  Directional coupling of light in nanophotonic circuits has recently attracted
increasing interest, with numerous experimental realizations based on broken
rotational or mirror symmetries of the light-matter system. The most prominent
underlying effect is the spin-orbit interaction of light in subwavelength
structures. Unfortunately, coupling of light to such structures is, in general,
very inefficient. In this work, we experimentally demonstrate an order of
magnitude enhancement of the directional coupling between two nanowaveguides by
means of a whispering gallery microcavity. We also show that both
transversmagnetic and transverse electric modes can be used for the
enhancement.
