Design And Study On Radiation Characteristics Of A THz Emitting Waveguide Periodically Loaded With Metallic Micro-structured Gratings

The terahertz (THz) frequency range that covers from0.1to10THz has becomea frontier for research in physics, chemistry, biology, materials science, and medicine.Recently, significant advances in THz science and technology have opened up a widerange of potential research opportunities. It’s possible to using the low cost fiber laserwhose center wavelength is1550nm to replace the expensive Ti-Sapphire laser as thedevelopment of technology. The subject is also part of the National Natural ScienceFoundation project "New hybrid waveguide device design and fabrication for THzemitters"(Grant No.:64072011).In this paper, on the basis of Air-GaAs-Si asymmetrical waveguide structure ofTHz generation by optical rectification, to reduce the number of extra processingsteps for fabrication, a compact metal grating coupler on the surface of GaAs isdesign to replace the etching grating on the surface of a THz emitting waveguidedevise.We study the matrix theory of an multilayer planar waveguide which may havemedia of complex refractive indices. By this method, applied to a THz emittingwaveguide periodically loaded with metallic micro-structured gratings, we simulatenumerically of propagation characteristics for asymmetrical waveguide with andwithout gold films in different frequencies and different golden thickness. Accordingto the theory of finite planar waveguide using perfectly matched layers (PMLs), underthe boundary condition of PMLs, the complete modal spectrum of asymmetricalwaveguide with and without metallic films is analyzed and derived. Then making useof eigenmode expansion and THz coupling output theory, we get the derivation ofscattering matrix, which consist of reflection and transmission matrices on theinterface of basic unit in THz emitting waveguide periodically loaded with metallicmicro-structured gratings. Furthermore, reflectivity, transmittivity and emissivity ofthe THz emitting periodical discontinuous waveguide are obtained with the method ofperiodicity.