Research On The Key Technologies Of Interferometric Optical Micro-nanofiber For Gas Sensing

Gas sensing technology has a great research value and application demands in many areas.Exploring the new sensing mechanism,developing novel sensor,and broadening the gas sensing application have become a focus of research.In this study,the highly sensitive and selective optical fiber gas sensor is realized by combination of gas sensing coating with high sensitive refractive index sensing device due to their strong evanescent field interaction with the external environment.First,the model theory of micro-nanofibers is introduced,and the tapered transition regions with adiabatic and non-adiabatic conditions are analyzed,respectively.Low-loss transmission of fundamental mode can be achived under adiabatic conditions.While,fractional energy of fundamental mode couples into higher order modes under non-adiabatic condition.The interferometric micro-nanofiber devices with different conical and different waist regions are prepared by controlling the the speeds of the stages and moving ranges.Therefore,high-performance interferometric optical microfiber devices were fabricated which provided experimental basic for future studies on realization of gas sensing.Secondly,the humidity sensing characteristics of interferometric micro-nanofiber devices are studied which with high refractive index sensitivity.Due to the water vapor molecules adsorbed on the surface of the silicon fiber makes the local refractive index change,the humidity change information can be obtained by monitoring the wavelength shift of the interference spectrum.The microfiber device possesses a low temperature cross sensitivity and it designed as “U-shape” sensing probe,making it compactness and conveniently for gas detedtion In a comparison of the sensing performance of the sensor with different diameter,results suggest that the microfiber with diameter of 4.75 ?m presents high humidity sensitivity of 114.7 pm/RHU?per relative humidity unit?ranging from 30% to 90% and good linearity.Finally,optical microfiber interferometer is used as a conversion element of the gas sensor,then GO-ZnO nanocomposities coated on the surface of the fiber for NH₃ detetion.The hybrid nanocomposities of zinc oxide?ZnO?functionalized graphene oxide?GO?not only display the indidual properties of the ZnO and of GO,but also show additional synergistic effects that are desirable and advantage for high sensitivity and selectivity to target gas molecules.The electrons transfer between ammonia molecules and GO-ZnO after ammonia absorption,and leading to the refractive index change of the microfiber surface.The experimental results suggest that the sensor exhibit a good singal repeatability,excellent selectivity and high sensitivity to different ammonia concentrations from 4 ppm to 140 ppm at room temperature,the response time and the recovery time are 2 min and 1.5 min,respectively.To sum up,the combination of micro-nanofiber devices and nano composite materials provides a valuable method and idea for achieving highly sensitivity and selective gas sensing.As research continues,the gas sensing technology based on micro-nanofiber will be widely developed and applied,and it will also be a strong competitor for the exsisting gas senseors.