The Imaging Properties And Beam Control Of Graphene Sheet Discrete Waveguide Arrays

Metamaterials are artificial subwavelength-structured media that exhibit unusual optical properties. They have become important for engineering electromagnetic space and controlling the propagation of light and waves. Optical waves propagating in such an environment exhibit many dramatic effects that don’t exist in natural materials. The concept of hyperbolic metamaterials may generate a family of metadevices that will permit the functionalities of a wide range of photonic systems.In order to break through the diffraction limit, the plasmonic metamaterials were proposed. The surface plasmon polaritons (SPPs) supported by graphene undergo stronger field confinement and lower propagation loss when compared with those on metals. More interestingly, the surface conductivity of graphene may be flexibly tuned by chemical doping or an external static electric and magnetic field. These features make graphene a promising material in developing tunable plasmonic devices working at deep subwavelength scale.In this thesis, we shall discuss the imaging properties and beam control of monolayer graphene sheet discrete waveguide arrays. The main contents and innovations of our works are:Firstly, we theoretically analyze the propagation of SPPs supported by graphene in monolayer graphene arrays. The results are verified by using the FDFD method.Secondly, we have investigated the Talbot effect in MGSAs under the condition of weak coupling. The Talbot distance decreases exponentially as the period of the MGSA decreases and could be a very small percentage of the incident wavelength (λ/20). Our fully-vectorial simulations agree well with the analytic results based on coupled mode theory. We also showed that the Talbot distance can be tuned by varying the chemical potential of graphene and employing different embedding materials. The study extends the Talbot effect realization in a new platform and may find applications in developing graphene-based imaging devices at deep-subwavelength scale.Thirdly, the spatial plasmonic Bloch oscillations (PBOs) in MGSAs under the condition of weak coupling are identified by performing FDFD simulations and theoretical analyses. The Wannier-Stark ladders can be generated in two different MGSAs systems constructed by spatially modulating the chemical potential of the individual graphene sheets or the width of dielectric layer. The SPP beams in the periodic MGSAs manifesting themselves as periodic transverse motion under the conditions of multiple waveguides excitation are observed by FDFD simulations. Furthermore, the period of BOs increases as the variation gradient of the chemical potential of the MGSA decreases or as the incident wavelength increases. Our fully-vectorial simulations are consistent with the analytic results based on coupled mode theory. Contrasts with the characteristic BOs observed in fully periodic MGSAs, the evolution in aperiodic MGSAs undergoes fragmented oscillation. The study of PBOs may provide interesting potential applications in graphene-based routing and switching devices at deep-subwavelength scale.Fourthly, we theoretically investigate the plasmonic Zitterbewegung effect in binary graphene sheet arrays. The SPPs modes of two minibands in the arrays are realized by alternately varying the chemical potentials of individual graphene sheets. Numerical simulations show that SPPs experience characteristic trembling motion in the designed MGSAs under conditions of broad beam excitation with certain incident angle. The oscillating periods of the plasmonic ZB are strongly dependent on the propagation constant mismatch and varied in the range of micrometer while the amplitude reaches tens of nanometers, making the ZB effect easier to be observed in practice.Lastly, we studied the nonlinear absorption (NLA) and optical limiting characteristics of a range of monolayer graphene suspensions at the wavelength of800nm by using Z-scan method with50fs femtosecond pulses. Large reverse saturable absorptions were observed and believed to arise from two-photon absorption (TPA). This NLA characteristic leds to a sharp trend of efficient transmittance reduction at the input laser energy density above0.3J/cm2. In addition, we compared the NLA properties of graphene suspensions at different concentrations. The concentration dependence of TPA coefficients is discussed in detail. The reduction of the solvent leads to an enhancement of TPA coefficient and optical limiting response at a low concentration. At higher concentration above10mg/L, aggregation effect might play a role in reducing TPA coefficient leading to the decrease of the TPA cross section.