In radiofrequency antenna engineering, the array factor made long-distance communication with steerable transmission and receiving possible. At optical frequencies, low-loss signal transmission via free space by using nano antennas is still in its infancy. Here, we suggest applying the array factor to the optical frequency regime by shaping the radiation pattern of plasmonic metasurfaces featuring nano antenna arrays. We arrange dipolar gold nanoantennas operating at 785 nm wavelength in wavelength-sized arrays and control the phase that drives the antenna elements. We obtain collimated and unidirectional radiation from this metasurface upon illumination with circularly polarized light, which is not prone to major losses as in common plasmonic waveguide structures. We furthermore demonstrate switching the unidirectional emission to opposite directions with additional beamsteering by modifying the array factor. Our experiment corroborates the evidence for spin orbit coupling between the helicity of light and suitably designed plasmonic metasurfaces, which can exhibit the spin-Hall effect for light.

We experimentally demonstrate an ultra-thin plasmonic optical rotator in the visible regime that induces a polarization rotation that is continuously tunable and switchable by an external magnetic field. The rotator is a magneto-plasmonic hybrid structure consisting of a magneto-optical EuSe slab and a one-dimensional plasmonic gold grating. At low temperatures, EuSe possesses a large Verdet constant and exhibits Faraday rotation, which does not saturate over a regime of several Tesla. By combining these properties with plasmonic Faraday rotation enhancement, a large tuning range of the polarization rotation of up to 8.4° for a film thickness of 220 nm is achieved. Furthermore, through experiments and simulations, we demonstrate that the unique dispersion properties of the structure enable us to tailor the wavelengths of the tunable polarization rotation to arbitrary spectral positions within the transparency window of the magneto-optical slab. The demonstrated concept might lead to important, highly integrated, non-reciprocal, photonic devices for light modulation, optical isolation, and magnetic field optical sensing. The simple fabrication of EuSe nanostructures by physical vapor deposition opens the way for many potentially interesting magneto-plasmonic systems and three-dimensional magneto-optical metamaterials. A tunable and switchable ultrathin-film optical rotator with a variable working wavelength is experimentally realized by a team in Germany. Scientists at the University of Stuttgart and the Max Planck Institute for Solid State Research fabricated a plasmonic optical rotator for visible light whose polarization rotation can be continuously tuned and switched by applying a magnetic field. They realized this by combining a magneto-optical EuSe slab having a high Verdet constant and a high saturation magnetic flux density with a one-dimensional plasmonic gold grating. The unique dispersion properties of the structure enable free tuning of the working wavelength by varying the grating parameters. The team anticipates that the concept will lead to highly integrated non-reciprocal photonic devices for actively controlled light modulation, magnetic field sensing and optical isolation. Furthermore, the simple fabrication of EuSe nanostructures by physical vapour deposition opens the way for a wide range of magneto-plasmonic systems and three-dimensional magneto-optical metamaterials.

Optical nanoantennas tailor the transmission and reception of optical signals. Owing to their capacity to control the direction and angular distribution of optical radiation over a broad spectral range, nanoantennas are promising components for optical communication in nanocircuits. Here we measure wireless optical power transfer between plasmonic nanoantennas in the far-field and demonstrate changeable signal routing to different nanoscopic receivers via beamsteering. We image the radiation pattern of single-optical nanoantennas using a photoluminescence technique, which allows mapping of the unperturbed intensity distribution around plasmonic structures. We quantify the distance dependence of the power transmission between transmitter and receiver by deterministically positioning nanoscopic fluorescent receivers around the transmitting nanoantenna. By adjusting the wavefront of the optical field incident on the transmitter, we achieve directional control of the transmitted radiation over a broad range of 29°. This enables wireless power transfer from one transmitter to different receivers.

Plasmonic nanoantennas confine electromagnetic fields at infrared wavelengths to volumes of only a few cubic nanometers, resulting in huge local fields in the vicinity of the resonantly excited metal particles. We exploited these fields to enhance the infrared vibrational bands of molecular monolayers with ultra-high sensitivity.

Properties of light propagating in some materials can be influenced by a static magnetic field. Such magneto-optical effects are useful, but their strength is limited traditionally by the materials used. Scientists demonstrate that a hybrid structure of a magneto-optical photonic waveguide with plasmonic (gold) nanowires significantly boosts an important effect, the so-called transverse magneto-optical Kerr effect, through resonant interaction between the waveguide photons and the plasmons.

Light propagation is usually reciprocal. However, a static magnetic field along the propagation direction can break the time-reversal symmetry in the presence of magneto-optical materials. The Faraday effect in magneto-optical materials rotates the polarization plane of light, and when light travels backward the polarization is further rotated. This is applied in optical isolators, which are of crucial importance in optical systems. Faraday isolators are typically bulky due to the weak Faraday effect of available magneto-optical materials. The growing research endeavour in integrated optics demands thin-film Faraday rotators and enhancement of the Faraday effect. Here, we report significant enhancement of Faraday rotation by hybridizing plasmonics with magneto-optics. By fabricating plasmonic nanostructures on laser-deposited magneto-optical thin films, Faraday rotation is enhanced by one order of magnitude in our experiment, while high transparency is maintained. We elucidate the enhanced Faraday effect by the interplay between plasmons and different photonic waveguide modes in our system.

For radio engineers it is a common task to combine several antennas to form an antenna array. This gives them several degrees of freedom for shaping the radiation pattern according to their needs. By selecting different types of individual elements, their relative position in space, their respective orientation, and the amplitude and phase of the induced currents, one can engineer the radiated beam properties [262]. In the new research field of optical nanoantennas, the possibilities of arraying antennas have hardly been explored yet. This is mainly due to the challenges in fabricating and driving the arrays, as well as the yet limited possibilities of characterization. Nevertheless, application of RF antenna array concepts into optical regimes promises tremendous technological advances: increasing the directivity and gain aids in distant signal transmission and reception (similarly to the concepts used in satellite communication), coupling nanoemitters and nanoreceivers to antenna arrays enhances their efficiency with the potential of bridging the size gap between optical radiation and subwavelength emitters or detectors and employing phase retarders allows for steering of optical beams.

Nanoantennas confine electromagnetic fields at visible and infrared wavelengths to volumes of only a few cubic nanometres. Assessing their near-field distribution offers fundamental insight into light-matter coupling and is of special interest for applications such as radiation engineering, attomolar sensing and nonlinear optics. Most experimental approaches to measure near-fields employ either diffraction-limited far-field methods or intricate near-field scanning techniques. Here, using diffraction-unlimited far-field spectroscopy in the infrared, we directly map the intensity of the electric field close to plasmonic nanoantennas. We place a patch of probe molecules with 10 nm accuracy at different locations in the near-field of a resonant antenna and extract the molecular vibrational excitation. We map the field intensity along a dipole antenna and gap-type antennas. Moreover, this method is able to assess the near-field intensity of complex buried plasmonic structures. We demonstrate this by measuring for the first time the near-field intensity of a three-dimensional plasmonic electromagnetically induced transparency structure.

We demonstrate experimentally a plasmonic enhancement of the transverse magneto-optical Kerr effect. The enhanced Kerr effect modulates the transmitted light intensity by a large value of 1.5%, while high transparency of the system is maintained.

We experimentally demonstrate the first optical nanoantenna link (λ = 785 nm) which enables low-loss communication across a distance of 38 λ and allows dynamic reconfiguration of the link using a phased array transmitter.

Radiative coupling between oscillators is one of the most fundamental subjects of research in optics, where particularly a Bragg-type arrangement is of interest and has already been applied to atoms and excitons in quantum wells. Here we explore this arrangement in a plasmonic structure. We observe the emergence of an octave-wide photonic band gap in the optical regime. Compared with atomic or excitonic systems, the coupling efficiency of the particle plasmons utilized here is several orders of magnitude larger and widely tunable by changing the size and geometry of the plasmonic nanowires. We are thus able to explore the regime where the coupling distance is even limited by the large radiative decay rate of the oscillators. This Bragg-stacked coupling scheme will open a new route for future plasmonic applications such as far-field coupling to quantum emitters without quenching, plasmonic cavity structures and plasmonic distributed gain schemes for spasers.

We demonstrate the use of a genetic algorithm based inverse design technique to target and fabricate helical structures via PnP. We furthermore show their inversion into other functional materials and their application as chiral metamaterials.

The chiral nature of many biomolecules would make highly sensitive enantiomer detection desirable. Utilizing the concept of optical chirality in nanophotonics and plasmonics we numerically analyze and compare different structures to meet the design criteria for increased sensitivity of such sensors. We demonstrate the differences between planar structures that are easily fabricated and three-dimensional designs that are capable of higher enhancement of optical chirality. Additionally, a sensor scheme combining both enantiomers of a chiral plasmonic nanostructure is proposed and investigated.

Plasmonic nanoantennas can enhance the radiative decay rate of quantum emitters via the Purcell-effect. Similar to their radiofrequency equivalents, they can also direct the emitted light into preferential directions. In this paper we first investigate plasmonic Yagi-Uda antennas that are able to confine light to and direct light from subwavelength size volumes. Hence, enhanced transition rates and directed emission are expected when near-field coupling between quantum emitters and the antennas is achieved. Second, we present suitable techniques to couple different quantum systems to plasmonic antennas. We use top-down fabrication techniques to achieve positioning of individual quantum emitters relative to plasmonic nanostructures with an accuracy better than 10?nm. We assure a sufficiently small distance for an efficient near-field coupling of the transition dipole to the plasmonic nanoantenna, which is, however, large enough not to quench the transition. The hybrid system using quantum dots, molecules, or nitrogen-vacancy (NV)-centers in diamond can serve as an efficient single photon source. It is suitable for high-speed information transfer at optical frequencies on the nanoscale for future applications.

Daniel Dregely et al. (see their Feature Article on pp. 666–677) investigated plasmonic Yagi-Uda antennas and measured experimentally the modes supported by the antenna geometry by means of optical near-field microscopy technique. By expanding the single antenna to a two-dimensional antenna array with the antenna axes pointing out of the substrate plane, superior directive properties were obtained compared to the single antenna. The authors present three different methods to couple quantum systems to plasmonic antennas. Two-step electron beam lithography allows for reliable positioning of core-shell quantum dots and nitrogen-vacancy centers in nanodiamonds with a sub-10 nm accuracy. The hybrid system of directive plasmonic antennas and quantum emitters can serve as an efficient single photon source. It is suitable for high-speed information transfer at optical frequencies on the nanoscale for future applications.

We demonstrate the coupling of single color centers in diamond to plasmonic and dielectric photonic structures to realize novel nanophotonic devices. Nanometer spatial control in the creation of single color centers in diamond is achieved by implantation of nitrogen atoms through high-aspect-ratio channels in a mica mask. Enhanced broadband single-photon emission is demonstrated by coupling nitrogen–vacancy centers to plasmonic resonators, such as metallic nanoantennas. Improved photon-collection efficiency and directed emission is demonstrated by solid immersion lenses and micropillar cavities. Thereafter, the coupling of diamond nanocrystals to the guided modes of micropillar resonators is discussed along with experimental results. Finally, we present a gas-phase-doping approach to incorporate color centers based on nickel and tungsten, in situ into diamond using microwave-plasma-enhanced chemical vapor deposition. The fabrication of silicon–vacancy centers in nanodiamonds by microwave-plasma-enhanced chemical vapor deposition is discussed in addition.

Plasmonic oligomer clusters are assemblies of closely packed metallic nanoparticles. They provide a rich set of spectral features such as Fano lineshapes and a simultaneous tunability of the supported resonances in the optical wavelength regime. In this study, we investigate numerically and experimentally clusters of plasmonic nanoparticles that exhibit multiple Fano resonances due to the interference of one broad superradiant mode and multiple narrow subradiant modes. In particular we investigate oligomers with multiple ring modes and elongated chains of nanoparticles surrounded by one ring of nanoparticles. We show that the number of nanoparticles and their respective arrangement in the cluster strongly influence the spectral position and modulation depth of the spectral signature of the supported modes. Our study opens up the pathway to "plasmonic super molecules" that show unprecedented tunability, which renders them highly suitable for applications such as multiwavelength surface-enhanced Raman scattering.