The topic of chiral light-matter interaction attracts a lot of interest during several last years due to the promising applications in nanophotonics and quantum optics [1]. Non-zero transverse component of the spin momentum density, inherent for the fields with complex spatial profiles, leads, for instance, to the so-called spin-momentum locking, when the direction of light propagation becomes coupled to the spin orientation of the source emitter and, therefore, to the associated photon polarization state [2,3]. Many types of quantum emitters, e.g. quantum dots or 2D materials, in practical schemes exhibit dipole transitions polarized in the plane of substrate. Efficient integration of such emitters with planar photonic circuits requires coupling of these transitions to the planar optical nanowaveguides. As compared with conventional homogeneous dielectric nanowaveguides, discrete waveguides provide one with additional freedom in their dispersion engineering due to the mutual coupling of the resonances of their constituent elements.
Here we theoretically address the subject of coupling of a quantum emitter to a discrete nanophotonic waveguide. Numerical calculations presented in Fig.1(a-c) show that specially designed waveguide can possess two orthogonal modes polarized in the plane of the substrate that cross at a certain frequency and wavenumber. From these calculations we expect that electric dipole transitions orthogonally polarized in the plane of substrate and placed below or above such a waveguide couple to both these modes. Therefore, at the crossing frequency out-of-plane spin state of an emitter can be mapped onto two orthogonal modes of the discrete waveguide and transferred over relatively large distances. We also demonstrate the possibility of routing of the emitted circularly polarized photons in the substrate plane by a specially designed hybrid planar system shown in Fig.1(d). The phase difference between two modes of the discrete waveguide determined by the polarization of emitter transition allows for unidirectional coupling to a homogeneous waveguide by changing the handedness of the transition.
[1] P. Lodahl et.al. Nature, v.541, pp. 473–480, 2017.
[2] K. Y. Bliokh, F. Nori, Phys. Rep., v.592, pp. 1-38, 2015.
[3] J. Petersen et.al., Science, v.346, pp. 67-71, 2014.
Optical properties of nanostructures , Optics and transport on 2D materials
