Research Of Plasmonic Analogue Of Electromagnetically-induced Transparency And Related Devices

Electromagnetically-induced transparency(ETI)is a phenomenon that utilizes a coupling beam which degrades the absorption intensity of a multi-energy level atom system,realizing high transmission within absorption peak,i.e.,rendering the system"transparent" to the incident pump light.The applications of this phenomenon are of great importance such as lasing without inversion,slow light and so on.Thanks to the development of Plasmonics and Metamaterials,this phenomenon whose experimental realization conditions are extremely strict in quantum optics can be transferred to construct optical analogues in tradition optics regime.Nevertheless,the analogues are mostly in sub-wavelength scale which may solve problems ranging from optical switch,light speed control,light storage,nonlinear optics and index sensing in microstructures,which makes them available functional structure unit cell for future nanophotonic chip designs.Based on the background and significance,this paper concludes the evolution process and the construction methods of EIT analogues,discriminates and quantitatively explains the principle of micro/nano EIT analogues as well.Because of the restrictions of our experimental conditions,this paper mainly utilizes analytical analysis and numerical simulation experiment methods to do researches,including electromagnetic theory of Plasmonics,temporal couple mode theory,transfer matrix function,finite difference time domain and finite element method,etc.Main creative achievements of this paper are listed from several aspects below.In single side coupled double resonant rings system,by setting different locations of the rings to build bright/dark modes and using the destructive interference among bright mode excitation pathways,bright mode excitation is cancelled while dark mode being excited.In this way,the initial single resonant ring strong absorption is weakened to a great extent resulting in the structure to be "transparent" to this critical wavelength and the adjacent ones.Assisting by the couple mode theory and transfer matrix function and combining numerical simulations,one explains the influence of geometry elements to the transmission level and the bandwidth of the transparency window.Meanwhile,the light speed in the transparency window is slowed down proved by some calculations.By utilizing the Akaike information criterion(AIC)method,the formation of transparency in this system is proposed to be quantitatively explained,eliminating the misunderstanding of judging the formation only by checking the phenomenon.In the design of double graphene coated grating structure EIT analogues,the grating height related dispersion equations are deduced,pointing out that the resonant wavelength has quantitative relationship with grating height and can be proved by simulations.The model uses double resonance scheme,"building up" a transparency window within two absorption peaks,realizing slow light as well.The working wavelength region can be dynamically controlled based on the excellent tunabiliy of graphene.In similar ways,in this structure,the AIC method is used to discern the formation.If the grating is gradiently designed in lateral period,the so called "rainbow trapping" distributed light storage can be realized.In double sides coupled resonant ring research,by using double resonances scheme,one builds transparency window and discusses the mode issues of different transparency windows,and the higher order modes with high sensitivity are thus proved as well.In double graphene nanoribbons coated grating structure research,one realizes broad bandwidth and high transmission.One can also realize "rainbow trapping" applications similarly.In addition,other than the three traditional methods,this paper also provides U-shaped tunnel assisted method,symmetric inside-outside oscillators method and hybrid construction method.In U-shaped tunnel assisted method,by artificially creating interference pathways through tunnel,the transmission is enhanced,opening the light pathway through initial absorption peaks.In symmetric inside-outside oscillators,with no need to break the symmetry,the transparency can be realized just by utilizing the inside oscillator analogue of dark mode interference with the bright one.And in the hybrid construction,using symmetry breaking,bright-dark mode and double resonance methods together,a transparency window is created.The three minority designs are all involved with slow light and sensing explorations.Except for EIT analogues,this paper also contains plasmonic nanofocusing using local control of graphene Fermi energy,and the focal point radius is no more than 2nm,the field intensity is exponentially enhanced.Proposing that by using edge and propagating plasmon modes to form resonance to enhance the absorption,the tungsten covered ridges absorber is constructed.After optimization,the highest absorption reaches 99.9%.By the modulation of epsilon-near-zero(ENZ)mode,the bandwidth of single band absorber can be efficiently widened.Proposing that by ENZ material cooperating with certain boundary conditions,cloaking and super-reflection can be realized,the structure can guide light through totally or otherwise,totally blocked.This idea has potential applications in electromagnetic cloaks.Finally,proposing a band stop plasmonic metal filter in visible regime,by cascading cavities,ultra-broad bandwidth and ultra-low transmission are in principle realized.Overall,this paper mainly centers on the design of plasmonic analogue of EIT devices,the design and exploration of some other kinds of micro/nano optical devices are also involved,which are state of the art and application potential topics in nanophotonics.Incorporating more mature but still expecting future development micro/nano fabrication techniques,one has reasons to believe the ideas and designs in this paper are helpful to the development of micro/nano photonics in the future and make their uses in industries and life to raise productivity.