Figure 2. Elliptical polarization state of light in a cone-shaped microtube cavity.

(a) In a rolled-up asymmetric microtube being pumped by a laser beam (532 nm), the linearly polarized light evolves into elliptically polarized one with the major axis tilted out of (with an angle ϕ) the tube axis. (b) Resonant mode intensity maps of a linear polarization (Lp) state measured from a symmetric tube where spin–orbit interaction is absent and an elliptical polarization (Ep) state measured in the presence of spin–orbit coupling of light in an asymmetric tube. In the corresponding polar diagrams shown in (c) the linear polarization (dashed line) is oriented parallel to tube axis while the elliptical polarization exhibits a tilt angle ϕ with respect to the tube axis.