Design and applications of optical transformation devices
This thesis provides an insight into the designing, physical realization and characterization of optical transformation devices. It begins with an introduction to the discrete coordinate transformation with a design example of a carpet cloak. The realization and characterization of materials, namely a dielectric disk matrix and polyurethane/BaTiO3 foam composite, for constructing transformation optics devices are studied both numerically and experimentally. Two different kinds of low loss and broadband all-dielectric realisations of OT devices are designed and experimentally demonstrated. First, the cloaking structure made of a high-ǫ dielectric-loaded foam mixture is reported. A polyurethane foam, mixed with different ratios of barium titanate is used to produce the required range of permittivities, and the invisibility cloak is demonstrated to work for all incident angles, over a wide range of microwave frequencies. Then, based on a study on the properties of periodic dielectric particles, the cloak, realized with periodic dielectric cylinders, is proposed. The required dielectric map for the cloak is achieved by means of manipulating the dimensions, or spatial density, of the periodically distributed dielectric cylinders embedded in the host medium, whose permittivity is close to one. The scattering reduction effects are verified through both simulation and experimental results. The performances of the two different kinds of cloak are also compared quantitatively. Last, but not least, an extraordinary-transmission (ET) device made from commercially available ceramics and Teflon is designed, which exhibits broadband transmission through a sub-wavelength aperture. It is verified both numerically and experimentally that the device can provide transmission with a -3 dB bandwidth of more than 1 GHz, in a region which would otherwise be a stop band caused by the sub-wavelength aperture in an X-band waveguide.
- Theses