Through the effect of Purcell enhancement, nanoantennas strongly modify the local density of optical states and control the emission of coupled emitters. These antennas determine, in addition to the emission spectrum and polarization, also the angular distribution of the emitted photons, i.e., the radiation pattern. Nearly all directional nanoantennas reported so far, rely on external excitation schemes such as a laser or scanning tunneling microscope (STM) tip, which severely hamper on-chip integration. Here, we experimentally demonstrate for the first time, unidirectional light emission from electrically driven in-plane two-wire nanoantennas in the shape of the letter V. The antenna wires are connected with narrow electrical leads which support electrical currents while preserving the resonant properties of the antenna . A nanoscopic tunneling gap is formed at the feed point of the antenna through a controlled electromigration procedure. Strong far-field interference between the spontaneous dipolar light emission of the tunnel junction and the fundamental quadrupolar resonance of the antenna gives rise to a directional radiation pattern . We show that this directivity can be actively tuned with the applied voltage, and passively tuned with the antenna geometry. The experimental findings are analyzed in detail through electro-optical characterization and extensive numerical simulations. These fully configurable ultra-fast tunneling nanoantennas seamlessly exploit light-matter interactions at the nanoscale and set a new paradigm for directing optical energy on chip using an extremely small footprint.  Kern et al. Nature Photonics (2015) 9, 582–586;  Vercruysse et al. ACS Nano (2014) 8(8), 8232−8241.
Surya Prakash Gurunarayanan, Niels Verellen, Vyacheslav S. Zharinov, Finub James Shirley, Victor V. Moshchalkov, Marc M. Heyns, Joris Van de Vondel, Iuliana P. Radu, and Pol Van Dorpe, "Unidirectional light-emission from in-plane tunneling nanoantennas (Conference Presentation)," Proc. SPIE 10530, Ultrafast Phenomena and Nanophotonics XXII, 105300I (Presented at SPIE OPTO: January 30, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2288380.5751515703001.
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