Abstract

In a biaxial birefringent crystal there are two directions at which the refractive index surfaces intersect, leading to the phenomenon of conical refraction [1]. These conical intersections are analogs of Dirac points, and are generically present in non-chiral optical materials. One of the most interesting aspects of Dirac points is that they carry an associated topological charge. As such the propagation of light through a periodic biaxial crystal is related to a periodic electronic system supporting multiple Dirac points in the first Brillouin zone. Since Dirac points carry topological charge it is natural to ask whether we could gap this system in such a way as to leave a topologically interesting result. We show that this is indeed possible, and that opening a gap using the Faraday effect can lead to a form of optical topological insulator. This is a novel realisation of a photonic topological insulator, as it dos not rely on the use of a specific lattice [2] to produce multiple Dirac points, but instead exploits the ubiquitous polarization degeneracies of optical materials.

© 2017 IEEE