Research On Applications Of Grapheneassisted Microfiber Devices

The research of micro/nano photonic devices covers the generation,modulation and detection of optical signals on micron and nanometer dimensions.Microfiber is a typical micro/nano optical infrastructure with low transmission loss,large proportion of evanescent field,small bending radius,light weight,and easy operation.It is an important basis for the research of micro/nano photonic devices.However,the material of microfiber is generally SiO₂,due to the limitation of SiO₂,the function development of microfiber devices is limited.The existence of the evanescent field of the microfiber makes it easy for microfiber to interact with the surrounding medium,so compounding functional materials with microfiber has become a feasible solution.As a typical two-dimensional material,graphene has many unique properties due to its distinctive atomic structure,such as excellent photothermal property.The preparation of graphene is mature and simple.Sheet graphene can be easily ultilized to modify characterize of various micro/nano photonic devices,including microfiber.The combination of graphene and microfiber has become a new research idea of microfiber devices.Therefore,in this thesis,combining the respective characteristics of graphene and optical microfiber,two graphene-assisted optical microfiber devices are proposed,and their application properties are studied separately.One is a straight microfiber device with graphene-wrapped structure,which is experimentally explored for its application in the field of optical manipulation.The other is a curved microfiber device with graphene-and PDMS-coated sandwich structure,which is applied in the field of all-optical modulation and temperature sensing.The main research contents of the thesis include:1.Combined with the solving of Maxwell’s equations and the simulation of optical microfiber mode field,the optical transmission characteristics of optical microfiber are explored.The influence of factors such as the diameter and working wavelength of the optical microfiber on the mode field distribution is studied:When the diameter of the optical microfiber is smaller or the working wavelength is longer,the limiting effect of optical microfiber on light is smaller,and more energy will leak into the surrounding medium.2.A straight microfiber device with graphene-wrapped structure is proposed,and the application of this device in the field of light manipulation is experimentally explored.The prepared graphene is transferred to the surface of the optical microfiber,and then tightly wrapped in the tapered waist region of the optical microfiber.By controlling the power of the incident light,different functions of the device can be achieved.（1）When the power is relatively low,the microfiber can effectively capture the particles in liqiuid environment,and the optical forces including scattering force and gradient force play a leading role during this capture process.（2）When the incident light power is in the appropriate range（30-90 mW）,the device can realize the stable growth of a single bubble.Using Marangoni convection around microbubbles,the device can collect particles in a liquid environment.（3）When the incident light power is higher,multiple microbubbles grow violently in the liquid environment,and the bubbles separated from the micro-nano fiber are gathered into a"bubble cloud"in the liquid.There are vortices around the optical microfiber device,which can capture single or multiple microbubbles and realize the rotation and self-assembly function of the captured object.3.A curved microfiber device with graphene-and PDMS-coated sandwich structure is proposed,and the performance of the device in all-optical tuning and temperature sensing is experimentally explored.The wavelength of this device will red-shift as the pump light power of the external irradiation increases,and the modulation efficiency is measured to be 2.04 pm/mW.In addition,the device can be used for temperature sensing.When the ambient temperature rises by 18.6℃,the wavelength will blue-shift 1.53 nm with a fitted temperature sensing sensitivity of 79.01 pm/℃.