  Structured illumination allows for satisfying the first Kerker condition of
in-phase perpendicular electric and magnetic dipole moments in any isotropic
scatterer that supports electric and magnetic dipolar resonances. The induced
Huygens' dipole may be utilized for unidirectional coupling to waveguide modes
that propagate transverse to the excitation beam. We study two configurations
of a Huygens' dipole -- longitudinal electric and transverse magnetic dipole
moments or vice versa. We experimentally show that only the radially polarized
emission of the first and azimuthally polarized emission of the second
configuration are directional in the far-field. This polarization selectivity
implies that directional excitation of either TM or TE waveguide modes is
possible. Applying this concept to a single nanoantenna excited with structured
light, we are able to experimentally achieve scattering directivities of around
23 dB and 18 dB in TM and TE modes, respectively. This strong directivity paves
the way for tunable polarization-controlled nanoscale light routing and
applications in optical metrology, localization microscopy and on-chip optical
devices.
