  Topological insulators subject to a time-symmetry-breaking perturbation are
predicted to display a magneto-electric effect that causes the electric and
magnetic induction fields to mix at the material's surface. This effect induces
polarization rotations of between ~1-10 mrad per interface in incident
plane-polarized light normal to a multilayered structure. Here we show,
theoretically and numerically, that, using a waveguide geometry with a
topological insulator guide layer and dielectric cladding, it is possible to
achieve rotations of between ~100-1000 mrad and generate an elliptical
polarization with only a three-layered structure. Both the rotation angle and
ellipticity are dependent on the permittivity contrast of the guide and
cladding layers and the strength of the time-symmetry-breaking perturbation.
This geometry is beneficial, not only as a way to enhance the magneto-electric
effect, rendering it easier to observe, but also as a method for controlling
the polarization of light in the next generation of photonic devices.
