Plasmonic Metalens to Generate an Airy Beam.

Airy beams represent an important type of non-diffracting beams-they are the only non-diffracting wave in one dimension, and thus they can be produced with a cylindrical geometry that modifies a wavefront in one dimension. In this paper, we show the design of a cylindrical plasmonic metalens consisting of an array of nanoslits in a gold thin layer that modulates the phase of a Gaussian beam to generate an airy beam propagating in free space. Based on the numerical results, we show that it is possible to generate an airy beam by only matching the phase of wavefronts coming out from the array of gold nanoslits to the airy beam phase at plane z=0. We numerically demonstrate that the airy beam exhibits bending over propagation and self-healing properties. The transmission efficiency is around 60%. The simplicity of the proposed structure open new perspectives in the design of flat metasurfaces for light-focusing applications.

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.

Integrated Optical Filters with Hyperbolic Metamaterials.

The growing development of nanotechnology requires the design of new devices that integrate different functionalities at a reduced scale. For on-chip applications such as optical communications or biosensing, it is necessary to selectively transmit a portion of the electromagnetic spectrum. This function is performed by the so-called band-pass filters. While several plasmonic nanostructures of complex fabrication integrated to optical waveguides have been proposed, hyperbolic metamaterials remain almost unexplored for the design of integrated band-pass filters at optical wavelengths. By making use of the effective medium theory and finite integration technique, in this contribution we numerically study an integrated device consisting of a one-dimensional hyperbolic metamaterial placed on top of a photonic waveguide. The results show that the filling fraction, period, and number of layers modify the spectral response of the device, but not for type II and effective metal metamaterials. For the proposed Au-TiO2 multilayered system, the filter operates at a wavelength of 760 nm, spectral bandwidth of 100 nm and transmission efficiency above 40%. The designed devices open new perspectives for the development of integrated band-pass filters of small scale for on-chip integrated optics applications.

Plasmonic-Induced Transparencies in an Integrated Metaphotonic System.

In this contribution, we numerically demonstrate the generation of plasmonic transparency windows in the transmission spectrum of an integrated metaphotonic device. The hybrid photonic-plasmonic structure consists of two rectangular-shaped gold nanoparticles fully embedded in the core of a multimode dielectric optical waveguide, with their major axis aligned to the electric field lines of transverse electric guided modes. We show that these transparencies arise from different phenomena depending on the symmetry of the guided modes. For the TE0 mode, the quadrupolar and dipolar plasmonic resonances of the nanoparticles are weakly coupled, and the transparency window is due to the plasmonic analogue of electromagnetically induced transparency. For the TE1 mode, the quadrupolar and dipolar resonances of the nanoparticles are strongly coupled, and the transparency is originated from the classical analogue of the Autler-Townes effect. This analysis contributes to the understanding of plasmonic transparency windows, opening new perspectives in the design of on-chip devices for optical communications, sensing, and signal filtering applications.

Excitation of surface plasmon polaritons in a gold nanoslab on ion-exchanged waveguide technology.

Integrated metaphotonic devices has opened new horizons to control light-guiding properties at nanoscale; particularly interesting is the application of plasmonic nanostructures coupled to dielectric waveguides to reduce the inherent light propagation losses in metallic metamaterials. In this contribution, we show the feasibility of using ion-exchanged glass waveguides (IExWg) as a platform for the efficient excitation of surface plasmon polaritons (SPP). These IExWg provide high coupling efficiency and low butt-coupling with conventional dielectric optical waveguides and fibers, overcoming the hard fabrication tunability of commonly used CMOS-guiding platforms. We present a near-field scanning optical microscopy characterization of the propagation characteristics of SPP supported in a gold nanoslab fabricated on top of an IExWg. We found that the SPP can be only be excited with the fundamental TM photonic mode of the waveguide. Thanks to the low propagation loss, low birefringence, and compatibility with optical fibers, glass waveguide technology is a promising platform for the development of integrated plasmonic devices operating at visible and near infrared wavelengths with potential applications in single molecule emission routing or biosensing devices.

Integrated metaphotonics: symmetries and confined excitation of LSP resonances in a single metallic nanoparticle.

Using numerical simulations, we demonstrate that the dipolar plasmonic resonance of a single metallic nanoparticle inserted in the core of a dielectric waveguide can be excited with higher order photonic modes of the waveguide only if their symmetry is compatible with the charge distribution of the plasmonic mode. For the case of a symmetric waveguide, we demonstrate that this condition is only achieved if the particle is shifted from the center of the core. The simple and comprehensive analysis presented in this contribution will serve as basis for applications in integrated nanophotonic/metamaterials devices, such as optical filters, modulators and mode converters.

Hybrid integrated optical waveguides in glass for enhanced visible photoluminescence of nanoemitters.

Integrated optical devices able to control light-matter interactions on the nanoscale have attracted the attention of the scientific community in recent years. However, most of these devices are based on silicon waveguides, limiting their use for telecommunication wavelengths. In this contribution, we propose an integrated device that operates with light in the visible spectrum. The proposed device is a hybrid structure consisting of a high-refractive-index layer placed on top of an ion-exchanged glass waveguide. We demonstrate that this hybrid structure serves as an efficient light coupler for the excitation of nanoemitters. The numerical and experimental results show that the device can enhance the electromagnetic field confinement up to 11 times, allowing a higher photoluminescence signal from nanocrystals placed on its surface. The designed device opens new perspectives in the generation of new optical devices suitable for quantum information or for optical sensing.