The Theory Of Impedance-Tunable Transformation Optics And Its Application

Transformation optics based on form invariant coordinate transformations of Maxwell’s equation emerges as an active new field of controlling electromagnetic fields and gives people a unique approach for design of various optical elements. Especially the finite-embedded coordinate transformation accelerates the transformation-optical design and provides more flexibility to the controlling and guiding electromagnetic waves.In chapter 1,the research progress of transformation optics is introduced. Some transformation-optical design by finite-embedded coordinate transformation are demonstrated and the limitations resulted from reflections are analyzed.In chapter 2, we present a new strategy to manipulate impedance match by proposing impedance-tunable transformation optics in the geometric optics limit, on which the impedance coefficients are reset in the original space without changing the refractive index. The theory is applied to the some continuous transformation-optical designs.In chapter 3, using the impedance-tunable transformation optics, a reflectionless 2D impedance-tunable beam compressor has been designed without combining conventional method of inserting an antireflective coating. A reflectionless 2D compact beam bend has been designed, where the direction and magnitude of the guiding waves can be tuned. We generalize the bend design method to the reflectionless design of 2D beam shifters and splitters. Based on the impedance-tunable transformation optics, conversion from cylindrical waves to plane waves structure was proposed, and soon can be used as a high-directivity antenna.In chapter 4, we generalize the impedance-tunable transformation optics to the design of waveguide devices that the refractive index in the original space also can be tunable. By tuning the impedance coefficients and the refractive index simultaneously, reduced-parameter transformation medium can be obtained for the design of high-efficiency metallic waveguide couplers. Two different schemes have been applied to the design of dielectric waveguide couplers, both of which can reach a very high efficiency. Through setting large refractive index coefficients of the transformation medium, the lower performance of the coupler due to the geometric optics limit can be improved, and reduced-parameter materials of a dielectric waveguide also can be obtained.In chapter 5, we apply the impedance-tunable transformation optics to the design of 3D optical elements, where the coordinate stretching rates in electric and magnetic direction are not consistent at the boundary. Using the designed structure by tunning the impedance coefficients, a coaxial waveguide coupler connected with arbitrary outer and inner radius has been designed with high efficiency. An approach to design coaxial waveguide bends was presented using isotropic media.In chapter 6, main results are summarized.