Spin-orbit coupling mediated transverse spin mode rotation in a uniaxial crystal.

We demonstrate topological features in a spin-orbit coupled inhomogeneously polarized beam of light due to propagation of a linearly polarized focused Gaussian beam through a tilted-rotated (θ-ϕ) quartz crystal plate. The crystal plate is kept in a polarization interferometer, and transverse and longitudinal phase difference is introduced between the o- and e-wave-beams via (θ-ϕ) variation. The curvature in the phase difference, originating at a phase saddle, at the stem of an intensity forklet pattern, enables continuous rotation of the output two-lobe intensity pattern as a function of (θ-ϕ). The transverse spin-shift of the rotating output beam shows variation in both magnitude and slope. Such a study of exploring topological features arising due to spin-orbit coupling in simple optical systems is of fundamental interest and is expected to open up potential applications in the investigation of material anisotropy and polarization-sensitive sensing.

Wave dislocation line threaded polarization interferometer.

Constructing a closed-circuit polarization interferometer, wherein a wave dislocation line can be visualized to thread the parameter space, is a topic of fundamental and applied research interest. Proposed by Berry [Proc. R. Soc. A463, 1697 (2007)10.1098/rspa.2007.1842] in the scalar wave domain, this universal phenomenon is simulated and experimentally demonstrated in the vector domain using a rotated-tilted quartz crystal plate in a polarization interferometer. The phase difference between overlapping ordinary and extraordinary paraxial ray beams passing through the crystal plate is varied continuously. The appearance of ±1 dislocation number spiral- and saddle-type topological structures in the complex Stokes phase is a result of satisfying ± π/2 phase difference between the ray beams and around the zero-crossings of the Stokes parameters.