Universal method for the synthesis of arbitrary polarization states radiated by a nanoantenna

Abstract

Abstract:Optical nanoantennas efficiently convert confined optical energy into free-space radiation. The polarization of the emitted radiation depends mainly on nanoantenna shape, so it becomes extremely difficult to manipulate it unless the nanostructure is physically altered. Here we demonstrate a simple way to synthetize the polarization of the radiation emitted by a single nanoantenna so that every point on the Poincaré sphere becomes attainable. The nanoantenna consists of a single scatterer created on a dielectric waveguide and fed from its both sides so that the polarization of the emitted optical radiation is controlled by the amplitude and phase of the feeding signals. Our nanoantenna is created on a silicon chip using standard top-down nanofabrication tools, but the method is universal and can be applied to other materials, wavelengths and technologies. This work will open the way towards the synthesis and control of arbitrary polarization states in nano-optics.A fundamental property of coherent light is its polarization, which is defined by the orientation of its electric field, and determines the forces which light exerts on charges. Polarization is therefore an essential concept to describe the interaction of light with matter, and as such, its generation and measurement is crucial in polarimetry applications ranging from astronomy [1] to thin film ellipsometry. Polarization also plays a key role in the efficient reception and detection of light [2] as well as in quantum optics [3][4][5]. Recent work on circularly polarized light, which carries spin angular momentum, has revealed interesting applications including generation of spinning forces on particles [6], detection of molecular spinning [7] and novel methods for ultrafast magnetic storage [8,9], requiring a very fast switching between left and right handed circular polarization.The emission and/or reception of light can be achieved with the use of optical nanoantennas that efficiently convert confined optical energy into free-space radiation [10][11][12][13][14][15][16]. In the far-field, the radiation emitted by a nanoantenna has a given polarization, determined by the radiation angle, wavelength and properties of the specific nanostructure, specially its geometry. The polarization is essentially fixed for a given wavelength unless the nanostructure is physically or mechanically altered. Therefore, achieving a fast and tunable control in the emitted polarization of a nanoantenna has remained elusive so far. In this work we describe a universal method to achieve this. Although the concept of nanoantennas in plasmonics usually refers to structures which convert localized near fields into radiating waves, and vice versa, in this work we consider a traditional definition of antenna as that of a transitional structure between free-space and a guiding device [17]. The idea stems from a recent series of works in which the direction of propagation of surface plasmons is selected by the polarization of the incident light [18][19][20][21][22]. This rel...

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