Amplitude and Phase Control of Guided Modes Excitation from a Single Dipole Source: Engineering Far‐ and Near‐Field Directionality

The design of far‐field radiation diagrams from combined electric and magnetic dipolar sources has recently found applications in nanophotonic metasurfaces that realize tailored reflection and refraction. Such dipolar sources also exhibit important near‐field evanescent coupling properties with applications in polarimetry and quantum optics. Here, a rigorous theoretical framework is introduced for engineering the angular spectra encompassing both far‐ and near‐fields of electric and magnetic sources and a unified description of both free space and guided mode directional radiation is developed. The approach uses the full parametric space of six complex‐valued components of magnetic and electric dipoles in order to engineer constructive or destructive near‐field interference. Such dipolar sources can be realized with dielectric or plasmonic nanoparticles. It is shown how a single dipolar source can be designed to achieve the selective coupling to multiple waveguide modes and far‐field simultaneously with a desired amplitude, phase, and direction. Exploiting the full 3D polarization of electric and magnetic dipole sources, herein a theoretical framework is demonstrated to achieve full control over relative phase, amplitude ratios, and propagation direction of multiple excited guided modes and far‐field radiation simultaneously, providing an essential strategy for light routing in all kinds of photonic circuitries, quantum technologies, and optical forces.