Directional Fluorescence Emission by Individual V-Antennas Explained by Mode Expansion

Abstract

Specially designed plasmonic antennas can, by far-field interference of different antenna elements or a combination of multipolar antenna modes, scatter light unidirectionally, allowing for directional light control at the nanoscale. One of the most basic and compact geometries for such antennas is a nanorod with broken rotational symmetry, in the shape of the letter V. In this article, we show that these V-antennas unidirectionally scatter the emission of a local dipole source in a direction opposite the undirectional side scattering of a plane wave. Moreover, we observe high directivity, up to 6 dB, only for certain well-defined positions of the emitter relative to the antenna. By employing a rigorous eigenmode expansion analysis of the V-antenna, we fully elucidate the fundamental origin of its directional behavior. All findings are experimentally verified by measuring the radiation patterns of a scattered plane wave and the emission pattern of fluorescently doped PMMA positioned in different regions around the antenna. The fundamental interference effects revealed in the eigenmode expansion can serve as guidelines in the understanding and further development of nanoscale directional scatterers.

Design of plasmonic directional antennas via evolutionary optimization

“…The vast opportunities of light-based nanotechnology lead to tremendous research efforts on light-matter interaction at sub-wavelength scales, and in particular gave rise to the broad field of plasmonics, as localized surface plasmon-polariton (LSP) resonances in metallic nanostructures can strongly confine far-field radiation [1]. By variations of the particle geometry or its material it is possible to tailor manifold optical properties like resonance positions [2], polarization conversion [3], optical chirality [4], localized heat generation [5,6] or nonlinear optical effects [7,8] with many applications like field enhanced spectroscopy [9] or refractive index sensing [8,10].…”

“…Another optical functionality that is in the focus of the plasmonics community is the directional routing of light. Not only individual nanostructures were demonstrated for directional scattering of far-field light [11][12][13], color-routing [14], quantum emitter radiation steering [9,[15][16][17][18][19], electro-luminescence [20,21] or directional non-linear emission [22]. Also metasurfaces for directional scattering and color-routing have been proposed [23,24].…”

“…Also metasurfaces for directional scattering and color-routing have been proposed [23,24]. Such photonic devices imply applications like on-chip light routing and de-multiplexing [25] or sensing [9,10].…”

Understanding the Physical Behavior of Plasmonic Antennas Through Computational Electromagnetics

“…They are considered as excellent tools to probe and control light-matter interaction at the nanoscale (e.g., the interaction between light and molecules) and therefore have become an essential element in the discipline of nanophotonics [1,2]. Till now, the concept of nanoantennas has been applied to many different fields [3][4][5][6][7][8][9][10][11] covering single-molecule detection, magnetic recording, bio-imaging, photochemistry, nanoscale signal processing, optical functional material, and so on.…”

Control of fluorescence enhancement and directionality upon excitations in a thin-film system

“…1 Introduction Fluorescence is a process of photon emission from excited fluorophores. The emission properties of a fluorophore, e.g., fluorescence intensity, lifetime, and emission directionality, can be engineered through coupling with the electromagnetic (EM) resonances in various photonic nanostructures, such as metallic nanoparticles [1][2][3][4][5][6][7][8][9][10], optical antennas [11][12][13][14][15], and photonic/plasmonic crystals [16][17][18][19]. This is because photonic nanostructures can create a structuredefined complex dielectric environment that interacts with EM waves.…”