Design of Reconfigurable Intelligent Surfaces for Wireless Communication: A Review

Existing literature reviews predominantly focus on the theoretical aspects of reconfigurable intelligent surfaces (RISs), such as algorithms and models, while neglecting a thorough examination of the associated hardware components. To bridge this gap, this research paper presents a comprehensive overview of the hardware structure of RISs. The paper provides a classification of RIS cell designs and prototype systems, offering insights into the diverse configurations and functionalities. Moreover, the study explores potential future directions for RIS development. Notably, a novel RIS prototype design is introduced, which integrates seamlessly with a communication system for performance evaluation through signal gain and image formation experiments. The results demonstrate the significant potential of RISs in enhancing communication quality within signal blind zones and facilitating effective radio wave imaging

Novel Specialty Optical Fibers and Applications

Novel Specialty Optical Fibers and Applications focuses on the latest developments in specialty fiber technology and its applications. The aim of this reprint is to provide an overview of specialty optical fibers in terms of their technological developments and applications. Contributions include:1. Specialty fibers composed of special materials for new functionalities and applications in new spectral windows.2. Hollow-core fiber-based applications.3. Functionalized fibers.4. Structurally engineered fibers.5. Specialty fibers for distributed fiber sensors.6. Specialty fibers for communications

Advanced Photonic Sciences

The new emerging field of photonics has significantly attracted the interest of many societies, professionals and researchers around the world. The great importance of this field is due to its applicability and possible utilization in almost all scientific and industrial areas. This book presents some advanced research topics in photonics. It consists of 16 chapters organized into three sections: Integrated Photonics, Photonic Materials and Photonic Applications. It can be said that this book is a good contribution for paving the way for further innovations in photonic technology. The chapters have been written and reviewed by well-experienced researchers in their fields. In their contributions they demonstrated the most profound knowledge and expertise for interested individuals in this expanding field. The book will be a good reference for experienced professionals, academics and researchers as well as young researchers only starting their carrier in this field

Sonic and Photonic Crystals

Sonic/phononic crystals termed acoustic/sonic band gap media are elastic analogues of photonic crystals and have also recently received renewed attention in many acoustic applications. Photonic crystals have a periodic dielectric modulation with a spatial scale on the order of the optical wavelength. The design and optimization of photonic crystals can be utilized in many applications by combining factors related to the combinations of intermixing materials, lattice symmetry, lattice constant, filling factor, shape of the scattering object, and thickness of a structural layer. Through the publications and discussions of the research on sonic/phononic crystals, researchers can obtain effective and valuable results and improve their future development in related fields. Devices based on these crystals can be utilized in mechanical and physical applications and can also be designed for novel applications as based on the investigations in this Special Issue

Multi-Plane Light Converter based on metasurface and Machine Learning to understand the mode sorter’s applications

This scientific study delves into the realm of metasurfaces, offering an exhaustive investigation into their underlying principles, practical applications, and the fabrication methods imperative for their realisation. A focal point of this exploration is the detailed exposition of the fabrication process for the Multi-Plane Light Convertor (MPLC) device, supported by captured images validating the precision of each critical step. Initial results indicate the satisfactory functioning of the MPLC, yet further analyses and optimisations are deemed essential to unlock its full potential. The MPLC device demonstrates versatile applications across telecommunications, energy-related fiber sensing, medical imaging, and biological tomoholography. However, at present, no physical devices based on metasurfaces are available that can fully implement these functions. In parallel, a novel and robust fibre bend sensor has been developed, showcasing the capability to precisely locate bends through inter-modal coupling. Modal decomposition reduces sensitivity to relative phase, revealing features providing accurate information about the shape or position of bends within the fiber. The simplicity and cost-effectiveness of this approach offer potential applications in wearable technology, motion sensors and aircraft wing shape sensing. Both experiments revolve around the concept of a mode sorter. The first experiment focuses on creating a novel device not yet available on the market, specifically the Multi-Plane Light Converter (MPLC). The second set of experiments, on the other hand, is centered around the practical application of the mode sorter as an instrumental component. The combination of mode de-multiplexing with machine learning holds promise for powerful applications, particularly in scenarios where constant variations in relative phase can be treated as noise, such as monitoring atmospheric conditions or extracting information from environments with dense scattering. Practical deployment considerations include the need for retraining in cases of significant system or fiber type changes. Once fully trained, retraining intervals are typically weeks to months under normal temperature fluctuations, necessitating further research into extreme temperature variations encountered in applications like aviation. The use of multi-core fibers is recommended to enhance sensitivity to multiple directions. In summary, the study demonstrates the feasibility of utilizing machine learning for accurate millimetric-scale curvature detection by incorporating a mode sorter into the optical setup. While exhibiting robust performance, limitations exist in detecting bends or movements not introducing changes in inter-modal coupling and relative phase shifts. The consistent alignment and outcomes observed in experiments underscore the stability and reliability of the experimental setup, instilling confidence in the algorithm’s performance

Solution-Processed Perovskite Photodetectors

Photodetectors enable conversion from light signals to electrical signals and are widely used in both the civil and military field for applications such as missile guidance, optical communication, imaging and biomedical sensing. Although various semiconductors have been employed in photodetectors, their high cost and complexity of fabrication have hindered their further development. Recently, perovskites have attracted substantial interest due to their impressive optoelectronic properties, including tuneable bandgaps, large absorption coefficient, long diffusion length and high carrier mobility. However, perovskites are generally not stable when exposed to ambient air, which seriously degrades the device performance. In this thesis, all-inorganic perovskite quantum dot (QD)-based photodetectors are investigated to enhance the material quality, device photoresponse and environmental stability. Three efficient strategies are developed to optimise the material film morphology and optical properties, as well as light confinement. I also managed to develop perovskite QD detectors on flexible substrates. Firstly, caesium lead bromide (CsPbBr3) QDs were optimised by blending ZnO nanoparticles (NPs), and further employed in a heterostructured photodetector. The as-fabricated device exhibited an improved photoresponse, including a 10-fold improved responsivity (0.4 mA W-1) and a short response time of 73.5 ms, as well as an excellent air stability (~ 7 month) due to the enhanced film morphology and optical properties after the decoration of ZnO NPs. Secondly, CsBr/KBr additives and a photovoltaic architecture were developed to further boost the device performance. An enhanced surface morphology and crystal quality with reduced defects were achieved by CsBr/KBr mediation. The resulting flexible photodetectors exhibited a better photoresponse, good flexibility and outstanding electrical stability. Specifically, this optimized photodetector showed a high responsivity of 10.1 A W-1, a large detectivity approaching 1014 Jones, and an on/off ratio around 104. In addition to the material optimisations, anodic aluminium oxide plasmonic structures were adopted with control of geometry and decoration of metallic NPs in the perovskite photodetectors, which enabled efficient light transmission and collection, and resulted in a 40-fold enhancement in device photoresponse. In the future, I will continue to focus on material and structural optimisations to develop high-performance and stable optoelectronics. In addition, perovskite-based focal plane arrays have great potential to be investigated

Advanced Nanomaterials for Electrochemical Energy Conversion and Storage

This book focuses on advanced nanomaterials for energy conversion and storage, covering their design, synthesis, properties and applications in various fields. Developing advanced nanomaterials for high-performance and low-cost energy conversion and storage devices and technologies is of great significance in order to solve the issues of energy crisis and environmental pollution. In this book, various advanced nanomaterials for batteries, capacitors, electrocatalysis, nanogenerators, and magnetic nanomaterials are presente

Structuring high-order harmonic generation with the angular momentum of light

Tesis por compendio de publicaciones[ES] Los pulsos láser ultracortos son una herramienta única para explorar las dinámicas más rápidas de la materia. Sorprendentemente, los pulsos de láser más cortos obtenidos hasta la fecha se producen a partir del fenómeno no lineal de conversión de frecuencias de generación de armónicos de orden alto (HHG), que resulta en la emisión de pulsos con duraciones de attosegundo. Es importante destacar que estos pulsos de attosegundo pueden exhibir una propiedad muy interesante, el momento angular, que presenta dos formas diferentes, el momento angular de espín (SAM) y el momento angular orbital (OAM), y que abre nuevos escenarios para las interacciones luz-materia a escalas espaciales nanométricas y temporales ultracortas. En esta tesis desarrollamos un conjunto de esquemas para la crea- ción de armónicos de orden alto y pulsos de attosegundo con nuevas propiedades de momento angular mediante la estructuración del pro- ceso de HHG a través de las características de los haces incidentes. Para ese propósito, primero abordamos la descripción de los mecanismos físicos fundamentales de la HHG. En particular, estudiamos la ioniza- ción túnel en moléculas, descubriendo que depende de la ubicación del electrón dentro de la molécula, debido a la naturaleza extendida de estas. Esta característica deja huellas importantes en los espectros de HHG y de fotoelectrones. Por lo tanto, hemos desarrollado una receta para implementar este fenómeno en los modelos de campos intensos existentes. A continuación, predecimos y describimos teóricamente la gene- ración de haces láser en el ultravioleta extremo (XUV) con nuevas propiedades de momento angular que, en la mayoría de los casos, son también creadas y caracterizadas experimentalmente por nuestros colaboradores del grupo Kapteyn-Murnane en JILA, en la Universidad de Colorado (EE. UU.), y del grupo del Prof. M.-Ch. Chen del Instituto de Tecnologías Fotónicas de la Universidad Tsing Hua (Taiwán). Para empezar, demostramos la generación, por primera vez, de haces de luz con OAM variable en el tiempo, una propiedad que denominamos como el auto-torque de la luz. Es importante destacar que los haces con auto-torque surgen naturalmente en el régimen XUV cuando el campo incidente para la HHG está formado por dos vórtices infrarro- jos retardados en el tiempo. Bajo esta configuración, el OAM de los armónicos de orden alto cambia a lo largo del tiempo en una escala de tiempo de attosegundos, siendo la cantidad de auto-torque controlada a través de las propiedades temporales de los pulsos incidentes. Por lo tanto, creemos que los haces con auto-torque pueden servir como nuevas herramientas para la manipulación láser-materia. Además, mostramos cómo el OAM puede servir como instrumento para mani- pular las propiedades espectrales y de divergencia de los armónicos de orden alto. Empleando dos vórtices con el contenido adecuado de OAM como pulsos incidentes, obtenemos peines de frecuencias de armónicos de orden alto con un espaciado entre líneas espectrales sintonizable y baja divergencia. Este control es particularmente intere- sante para espectroscopía y formación de imagen en el XUV o incluso en los rayos X blandos. Además, presentamos varios esquemas para el control de la eliptici- dad de los pulsos de attosegundo y de los armónicos de orden alto. Utilizando la configuración no colineal contrarrotante, extraemos el escalado de la elipticidad de los armónicos de orden alto con la de los haces incidentes y desvelamos la información sobre la respuesta dipolar oculta en esa conexión. Además, mostramos la generación de vórtices polarizados circularmente a partir de la HHG usando un campo incidente bi-circular vorticial. Destacablemente, al seleccionar correctamente el OAM del campo incidente, podemos obtener, o bien pulsos de attosegundo polarizados circularmente, o bien armónicos de orden alto con baja carga topológica. Por último, demostramos teóricamente la generación de trenes de pulsos de attosegundo con estados de polarización ordenados temporalmente mediante la combi- nación de dos campos incidentes bi-circulares vorticiales retardados en el tiempo. Creemos que la generación de pulsos de attosegundo con elipticidad controlada se puede emplear para el estudio de la dinámica ultrarrápida de SAM en moléculas quirales o materiales magnéticos. [EN] Ultrashort laser pulses are a unique tool to explore the fastest dy- namics in matter. Remarkably, the shortest laser pulses to date are produced from the non-linear frequency upconversion phenomenon of high-order harmonic generation (HHG), which results in the emis- sion of pulses of attosecond durations. Importantly, such attosecond pulses can exhibit a very exciting property, the angular momentum, which presents two different forms, the spin angular momentum (SAM) and the orbital angular momentum (OAM), and that brings new sce- narios for the light-matter interactions at the nanometric spatial and ultrashort temporal scales. In this thesis work, we develop a compilation of schemes for the creation of high-order harmonics and attosecond pulses with novel angular momentum properties by structuring the HHG process through the characteristics of the driving beams. For that purpose, we first address the description of the fundamental physical mechanisms of HHG. In particular, we study the tunnel ionization in molecules, finding that it is site-specific—its rate depends on the position of the electronic wavefunction at the ion sites—, due to the extended nature of the molecules. This characteristic leaves important signatures in the HHG and photoelectron spectra. Therefore, we provide a recipe for implementing the site-specificity in the existing strong-field models. Afterwards, we theoretically predict and describe the creation of extreme-ultraviolet (XUV) beams with novel angular momentum prop- erties, which, in most of the cases, are experimentally generated and characterized by our collaborators from the Kapteyn-Murnane group in JILA, at the University of Colorado (USA) and from the group of Prof. M.-Ch. Chen at the Institute of Photonics Technologies of the Tsing Hua University (Taiwan). To begin with, we demonstrate the generation, for the first time, of light beams with time-varying OAM, a property which we denote as the self-torque of light. Importantly, self- torqued beams arise naturally in the XUV regime from HHG driven by two time-delayed infrared vortex beams. Under this configuration, the OAM of the high-order harmonics changes along time in the attosec- ond time-scale, being the amount of self-torque controlled through the temporal properties of the driving pulses. Thus, we believe that self-torqued beams can serve as unprecedented tools for laser-matter manipulation. In addition, we show how the OAM can serve as an instrument to manipulate the spectral and divergence properties of the high-order harmonics. By driving HHG with two vortex beams with properly selected OAM, we obtain high-order harmonic frequency combs with tunable line-spacing and low divergence. Such control is particularly interesting for XUV/soft-X-ray spectroscopy and imaging. Moreover, we present several schemes for the ellipticity control of the high-order harmonics and attosecond pulses. Using the non-collinear counter-rotating scheme, we extract the scaling of the ellipticity of the high-order harmonics with that of the driving beams’ and we unveil the information about the non-perturbative dipole response hidden in that connection. Also, we show the generation of circularly polarized vortex beams from HHG driven by a bi-circular vortex field. Interest- ingly, by properly selecting the OAM of the driving field we can obtain either circularly polarized attosecond pulses, or high-order harmonics with low topological charge. Finally, we theoretically demonstrate the generation of attosecond pulse trains with time-ordered polarization states by combining two time-delayed bi-circular vortex driving fields. We believe that the generation of attosecond pulses with controlled ellipticity can be employed for the study of ultrafast spin dynamics in chiral molecules or magnetic materials

Rydberg excitons in cuprous oxide : macroscopic quantum systems coupled to nanoplasmonic and nanophotonic components

Excitons in cuprous oxide have large binding energies, which implies that different principal quantum number state excitons can be created as they are energetically not spaced too closely to each other nor to the ionization continuum. High principal quantum number Rydberg excitons in cuprous oxide are macroscopic quantum systems with spatial extensions in the several hundreds of nm up to several µm range. This implies, that excitation with a focused light beam leads to a large overlap of light and matter wavefunctions and should lead to an enhanced optical transition. In this thesis, we are going to show that the dipole selection rules in cuprous oxide Rydberg excitons can be manipulated via excitation with orbital angular momentum light or via the quadrupole field of plasmonic antennas. Both such light fields posses a strong field gradient or an additional angular momentum. This way, different angular momentum quantum number state excitons can be switched on and off, which is attractive for quantum state engineering. The mesoscopic size of cuprous oxide Rydberg excitons also implies that already µm-sized structures lead to mesoscopic quantum size effects. This can be advantageous for the realization of quantum technologies, such as optical switching applications, based on cuprous oxide Rydberg excitons