Nonlinear optical frequency generation enabled by 2D structuring of matter

Abstract

Optical nonlinearity is determined by the structure of materials and, therefore, nanostructuring provides an opportunity to engineer nonlinear optical properties. In this thesis: I have developed the first Coulomb-coupled-oscillator model of nonlinear optical frequency generation in 2D dielectric nanostructures. The model demonstrated that in the confined geometry of a 2D nanoparticle the collective nonlinear response of the atomic array can arise from the Coulomb interactions of the optical electrons, even if the individual atoms exhibit no nonlinearity. I have discovered that, within the Coulomb-coupled-oscillator model, a 2D nanoparticle’s odd order nonlinearities scale with its area, while its even order nonlinearities scale with its perimeter. This result facilitates the design and optimization of nonlinear dielectric nanostructures for nanophotonics. I have observed that the presence of defects in 2D nanoparticles can lead to harmonic generation within the Coulomb-coupled oscillator model. The results show that defects have a large influence on even harmonic generation of 2D nanostructures. Information could be encoded in atomic defects via defect engineering and read by its harmonic generation signature. I have demonstrated the first fibre integrated all-dielectric metasurface for second harmonic generation. The metasurface is a double chevron array that supports a closed mode resonance for the fundamental wavelength at 1.5 µm with a quality factor of 30. A normalized second harmonic conversion efficiency of 8 × 10⁻³ /GW has been demonstrated, exceeding the previously achieved value for a silicon metamaterial by two orders of magnitude. The results of this thesis can be applied to design nonlinear metamaterials and provide guidance on enhancing and controlling the nonlinear response of nanoscale planar optical devices.

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Identifiers

ORCID for Jie Xu: orcid.org/0000-0002-8421-5097

ORCID for Eric Plum: orcid.org/0000-0002-1552-1840

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