<p>Optical imaging methods are limited by the wavelength of light that they use and the amount of scatter that must be imaged through. Super-resolution imaging and sensing methods are those that bypass or mitigate such restrictions. Two super-resolution approaches are presented here using spatially or temporally structured light. Temporal intermittence or blinking of fluorescent emitters is exploited for localization through significant depths of heavy scatter to high resolution, and an efficient algorithm for doing so is presented.</p> <p>Such temporal structure of emission allows far greater resolution than previous comparable imaging methods, providing opportunities in biophotonics and environmental sensing. Spatial structure can be imposed on coherent light that passes through a heavily scattering medium, in the form of a speckle pattern. Speckle intensity correlations are sensitive to the motion of a moving object obscured by scatter, and we demonstrate that this scatter can act as an analyzer, enhancing this sensitivity as the amount of scatter increases. This increased sensitivity is studied using random matrix theory, and eigenchannel analysis is proposed as an explanation. Simulations demonstrate that a randomly scattering analyzer can give sub-wavelength geometric information about a translated, hidden object. Relative motion of structured illumination is explored, with simulations and mathematical analysis demonstrating far-subwavelength sensitivity using moving fields with multiple different types of structure. This work could enable a new approach for material inspection and characterization, and provide improvements in microscopy. </p>

[pt] Optomecânica, o estudo de forças induzidas pela luz sobre a matéria, teve grandes avanços nos últimos anos com diversas implicações sobre todas as ciências naturais. Pinças ópticas, por exemplo, são amplamente usadas na física, química e biologia para aprisionar nano e micropartículas com índice de refração maior do que o meio que a cerca usando, em geral, feixes Gaussianos. Generalizando essa técnica, trabalhos recentes começaram a explorar estados de ordem maior dos feixes eletromagnéticos e suas superposições para aprisionamento óptico, criando feixes com fase, modo e amplitude ajustáveis. Esses novos graus de liberdade permitem o uso de potenciais arbitrários e até mesmo forças dependentes do tempo capazes de induzir movimento controlado no objeto aprisionado. Nesse contexto de feixes estruturados, nós podemos explorar não apenas as forças atrativas entre luz e matéria, mas também as forças repulsivas que ocorrem quando o índice de refração da partícula é menor que o do meio circundante. Neste trabalho vamos explorar ambos cenários a partir da criação de feixes holográficos com um Modulador Espacial de Luz (SLM). Mais especificamente, vamos focar na implementação do feixe de foco escuro, ou feixe de garrafa, onde as partículas encontram equilíbrio em uma região sem incidência de luz. Resultados experimentais são apresentados e comparados com simulações numéricas baseadas na teoria de Lorentz-Mie e possíveis aplicações dessas pinças óticas inversas são discutidas em optomecânica e biologia. / [en] Optomechanics, the study of light-induced forces upon matter, has seen tremendous advances in recent years with broad implications to all natural sciences. Optical tweezers, for instance, are now widely used in physics, chemistry and biology to trap nano- and micro-objects with a refractive index greater than of its surrounding medium using typically Gaussian laser beams. Generalizing these techniques, recent works began to explore higher-order states of the electromagnetic field and its superpositions for optical trapping, creating beams with customized phase, mode and amplitude. These new degrees of freedom allows for optical potentials beyond the harmonic approximation, enabling virtually arbitrary potential forms and even time-dependent forces capable of inducing controlled motion on the trapped object. Within this context of structured light beams, we can explore not only the attractive forces between light and matter but the repulsive ones that arise when the particle s refractive index is smaller than that of its medium. In this work we explore both scenarios by creating holographic beams with a Spatial Light Modulator (SLM). Specifically, we focus on the implementation of the dark focus beam, or optical bottle beam, where particles may find equilibrium in a region with no incidence of light. Experimental results are presented and compared to Lorentz-Mie numerical simulations and possible applications of these inverted optical tweezers in optomechanics and biology are discussed.

The creation of a digital model of a physical artifact can be a viable method for preserving physical artifacts from deterioration. The purpose of this thesis is to explore how to make digital artifact creation more accessible to non-scanning experts in order to expand the field of historical preservation to all people. The goal of the thesis is to determine which method of digital artifact capture produces the highest fidelity digital artifact while balancing user accessibility, cost, and usability. This study analyzed this through the creation of an online survey that asked participants to compare models created utilizing various digital capture methods. The results of the survey suggest that photogrammetry is currently the best method of high-fidelity digital artifact creation that balances accessibility, cost, and usability. The results also suggest that photogrammetry is effective at creating digital models of small artifacts with characteristics that typically cause errors in data capture and three-dimensional model creation. These results support the potential for democratizing digital artifact creation to include the contributions of non-experts from all communities and backgrounds, potentially deepening historical knowledge.

When nematic liquid crystals are placed between parallel glass plates with differing alignment directions, the bulk will twist in order to match the boundary conditions. This phenomenon of a twisted cell has been used extensively for the development of everyday liquid-crystal displays. However, there has been limited study of the twisted cell beyond the 90-degree twist case. In this thesis, I explore the behaviour of inhomogeneous liquid-crystal devices where the front and back alignment layers are uniquely and spatially patterned. This creates a non-symmetric device which can act on light differently depending on the orientation of the device and an externally applied voltage. The effect on the polarization of light is theoretically modelled using Jones matrices, and elastic continuum theory is employed to fully understand how the twist and tilt distributions of the liquid crystals change with field strength. Different pattern configurations were fabricated, tested, and characterized, revealing the complex behaviour that occurs with an applied electric field. Liquid-crystal devices provide a bespoke way of tailoring the spatial distribution of light and photons. A set of quantum key distribution experiments through underwater channels, leveraging these devices to encode information on structured photons, is also presented.

The growth of data capacity in optical communications links, which form the critical backbone of the modern internet, is facing a slowdown due to fundamental nonlinear limitations, leading to an impending "capacity crunch" on the horizon. Current technology has already exhausted degrees of freedom such as wavelength, amplitude, phase and polarization, leaving spatial multiplexing as the last available dimension to be efficiently exploited. To minimize the significant energy requirements associated with digital signal processing, it is critical to explore the upper limit of unmixed spatial channels in an optical fiber, which necessitates ideally packing spatial channels either in real space or in momentum space. The former strategy is realized by uncoupled multi-core fibers whose channel count has already saturated due to reliability constraint limiting fiber sizes. The later strategy is realized by the unmixed multimode fiber whose high spatial efficiency suggest the possibility of high channel-count scalability but the right subset of mode ought to be selected in order to mitigate mode coupling that is ever-present due to the plethora of perturbations a fiber normally experiences. The azimuthal modes in ring-core fibers turn out to be one of the most spatially efficient in this regard, by exploiting light’s orbital angular momentum (OAM). Unmixed mode counts have reached 12 in a ~1km fiber and 24 in a ~10m fiber. However, there is a fundamental bottleneck for scalability of conventionally bound modes and their relatively high crosstalks restricts their utility to device length applications. In this thesis, we provide a fundamental solution to further fuel the unmixed-channel count in an MMF. We utilize the phenomenon of topological confinement, which is a regime of light guidance beyond conventional cutoff that has, to the best of our knowledge, never been demonstrated till publications based on the subject matter of this thesis. In this regime, light is guided by the centrifugal barrier created by light’s OAM itself rather than conventional total internal reflection arising from the index inhomogeneity of the fiber. The loss of these topologically confined modes (TCMs) decreases down to negligible levels by increasing the OAM of fiber modes, because the centrifugal barrier that keeps photons confined to a fiber core increases with the OAM value of the mode. This leads to low-loss transmission in a km-scale fiber of these cutoff modes. Crucially, the mode-dependent confinement loss of TCMs further lifts the degeneracy of wavevectors in the complex space, leading to frustration of phase-matched coupling. This thus allows further scaling the mode count that was previously hindered by degenerate mode coupling in conventionally bound fiber modes. The frustrated coupling of TCMs thus enables a record amount of unmixed OAM modes in any type of fiber that features a high index contrast, whether specially structured as a ring-core, or simply constructed as a step-index fiber. Using all these favorable attributes, we achieve up to 50 low-loss modes with record low crosstalk (approaching -45 dB/km) over a 130-nm bandwidth in a ~1km-long ring-core fiber. The TCM effect promises to be inherently scalable, suggesting that even higher modes counts can be obtained in the future using this design methodology. Hence, the use of TCMs promises breaking the record spectral efficiency, potentially making it the choice for transmission links in future Space-Division-Multiplexing systems. Apart from their chief attribute of significantly increasing the information content per photon for quantum or classical networks, we expect that this new light guidance may find other applications such as in nonlinear signal processing and light-matter interactions.

No / Excavations in the 1920s and 1970s at the Sculptor’s Cave, North-East Scotland, revealed that the site was used for mortuary rituals during the Late Bronze Age (c. 1100–800 BC) and Roman Iron Age (late first to fourth centuries AD), whilst a series of Pictish symbols carved into its entrance walls suggest that the cave’s importance continued into the Early Medieval Period. A new programme of analysis has utilised advanced 3D digital documentation and 3D metrology (specifically, 3D laser scanning) to enable this inaccessible site to be appreciated by wider audiences and analysed remotely. Detailed in situ recording of the Pictish symbols was undertaken using macro-level structured light scanning and the high-fidelity digital models blended with terrestrial laser scan data of the cave interior to show the location and detail of the carvings. This chapter examines the value of emerging digital approaches in the analysis, presentation and management of the Sculptor’s Cave, from the elucidation of additional carved details and the monitoring of surface degradation, to the dissemination of this difficult-to-access site to the wider public via online platforms. / Historic Environment Scotland provided funding for scanning work. Collaborators Visualising Heritage and Fragmented Heritage at the University of Bradford, funded by HEIF (via the University of Bradford) and the Arts and Humanities Research Council (AH/L00688X/1), respectively.

2025 / The development of fiber amplifiers plays a critical role in a wide range of applications, including high-energy systems, weak signal sensing and imaging, and optical communications, where Erbium-doped fiber amplifiers (EDFAs) are commonly utilized. In particular, the increasing demand for amplifiers capable of supporting a high number of data channels is essential to avoid the looming “capacity crunch” in information networks. However, any significant expansion in capacity will inevitably drive a substantial rise in energy consumption. Consequently, the integration of additional data channels in telecommunications must be approached with energy efficiency in mind. Spatial division multiplexing (SDM) has emerged as a promising solution, leveraging spatial dimensions such as modes or fiber cores to enable data parallelism, and is becoming the preferred technology for reducing energy usage in optical networks. This thesis examines the amplification dynamics and properties of multimode (MMF) ring-core fibers (RCFs) that can stably support spatial modes carrying orbital angular momentum (OAM), which can serve as independent, uncoupled signal channels. Notably, RCFs featuring topologically confined modes (TCMs) have demonstrated the highest uncoupled mode capacity among MMFs to date. We explore how these fibers can be turned into amplifiers by utilizing χ^(3) material nonlinearities and by developing doped MMF-EDFAs.In this work, we investigate the nonlinear effects of OAM modes in multimode fibers, with a particular focus on acousto-optic interactions between these modes and phonons, leading to the generation of Stimulated Brillouin Scattering (SBS). Traditionally, SBS in single-mode fiber amplifies a narrowband Stokes signal using a powerful pump, operating through a self-phase matching process. However, by utilizing OAM modes, we exploit their distinctive phase characteristics to exert greater control over this interaction. This leads to the introduction of a novel OAM conservation law, which governs the modulation of inter-modal interactions between the pump, phonons, and Stokes, allowing for adjustable nonlinear gain. Furthermore, the chiral properties of OAM modes enable the launch of superposition-state pumps in RCFs, resulting in polarization rotation, a phenomenon known as optical activity. This optical activity, characterized as a stable birefringent interference effect due to its geometrodynamic nature, creates a special phase-matching and polarization-selective condition. This condition allows for complete spatial phase conjugation of the pump state, as the Stokes signal must retrace the pump’s polarization rotation to achieve significant gain. This mechanism also provides control over Stokes growth and the gain threshold condition. Overall, our analysis demonstrates that OAM modes offer up a versatile degree of freedom for controlling amplification through fiber nonlinearities. RCFs and OAM modes present significant potential for developing high-data-capacity SDM-EDFAs, offering key advantages for stimulated emission-based amplification. The strong confinement of these modes within a doped fiber core enhances their interaction with erbium ions, facilitating the creation of highly absorbing and emitting amplifiers that outperform their single-mode and multi-core EDFA counterparts. Another benefit of using OAM modes lies in their similar intensity profiles, with their orthogonality primarily derived from distinct phase characteristics. Since EDFA amplification depends on intensity rather than phase, this architecture enables high, equalized gain and low-noise amplification across numerous spatial channels. We experimentally characterize an RCF-EDFA that leverages these advantages and topological confinement to achieve high-gain amplification across a record number of uncoupled OAM modal channels. Furthermore, simulations of an optimized, deployment-ready version of the EDFA further demonstrate its ability to amplify numerous spectral and spatial data channels simultaneously while maintaining high energy efficiency. This performance is made possible through a proposed pumping scheme in which the pump consists of a superposition of OAM fiber modes, like the signal, benefiting from the large and stable mode ensemble. By sculpting the modal distribution of the pump, the amplifier architecture is optimized to increase pump-signal overlap, achieving both high, equalized gain and low noise figures while reducing pump power requirements. This thesis explores this parameter space, through both simulations and experimental investigations, with the aim of developing optimal SDM fiber amplifiers that address the capacity, energy efficiency, and cost demands of future optical fiber networks.

Nowadays there is a strong demand for lighter vehicles in order to increase the pay load. Through this the specific fuel consumption is decreased, the amount of greenhouse gases is lowered and the transport economy improved. One possibility to optimize the weight is to make the components from high strength steels and join them by welding. Welding is the main joining method for fabrication of a large proportion of all engineering structures. Many components experience fatigue loading during all or part of their life time and welded connections are often the prime location of fatigue failure.Fatigue fracture in welded structures often initiates at the weld toe as aconsequence of large residual stresses and changes in geometry acting as stress concentrators. The objective of this research is to increase the understanding of the factors that control fatigue life in welded components made from very high strength steels with a yield strength of more than 800 MPa. In particular the influences of the local weld toe geometry (weld toe radius and angle) and residual stress on fatigue life have been studied. Residual stresses have been varied by welding with conventional as well as Low Transformation Temperature (LTT) filler materials. The three non-destructive techniques Weld Impression Analysis (WIA), Laser Scanning Profiling (LSP) and Structured Light Projection (SLP) have been applied to evaluate the weld toe geometry.Results suggest that all three methods could be used successfully to measure the weld toe radius and angle, but the obtained data are dependent on the evaluation procedure. WIA seems to be a suitable and economical choice when the aim is just finding the radius. However, SLP is a good method to fast obtain a threedimensional image of the weld profile, which also makes it more suitable for quality control in production. It was also found that the use of LTTconsumables increased fatigue life and that residual stress has a relatively larger influence than the weld toe geometry on fatigue strength of welded parts.

The inclusion of precision dairy farming technologies in dairy operations is an area of increasing research and industry direction. Machine vision based systems are suitable for the dairy environment as they do not inhibit workflow, are capable of continuous operation, and can be fully automated. The research of this dissertation developed and tested 3 machine vision based precision dairy farming technologies tailored to the latest generation of RGB+D cameras. The first system focused on testing various imaging approaches for the potential use of machine vision for automated dairy cow feed intake monitoring. The second system focused on monitoring the gradual change in body condition score (BCS) for 116 cows over a nearly 7 month period. Several proposed automated BCS systems have been previously developed by researchers, but none have monitored the gradual change in BCS for a duration of this magnitude. These gradual changes infer a great deal of beneficial and immediate information on the health condition of every individual cow being monitored. The third system focused on automated dairy cow feature detection using Haar cascade classifiers to detect anatomical features. These features included the tailhead, hips, and rear regions of the cow body. The features chosen were done so in order to aid machine vision applications in determining if and where a cow is present in an image or video frame. Once the cow has been detected, it must then be automatically identified in order to keep the system fully automated, which was also studied in a machine vision based approach in this research as a complimentary aspect to incorporate along with cow detection. Such systems have the potential to catch poor health conditions developing early on, aid in balancing the diet of the individual cow, and help farm management to better facilitate resources, monetary and otherwise, in an appropriate and efficient manner. Several different applications of this research are also discussed along with future directions for research, including the potential for additional automated precision dairy farming technologies, integrating many of these technologies into a unified system, and the use of alternative, potentially more robust machine vision cameras.

Cette thèse s'inscrit dans le cadre d'un projet national nommé SRDViand dont le but fut de développer un système robotisé pour le désossage et la découpe des animaux de boucherie. Afin de déterminer les trajectoires de découpe de manière intelligente, un système de lumière structurée a été développé. Il se réfère à des systèmes de vision qui utilisent des modèles de projection de lumière pour des tâches de reconstruction 3D. Afin d'obtenir les meilleurs résultats, la définition d'une nouvelle méthode d'étalonnage pour les systèmes de lumière structurée a été établie. Basé sur un large état de l'art et également sur la proposition d'une classification de ces méthodes, il a été proposé d'étalonner une paire caméra projecteur en utilisant l'asservissement visuel. La validité et les résultats de cette méthode ont été éprouvés sur la base de nombreux tests expérimentaux menés dans le cadre du projet SRDViand. Suite à l'élaboration de cette méthode, un prototype permettant la découpe des bovins a été réalisé. / This thesis is part of a national project named SRDViand whose aim was to develop a robotic system for the deboning and cutting of animals meat. To determine the cut paths, a structured light system has been developed. It refers to vision systems that use light projection models for 3D reconstruction tasks. To achieve best results, the definition of a new calibration method for structured light systems was established . Based on a large state of the art and also with a proposed classification of these methods, it has been proposed to calibrate a camera projector pair using visual servoing . The validity and the results of this method were tested on the basis of numerous experimental tests conducted under the SRDViand project. Following the development of this method, a prototype bovine cutting was performed .