And Hydrogen Sensing Characteristics

Hydrogen has the characteristic of high heat release.When the hydrogen is burned in the air,the product is only the water.Therefore,hydrogen is not only a clean and renewable energy source,but also one of the most promising new energy sources in the new era.However,due to its low density,colorless,odorless,and easy to diffuse,hydrogen is prone to leakage during transportation and storage.The leak of hydrogen is not only difficult to detect,but also causes the explosion,as the explosion limit of hydrogen is low(4%),so real-time and accurate monitoring of the concentration of hydrogen is particularly important.The fiber optic sensor has the advantages of small sizes,various of structures,anti-electromagnetic interference and remote monitoring.It has excellent sensing characteristics in the harsh environments such as high temperature,high pressure,strong current and strong magnetic field,which has earned more and more attention in the field of hydrogen sensing.In this paper,We will conduct theoretical and experimental research around the relevant characteristics of fiber optical Fabry-Perot(Fabry-Perot,F-P)interferometer,such as sensing principle,structural parameter design,preparation method,corresponding temperature sensing experiment and hydrogen sensing experiment.The main research work includes the following aspects:(1)Based on the principle of F-P interferometer,the theoretical model of fiber F-P interferometer is established.Based on this,we will design three kinds of fiber sensor probe structures of F-P interferometer which are suitable for temperature sensing:extrinsic F-P interferometer,the air-cavity type F-P interferometer and the end-coated type F-P interferometer,analyze the sensing principle of each type of F-P interferometer and simulate the influence of structural parameters on the F-P interferometer.Further,through in-depth investigation and comparative analysis by us,the palladium-tungsten trioxide(Pd-WO3)was selected as the hydrogen sensitive membrane,and we also analyze the hydrogen sensing mechanism of Pd-WO3 in theory,which provided the theoretical foundation and technical foundation of the structural design of fiber optical hydrogen sensor based F-P interferometer.(2)According to the structural characteristics of the proposed three kinds of the fiber F-P interferometers,select the appropriate preparation scheme,prepare the corresponding sensing probes,and test the temperature sensing characteristics.The experimental results show that the temperature sensitivity of the extrinsic fiber F-P sensor can reach-1.25696nm/℃,the hysteresis and the repeatability are good.The temperature sensitivity of the air-cavity type fiber F-P sensor can reach-5.6144nm/℃,its linear fitting and hysteresis are good.The temperature sensitivity of the end-coated type F-P sensor can reach 5.27078nm/℃,and its linear fitting is good.(3)Considering the experimental conditions and hydrogen sensing requirements,select the air cavity type F-P interferometer and the tail end-coated type F-P interferometer for the hydrogen sensing experiment.Select the appropriate method to fabricate the Pd-WO3 sol gel,and apply it coated on the surface/end surface of the F-P interferometer.At the same time,build the hydrogen sensing experimental platform and improve mend the gas sensing chamber.The hydrogen sensing experiment was carried out in the range of 0-2.5%hydrogen concentration.The experimental results show that the hydrogen sensitivity of the air-cavity type fiber F-P sensor can reach-1.50017 nm/%,and the linear fit is better.The end-coated fiber optical F-P sensor has a hydrogen sensitivity of 1.3966nm/%,and has good linearity.In summary,based on the sensing principle of fiber optical F-P interferometer,we have designed and fabricated three kinds of fiber optical F-P interferometer sensors.Their sensing probes have the advantages of simple structure,flexible design,high responsiveness and good sensing characteristics.By testing and analyzing with the temperature characteristics of the three F-P interferometers,finally,the air-cavity type F-P interferometer and the end-coated F-P interferometer sensor probe are selected to combine with the hydrogen sensitive film,and a highly sensitive measurement of hydrogen concentration is achieved.