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

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, 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.

Toggling Near‐Field Directionality via Polarization Control of Surface Waves

“…[32][33][34][35] Notably, recent studies show that the near-field directionality can go beyond the rudimentary spin-momentum locking, if the excitation source is the composite electric and magnetic dipoles. [23][24][25] For example, Huygens and Janus dipoles are constructed by the orthogonal electric and magnetic dipoles, which are in phase and 90°out of phase to each other, respectively. [25] As a result, the near-field directionality of Huygens and Janus dipoles is related to the real and imaginary parts of the Poynting vector, respectively.…”

“…It enables many applications, such as nanorouters [10,11], nanopolarimeters [12], nanoscopic position sensing [13,14], near-field microscopy [1], and the development of on-chip information processing and complex quantum networks [3,[15][16][17][18][19]. In general, it is achieved through the judicious design of either asymmetric waveguide structures [20][21][22] or complex excitation sources [7,[23][24][25][26][27][28], such as the extensively-studied circularly polarized dipoles. Circular electric (magnetic) dipoles [5,25,[29][30][31] are featured with a spinning electric (magnetic) dipole moment.…”

“…Correspondingly, their near-field directionality is determined by the spin-momentum locking and can be understood from the perspective of quantum spin Hall effect of light [32][33][34][35]. Notably, recent studies show that the near-field directionality can go beyond the rudimentary spin-momentum locking, if the excitation source is the composite electric and magnetic dipoles [23][24][25]. For example, Huygens and Janus dipoles are constructed by the orthogonal electric and magnetic dipoles, which are in phase and 90° out of phase to each other, respectively [25].…”

Dynamic Absorption Enhancement and Equivalent Resonant Circuit Modeling of Tunable Graphene-Metal Hybrid Antenna

“…Specifically, absorption strength in graphene is one of the most crucial measures for control over photon collection. The assumptive schemes [18,19] have provocatively forecasted 100% (i.e., unity) absorption in resonantly excited graphene nanoantennas [20], demonstrating robust light-matter interactions in atomically thin graphene sheets.…”

Group‐Velocity‐Controlled and Gate‐Tunable Directional Excitation of Polaritons in Graphene‐Boron Nitride Heterostructures

“…While the directional excitation of surface plasmons has been realized via asymmetric structural designs, their direction of excitation is predefined and cannot be reconfigured on‐the‐fly if the excitation source is fixed. Until now, the active switching of the excitation direction of polaritons relies primarily on the modulation of the source, including the tuning of the incident angle or the helicity (i.e., polarization) of incident light, and the spatiotemporal phase between incident coherent pulses . Therefore, demonstrating actively tunable directional excitation of highly squeezed polaritons, without resorting to the modulation of the source, remains an open challenge that is highly sought after due to its importance for the development of advanced nano‐photonic technology.…”