Magneto-optics of dichroic chiral photonic crystals: resonant diffraction transmission and higher-order reflections at grazing angles
Magneto-optical effects in structured anisotropic media have attracted significant attention due to their potential in tunable photonic devices. In particular, dichroic cholesteric liquid crystals (i.e., cholesterics in which the real parts of the local dielectric permeability tensor are equal each other, and the imaginary parts differ) provide a unique system in which absorption anisotropy rather than anisotropy of real pars of the local dielectric permeability controls the optical response. In this work, we investigated the magneto-optical properties of dichroic cholesteric liquid crystals under oblique light incidence. To analyze the optical characteristics, we used the Berreman method, which is a matrix approach to solving Maxwell's equations. The unique properties of such structures were revealed, namely, resonant Bragg diffraction transmission instead of diffraction reflection and higher orders of diffraction reflection under oblique light incidence at grazing angles. It was shown that at light oblique incidence in the presence of an external magnetic field, new Dirac points appear in the spectra of such structures at each order of diffraction reflection. Furthermore, it is shown that an external magnetic field suppresses the shift of the polarization of eigenmodes from circular to linear polarization as the angle of incidence increases. This system can be used as a narrowband filter with a widely tunable wavelength.