Photonic Topological Insulators and their applications as Waveguides and Antennas
Photonic topological insulators (PTIs) represent an area of emerging research into a new class of materials and devices with exciting electromagnetic properties. These materials are capable of supporting directional conducting modes along their surface or edge at frequencies that lie in the material bandgap. The presence of the bandgap ensures that the bulk of the material behaves as an insulator, which allows for a very high degree of energy confinement at the surface. This work briefly details a few variations on PTIs and then proceeds to focus on the creation of interface modes for 3D dielectric structures using only a 1D integration technique to obtain the geometric phase that is required for a material to be classified as topological. This 1D Zak phase allows for a simpler method to create topological waveguides with propagation path bends in fixed directions, along with a directional dependence based on the rotational nature of the fields. A shift towards more traditional forms of PTIs in the latter half of the thesis focuses on the application aspects of topological insulators. The use of metallic spin PTI metasurfaces as antennas been demonstrated with device operation broken down into (1) confined and (2) leaky wave propagation. While the confined mode is best known for its use as energy guiding structures, abrupt truncations can allow for radiation at the aperture with a `self-matched' property, allowing for immunity to the reflection caused due to the aperture impedance mismatch. Operation of the same PTI structure above the light cone in its leaky region enables the use of the PTI metasurface as a leaky wave antenna having an azimuth phase variation, with energy wrapped around in a closed loop propagation path. These waves possess an inherent orbital angular momentum (OAM), and control of the OAM beam charge can be achieved by the manipulating the physical and electrical path lengths. This control is invaluable to switching and multiplexing of different beam orders, which has a pivotal role to play in affecting the channel capacity and increasing data transmission rates for communication systems, among other important applications.