The Investigations Of Abnormal Scattering Characteristics And Design Of Related Devices With Abrupt Phase Gratings

As a kind of optical element,optical grating is widely used to control the propagation of electromagnetic waves,which greatly promotes the development of science,including physics,astronomy and so on.Recently,the gradient grating and metasurfaces with abrupt phase has become a hot topic in electromagnetics due to its abnormal diffraction characteristics.In this thesis,we focus on the diffraction characteristics of these gratings,and design some grating devices with special functionalities.Firstly,the mode conversion is realized by constructing air grooves in the ZIM waveguides.We have analytically and numerically demonstrated the perfect mode conversion for straight waveguides.Furthermore,we also obtain the mode conversion in bending waveguide structures and even multi-port waveguide systems.In addition,the proposed mode converter can function as an optical diode,which can effectively realize unidirectional transmission.Secondly,we have demonstrated that metallic grating structure with gradient index materials(GIMs)can be used to realize omnidirectional reflection,regardless of the polarizations of the incident waves.By bending the straight metallic grating structure into a metal grating ring,we design a metacage that can effectively shield electromagnetic waves,regardless of the polarizations of the incident waves and the impedance properties of the filled materials.Finally,we design a special grating to achieve the abnormal transmission.Different from most of the research methods of grating structures,we study the structure of the grating from the Huygens principle,and calculate the efficiency of each diffraction order accurately.