Controlling light-matter interaction with resonant semiconductor nanostructure
This thesis aims to bridge dielectric materials' optical and electronic properties to obtain full control of light-matter interaction at the nanoscale. The outcomes may open the way for tunable, ultra-thin, cost-effective, and energy-saving optoelectronic devices. This research first studies the optical modes of dielectric nanostructures, including toroidal dipole (TD) excitation under illuminations of structured light. The quantitative comparison between the structured light and plane wave illuminations shows a lot of promise for exciting dominant toroidal response in the geometrically simple photonic systems. The tightly focused radially polarised illumination shows a near-pure excitation of the TD in dielectric nanodisk. Additionally, it will be shown that the focused doughnut pulse could be a promising tool for the resonant excitation of toroidal response in photonic structures. Toroidal excitations are a potential way of increasing light-harvesting and boosting nonlinear light-matter interactions. This thesis is then involved in pioneering research in light detection by utilising nontrivial optical modes of dielectric nanostructures to improve the electrical characteristics of conventional photodetectors. It would open the way for all-dielectric nanophotonics to be at the same level of consumer products as electronics. We study the realisation of the high-speed and highly efficient photodetectors using germanium (Ge) metasurfaces. Semiconductors such as Ge are materials that are compatible with the complementary metal–oxide–semiconductor process and thus are the proper building material for the high-volume foundry process of photonic integrated circuits (PICs). The optical properties and steady-state and transient electric behaviours will be studied to analyse the electrical response at the telecommunication C-band, a major spectral choice for optical communication and signal processing in PICs. We also propose a polarisation-independent metasurface superabsorber by exploring the quasi-bound state in the continuum (QBIC) to improve photodetectors’ electrical characteristics, including their responsivity. As the asymmetry parameter mostly governs the Q-factor of QBICs, it gives a straightforward and efficient way of optimising the light absorption using critical coupling. The metasurface is designed to operate at the C-band, but it can be tuned for other bands in the telecommunication frequency range. Two designs boosting the light collection efficiency up to 50% in the transmission and up to 100% in the reflection modes will be proposed in this thesis. Despite the symmetry-broken nature of QBICs, our metasurface is insensitive to the polarisation of incoming light and thus provides great flexibility in the practical applicability of QBIC-based metasurfaces.
Nanophotonics, Dielectric Metasurfaces, anzsrc-for: 400909 Photonic and electro-optical devices, sensors and systems (excl. communications)
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