Unidirectional coupling of a quantum emitter to a subwavelength grating waveguide with engineered stationary inflection point

TL;DR

This paper introduces a novel waveguide design that enables highly efficient, asymmetric coupling of quantum emitters with circular polarization, leveraging mode mixing to achieve a stationary inflection point for improved nanophotonic interfaces.

Contribution

The work presents a new waveguide structure with mode mixing to create a stationary inflection point, enhancing coupling efficiency and tolerance for quantum emitters in chiral nanophotonics.

Findings

High coupling efficiency achieved with the proposed waveguide design.

Homogeneous polarization distribution maintains circular polarization over large areas.

Design offers high tolerance to emitter position variations.

Abstract

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.