Coupling And Detecting Of The Electromagnetic Modes In Optical Nano Antenna

It is well known that antenna is a kind of device which can converse guided waves on an electric circuit into electromagnetic waves in free space(or vice verse),In the history of more than one hundred years,antenna is gradually used in communication,detection,sensing and other fields.From the transmission of audio and video waves to radar’s function of detecting,the work frequencies of antenna are also extended from microwave to infrared and visible light.In recent years,people pay special attention to the research of infrared and optical frequency antenna.Withthe development of metamaterial and micro-nano processing technology,design and preparation of the infrared and optical antenna in sub wavelength scales is possible.At present,optical antenna shows attractive application prospects in the unidirectional radiation,field enhancement,bio-sensing,holographic imaging,communication and sensing.Based on these,this article studies the coupling and detecting of electromagnetic modes in optical antenna.The article includes the following parts.First,we studied the coupling of electromagnetic modes in dielectric optical antenna and realize dual Fano resonances.We first analyze the scattering properties of an individual silicon nano-cylinder in the long-wavelength limit and confirm that in this system,there are electric and magnetic modes.Then,we introduce the coupled electric and magnetic dipole method and analyze the coupling between two silicon nano-cylinders,showing there are electric-electric,electric-magnetic,magnetic-magnetic interactions in this system.After that,using FDTD method,we study the scattering property of a single silicon nano-cylinder with different diameter.We also find that a single electric mode can couple with a single magnetic mode.Further,we realize dual Fano resonances in a two silicon nano-cylinders system,due to the coupling between an electric dipole mode in one cylinder and a magnetic dipole mode in the other one.We also found that the polarization direction of the incident light and the distance between the two nano-cylinders can tune the wavelength and the strength of the Fano resonance.Through designing of the structure sizes and utilizing the dual Fano resonances,a broadband light scattering is realized.In the experiment,using the methods of electron beam lithography and inductively coupled plasma,we prepare silicon nano-cylinder arrays,measure the reflection spectrum by spectrometer,and get some information from the scattering light of the sample.The study provides a physical pathway of preparing loss-less optical antenna,which can be used in filtering,solar cells,and biological sensors.Second,we study the cathodeluminance(CL)electromagnetic modes of metallic optical antenna and shows propertied of the radiation of the three kinds of optical antenna due to the excitation of different kinds of localized surface plasmons.We find the existence of electric dipole,magnetic dipole,electric quadrupole modes and etc.In detail,we study three kinds of optical metallic nano antenna structures(respectively"U","II","H"shape)under the electron beam irradiation using FDTD method and get the corresponding scattering spectrum of the excited electromagnetic modes.We also calculate the near field distribution of the excited electromagnetic modes of the three kinds of antennas.We find that there are electric dipole,magnetic dipole,electric quadrupole modes and magnetic quadrupole modes in all of these antennas respectively which results from the excitation of different kind of localized surface plasmons.In the experiment,using the method of electron beam lithography,we prepare the sample of the three kinds of antennas.By point excitation,line scanning,and the surface scanning method of CL means,we detect the excitated electromagnetic modes at different positions of the sample.Research finds that the three kinds of nano gold antenna show an agreement between the experiment and numerical simulation results.Then we study the u-shaped nano gold antenna and measure the spectrum corresponding to the main excitation mode.We show the change of the modes excited and their spectrums which result from the different kinds of localized plasmons excited.The study can be applied to the development of the miniaturization of high resolution imaging and spectral analysis techniques.All in all,we studied the coupling and detecting of the electromagnetic modes in dielectric and metallic nano optical antenna.We achieve dual double Fano resonances induced by electromagnetic modes coupling.Based on the cathodeluminance technology,we study the cathodeluminance(CL)electromagnetic modes of metallic optical antenna,resulting from the different kinds of localized plasmons excitation.These researches deepen our understanding of the different kinds of electromagnetic modes of metallic optical antenna and the laws of scattering properties.The antennas studied can be applied to develop high-performance solar cells,high sensitive biological sensing,high resolution imaging and spectral analysis technology,and etc.