  Chiral light matter interaction enables new fundamental researches and
applications of light. The interaction has traditionally faced challenges in
low directionality and efficiency based on spin orbit interaction of light in
microscopic waveguides. It is pivotal to exploit photonic integrated circuits
to efficiently engineer photonic chiral behavior. Here, we present ultra
directional high efficient chiral coupling in silicon photonic circuits based
on low order to high order mode conversion and interference. We show that the
directionality of chiral coupling, in principle, can approach minus/plus 1 with
circular polarization inputs, benefited from the underlying mechanism of
complete destructive and constructive interference. The chiral coupling
efficiency can exceed 70%, with negligible scattering to nonguided modes, much
higher than conventional coupling mechanisms. Moreover, the chiral silicon
photonic circuits can function as a perfect 3 dB power splitter for arbitrarily
linear polarization inputs, and also open up the possibility of on chip
chirality determination to further flourish the development of chiral optics.

Applied Physics;Optics