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Background: Dielectric nanoantennas have recently emerged as an alternative solution to plasmonics for nonlinear light manipulation at the nanoscale, thanks to the magnetic and electric resonances, the strong nonlinearities, and the low ohmic losses characterizing high refractive-index materials in the visible/near-infrared (NIR) region of the spectrum. In this frame, AlGaAs nanoantennas demonstrated to be extremely efficient sources of second harmonic radiation. In particular, the nonlinear polarization of an optical system pumped at the anapole mode can be potentially boosted, due to both the strong dip in the scattering spectrum and the near-field enhancement, which are characteristic of this mode. Plasmonic nanostructures, on the other hand, remain the most promising solution to achieve strong local field confinement, especially in the NIR, where metals such as gold display relatively low losses. Results: We present a nonlinear hybrid antenna based on an AlGaAs nanopillar surrounded by a gold ring, which merges in a single platform the strong field confinement typically produced by plasmonic antennas with the high nonlinearity and low loss characteristics of dielectric nanoantennas. This platform allows enhancing the coupling of light to the nanopillar at coincidence with the anapole mode, hence boosting both second- and third-harmonic generation conversion efficiencies. More than one order of magnitude enhancement factors are measured for both processes with respect to the isolated structure. Conclusion: The present results reveal the possibility to achieve tuneable metamixers and higher resolution in nonlinear sensing and spectroscopy, by means of improved both pump coupling and emission efficiency due to the excitation of the anapole mode enhanced by the plasmonic nanoantenna.

Dielectric nanocavities are emerging as a versatile and powerful tool for the linear and nonlinear manipulation of light at the nanoscale. In this work, we exploit the effective coupling of electric and toroidal modes in AlGaAs nanodimers to locally enhance both electric and magnetic fields while minimizing the optical scattering, thereby optimizing their second-harmonic generation efficiency with respect to the case of a single isolated nanodisk. We also demonstrate that proper near-field coupling can provide further degrees of freedom to control the polarization state and the radiation diagram of the second-harmonic field.

We reveal that nonlinear effects at the nanoscale can be enhanced by bound states in the continuum. We demonstrate SHG from subwavelength AlGaAs nanoantennas with record-high conversion efficiency that exceeds by two orders of magnitude the conversion efficiency observed at the conditions of magnetic dipole Mie resonances. This gain is achieved due to the engineering of the mode structure that allows exploiting a high-Q supercavity mode at the fundamental frequency. These results constitute a significant step towards the development of highly-efficient frequency conversion metadevices in the subwavelength circuitry.

High-permittivity semiconductor nanoresonators have shown great potential for enhanced nonlinear light–matter interactions at the nanoscale due to the availability of a rich variety of resonances combined with low optical losses and a strong bulk nonlinearity. Second-harmonic generation in AlGaAs nanoantennas can be extremely efficient and exhibits a complex radiation pattern. However, the complexity of this far-field profile imposes severe constraints on practical applications and detection efficiency. In this work, we demonstrate, both experimentally and numerically, the control over the angular distribution of the second-harmonic radiation pattern from a monolithic AlGaAs-on-AlOx nanodisk by varying the polarization and the angle of incidence of the pump beam. By tuning the angle of incidence of a beam with s-polarized light from 0 to 45°, the detected second-harmonic signal is monotonically increased up to over an order of magnitude due to the strong dependence of the nonlinear radiation pattern on the pump beam properties. Our results demonstrate that precise angular measurements of the pump inclination can be performed with a relative intensity change of the second-harmonic signal up to 0.25 deg–1 and polarization discrimination, therefore establishing a new technique for background-free nanoscale nonlinear goniometry.

We demonstrate the shaping of the second-harmonic (SH) radiation pattern from a single AlGaAs nanodisk antenna using coplanar holographic gratings. The SH radiation emitted from the antenna toward the—otherwise forbidden—normal direction can be effectively redirected by suitably shifting the phase of the grating pattern in the azimuthal direction. The use of such gratings allows increasing the SH power collection efficiency by 2 orders of magnitude with respect to an isolated antenna and demonstrates the possibility of intensity-tailoring for an arbitrary collection angle. Such reconstruction of the nonlinear emission from nanoscale antennas represents the first step toward the application of all-dielectric nanostructures for nonlinear holography.

We demonstrate experimentally the generation of sum-frequency signal and heralded photons with non-classical correlations via spontaneous parametric down-conversion in AlGaAs nanodisks.

We demonstrate a 5-fold enhancement of second harmonic generation efficiency and control on polarization of thereby generated photons exploiting the near-field coupling between electric and toroidal dipole modes in AlGaAs nanodimers.

We report a theoretical model for the study of second harmonic generation in cylindrical structures of finite height. By changing the structure of the pump beam we demonstrate switching from magnetic to electric dipole radiation in the generated second harmonic frequency.

We fabricate AlGaAs nanoantennas on a glass substrate and demonstrate the highest nonlinear conversion efficiency of 10-4 with the capability for shaping the radiation patterns and polarization of the second harmonic emission in both forward and backward directions. We also decode dynamic multipolar contributions to the second harmonic generation within such nanoantennas.

Summary form only given. Two-dimensional (2D) transition-metal di-chalcogenides (TMDCs) with intrinsically-broken crystalline inversion symmetry have shown great promise for future nonlinear light sources. However, the sub-nanometer thickness of such active materials limits their overall nonlinear conversion efficiency. In this work, we demonstrate, for the first time to our knowledge, enhanced second-harmonic generation (SHG) from 2D MoSe 2 through integrating it with Si waveguide. Light from free space is coupled into a planar silicon waveguide by the inscribed grating coupler on the right. A MoSe 2 monolayer crystal is placed on top of the waveguide and is strongly bond to the surface by Van der Waals interactions. The evanescent field of the guided mode at the fundamental frequency (FF) of ~ 1550 nm interacts with the MoSe 2 material on top to generate second harmonic (SH). This structure increases the light-matter interaction length dramatically compared to free-space excitation, as well as allows for exact phase matching second order nonlinear processes through engineering of the waveguide dispersion. As a result, our MoSe 2 -Si platform could dramatically boost the SHG. Under the excitation by a focused FF beam at around 0.8 eV (resonant with the excitonic transitions in the 2D materials), we observed approximately 5 times enhancement of the SH signal at 1.6 eV, when exciting the monolayer by the evanescently-coupled waveguide mode, as compared to pumping the MoSe 2 piece directly from free space. The observed six-fold rotational pattern reflects the three-fold rotational symmetry of the crystal, and identifies the measured signal as SHG. The scheme we demonstrate here is Si based and ready for integration with silicon photonics platform. Especially, our work shows the light-matter interaction length of 2D TMDCs limited by monolayer thickness could be overcome by integration with a waveguide, which paves the way for many other nonlinear optical applications f

Two-dimensional transition-metal dichalcogenides (TMDCs) with intrinsically broken crystal inversion symmetry and large secondorder nonlinear responses have shown great promise for future nonlinear light sources. However, the sub-nanometer monolayer thickness of such materials limits the length of their nonlinear interaction with light. Here, we experimentally demonstrate the enhancement of the second-harmonic generation from monolayer MoSe2 by its integration onto a 220-nm-thick silicon waveguide. Such on-chip integration allows for a marked increase in the interaction length between the MoSe2 and the waveguide mode, further enabling phase matching of the nonlinear process. The demonstrated TMDC–silicon photonic hybrid integration opens the door to second-order nonlinear effects within the silicon photonic platform, including efficient frequency conversion, parametric amplification and the generation of entangled photon pairs.

We demonstrate experimentally sum-frequency generation in AlGaAs nano-resonators, establishing a quantum-classical correspondence with spontaneous parametric down-conversion. We predict that AlGaAs nano-resonators can be utilized as high-rate sources of photon pairs with non-classical correlations.