  The electromagnetic field scattered by nano-objects contains a broad range of
wave vectors and can be efficiently coupled to waveguided modes. The dominant
contribution to scattering from subwavelength dielectric and plasmonic
nanoparticles is determined by electric and magnetic dipolar responses. Here,
we experimentally demonstrate spectral and phase selective excitation of Janus
dipoles, sources with electric and magnetic dipoles oscillating out of phase,
in order to control near-field interference and directional coupling to
waveguides. We show that by controlling the polarisation state of the dipolar
excitations and the excitation wavelength to adjust their relative
contributions, directionality and coupling strength can be fully tuned.
Furthermore, we introduce a novel spinning Janus dipole featuring cylindrical
symmetry in the near and far field, which results in either omnidirectional
coupling or noncoupling. Controlling the propagation of guided light waves via
fast and robust near-field interference between polarisation components of a
source is required in many applications in nanophotonics and quantum optics.
