  In this work, we propose an approach for the design of a waveguide structure
that allows for efficient and highly asymmetric coupling of the quantum sources
with circularly polarized transition dipole moments to the guided mode of the
structure. The approach is based on the mixing of the two quasi-degenerate
modes of a periodic waveguide with an auxiliary single-mode waveguide leading
to the formation of the dispersion with a stationary inflection point and
consequently to the high coupling efficiency of this mode with a dipole source.
We show that the distribution of the field polarization inside the waveguide is
relatively homogeneous maintaining the circular polarization in a large area.
Consequently, this leads to a high degree of tolerance of the coupling
asymmetry and strength to the position of the quantum emitter. We believe, that
our results will extend the variety of designs of the efficient chiral
nanophotonic interfaces based on planar semiconductor nanostructures.
