Advanced Wavefront Control with Linear and Nonlinear Metasurfaces

Abstract

Metasurfaces offer unique opportunities for functional flat optics and allow controlling the transmission, reflection, and polarization of light. In particular, all-dielectric resonant metasurfaces have reached remarkable efficiencies and performances. The meta-atoms based on generalized Huygens' principle give flexible full-range phase modulation with nearly no loss. Holographic calculations can carefully map out the spatial arrangement of the meta-atoms and exploit the potential of the metasurface platform for wavefront control. Such advanced and complex wavefront engineering is fully studied and extended to the nonlinear regime, where the nonlinear optical response of metasurfaces opens up new degrees of freedom. This offers a paradigm shift in nonlinear optics. The nonlinear metaholograms are expected to revolutionize subwavelength photonics by enhancing substantially the nonlinear response of natural materials combined with an efficient control of the phase of their nonlinear waves. It is believed that the joint effects of advanced wavefront control in linear and nonlinear optics could eventually lead to integrated photonic computing and nanophotonics quantum circuits.

In this thesis, the development of the nonlinear holographic metasurfaces is presented in a progressive order. In Chapter 1, we provide a comprehensive introduction to the development of metasurfaces, followed by the motivation of creating practical nanophotonic devices. Chapter 2 explains the principles of designing holographic Metasurfaces and phase modulating meta-atoms. We demonstrate a complex wavefront control using the highly efficient polarization-insensitive holographic Huygens' metasurface based on resonant silicon meta-atoms. Moving forward, we demonstrate the transparent meta-holograms based on silicon metasurfaces that allow high-resolution grayscale images to be encoded. The holograms feature the highest diffraction and transmission efficiencies, and operate over a broad spectral range. Chapter 3 explores various types of nonlinear nano-antennas. The multipolar nature of nonlinear resonance is firstly proved by experiment using a nonlinear setup. Our method of optical diagnostics provides a fast and convenient way to acquire the information on materials' nonlinear responses, and it links the nonlinear behaviors of materials to their intrinsic properties. Both numerically and experimentally, the third-harmonic generation (THG) from silicon dimers composed of pairs of two identical silicon nanoparticles demonstrates the multipolar harmonic modes near the Mie resonances that allow shaping of directionality of nonlinear radiation. Efficient control of both electric and magnetic components of light leads to the enhancement of nonlinear effects near electric and magnetic Mie resonances with an engineered radiation directionality. Second harmonic generation (SHG) from III-V based nano-structures reveal that AlGaAs nanodisk antennas can emit second harmonic in preferential direction with a backward-to-forward ratio of up to five, and they can also generate complex vector polarization beams, including beams with radial polarization. We distinguish experimentally the contribution of electric and magnetic nonlinear response by analyzing the structure of polarization states of SHG vector beams. The transition between electric and magnetic nonlinearities is controlled continuously by tuning polarization of an optical pump. Finally, Chapter 4 presents a general theoretical approach and experimental platform for nonlinear wavefront control with highly-efficient nonlinear dielectric metasurfaces. This approach is based on the generalized Huygens' principle extended to nonlinear optics and it allows creating arbitrary phase gradients and wavefronts via excitation of electric and magnetic Mie-resonance multipoles. Based on our concept, we design and demonstrate experimentally the first nonlinear all-dielectric metasurface that generates a third harmonic signal with a high precision in its wavefront control. Multipolar analysis and numerical calculations are performed over a broad pump spectral range with comparisons to the experimental results. Chapter 5 summarizes the key achievements of this work and discusses the future applications based on these results.