Resistance of Helical Photonic Structure Band Gap to Partial Disordering

The influence of changes in the optical axis tilt angle on parameters of the selective reflection band in helicoidal photonic structures is considered. Helical symmetry of the permittivity tensor causes Bragg’s reflection at wavelengths close to the screw (helicoid) pitch for circular polarization of light. The study has discovered and explained the resistance of the shortwave boundary of the band gap to the optical axis tilt towards the helical axis (normal to the plane of layers) in helical photonic structures. For a conical helical structure, the longwave boundary of the reflection area changes more than for a structure with a normal cone opening with the optical axis perpendicular to the helical axis. The wavelength for the edge mode at the shortwave boundary is strictly preserved under arbitrary distortions. The results obtained by numerical simulation with the use of anisotropic transfer matrix and Berreman transfer matrix agree with each other and are confirmed by analytical derivation. The results are important when studying electromagnetic wave propagation in helical photonic structures, as well as in the Earth’s ionosphere.