Graphene Coated Nano-scale Optical Fiber Biosensor

With the continuous development of surface plasmon resonance sensing technology,the application of fiber biosensors based on surface plasmon resonance is becoming more and more extensive.Optical fiber sensors based on surface plasmon resonance are widely used in biochemical sensing because of their features of label-free,high sensitivity,no damage,and real-time monitoring.However,the current surface plasmon resonance sensor is based on thin metal films,and due to the large loss of metal,it's not sensitive to the changes of the refractive index of external environment.Therefore,this paper has studied the graphene coated nano-scale optical fiber biosensor.The main work of the paper is as follows:First,this paper reviews the surface plasmon resonance sensors.It mainly introduces the sensor based on fiber structure,Klechmann structure,and grating coupling.In addition,this paper also introduces some performance parameters of the three-dimensional resonant sensors,and how to improve the performance parameters of the sensor by changing the structural parameters of the sensor.Different from traditional fibers,nano fibers transmit information by surface evanescent wave,also,nano fibers can transmit the surface plasmon polaritons generated between graphene and dielectric media.Graphene has the nature of metal in a specific condition,and plasmon resonance will generate between graphene and the dielectric media.Since the refractive index of graphene is sensitive to external influences,when the external refractive index changes,the refractive index of graphene will change,thus affecting the transmission phase and polarization state in the fiber to achieve the role of sensing.In this paper,a graphene coated nano-scale fiber biosensor based on surface plasmon resonance is designed.This structure is placed in biological sample,composed of a layer of graphene cladding on the silicon core.The change of the refractive index of the outer cladding can cause a change in the fiber transmission,which is the main mechanism of the sensor.The theoretical model is built based on this principle and the scattering equation in interface of graphene and silicon core is obtained by solving Maxwell's equations.And then,the scattering equations of TM and EH modes can be derived,the distribution of electromagnetic field of TM and EH modes around the graphene-dielectric interface is also discussed.Simulation model is built in COMSOL and the process of detecting specific biological sample is simulated.In this paper,the way of information transmission in optical fiber is different from that of the traditional optical fiber sensor.A coupled source of several different modes of fiber propagation is used,so in the optical fiber propagation process,due to the destruction of interference generated by the swing of the " Crescent " shape,the biological sample with specific refractive index can be detected according to the change of crescent shape and other transmission information at the output.In the study of nano-scale fiber optic biosensor,the feasibility of this design is proved by numerical simulation,which laid the foundation for the future experimental research.