INFLUENCE OF THE THICKNESS OF THE n-Si SUBSTRATE AND ITS DOPING LEVEL ON THE ABSORBING PROPERTIES OF SILICON PLASMON STRUCTURES IN THE INFRARED RANGE

The absorption spectra of Si/SiO2/Si3N4/Si+ and Si/SiO2/Si+ structures with an island surface layer are calculated using the finite difference time domain method. The absorption spectra were modeled depending on the thickness of the substrate and its doping level. It was found that the thickness of the i-Si substrate does not affect the overall absorption of the structure. At the same time, an increase in the thickness of the n-Si substrate leads to an expansion of the absorption band with an intensity of more than 70%. It is established that the doping level of the substrate affects the absorption value of the structures and bandwidth with an absorption value above 80%. It is shown that a wide absorption band with intensity of more than 80% occurs at the doping level of the substrate in the range of 2 . 1019—5 . 1019 cm–3. Dispersion relations in the Si+/SiO2/Si+ structure with an unstructured surface layer are obtained. These dispersion relations may indicate the existence of plasmon oscillations in the system. It is established that a violation of the phase synchronization of the modes at both Si/dielectric interfaces at a significant difference between the doping levels of the substrate and the surface layer can lead to a decrease in the absorption.

Integrated high-contrast diffraction gratings for surface electromagnetic waves

We propose and theoretically and numerically investigate integrated high-contrast diffraction gratings for surface electromagnetic waves. We consider two platforms for the on-chip gratings: surface plasmon-polaritons propagating along metal-dielectric interfaces and Bloch surface waves propagating along interfaces of photonic crystals. We demonstrate that the optical properties of the studied integrated gratings are qualitatively close to the ones of the conventional high-contrast diffraction gratings. If the “parasitic” out-of-plane scattering is suppressed, the reflectance and transmittance of the on-chip gratings are not only qualitatively, but also quantitatively close to the corresponding values of the conventional “free-space” gratings. The obtained results may find application in novel integrated optical circuits.

Giant Second Harmonic Generation Enhancement by Ag Nanoparticles Compactly Distributed on Hexagonal Arrangements

The association of plasmonic nanostructures with nonlinear dielectric systems has been shown to provide useful platforms for boosting frequency conversion processes at metal-dielectric interfaces. Here, we report on an efficient route for engineering light–matter interaction processes in hybrid plasmonic-χ(2) dielectric systems to enhance second harmonic generation (SHG) processes confined in small spatial regions. By means of ferroelectric lithography, we have fabricated scalable micrometric arrangements of interacting silver nanoparticles compactly distributed on hexagonal regions. The fabricated polygonal microstructures support both localized and extended plasmonic modes, providing large spatial regions of field enhancement at the optical frequencies involved in the SHG process. We experimentally demonstrate that the resonant excitation of the plasmonic modes supported by the Ag nanoparticle-filled hexagons in the near infrared region produces an extraordinary 104-fold enhancement of the blue second harmonic intensity generated in the surface of a LiNbO3 crystal. The results open new perspectives for the design of efficient hybrid plasmonic frequency converters in miniaturized devices.

Broadband mid-infrared plasmon-polaritons in metallic-dielectric interfaces

We report real-space near-field images of mid-infrared (IR) surface plasmon-polariton (SPP) waves in the insulating/metal/insulating (IMI) heterostructure: hexagonal boron nitride/gold/silicon dioxide (hBN/Au/SiO2). The SPPs are observed in the 750 – 1500 cm-1 (~13.3 – ~6.7 μm) range, feature micrometer-sized wavelengths and propagation lengths (LSPP) exceeding 20 μm at room temperature. Comparatively, real-space mapping of SPP waves in the mid-IR has been shown only in graphene, but with nanometer sized-wavelength and LSPP ~ 10 μm at cryogenic temperatures. Interestingly, we show interference between different polariton types in the IMI since the lower momenta SPPs in the metal surface interfere with higher momenta hyperbolic phonon polaritons (HPhP) in the hBN top layer creating SPP-HPhP overlapped waves. In agreement with theory, we quantify momentum and damping governing the SPP waves. Tunability is discussed upon changing the IMI heterostructure. Our theory predicts SPP group velocities reaching 20 % of the light velocity in vacuum and 0.2 – 0.4 ps lifetimes. We further demonstrate that the SPP waves interact with SiO2 and hBN phonons in the strong coupling regime. As a general effect of the metal/dielectric interface, the mid-IR SPP waves can be compelling for fast metal-based plasmonics, whilst their ability to strongly couple to phonons can be further explored for enhanced sensing in the mid-IR.

Novel non-plasmonic nanolasers empowered by topology and interference effects

Historically, nanophotonics deals with a control of light at the nanoscale being closely connected with the rapid advances in plasmonics – the physics of surface plasmon polaritons supported by metal–dielectric interfaces. Properly engineered nanostructures allow the subwavelength propagation of light and its strong confinement in nanowaveguides and nanocavities, making possible the field enhancement and lasing. Spaser was suggested as a special type of nanolaser with a very small footprint that can be modulated quickly thus becoming a good candidate for on-chip optical data processing. However, recent developments in the physics of high-index dielectric nanoparticles and resonant dielectric metasurfaces allowed to advance the field of nanophotonics and introduce novel nonplasmonic nanostructures and nanolasers empowered by topology and interference effects. Here we present first some examples of experimentally realized spasers, and then discuss the recent developments in the cutting-edge high-index dielectric nanostructures employed for nonplasmonic nanolasers based on Mie resonances, anapole states, bound states in the continuum, and the physics of topological phases.

Optical properties of silicene-dielectric interfaces from IR to far UV

Since the growth of single layer of Si has emerged, silicene became a potential candidate material to make up the disadvantage of graphene. In this paper, the complex surface conductivity is applied to characterize the properties of silicene and we investigate the optical characterization of silicene-dielectric interfaces from IR to far UV range. The silicene-Si and silicene-Ge interfaces along both parallel and perpendicular polarization directions of electromagnetic field with normal incidence are considered in this work. The optical properties of the silicene-dielectric systems proposed in this paper lay a foundation for the performance of complex silicene-based optoelectronic devices such as sensors, detectors, filters, UV absorbers and so on.