Research On Performance Of Fiber-optic Hydrogen Sensor Based On Optical Heating And Self-compensation

In recent years,hydrogen has attracted much attention and research from scholars because of its good combustion performance,non-polluting products and wide sources.It is expected to replace fossil fuels to solve the global concerns of energy consumption and ecological environment deterioration.However,hydrogen is the gas with the smallest relative molecular mass.It is easy to leak and cause explosion in the application process.In order to ensure the safe use of hydrogen energy,it is necessary to develop a safe and reliable hydrogen sensor to monitor the hydrogen concentration in the environment in real time.At present,hydrogen sensors based on electrochemical principles are relatively mature in the market,but these sensors have the possibility of generating sparks in the process of use,and there are great potential safety hazards.The fiber-optic hydrogen sensor uses light as transmission signal,which has the inherent safety advantage.However,the stability,response and recovery rate,repeatability and sensitivity of the fiber-optic hydrogen sensor still have some defects.A micro-mirror reflective optical fiber hydrogen sensor based on WO₃-Pd₂Pt-Pt thin film with self-compensation function is fabricated in this paper,the main research contents of this sensor are as follows:（1）WO₃-Pd₂Pt-Pt thin films were deposited on the end of temperature measuring grating by vacuum evaporation and magnetron sputtering.The ratio of reflective light intensity between reference grating and thin film was used as eigenvalue to compensate for the influence of interference factors such as fluctuation of light source,bending loss of optical fiber and connection loss,so as to realize the self-compensation effect of optical fiber hydrogen sensor.And the influence of different sampling points on the long-term stability and gradient of the sensor is compared,the intensity corresponding to the best sampling point is selected as the calculation characteristic value of the film reflection intensity.（2）As we know that the temperature of hydrogen sensitive film will affect the material activity,which affects the hydrogen response performance of the sensor.After introducing the optical heating scheme,we compare the 800 ppm response of the sensor under different heating intensity,and verify that the temperature of the film has a great influence on its hydrogen response performance.Therefore,the optical power reaching the sensor probe is adjusted by the optical attenuator to change the film temperature,and the repeatability,response and recovery rate and sensitivity of the sensor under different power are compared in order to find the most suitable optical power.（3）Finally,based on the previous experiment,the optical heating scheme was introduced.The sensing probe and the heating fiber were wrapped in an optical heating structure with pores to ensure the circulation of hydrogen during the experiment.The980 nm pump light source heats the optical heating structure by the heating fiber.The Proportion Integration Differentiation（PID）control judges the internal temperature of the structure according to the central wavelength drift of the temperature grating,and adjusts the output power of the laser in real time to ensure the stability of the temperature in the structure when the ambient temperature changes.Then the same-day repeatability,gradient and next-day repeatability of the sensor before and after the introduction of optical heating are compared,and the influence of optical heating scheme on the sensor is obtained.