Efficient Spin‐Direction Coupling between Circular Polarized Electric and Magnetic Dipoles and Photonic Modes

Abstract

Integrated single photon sources are essential elements in quantum computing, simulation, communication, and photonic neural networks. The directional radiation and scattering of single‐photon sources play a crucial role in light manipulation and rely on electric and magnetic dipole moments. Although clever physical insights and designer intuition strategies have been successfully applied in the development of integrated sources, inverse strategies could enhance and maximize its performance. Recently, topology‐optimized couplers for on‐chip single‐photon sources are designed to efficiently couple a guided mode and an electric dipole. However, the superposition of orthogonal electric and magnetic dipoles can also be harnessed due to the additional degrees of freedom via their interference. Here, the authors have extended the strategy to couplers that enhance spin‐direction coupling of circularly polarized, Huygens, and Janus dipoles. The authors demonstrate that optimization not only increases the coupling to a desire mode but also enhances the electric and magnetic local density of states (LDOS) while maintaining the amplitude and phase relation between the orthogonal dipoles for unidirectional coupling. Currently, coupling efficiency and enhanced LDOS of up to 88%, 94%, and 93% and up to 9.4, 18.6, and 14.9 are obtained for these dipoles. The topology optimization improves the performances of 3D integrated photonic devices.

Subwavelength Grating Waveguide Supported by a Magnetic Dipole Mode

“…12,13 Given the success of metamaterials in planar-optics with MD resonant split-ring, the introduction of MD mode into the SWG waveguide may enhance the function of the SWG waveguide in integrated optics. For example, the interaction between ED and MD modes has facilitated advancements in near-field directional excitation of the waveguide mode using Janus dipole, 14,15 and backscattering-suppressed nanoparticle chain waveguiding enabled by Huygens dipole. 16 According to the Mie theory, a dielectric nanoparticle with high refractive index such as a silicon nanodisk can support strong MD Mie resonant mode, which has comparable or even stronger strength than the ED mode.…”

“…To simplify its design in these applications, SWG waveguide is normally homogenized as an effective strip waveguide using an anisotropic permittivity tensor under the condition that the rectangle nanoparticles consisting of SWG waveguide are nonresonant. , In addition, these rectangle nanoparticles have a typical electric dipole (ED)-like profile. − To date, the corresponding magnetic dipole (MD) counterpart has not been reported due to several orders of magnitude weaker magnetic response than electrical response in natural matter. , Given the success of metamaterials in planar-optics with MD resonant split-ring, the introduction of MD mode into the SWG waveguide may enhance the function of the SWG waveguide in integrated optics. For example, the interaction between ED and MD modes has facilitated advancements in near-field directional excitation of the waveguide mode using Janus dipole, , and backscattering-suppressed nanoparticle chain waveguiding enabled by Huygens dipole …”