  We investigate the spin-orbit coupling of light in three-dimensional
cylindrical and tube-like whispering gallery mode resonators. We show that its
origin is the transverse confinement of light in the resonator walls, even in
the absence of inhomogeneities or anisotropies. The spin-orbit interaction
results in elliptical far-field polarization (spin) states and causes spatial
separation of polarization handedness in the far field. The ellipticity and
spatial separation are enhanced for whispering gallery modes with higher
excitation numbers along the resonator height. We analyze the asymmetry of the
ellipticity and the tilt of the polarization orientation in the far field of
cone-like microcavities. Furthermore, we find a direct relationship between the
tilt of the polarization orientation in the far field and the local inclination
of the resonator wall. Our findings are based on FDTD-simulations and are
supported by three-dimensional diffraction theory.
