Daniel Ploss

Functional plasmonic nanocircuits with low insertion and propagation losses

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.

Experimental cross-polarization detection of coupling far-field light to highly confined plasmonic gap modes via nanoantennas

We experimentally demonstrate the coupling of far-field light to highly confined plasmonic gap modes via connected nanoantennas. The excitation of plasmonic gap modes is shown to depend on the polarization, position, and wavelength of the incident beam. Far-field measurements performed in crossed polarization allow for the detection of extremely weak signals re-emitted from gap waveguides and can increase the signal-to-noise ratio dramatically.

Engineered disorder and light propagation in a planar photonic glass.

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.

Generation and subwavelength focusing of longitudinal magnetic fields in a metallized fiber tip

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.

Low loss wireless interconnects in plasmonic nanocircuitry

Wireless transfer of electromagnetic radiation requires antennas with well-designed directivity and high efficiency. In optics those antennas offer a particularly interesting application in the intermediate domain between far- and near-field [1]. Replacing waveguide interconnects in plasmonic circuitry by wireless transfer channels can significantly decrease losses, thus avoiding a major drawback of nanoplasmonics [2].

Probing nanoplasmonic waveguides and couplers with optical antennas

Plasmonic gap waveguides combine subwavelength light confinement with the possibility to guide and manipulate light on the nanoscale. This concept for nano-optics and optical circuitry requires transferring light from the far field into the nanoworld via optical antennas, to guide it in highly confined waveguides and to distribute it via directional couplers. Here we experimentally demonstrate that all these elements can work together. In particular, we experimentally demonstrate the operation of subwavelength nanoplasmonic couplers. To this end we fabricated respective structures using a focused ion beam (FIB) machine (Fig. 1 a) and evaluated their optical properties at the communication wavelength λ = 1.5 µm.

Young’s Double-Slit, Invisible Objects and the Role of Noise in an Optical Epsilon-near-Zero Experiment

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 μm, 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 neff and its zero-crossing as an intrinsic measured reference, which is in agreement w...

Negative refraction due to discrete plasmon diffraction

We experimentally demonstrate spectrally broad (λ0=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 arrays interface and refocusing in an adjacent metal layer.

Near-field investigation of a periodic plasmonic metasurface

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.

Embedded plasmonic waveguides with Yagi-style antennas

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.