FDTD Method Applied To Several Half-space Problems And Periodic Problems

There are many half-space problems and periodic problems, which have been fastdeveloped and widely applied in optics and electromagnetics. In this dissertation, severalhalf-space and periodic problems are studied by using the Finite-DifferenceTime-Domain (FDTD) method.The laser scattering by a microstructure defect in optical material are analyzed byusing the FDTD method as a half-space problem, where the plane wave is incident at anarbitrary angle. The driving waves are composed of the incident wave, reflected wave andtransmitted wave.The transmission through slits on single and stacked metallic plates of finitethickness with a plane wave incident at an arbitrary angle are analyzed by using thefinite-difference time-domain (FDTD) method with two driving waves, i.e. the incidentwave and reflected wave. We calculate field distribution near the slits, magnetic surfacecurrents on the aperture of the slit and then obtain the transmission cross sections of slits.The computed results demonstrate the efficiency of this method. This algorithm is alsoavailable for analyzing the scattering and transmission by slits with different shape,location, including dielectric media filled in multiple metallic plates illuminated by aplane wave at an arbitrary angle of incidence.A new finite-difference time-domain (FDTD) algorithm for efficient fieldcomputation in resonator narrow-band structure (such as periodic structure) is applied toget the complex electric field of one-dimensional periodic structure. In order to performthe near-to-far-field extrapolation for this structure, an approach by using the periodicGreen's function and the Floquet-mode method are discussed. Only near fields in a singlecell of the periodic structure are used to calculate far fields in these two methods.FDTD method incorporated with periodic boundary condition is applied to solve thenear fields for dielectric gratings with plane wave illumination. Then the diffractioncharacteristics of transmission gratings are analyzed. The required computational resourcesare small since the size of domain to be solved is restricted to a single cell of the dielectricperiodic structure. Owing to the presence of a surface of dielectric, it is required to imposethree waves, including incident plane wave, reflected and transmitted waves at thetotal-scattered field boundary. The presented scheme is useful to study the diffractionproblem of dielectric gratings with arbitrary shape and complicated configuration.Two-dimensional periodic structure with electromagnetic wave incidenceperpendicularly is studied by FDTD method in virtue of the Floquet theorem and UPMLabsorbing boundary. The EMP shielding effectiveness to wire-mesh reinforcement andreinforced-concrete layer with periodic structures is analyzed by that method. The resultsare obtained by Hybrid STF-FDTD approach that allows us to compute the shieldingeffectiveness of some typical size of the reinforcement meshes with extremelyslow-decaying pulse incidence. Some valuable conclusions are reached, which can beapplied for engineering.We describe a photonic crystal (PC) structure made up of a dielectric bottomcovered by a photonic crystal slab. Combining the UPML absorbing boundary, therelative extraction effects of PC slab refractive index, PC slab thickness, PC air-holeradius PC air-hole depth on light extraction efficiency of that structure are investigated byusing a conformal finite-difference time-domain method for modeling curved dielectricsurfaces. The results are obtained by a discrete Fourier transform which allows us tocompute the efficiency at different frequencies in a single simulation run. Large lightextraction from a dielectric bottom can be achieved as the bottom covered with PC. Suchstructure might provide a solution to the low light extraction efficiency of (organic)light-emitting diodes.