Mumerical Simulation Of Vortex Beam Propagation Characteristics Based On FDTD

Limited channel capacity and data transfer rate restrict users reasonable work gradually,traditional methods of channel multiplexing have been overwhelmed.While orbital angular momentum(OAM)describes the orbital part of the electromagnetic wave carrying momentum and the wavefront of the beam shows the spiral characteristics,as well as its high dimensional and orthogonality features,which makes it have the great potential applications in microwave region.It could extend the channel capacity to infinite theoretically,which makes the near-field communication to develop in the orientation of utilizing OAM carrying multiple modes of electromagnetic wave.This research focuses on the properties of the electromagnetic wave carrying OAM modes and its interaction with particles.Based on the scattering problems,the finite-difference time-domain(FDTD)method is adopted to study.(1)In order to overcome the particle scattering problems in the low efficiency of the frequency domain as the leading research methods and intuitively dynamically observe the scattering characteristics of target,the theory of FDTD is employed,including the numerical stability,the setting of the excitation source,setting of absorbed boundry condition(ABC),near to far field transf ormation,the far field calculation of radar scattering cross-section(RCS)and the establishment of target,which respectively utilizing scattering field method and total \scattering field method ot establish the simulation space.Besides,compared with th e analytical solution,the far field RCS of the scattering of the simple isotropic sphere,lossy isotropic sphere and dispersive sphere with planewave verifies the correctness of the simulation space set up.(2)For the synthesis of electromagnetic wave carrying OAM,based on the scattering field method,the algorithm could synthesize target frequency 10 GHz and any target modes OAM beam via make the Laguerre Gaussian mode information integrate in the time domain pulse.According to the research,the influ ence of different modes and waists with beam divergence and compare with the theoretical value,the influence of different focal length of the convergence degree of the beam,the topology transformation from fractional to integral OAM beam,calculation of the mode pure based on FDTD and the method of enhancing the target OAM mode pure are completed.For the total/scattering field method,the phase of incident field at the boundary is modified to generate electromagetic wave carrying OAM at the target frequency and mode.(3)In order to study scattering characteristics of particle to OAM beam,including the far field RCS law of isotropic medium sphere and metal sphere to different modes of OAM beam and the far field RCS law of isotropic medium brick of different sizes to single mode OAM beam are studied based on the scattering field method.And the far field RCS law of dispersive medium spheres of different sizes to single mode OAM beam scattering is studied.