Optical Nonlincarity And Time-evolution Of Plasmonic System

In this thesis,we focus our work on the optical nonlinearity and time-evolution of plasmonic materials(such as noble metal plasmonic particles and graphene plasmonic particles).By employing the dispersion relation method,we establish the nonlinear dynamical equations for the electric polarizations to study the optical bistability,temporal evolution and modulational instability.In addition,we achieve the optical ultra-fast switching,communication security and so on.The main results are as follows.1.Enhancement of optical nonlinearity by core-shell bimetallic plasmonic nanostructuresWe propose an alternative way to enhance optical nonlinearity from nanocomposites containing nonlinear bimetallic plasmonic nanostructures.The optical nonlinearity enhancement is due to two aspects:firstly,the intrinsic large nonlinearity of metallic material in core and shell;secondly,the coupling of dipole modes gives rise to symmetric and antisymmetric resonance,which strengthen the local fields in the core and shell.By fine adjustment of the core-shell size ratio,it is possible to achieve maximal enhancement of optical nonlinearity from bimetallic coated nanocomposites.2.Optical bistability and indefinitely switching of nonlinear graphene plasmonicsA new dispersion relation method is applied to derive a dynaruical equation for slowly varying amplitude of the dipole moment of the particle,and the optical bistability of the particle polarization is reseached.In addition,we realize the ultrafast switching between two states of bistability and the transition state of nonlinear particle exhibits an indefinite relationship with the applied external field parameters.As a consequence,we propose a new concept of indefinite switching.3.Low-threshold optical bistability and nanoradar induced by nonlinear graphene-wrapped nanodimerThe optical bistability and dynamics are investigated in nonlinear graphene-wrapped dielectric particle nanodimers.It is found that the bistable threshold can be effectively reduced in dimer structure.Moreover,we introduce the concept of nanoradar based on the operation of the nonlinear plasmonic nanodimer.The nanoradar action originates from the modulational instability,which causes a dynamical energy exchange between the nanodimer eigenmodes resulting in periodic scanning of the nanoantenna scattering pattern.Such a nanoradar demonstrates low operation threshold,ultrafast time response,and short self-ocillation period,being potentially useful for many applications in nanophotonics circuitry.4.Asymmetric states,Periodic circles and chaos in nonlinear graphene-wrapped nanodimerA novel nanoantenna of a nonlinear graphene-wrapped nanodimer is proposed in this thesis.The nonlinear coupled equations for the slowly varying amplitudes of the particle dipole moments driven by a plane wave at an arbitrary angle are derived.We also drive the expressions for the longitudinal and transversal instability growth rates by utilizing conventional linearization approach to analyze the stability of the uniform steady state solution with respect to small perturbations.In addition,we show and prove that the longitudinal instability will lead to the formation of asymmetric states,periodic circle states and chaotic states,while transversal instability doesn't.Our research may pave a way towards further experimental studies of nonlinear plasmonic nanostructures,and may have potential applications for active ultrathin and ultrafast optical devices,such as all-optical switcher and random number generator.5.Ultrafast cryptography with indefinitely switchable optical nanoantennaswe show that a bistable optical heterodimer features indefinite switching,i.e.,in response to a sufficiently strong signal pulse,the system can eventually transit to a counterpart steady state or remain in the initial position,depending on the pulse parameters.The essential nonlinearity of this operation makes indefinite-switching-enabled stream ciphering immune to algebraic attacks.In contrast to comnonly used cryptographic algorithms requiring thousands of logic gates,indefinite-switching-assisted cryptographic protocols can be realized with a single bistable element,benefiting from compactness and performance.Moreover,we demonstrate this principle by decrypting the word“enigma”with the remarkably high bit rate of 0.13 per one-terabits processing.Such high bit rate and small size make the systems promising as basic elements for all-optical cryptographic architectures.