Topological Photonic Crystal Fibres

The overall goal of this research project is to fabricate photonic crystal (PhC) fibres that allow for robust light
propagation due to topological protection. Topology, in the mathematical sense, is the study of quantities which are
conserved under smooth deformations and in physics these conserved quantities can be found in a wide range of
systems. This project would focus on using conserved photonic modes to guarantee that light guided by a topological
PhC fibre experiences no scattering loss. Reducing loss within the fibre enables better transmission of delicate
optical signals, including the transmission of single photons, which can be of particular importance in quantum
photonic circuitry.
The first stage of the project is to find a valid topologically protected state and investigate it theoretically. We hope
this process would ideally be completed within the first three to four months of the project. This step will involve first
reviewing current limitations of topological states in a range of geometries. These cutting-edge ideas will be used to
inform the design of our own novel geometries which will provide topologically protected modes that can be built into
an appropriate fibre design.
Once we have multiple novel systems, computational simulations can begin. These simulations will use COMSOL
Multiphysics (a finite element solver) to numerically verify the presence of protected topological states. It will do this
by computing the system's topological invariants and associated photonic modes. While this part of the project will
come after the theoretical design, some work to setup the geometries can begin as soon as each design looks
promising. 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 likely
here.
After a successful theoretical design has been derived and computationally verified, fabrication c an begin. This will
involve using the Centre for Photonics and Photonic Materials (CPPM) fibre fabrication room to design custom
preforms that replicate the predicted designs. These preforms will then be drawn into spools of fibre which can be
investigated in the optical labs. The performance of these fibres will be carefully analysed, with the intention of
confirming the presence of protected modes. We foresee potential challenges may occur in fabrication and a design
may have to be scrapped here if it appears too difficult to correctly fabricate. Even after fabrication there may be
challenges with the design not demonstrating the existence of topologically protected states or robust light
transmission. These will need to be carefully considered and any deficient designs will either need to be iterated
through or redesigned entirely