Fabry-Perot open resonator application for the investigations of a weak anisotropy in dielectric films

An experimental setup for studying of the degenerated angularly orthogonal modes in the Fabry-Perot resonator was created. Fabry-Perot open resonator is formed by axially symmetric mirrors with coupling elements in the form of holes. Connected to the resonator polarization diplexers with more than 40 dB isolation between channels of orthogonal polarization signals allow to detect the lifting of the degeneracy at weak violations of axial symmetry. It is shown that anisotropic thin dielectric film located in the plane of the caustic waist of the resonance mode, lifts the degeneracy of orthogonally polarized modes. The proposed method is promising for measurement of the weak permittivity anisotropy of thin films and sheets.