Reseach On Graphene Enhanced Microfiber Bragg Grating For Gas Sensors

As a new generation of sensing technology, optical fiber sensing plays an important role in the fields of aerospace, defense of military, biomedical and environment monitoring. In the past years, microfiber has been widely studied and used in the fiber sensing area, for its special characteristic of large proportion of evanescent field. And its combination with nano materials becomes a hot direction in the field of optical fiber sensing and chemical sensing. But how to achieve the trace sensing of molecules is also a major problem in this area.The discovery of graphene material provides a totally new method to the research on the evanescent field sensing technology of microfiber. As a kind of two-dimensional film material, graphene has good characteristics of molecular adsorption, relatively sensitive to the surrounding environment, and easy to be combined with microfiber waveguide in various ways. Therefore, the research on the combination of graphene and microfiber sensors has great significance, not only in the interdisciplinary of micro-optics and nano materials, but also in the value of the cutting-edge research in the future, like the field of super sensitive detection for molecular level.The thesis proposes a hybrid waveguide structure of graphene coated microfiber Bragg grating for gas sensing. The coated graphene will significantly enhance the evanescent field along the surface of the microfiber Bragg grating. At the same time, the adsorbed gas molecules on the surface of graphene, will change the carrier concentration of graphene, leading the optical index to be changed. Then the effective refractive index of the waveguide will be altered, causing a corresponding wavelength shift and attenuation. Through detecting the changes of the output signal, the concentration of trace molecular can be detected.Firstly, this thesis researches on the properties of microfiber Bragg grating and monolayer graphene film, theoretically analyzes the sensing characteristics of microfiber Bragg grating. At the same time, graphene is discussed to affect the transmitted field of micro fiber and easy to adsorb gas molecules. All of these will lay the theoretical basis of the research on the sensing properties of graphene-microfiber Bragg grating hybrid waveguide. Secondly, the preparation of microfiber Bragg gratings and characterization of graphene are described. Modeling and simulation are carried out to lay the foundation for the followed experimental study on graphene coated microfiber Bragg grating hybrid waveguide. Finally, do experimental research on the hybrid waveguide structure for gas sensing to verify the sensitization effect of graphene and the feasibility of the waveguide structure applied for optical sensing. Through optimizing the structure parameters, a good performance of graphene coated microfiber Bragg grating is obtained for sensing in practical research, realizing the high sensitivity of biochemical gas sensing.