Optical properties of topological insulator Bragg gratings: Faraday rotation enhancement for TM polarized light at large incidence angles

Using the transfer matrix formalism, we study the transmission properties of a Bragg grating constructed from a layered axionic material. Such a material can be realized by a topological insulator subject to a time-symmetry breaking perturbation, such as an external magnetic field or surface magnetic impurities. Whilst the reflective properties of the structure are only negligibly changed by the presence of the axionic material, the grating induces a Faraday rotation and ellipticity in the transmitted light. We find that for TM polarized light incident on a 16 layer structure at 76 degrees to the normal the Faraday rotation can approach ~232 mrad (~13 degrees), whilst interference from the multi-layered structure ensures high transmission. This is significantly higher than Faraday rotations for the TM polarization at normal incidences or the TE polarization at any incident angle. Thus, Bragg gratings in this geometry show a strong optical signal of the magneto-electric and, hence, provide an ideal system in which to observe this effect by optical means.