Research On Manipulating The Electromagnetic Wave Phase By Transformation Medium Plates

Metamaterials is a kind of artificially microstructured materials with exoticmaterial properties that are not found in the nature. The electromagnetic properties ofmetamaterials can be tuned at will and they have brought unprecedented applications,such as invisibility cloaks and superlens with a resolution beyond the diffraction limit.Metamaterials has been a hotspot in recent ten years, and, especially under thecoordinate transformation theory guidelines numerous novel photonic devices havebeen proposed and realized. Metamaterials designed on the basis of transformationoptics, also called transformation media, can be used to flexibly control and guide theelectromagnetic wave transmission.Recently, wave shape transformers and beam deflector have been proposedbased on the coordinate transformation theory. However, the device functionsdepend on the deformation and deflection of exit boundary in this group devices.In this paper, based on transformation optics, reverse transformation method isproposed to design transformation media to manipulate electromagnetic fieldsphase.This method can be extended to realize arbitrary wave transformation.Elements independent of shape of devices, which is useful to realize plug andplay optical devices. The specific work we carry out is as follows:1. We study to use transformation media to achieve the planar wave deflection. Areverse transform method, which develops form direct transform method can achievethe same effect. We establish the coordinate transformation and obtain thepermittivity and permeability tensors of the metamterials. Full wave simulaiton isgiven to validate the proposed transformation media. The power flow direction is notnormal to the wave front within the slab devices, but after propagation through thetransformation medium slab, the wave vector and the power flow possess the samedirection and both of them deviates from its initial incident direction in clockwise orcounter-clockwise direction. Based on transformation medium slab manipulating thedirection of exit wave, slab beam splitter and shifter are proposed. The designeddevices are validated by full wave simulations using the finite element method. Ourresult may be valuable in the design of high-directivity antennas and beam splitter.2. Using transformation medium cylinder to modulate beam phase. Based on thecoordinate transformation theory, the transformation medium cylinder has been proposed to convert planar wavefront to a helical one. Taking Gaussian beam forexample, it is transformed to LG beam. Full wave simulaiton are given to validate theproposed transformation medium cylinder based on finite element method. Such acylinder can be theoretically reflectionless, so the conversion efficiency can be higher.Adaptive behavior of reconfigurable metamaterials enables convenient generation ofarbitrary OAMs of photons. Our result provides a new approach to generate orbitalangular momentum and may be valuable in utilizing the Hall effect of light.3. We study to use transformation media to realize wave shape conversion. Wepropose to use slab transformation media to convert planar wave shapes to convex orconcave ones. By finite embedded coordinate transformations, a transformation isestablished from a parabola to a plane and the constitutive parameters of slabs areobtained. Using such transformers, Gaussian beam collimation and focusing can berealized. Numerical simulations are given to validate the performance of thetheoretical design.