Polarization-controlled orbital angular momentum of light passing through a cholesteric spherulite.

By using a polarization-resolved common-path diffraction phase microscope coupled with a spin-to-orbit converter, we experimentally study two-dimensional in-plane distributions of amplitude and phase of light transmitted through a spherulite formed in a frustrated cholesteric liquid crystal cell. These distributions measured at different orientations of the output linear polarizer (analyzer) are used to obtain the orbital angular momentum (OAM) spectra characterizing the OAM content of the beam. The experimental data are found to be in good agreement with the theoretical results describing both the distributions and the OAM spectra based on an analytically designed model of toron-like localized liquid crystal structures. We show that the OAM spectrum can be controlled by changing the analyzer azimuth angle so that the dominant mode evolves between the limiting cases of the vortex mode with l=-2 and the vortex-free mode with l=0.