Metallic microresonator spectral modes with inhomogeneously twisted nematic in magnetic field

A common, but not the only method for the spectral resonance shift in a microresonator is to change the cavity's optical path. A fundamentally different approach to separate polarized modes at the fixed optical path consists in inhomogeneous twisting of a medium within the cavity, which allows for the creation of high-sensitivity devices such as sensors, filters, microlasers, modulators, phase shifters, etc. An experimental and theoretical study of the polarization and spectral properties of a Fabry-Pérot microresonator formed by a pair of flat metallic mirrors with a planar-oriented nematic liquid crystal layer between them has been carried out. The specific chirality of the liquid crystal structure is induced by a magnetic field in the T-effect regime and is characterized by inhomogeneous twisting and the presence of a plane at the center of the nematic layer where the local director reverses the twist sign. Despite the small resulting deformation, these factors enhance the nonadiabatic propagation of light waves in the resonator, which, in turn, leads to significant anomalous shifts of the polarized resonant modes in the transmittance spectrum. The obtained experimental spectral shifts of the modes are consistent with the data of the numerical simulation using the 4 $\times$ 4 transfer matrix method and are explained by the contribution of the geometric phase, which paves the way to novel topological photonics devices.