A circularly polarized bounding ball is travelling in the +z direction.  A small slit occupies the x=0 plane begins where the blue tube wall becomes dotted.  As the wave travels along the slit, the probability of being inside the tube approaches 50% and corresponds to polarization with motion in the y direction.  The components for motion in the x direction radiate out as shown by the dotted thin lines representing wave crests.
Own work
Guy vandegrift