Arian Kriesch

Nanoscale Conducting Oxide PlasMOStor

We experimentally demonstrate an ultracompact PlasMOStor, a plasmon slot waveguide field-effect modulator based on a transparent conducting oxide active region. By electrically modulating the conducting oxide material deposited into the gaps of highly confined plasmonic slot waveguides, we demonstrate field-effect dynamics giving rise to modulation with high dynamic range (2.71 dB/μm) and low waveguide loss (∼0.45 dB/μm). The large modulation strength is due to the large change in complex dielectric function when the signal wavelength approaches the surface plasmon resonance in the voltage-tuned conducting oxide accumulation layer. The results provide insight about the design of ultracompact, nanoscale modulators for future integrated nanophotonic circuits.

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.

Conical-shaped titania nanotubes for optimized light management in DSSCs reach back-side illumination efficiencies > 8%

In the present work, we introduce the anodic growth of conical shaped TiO2 nanotube arrays. These titania nanocones provide a scaffold for dye-sensitized solar cell (DSSC) structures with significantly improved photon management, providing an optimized absorption profile compared with conventional cylindrical nanotube arrays. Finite difference time domain (FDTD) modelling demonstrates a drastically changed power-absorption characteristic over the tube length. When used in a back-side illumination DSSC configuration, nanocone structures can reach over 60% higher solar cell conversion efficiency (η) than conventional tubes. The resulting η ≈ 8% represents one of the highest reported values for Gratzel type DSSCs used under back-side illumination.

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.

Studies of plasmonic hot-spot translation by a metal-dielectric layered superlens

We have studied the ability of a lamellar near-field superlens to transfer an enhanced electromagnetic field to the far side of the lens. In this work, we have experimentally and numerically investigated superlensing in the visible range. By using the resonant hot-spot field enhancements from optical nanoantennas as sources, we investigated the translation of these sources to the far side of a layered silver-silica superlens operating in the canalization regime. Using near-field scanning optical microscopy (NSOM), we have observed evidence of superlens-enabled enhanced-field translation at a wavelength of about 680 nm. Specifically, we discuss our recent experimental and simulation results on the translation of hot spots using a silver-silica layered superlens design. We compare the experimental results with our numerical simulations and discuss the perspectives and limitations of our approach.

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.