Research On Humidity And Gas Sensing Of Optical Fiber Sensors Covered By Nano-porous Functional Film

Optical fiber sensors set the function of transmission and sensing as a whole,showing the irreplaceable characteristics,such as its small size and light weight,electromagnetic interference resistance,corrosion resistance,high stability,high precision and good compatibility with communication system.Optical fiber sensors have wide range of applications.In order to meet higher application requirement,the researchers constantly explore new materials and new solutions.Appling new functional materials into optical fiber sensing become the development trend of optical fiber sensing fields.In our research,the materials which have the nano-microporous structures were covered on the surface of side-polished fiber(SPF)and optical fiber micro-wires(OMF)as sensitive materials to fabricate novel sensors to boost the sensing sensitivity of humidity and gas.The measurement of environmental humidity and concentration of gas can be realized by utilizing the strong interaction between the functional materials and external environment.There were two main types of materials that we used in our research,dichromated gelatin(DCG)nano-porous structure and reduced graphene oxide(rGO)and polystyrene(PS)composited particles.DCG nano-porous structure was spin coated onto the polished surface of SPF to make a humidity sensor.The sensitivity of the proposed sensor raised an order of magnitude comparing to that of no porous structure.The three dimensional networks structure,for the first time,were applied to corporate with optical fiber for detecting the concentration of the ammonia gas by depositing the rGO/PS composite on the surface of OFM.Our works will certainly promote the development of optic fiber device that combine functional materials with nano-porous structure and optical fiber.The summary of innovations of this paper are as following:Firstly,an optical fiber humidity sensor combining DCG nanostructure film with SPF was fabricated and proved to be efficient.Sensing properties of the sensor was investigated by testing three parameters: sensitivity,reversibility and response speed.While the humidity changes from 30%RH to 50% RH,the sensitivity could reach 1.12nm/%RH.There were high linear relationship between transmission spectrum of the wavelength drifts and humidity,and the linear correlation coefficient was 99.31%.Furthermore,transmission spectra can be fully restored to the initial state after adjusting humidity periodically.The sensor showed good repeatability over humidity with a range from 30%RH to 50%RH.The response speed was higher than 0.049%RH/s.Secondly,an optical gas sensor combining three dimensional porous film of reduce oxide graphene and polystyrene composite with OFM was fabricated and proved to be efficient.The sensing characteristics of the sensor were precisely measured and the ammonia sensing sensitivity of 0.00165dB/ppm was achieved.The time of the sensing material releasing ammonia gas was less than 200 s,and the sensor shown significant repeatability.When the concentration of ammonia gas were below 4060 ppm,there was a significant linear correlation between power variation and ammonia gas concentration,with the linear correlated coefficient of 0.9785..