Nonradiating Photonics with Resonant Dielectric Nanostructures

Nonradiating sources of energy have traditionally been studied in quantum mechanics and astrophysics, while receiving a very little attention in the photonics community. This situation has changed recently due to a number of pioneering theoretical studies and remarkable experimental demonstrations of the exotic states of light in dielectric resonant photonic structures and metasurfaces, with the possibility to localize efficiently the electromagnetic fields of high intensities within small volumes of matter. These recent advances underpin novel concepts in nanophotonics, and provide a promising pathway to overcome the problem of losses usually associated with metals and plasmonic materials for the efficient control of the light-matter interaction at the nanoscale. This review paper provides the general background and several snapshots of the recent results in this young yet prominent research field, focusing on two types of nonradiating states of light that both have been recently at the center of many studies in all-dielectric resonant meta-optics and metasurfaces: optical {\em anapoles} and photonic {\em bound states in the continuum}. We discuss a brief history of these states in optics, their underlying physics and manifestations, and also emphasize their differences and similarities. We also review some applications of such novel photonic states in both linear and nonlinear optics for the nanoscale field enhancement, a design of novel dielectric structures with high-$Q$ resonances, nonlinear wave mixing and enhanced harmonic generation, as well as advanced concepts for lasing and optical neural networks.Comment: 22 pages, 9 figures, review articl

Recent advances in strongly resonant and gradient all-dielectric metasurfaces

We provide a critical overview of recent advances in all-dielectric, strongly resonant and gradient metasurfaces, as their performance is pushed to the extreme in view of emerging flat-optics applications

Reconfigurable phase-change optical metasurfaces: novel design concepts to practicable devices

Optical metasurfaces have been proven to be capable of controlling amplitude, phase and polarization of optical beams without the need of bulky geometries, making them really attractive for the development of compact photonic devices. Recently, their combination with chalcogenide phase-change materials (traditionally employed in non-volatile optical and electrical memories), whose refractive index can be reversibly and repeatedly controlled, has been proposed to yield low power consumption tunable metasurfaces having several functionalities in a single device. However, despite phase-change memories are commercially available since various decades now, the unification of phase-change materials with metasurfaces towards real life applications is becoming a formidable task, mainly due to the several engineering branches involved in this technology, which sometimes compromise each other in a non-trivial way. This includes thermo/optical, thermo/electric, and chemical incompatibilities which are typically not taken into account by researchers working in the field, resulting in devices having exciting reconfigurable properties, but at the same time, lack of practicability. This thesis is therefore dedicated to the development of novel phase-change metasurface architectures which could partially or totally address such engineering problems. Particular emphasis has been put in the realization of reconfigurable metasurfaces for active wavefront control, as such a functionality remains relatively unexplored. The first part of this thesis focuses in the first experimental demonstration of active, reconfigurable non-mechanical beam steering devices working the near-infrared. This was achieved via integration of ultra-thin films of chalcogenide phase-change materials (in this case, the widely employed alloy Ge2Sb2Te5) within the body of a dielectric spacer in a plasmonic metal/insulator/metal metasurface architecture. Active, and optically reversible beam steering between two different angles with efficiencies up to 40% were demonstrated. The second part of this work shows the work carried out in metal-free metasurfaces as a way to manipulate optical beams with high efficiency in both transmission and/or reflection. This was achieved via combination of all-dielectric silicon nanocylinders with deeply-subwavelenght sized Ge2Sb2Te5 inclusions. By strategic placement of the phase-change inclusions in the regions of high electric field density, independent and active control of the metasuface resonances is demonstrated, with modulations depths as high as 70% and 65% in reflection and transmission respectively. Multilevel, and fully reversible optically-induced switching of the phasechange layer is also reported, with up to 11 levels of tunability over 8 switching cycles. Finally, the last section of this thesis introduces the concept of hybrid dielectric/plasmonic phase-change metasurfaces having key functional benefits when compared to both purely dielectric and plasmonic approaches. The proposed architectures showed great versatility in terms of both active amplitude and phase control, offering the possibility of designing devices for different purposes (i.e. such as active absorbers/modulators or beam steerers with enhanced efficiency) employing the same unit-cell configuration with minor geometry re-optimizations. Initial device experimental demonstrations of such an approach are discussed, as well as their potential in terms of delivering in-situ electrical switching capabilities using a metallic ground plane as a resistive heater.Engineering and Physical Sciences Research Council (EPSRC

Design and Optimization of a 3-D Plasmonic Huygens Metasurface for Highly-Efficient Flat Optics

For miniaturization of future USAF unmanned aerial and space systems to become feasible, accompanying sensor components of these systems must also be reduced in size, weight and power (SWaP). Metasurfaces can act as planar equivalents to bulk optics, and thus possess a high potential to meet these low-SWaP requirements. However, functional efficiencies of plasmonic metasurface architectures have been too low for practical application in the infrared (IR) regime. Huygens-like forward-scattering inclusions may provide a solution to this deficiency, but there is no academic consensus on an optimal plasmonic architecture for obtaining efficient phase control at high frequencies. This dissertation asks the question: what are the ideal topologies for generating Huygens-like metasurface building blocks across a full 2π phase space? Instead of employing any a priori assumption of fundamental scattering topologies, a genetic algorithm (GA) routine was developed to optimize a “blank slate” grid of binary voxels inside a 3D cavity, evolving the voxel bits until a near-globally optimal transmittance (T) was attained at a targeted phase. All resulting designs produced a normalized T≥80 across the entire 2π range, which is the highest metasurface efficiency reported to-date for a plasmonic solution in the IR regime

Optical Metasurfaces with Advanced Phase Control Functionalities

The development of a metasurface platform with advanced micro- and nano-fabrication techniques has attracted a lot of attention. It exhibits a broad range of applications in the lens, hologram, image processing, vortex beam generation, information encoding, sensing, etc. Metasurfaces are ultrathin planar nanostructures made of subwavelength metallic or dielectric elements that can efficiently control the light characteristics such as polarisation, dispersion, amplitude, and phase. The high-index dielectric metasurfaces exhibit low loss and produce various types of resonant effects such as Mie-type resonances, Huygens' resonances, and so on. The Huygens' resonant regime of the dielectric metasurfaces exhibits the near-unity transmission window with a 2pi-phase coverage. The efficient 2pi-phase control capability with high transmittance feature makes the metasurfaces versatile tools for wavefront manipulation. The challenge is to realize the practical application of the metadevices such as beam deflection, optical image processing, sensing, hologram, lens, and so on. The performance of such metadevices can be made highly efficient by incorporating carefully engineered phase discretisation. Due to such engineered subwavelength wave discretisation, new functionalities that are not possible to date can be achieved by governing the phase response. In this thesis, I will first demonstrate the efficient control of deflection angle with high diffraction efficiency in the visible wavelength. I will also discuss deeply subwavelength metasurface resonators for terahertz wavefront manipulation. Then, I will focus on a novel dielectric resonant metagrating-based highly sensitive optical biosensing technique. Finally, I will demonstrate Mie-resonant dielectric metasurfaces can be used as a passive filter to perform image processing in the form of edge detection of a target object

High-Efficiency Topology Optimization for Very Large-Scale Integrated-Photonics Inverse Design

This work establishes the mathematical and algorithmic framework necessary for a large-scale, photonics inverse-design methodology that is fully compatible with (and experimentally validated on) commercial, semiconductor-foundry platforms. Specifically, this new methodology quickly and efficiently designs high-performing, multi-functional devices and systems that operate despite various sources of fabrication or operating variability. By overcoming typical tradeoffs between design dimensionality, device footprint, functional complexity, computational cost, and realizable performance, this work paves a practical and proven path toward very large-scale integrated photonics (VLSIP), a key step in designing interferometrically stable architectures within fields like quantum computing, machine learning, and even augmented reality. First, this work introduces the field of photonic inverse design within the context of high-yield photonic integration, highlighting fundamental challenges that continue to impede long-term scalability. The algorithmic framework for a high-efficiency, hybrid time-/frequency-domain adjoint solver, along with comprehensive manufacturing constraints, are then presented. The practicality of this new framework is tested by designing numerous compact, broadband, and robust devices, such as polarization splitters and rotators, full-aperture grating couplers, and 90-degree optical hybrids, all of which were fabricated and tested on different commercial foundry platforms. Finally, these individual devices were monolithically integrated to form a Stokes-Vector Receiver (SVR), a high-capacity direct-detect communications system amenable to long-haul signal processing algorithms. The ultra-compact SVR demonstrates reliable performance across the entire C-band, validating the notion that this new photonics design paradigm is not only compatible with large-scale commercial foundries, but yields high-performing systems robust to common forms of fabrication and environmental variability.Ph.D

The International Linear Collider Technical Design Report - Volume 4: Detectors

The International Linear Collider Technical Design Report (TDR) describes in four volumes the physics case and the design of a 500 GeV centre-of-mass energy linear electron-positron collider based on superconducting radio-frequency technology using Niobium cavities as the accelerating structures. The accelerator can be extended to 1 TeV and also run as a Higgs factory at around 250 GeV and on the Z0 pole. A comprehensive value estimate of the accelerator is give, together with associated uncertainties. It is shown that no significant technical issues remain to be solved. Once a site is selected and the necessary site-dependent engineering is carried out, construction can begin immediately. The TDR also gives baseline documentation for two high-performance detectors that can share the ILC luminosity by being moved into and out of the beam line in a "push-pull" configuration. These detectors, ILD and SiD, are described in detail. They form the basis for a world-class experimental programme that promises to increase significantly our understanding of the fundamental processes that govern the evolution of the Universe.Comment: See also http://www.linearcollider.org/ILC/TDR . The full list of signatories is inside the Repor