Topological Photonic Crystal Fibres

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The overall goal of this research project is to fabricate photonic crystal (PhC) fibres that allow for robust lightpropagation due to topological protection. Topology, in the mathematical sense, is the study of quantities which areconserved under smooth deformations and in physics these conserved quantities can be found in a wide range ofsystems. This project would focus on using conserved photonic modes to guarantee that light guided by a topologicalPhC fibre experiences no scattering loss. Reducing loss within the fibre enables better transmission of delicateoptical signals, including the transmission of single photons, which can be of particular importance in quantumphotonic circuitry.The first stage of the project is to find a valid topologically protected state and investigate it theoretically. We hopethis process would ideally be completed within the first three to four months of the project. This step will involve firstreviewing current limitations of topological states in a range of geometries. These cutting-edge ideas will be used toinform the design of our own novel geometries which will provide topologically protected modes that can be built intoan appropriate fibre design.Once we have multiple novel systems, computational simulations can begin. These simulations will use COMSOLMultiphysics (a finite element solver) to numerically verify the presence of protected topological states. It will do thisby computing the system's topological invariants and associated photonic modes. While this part of the project willcome after the theoretical design, some work to setup the geometries can begin as soon as each design lookspromising. Over three/four months I believe the designed geometries can be simulated and computationally tested.This timeline is very dependent on the success of each design, with delays and unforeseen problems highly likelyhere.After a successful theoretical design has been derived and computationally verified, fabrication c an begin. This willinvolve using the Centre for Photonics and Photonic Materials (CPPM) fibre fabrication room to design custompreforms that replicate the predicted designs. These preforms will then be drawn into spools of fibre which can beinvestigated in the optical labs. The performance of these fibres will be carefully analysed, with the intention ofconfirming the presence of protected modes. We foresee potential challenges may occur in fabrication and a designmay have to be scrapped here if it appears too difficult to correctly fabricate. Even after fabrication there may bechallenges with the design not demonstrating the existence of topologically protected states or robust lighttransmission. These will need to be carefully considered and any deficient designs will either need to be iteratedthrough or redesigned entirely