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. While 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 transverse magnetic (TM)-polarized light incident on a 16-layer structure at 76 degrees to the normal the Faraday rotation can approach similar to 232 mrad (similar to 13 degrees), while interference from the multilayered structure ensures high transmission. This is significantly higher than Faraday rotations for the TM polarization at normal incidences or the transverse electric (TE) polarization at any incident angle. Thus, Bragg gratings in this geometry show a strong optical signal of the magnetoelectric effect and, hence, provide an ideal system in which to observe this effect by optical means.