Plasmonic Coupled Modes in a Metal-Dielectric Periodic Nanostructure

In this study we investigate the optical properties of a 2D-gap surface plasmon metasurface composed of gold nanoblocks (nanoantennas) arranged in a metal-dielectric configuration. This novel structure demonstrates the capability of generating simultaneous multi-plasmonic resonances and offers tunability within the near-infrared domain. Through finite difference time domain (FDTD) simulations, we analyze the metasurface's reflectance spectra for various lattice periods and identify two distinct dips with near-zero reflectance, indicative of resonant modes. Notably, the broader dip at 1150 nm exhibits consistent behavior across all lattice periodicities, attributed to a Fano-type hybridization mechanism originating from the overlap between localized surface plasmons (LSPs) of metallic nanoblocks and surface plasmon polaritons (SPPs) of the underlying metal layer. Additionally, we investigate the influence of dielectric gap thickness on the gap surface plasmon resonance and observe a blue shift for smaller gaps and a spectral red shift for gaps larger than 100 nm. The dispersion analysis of resonance wavelengths reveals an anticrossing region, indicating the hybridization of localized and propagating modes at wavelengths around 1080 nm with similar periodicities. The simplicity and tunability of our metasurface design hold promise for compact optical platforms based on reflection mode operation. Potential applications include multi-channel biosensors, second-harmonic generation, and multi-wavelength surface-enhanced spectroscopy.

Plasmonic directional couplers using channel waveguides in random arrays of metal nanoparticles

Plasmonic directional couplers based on channel waveguides embedded in random arrays of metal nanoparticles (NPs) operating in near-infrared are fabricated using electron-beam lithography and investigated experimentally characterizing their performance with leakage-radiation microscopy. The power exchange between coupled waveguides, its spatial period and efficiency, along with the overall power transmission, are determined in the wavelength range from 700 to 800 nm. We introduce a simple coupled-mode approach based on three coupled waveguides. The composite system considers a waveguide consisting of NP-filled stripe with characteristics distinctly different from those of the channel waveguides. Using this model, we describe the performance of investigated composite plasmonic configurations and obtain good qualitative agreement with experimental observations.

3D thickness map reconstruction of dielectric thin films using scattering of surface plasmon polaritons

Thin films are key elements in the current development of nanotechnology, and their characterization has become an essential task. In this Letter, we report on a technique to reconstruct full 3D maps of dielectric thin films using the scattered light of decoupled surface plasmon polaritons. Patterned magnesium fluoride thin films were fabricated, and their 3D thickness map was fully reconstructed with high (<1  nm) precision. This technique can be applied and easily adjusted to identify inhomogeneities in wide areas (mm²-cm²) of dielectric samples with subnanometer precision, or to characterize the fabrication processes involved in the preparation of patterned multilayered systems.

Plasmonic channel waveguides in random arrays of metallic nanoparticles

We report detailed characterization of surface plasmon-polariton guiding along 1-, 1.5- and 2-μm-wide channels in high-density (~75 μm^-2) random arrays of gold 70-nm-high and 50-nm-wide nanoparticles fabricated on a 70-nm-thin gold film supported by a 170-μm-thick silica substrate. The mode propagation losses, effective index dispersion, and scattering parameters are characterized using leakage-radiation microscopy, in direct and Fourier planes, in the wavelength range of 740-840 nm. It is found that the mode supported by 2-μm-wide channels propagates over > 10 μm in straight waveguides, with the corresponding S-bends and Y-splitters functioning reasonably well. The results show that the SPP waves can efficiently be guided by narrow scattering-free channels cut through randomly corrugated surface regions. The potential of this waveguiding mechanism is yet to be fully explored by tuning the scattering mean-free path and localization length via the density and size of random nanoparticles. Nevertheless, the results obtained are encouraging and promising diverse applications of these waveguide components in plasmonic circuitry.

Local excitation of surface plasmon polaritons using nitrogen-vacancy centers

Surface plasmon polaritons (SPPs) are locally excited at silver surfaces using (∼100) nanometer-sized nanodiamonds (NDs) with multiple nitrogen-vacancy (NV) centers (∼400). The fluorescences from an externally illuminated (at 532 nm) ND and from nearby NDs, which are not illuminated but produce out-of-plane scattering of SPPs excited by the illuminated ND, exhibit distinctly different wavelength spectra, showing short-wavelength filtering due to the SPP propagation loss. The results indicate that NDs with multiple NV centers can be used as efficient subwavelength SPP sources in planar integrated plasmonics for various applications.

Efficient excitation of channel plasmons in tailored, UV-lithography-defined V-grooves

We demonstrate the highly efficient (>50%) conversion of freely propagating light to channel plasmon-polaritons (CPPs) in gold V-groove waveguides using compact 1.6 μm long waveguide-termination coupling mirrors. Our straightforward fabrication process, involving UV-lithography and crystallographic silicon etching, forms the coupling mirrors innately and ensures exceptional-quality, wafer-scale device production. We tailor the V-shaped profiles by thermal silicon oxidation in order to shift initially wedge-located modes downward into the V-grooves, resulting in well-confined CPPs suitable for nanophotonic applications.

Detuned-resonator induced transparency in dielectric-loaded plasmonic waveguides

We report on the experimental demonstration of detuned-resonator induced transparency in the near-infrared (~800 nm) using two detuned racetrack resonators side-coupled to a bus waveguide. Both resonators and the bus waveguide are in the form of dielectric-loaded surface plasmon polariton waveguides. Leakage radiation microscopy imaging is employed to measure transmission spectra, featuring local maxima at intermediate wavelengths with asymmetrical profiles that are found in good agreement with full-wave numerical simulation results.

Generation of diffraction-free plasmonic beams with one-dimensional Bessel profiles

We demonstrate experimentally generation of diffraction-free plasmonic beams with zeroth- and first-order Bessel intensity profiles using axicon-like structures fabricated on gold film surfaces and designed to operate at a wavelength of 700 nm. The central beam features a very low divergence (~8π mrad) for a narrow waist of the order of one wavelength and the ability to self reconstruct, which are the main signatures of diffraction-free beams.