Integrated Janus dipole source for selective coupling to silicon waveguide networks

The efficient selective and directional coupling of light to waveguiding circuitry at the nanoscale is one of the key challenges in nanophotonics, as it constitutes a prerequisite for many applications, including information processing, routing, and quantum technologies. Various exotic nanostructures and nanoparticle arrangements have been designed to achieve directional coupling with compact on-chip integration remaining one of the foremost hurdles to realizing many real-world devices. At the same time, selective coupling to one of several neighboring waveguides is much more difficult to achieve and control. To address this challenge, we demonstrate a subwavelength selective coupler integrated in a waveguide network, with selectivity controlled by wavelength, polarization, and angle of incidence. We utilize a Janus source, which is composed of a superposition of electric and magnetic dipoles, supported by a silicon nanocylinder. By placing the nanocylinder between identical single mode silicon waveguides, we successfully achieve selective coupling with a high contrast ratio between the waveguides. The operating wavelength of the Janus dipolar source can be easily tailored, and the coupling efficiency is also shown to be conveniently boosted by the addition of multiple nanocylinders. Our compact approach provides a direct path toward on-chip highly directional nanoscale sources for a plethora of applications, including information routing, metrology, and quantum technologies.