Epsilon-near-zero (ENZ) media disclose the peculiarities of electrodynamics in the limit of infinite wavelength but nonzero frequency for experiments and applications. Theory suggests that wave interaction with obstacles and disturbances dramatically changes in this domain. To investigate the optics of those effects, we fabricated a nanostructured 2D optical ENZ multilayer waveguide that is probed with wavelength-tuned laser light via a nanoscale wave launch configuration. In this experimental framework, we directly optically measure wave propagation and diffraction in a realistic system with the level and scale of imperfection that is typical in nanooptics. As we scan the wavelength from 1.0 to 1.7 mu m, we approach the ENZ regime and observe the interference pattern of a microscale Young's double slit to steeply diverge. By evaluating multiple diffraction orders we experimentally determine the effective refractive index n(eff) and its zero-crossing as an intrinsic measured reference, which is in agreement with theoretical predictions. We further verify that the double-slit and specifically placed scattering objects become gradually invisible when approaching the ENZ regime. We also observe that light-matter interaction intensifies toward ENZ and quantify how speckle noise, caused by tiny random imperfections, increasingly dominates the optical response and blue-shifts the cutoff frequency.

The interaction of light with matter strongly depends on the structure of the latter at wavelength scale. Ordered systems interact with light via collective modes, giving rise to diffraction. In contrast, completely disordered systems are dominated by Mie resonances of individual particles and random scattering. However, less clear is the transition regime in between these two extremes, where diffraction, Mie resonances and near-field interaction between individual scatterers interplay. Here, we probe this transitional regime by creating colloidal crystals with controlled disorder from two-dimensional self-assembly of bidisperse spheres. Choosing the particle size in a way that the small particles are transparent in the spectral region of interest enables us to probe in detail the effect of increasing positional disorder on the optical properties of the large spheres. With increasing disorder a transition from a collective optical response characterized by diffractive resonances to single particles scattering represented by Mie resonances occurs. In between these extremes, we identify an intermediate, hopping-like light transport regime mediated by resonant interactions between individual spheres. These results suggest that different levels of disorder, characterized not only by absence of long range order but also by differences in short-range correlation and interparticle distance, exist in colloidal glasses.

We experimentally demonstrate wave propagation in 2D nanophotonic epsilon-near-zero (ENZ) waveguides. We show an ENZ double-slit experiment, investigate ENZ diffraction and observe the disappearance of wavelength-scale obstacles close to the cut-off of the waveguide mode.

We experimentally demonstrate spectrally broad (λ 0 =1200–1800 nm) in-plane negative diffraction of SPPs in an array of plasmonic channel waveguides with negative mutual coupling resulting in negative refraction on the array's interface and refocusing in an adjacent metal layer.

The aim of near-field scanning optical microscopy (NSOM) is to reveal the distribution of the electromagnetic field around nanoscale objects. The full vectorial nature of this field is more difficult to measure than just its amplitude. It can only be fully reconstructed with exact knowledge of the optical properties of the probe. Here, we report and numerically explain that NSOM tips with a well-defined apex diameter selectively support azimuthally polarized light (|$E_{\text{azi}}$|$^2$/|$E_{\text{tot}}$|$^2$ $\approx$ 55$\,$% $\pm $ 5$\,$% for 1.4$\,$\mu m tip aperture diameter and \lambda$_0$ = 1550$\,$nm). We attribute the generation of azimuthal polarization in the metal-coated fiber tip to symmetry breaking in the bend and subsequent plasmonic mode filtering in the truncated conical taper.

Using a near-field scanning optical microscope we investigate the optical response of a plasmonic metasurface consisting of a sub-wavelength periodic pattern in an ultrathin (10nm) silver film, which shows extraordinarily suppressed transmission in the visible.

Plasmonic metasurfaces are investigated that consist of a sub wavelength line pattern in an ultrathin ( 10 nm) silver film, designed for extraordinarily suppressed transmission (EOST) in the visible spectral range. Measurements with a near-field scanning optical microscope (NSOM) demonstrate that far field irradiation creates resonant excitations of antenna like (bright) modes that are localized on the metal ridges. In contrast, bound (dark) surface plasmon polaritons (SPPs) launched from an NSOM tip propagate well across the metasurface, preferentially perpendicular to the grating lines.

We demonstrate experimentally and numerically that in fiber tips as they are used in NSOMs azimuthally polarized electrical fields (|E(azi)|2 / |E(tot)|2 ≈55% ± 5% for λ0 = 1550 nm), respectively subwavelength confined (FWHM ≈450 nm ≈λ0/3.5) magnetic fields, are generated for a certain tip aperture diameter (d = 1.4 μm). We attribute the generation of this field distribution in metal-coated fiber tips to symmetry breaking in the bend and subsequent plasmonic mode filtering in the truncated conical taper.

High quality CdS nanowires suspended in air were optically pumped both below and above the lasing threshold. The polarization of the pump laser was varied while emission out of the end facet of the nanowire was monitored in a 'head-on' measurement geometry. Highest pump-efficiency and most efficient absorption of the pump radiation are demonstrated for an incident electric field being polarized parallel to the nanowire axis. This polarization dependence, which was observed both above the lasing threshold and in the regime of amplified spontaneous emission, is caused by an enhanced absorption for parallel polarized optical pumping. Measured Stokes parameters of the nanowire emission reveal that due to the onset of lasing the degree of polarization rapidly increases from approximately 15% to 85%. Both, Stokes parameters and degree of polarization of the nanowire lasing emission are independent of the excitation polarization. The transversal lasing mode is therefore not notably affected by the polarization of the pumping beam, although the supply with optical gain is significantly enhanced for an excitation polarization parallel to the nanowire axis.

We experimentally demonstrate plasmonic nanocircuits operating as subdiffraction directional couplers optically excited with high efficiency from free-space using optical Yagi-Uda style antennas at λ0 = 1550 nm. The optical Yagi-Uda style antennas are designed to feed channel plasmon waveguides with high efficiency (45% in coupling, 60% total emission), narrow angular directivity (<40°), and low insertion loss. SPP channel waveguides exhibit propagation lengths as large as 34 μm with adiabatically tuned confinement and are integrated with ultracompact (5 × 10 μm(2)), highly dispersive directional couplers, which enable 30 dB discrimination over Δλ = 200 nm with only 0.3 dB device loss.

In near field scanning optical microscopy (NSOM) a sharp tip with a defined aperture allows for direct scanning and subwavelength imaging of samples that otherwise cannot be excited from the far field. To control the interaction between tip and sample ideally a specifically prepared polarization state of light is desirable [1-3]. By coupling a Gaussian beam with an optimized elliptical polarization into a single mode optical fiber, which tapers down to a well-chosen μm scale diameter and undergoes a 60 degrees bend, we can reproducibly prepare an azimuthal polarization state at the tip aperture.

∗To whom correspondence should be addressed †University of Erlangen ‡Caltech uum light source is spectrally filtered by a programmed acousto-optic tunable filter (operated at λ = 1200− 1850nm) (NKT Koheras, SuperK Extreme) and is subsequently directed through a polarization filter (1) and a non-polarizing beam splitter (NPBS), that directs 50% of the power to a reference diode (InGaAs). The main beam is focused with a high NA objective (NA = 0.9 from air and NA = 1.3 immersion, from substrate) that was carefully characterized to preserve the polarization properties of the laser beam. The diameter of the collimated beam was carefully measured (FWHM = 1.6mm) with an InGaAs camera and the effective numeric aperture of the experimental focal spot was determined for all subsequent evaluation steps. The focus of the objective is adjusted on the investigated excitation nano-antenna. At the same time, the objective images the complete nano-circuit, including the emission from the other antennas. The collimated beam, carrying the image, is polarization filtered (polarizer 2) and passes imaging optics to form a real image on an InGaAs NIR CCD camera (Xenics XS, 320 x 256 pixels). The setup features a variable magnification factor (150x, 300x) and an additional, switchable focusing unit to allow for Fourier plane imaging. By adjusting the polarization filter (2) perpendicular to polarization filter (1), the reflection of

We propose a novel scheme for plasmonic nanocircuits. While SPP waveguides show superior waveguiding properties in terms of tight confinement, a major prerequisite for subwavelength integration, they usually lack the ability to transport light over distances longer than a few tens of μm. Some photonic components that strongly benefit from a realization in plasmonics can be integrated in very small functional units but need low-loss interconnects for real-life applications. The transfer efficiency at the connections between low-loss (e.g. Si waveguides) and high-loss (e.g. plasmonic) waveguides is limited by the maximum achievable modal field overlap of the waveguides. This leads to the idea to form the transitions adiabatically.

We observe nonlinear switching of ultrashort (600fs) laser pulses in subwave-length plasmonic nanocircuits. This allows us to experimentally determine the third-order nonlinear coefficient of silver.

Plasmonic components allow for subwavelength integration while simultaneously generating extraordinary field enhancement thus amplifying nonlinear effects. Here we present first experimental results indicating nonlinear switching in a plasmonic directional coupler of a few micrometers length.

High confinement in plasmonic waveguides usually comes along with high loss. We present experiments on a new approach, which allows to tune adiabatically between high confinement and low loss waveguides, connected to optical Yagi-style antennas.

Plasmonic gap waveguides allow for subwavelength integration of optical circuitry. A side effect is extraordinarily high field enhancement. Here we present experimental and numeric results, which indicate nonlinear switching in a directional coupler.

Plasmonic gap waveguides allow for light confinement below the diffraction limit. In combination with an impedance matched nanoantenna they can be excited from the far field. In this contribution the authors investigated nanoantennas coupled to gap plasmonic waveguides with a near-field scanning optical microscope (NSOM), but also experimentally demonstrate the coupling of far-field optical beams to highly confined plasmonic gap modes.

We report the first experimental characterization of an optical antenna connected to a nanoplasmonic gap waveguide. Far-field measurements are performed in crossed polarization and enable the detection of extremely weak signals.