High-efficiency second-harmonic generation in coupled nano Fabry-Perot thin resonators.

In this paper we experimentally demonstrate second-harmonic generation (SHG) enhancement in thin 1D periodic plasmonic nanostructures on GaAs in the infrared spectral range. Due to the properly designed coupling of horizontal Fabry-Perot nanoresonators that occurs inside these structures, the obtained conversion efficiencies go up to the 10-7 W-1 range. Moreover, we demonstrate that the engineering of the plasmonic nanoantenna dimensions on the same GaAs layer can lead to SHG enhancement for pump wavelengths ranging from 2.8 µm to 3.3 µm.

Experimental demonstration of second-harmonic generation in high χ2 metasurfaces.

Metasurfaces able to concentrate light at various wavelengths are promising for enhancing nonlinear interactions. In this Letter, we experimentally demonstrate infrared second-harmonic generation (SHG) by a multi-resonant nanostructure. A 100 GaAs layer embedded in a metal-insulator-metal waveguide is shown to support various localized resonances. One resonance enhances the nonlinear polarization due to the transverse magnetic (TM)-polarized pump wavelength near 3.2µm, while another is set near the TE-polarized generated wavelength (1.6µm). The measured SHG efficiency is higher than 10-9W-1 for pump wavelengths ranging from 2.9 to 3.3µm, which agrees with theoretical computations. This is typically 4 orders of magnitude higher than the equivalent GaAs membrane.

4000-enhancement of difference frequency generation in a mode-matching metamaterial.

In the wake of the control of light at the sub-wavelength scale by nanoresonators, metasurfaces allowing strong field exaltations are an attractive platform to enhance nonlinear processes. Recently, high efficiency second harmonic and difference frequency generations were demonstrated in metasurfaces that generate a nonlinear polarization normal to the surface. Here, we introduce a mode matched resonator that is able to produce this particular nonlinear polarization in a layer of gallium arsenide associated with a gold metasurface. The nonlinear conversion mechanism is described as a two-step process in which efficiency is shown to yield a good colocalization and a strong enhancement of the pump fields, as well as a high extraction efficiency of the generated field. This mode-matched metasurface is able to reach a difference frequency generation (DFG) efficiency of 10-2W/W2. This opens a new paradigm where alternative nonlinear materials could be reintroduced in metasurfaces and yields even higher efficiency than high effective χ(2) structures.