  Non-Hermitian systems with their spectral degeneracies known as exceptional
points (EPs) have been explored for lasing, controlling light transport, and
enhancing a sensor s response. A ring resonator can be brought to an EP by
controlling the coupling between its frequency degenerate clockwise and
counterclockwise traveling modes. This has been typically achieved by
introducing two or more nanotips into the resonator s mode volume. While this
method provides a route to study EP physics, the basic understanding of how the
nanotips shape and size symmetry impact the system s non-Hermicity is missing,
along with additional loss from both in-plane and out-of-plane scattering. The
limited resonance stability poses a challenge for leveraging EP effects for
switches or modulators, which requires stable cavity resonance and fixed
laser-cavity detuning. Here we use lithographically defined asymmetric and
symmetric Mie scatterers, which enable subwavelength control of wave
transmission and reflections without deflecting to additional radiation
channels. We show that those pre-defined Mie scatterers can bring the system to
an EP without post tuning, as well as enable chiral light transport within the
resonator. Counterintuitively, the Mie scatterer results in enhanced quality
factor measured on the transmission port, through coherently suppressing the
backscattering from the waveguide surface roughness. The proposed device
platform enables pre-defined chiral light propagation and backscattering-free
resonances, needed for various applications such as frequency combs, solitons,
sensing, and other nonlinear optical processes such as photon blockade, and
regenerative oscillators.
