The nanowire optical antenna: Controlled directional emission and absorption of light by semiconductor nanowires

Abstract

We demonstrate experimentally and describe theoretically the strong directional emission and absorption of light by III-V semiconductor nanowires mediated by the resonant coupling to guided and leaky modes in the cylindrical structure. The absorption and emission of light can be modified and enhanced by its resonant interaction with nanostructures, such as semiconductor nanowires. Nanowires are characterized by a lateral dimension comparable to the wavelength of light and a much larger length, which enables their resonant interaction with light and the guiding of electromagnetic waves. Here, we demonstrate experimentally and describe theoretically the strong directional emission and absorption of light by III-V semiconductor nanowires mediated by the resonant coupling to guided and leaky modes in the cylindrical structure. The coupling to these eigenmodes of the nanowires depends strongly on their diameter and length, which opens a rich spectrum of possibilities for the control of the direction, efficiency and polarization of the emission and absorption of light [1]. The emission experiments have been performed with a Fourier microscope [2-4], i.e., by imaging the back focal plane of a microscope objective to map the emission of single nanowires and of nanowire arrays. We also introduce a technique termed time-reversed Fourier microscopy, which enables the detection of the directional absorption of polarized light by individual nanowires [5]. This techniques consists on focusing and scanning a laser beam at the back focal plane of the microscope objective. In this way, a sample under the objective is illuminated by a plane wave at an angle of incidence that is scanned to retrieve a map of the angular dependent absorption. Semiconductor nanowires behave as small optical antennas that are able to emit and absorb light in and from defined directions and polarizations. These directions and the polarization of the light are mostly determined by the nanowire diameter. In order to increase the possibilities for directional emission from individual nanowires, we have introduced hybrid nanowire-plasmonic antennas[6]. In these structures, the emission from a nanowire is scattered by metallic nanorods resonant at the emission wavelength. These rods are plasmonic resonantors that are placed at defined locations to achieve constructive interference of the emission in certain directions. In this way, we have demonstrated an hybrid nanowire-plasmonic Yagi-Uda nanoantenna with beamed emission. This device is illustrated in the figure below.