Imaging and Steering Emission from Phased Nanoantenna Arrays

Klas Lindfors Department of Chemistry, University of Cologne, Cologne, Germany 4th Physics Institute and Research Center SCoPE, University of Stuttgart, Stuttgart, Germany Ultrafast Nanooptics, Max Planck Institute for Solid State Research, Stuttgart, Germany Daniel Dregely 4th Physics Institute and Research Center SCoPE, University of Stuttgart, Stuttgart, Germany Markus Lippitz 4th Physics Institute and Research Center SCoPE, University of Stuttgart, Stuttgart, Germany Ultrafast Nanooptics, Max Planck Institute for Solid State Research, Stuttgart, Germany Department of Physics, University of Bayreuth, Bayreuth, Germany Nader Engheta Department of Electrical and Systems Engineering, University of Pennsylvania, Philadelphia, USA Michael Totzeck Corporate Research & Technology, Carl Zeiss AG, Oberkochen, Germany Harald Giessen 4th Physics Institute and Research Center SCoPE, University of Stuttgart, Stuttgart, Germany

Optical nanoantennas and nanoantenna arrays are promising components for optical signal transmission. Transmitting the signal via a free-space link (power law signal decay) instead of plasmonic waveguides (exponential signal decay) allows realizing low-loss optical communications links without sacrificing deep sub-wavelength field confinement at the transmitting and receiving points [1]. This is a promising route for reconciling the size mismatch between diffraction-limited integrated photonics and integrated electronics.

Controlling the phase difference of the signal that drives the elements in an array of optical nanoantennas, the array factor, gives an additional degree of freedom beyond the optical properties of the individual elements to engineer the properties of the device. This is illustrated in Fig 1a. In this work, we report on imaging and steering unidirectional emission from nanoantenna arrays.

a) The array factor provides an additional degree of freedom to engineer the properties of an optical nanoantenna array. b) By engineering the array factor we realize unidirectional emission as evidenced by the photoluminescence image.

We fabricate plasmonic nanoantennas using electron beam lithography and embed the structures in a homogeneous dielectric environment. To observe transmission of optical power from the transmitting nanoantenna array we position fluorescent material around the nanostructure. The fluorescence is excited by the optical power transmitted by the antenna array allowing us to map the intensity distribution around the structure under study. We have applied our imaging technique to observe transmission of optical power in wireless nanoantenna links. Here incident radiation is routed to different nanoscopic receivers dependent on the phase of the signal driving the elements of the array. By using a suitable array factor we even achieve polarization dependent unidirectional radiation(see figure 1b).

[1] A. Alù and N. Engheta, Phys. Rev. Lett. 104, 213902 (2010).

klas.lindfors@uni-koeln.de