Multifunctional metaphotonics and metasurfaces

Abstract

Future multifunctional optical systems will require densely integrated, tunable nanophotonic circuitry. For many years, plasmonics was a dominant platform for subwavelength optics, but the emerging field of resonant metaphotonics offers a versatile alternative. Metaphotonics merges principles from metamaterials and nanophotonics, offering new avenues for achieving exotic optical responses at scales much smaller than the wavelength of light. By leveraging resonances in high-index dielectric nanoparticles and metasurfaces, metaphotonics enables precise control over light-matter interactions at the nanoscale. Recent advances in material science, including polymers, perovskites, phase-change materials, and van der Waals structures, further expand the functional capabilities of metaphotonic systems. This allows for efficient spatial and temporal manipulation of light via multipolar resonances and bound states in the continuum, opening new avenues for photonic applications.

This thesis explores the nonlinear optical and photoluminescence properties of metaphotonic structures composed of both well-established and newly emerging materials. We develop novel strategies to enhance high-harmonic generation in semiconductor metasurfaces, control photoluminescence in halide perovskite nanostructures, and design systems with highly chiral linear and nonlinear response with van der Waals materials. Our work focuses on individual supercrystals assembled from perovskite nanocrystals and planar metasurfaces composed of diverse materials. The overarching goal is to underpin the development next-generation meta-devices for ultra-compact, efficient nonlinear frequency conversion, low-threshold nanolasers, and compact quantum light sources.

Chapter 1 introduces resonant phenomena in metaphotonics. This is followed by a review of selected works in the field of metaphotonics and emerging materials for metaphotonics. The chapter summarises the motivation and scope of the thesis.

Chapter 2 presents multiscale active supercrystal meta-atoms composed of halide perovskite nanocrystals. We experimentally characterise their optical properties, demonstrating visible and near-infrared Mie resonances in scattering. Accelerated photoluminescence due to the Purcell effect and the emergence of exciton-Mie mode polaritonic effects at cryogenic temperatures are also discussed.

Chapter 3 explores resonant nonlocal dielectric metasurfaces for enhanced fifth-harmonic generation in halide perovskites. For the first time, we demonstrate that structured perovskite metasurfaces supporting high-quality resonances in the visible range exhibit two orders of magnitude enhancement in fifth-harmonic generation within a deeply subwavelength-thin geometry.

Chapter 4 investigates even-order harmonic generation in high-Q resonant metasurfaces. We reveal significant harmonic enhancement under resonant conditions, achieving second-harmonic brightness approaching that of the third harmonic. For the first time, the fourth harmonic is demonstrated in a metasurface made of a centrosymmetric material. Additionally, we observe deviations from conventional power laws for even harmonics near the resonances.

Chapter 5 examines chiral third-harmonic generation in metasurfaces. For the first time, we demonstrate that van der Waals metasurfaces, empowered by quasi-bound states in the continuum, enhance third-harmonic signals by three orders of magnitude and exhibit wavelength-dependent nonlinear circular dichroism. Furthermore, metasurfaces with achiral meta-atoms arranged in a monoclinic lattice exhibit pronounced linear and nonlinear chiral responses despite their highly symmetric design.

Finally, Chapter 6 summarises the key findings, concludes the thesis, and outlines future research directions in nonlinear metaphotonics Show more