# Amplitude and phase control of guided modes excitation from a single dipole source:engineering far- and near-field directionality

## TL;DR

This paper presents a comprehensive theoretical framework for controlling the amplitude and phase of guided and radiative modes from a single dipole source, enabling tailored far- and near-field directionality in nanophotonics.

## Contribution

It introduces a unified approach to engineer both far- and near-field angular spectra of electric and magnetic dipoles for mode control.

## Key findings

- Single dipole can selectively excite multiple waveguide modes.
- Framework allows precise control of amplitude and phase of emitted fields.
- Applicable to dielectric and plasmonic nanoparticles.

## Abstract

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 we introduce a rigorous theoretical framework for engineering the angular spectra encompassing both far- and near-fields of electric and magnetic sources and develop a unified description of both free space and guided mode directional radiation. 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. We show 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.