Classical and Quantum Nanoscale Light Sources

Abstract

The growing demand for faster information transfer and processing requires highly-efficient devices with compact form factors. This can be realised by designing and developing nanoscale optical components that can be integrated into optical circuits. The functionality of such devices can be enhanced by using building blocks smaller than the wavelength of light and with carefully designed geometrical parameters to reach high concentrations of electromagnetic fields inside them. Such building blocks can also act like light sources, which can resonantly confine the light and re-emit it in a desired way. In this thesis I divide such building blocks into two classes: quantum and classical light sources. Classical light sources include nanoantennas, metamaterials and metasurfaces that are based on photoluminescence and nonlinear light generation, whereas quantum light sources are single-photon sources that may be based on cold atoms and ions, quantum dots, or defects in 2D materials or diamonds. In the past, much work has been done with plasmonic building blocks to increase the performance of nanoscale light sources, however, plasmonic resonances are accompanied by large dissipative losses. Recent developments of high-index dielectric nanoparticles suggest an alternative mechanism of light localisation via multipole resonances that can generate magnetic responses. The engineering of mode interference through, for example, adjustments to the resonators' shapes, or near-field manipulations between them, bring many novel effects. The subject of this thesis is nanoscale quantum and classical light sources based on such dielectric materials. The study of these systems provides knowledge of electromagnetic responses in order to control different types of sources for future applications. Chapter 1 provides an introduction to the different types of resonances and a review of concepts used in controlling quantum and classical light sources. This is followed by a review of the pioneering works on methods to enhance optical effects for different subwavelength structures. The chapter summarises the motivation and scope of the thesis. Chapter 2 describes the experimental methods used in the research, including the design and fabrication of nanostructures, and linear and nonlinear optical characterisation techniques. The chapter reports on functional optical components that I designed, fabricated and characterised for the research in this thesis. Chapter 3 focuses on observations of high-order harmonics in and resonators. It is shown that bound states in the continuum and Mie resonances lead to a dramatic enhancement of the efficiency of high-harmonic generation. The odd harmonics from the 3rd to 11th have been demonstrated from dielectric metasurfaces. The high-order harmonics up to the 7th have been observed from an individual subwavelength resonator. Chapter 4 explores photoluminescence from subwavelength dielectric resonators. The photoluminescence from resonators is identified as five-photon luminescence enabled by the interplay of Mie-type resonant modes. By using the designed and fabricated metasurface-based beam deflector, the photonic Rashba effect is observed, where the photons are splitted into two diffraction orders with left and right circular polarisation. Chapter 5 presents a study of spontaneous emission in quantum sources into free space, including theoretical analysis and experimental observations of the enhancement of the spontaneous emission rate of nitrogen-vacancy (NV) centres in diamond particles using nanoantennas. It has been shown that spherical silicon nanoantennas supporting resonances are able to reduce the lifetime of NV centres by 2 times, whereas the cylindrical ones can lead to an increased number of counts. Chapter 6 concludes the thesis and provides an outlook on how the presented research can be extended and how it can make an original contribution to the field of study. Show more