Manipulating the flow of light is critical in the design and fabrication of light-based devices ranging from solar cells, smart cameras, liquid crystal display (LCD) screens, projectors and light emitting diodes (LEDs). Thin films configured with spatial patterns or modulations in refractive index exhibit strong and richly varied interactions with light beams. In this thesis, we show that embedding planar films with specific geometries of waveguide lattices allows precise control over the inflow and outflow of light. Specifically, we demonstrate the fabrication of a new class of waveguide-encoded polymer films that are generated through a single-step, room temperature technique. Here, waveguide encoded lattices with a range of symmetries are spontaneously inscribed in photopolymerizable resins by self-trapped beams of incandescent light. We describe the generation of lattices consisting of five intersecting arrays of waveguides, which confer a range of unprecedented properties including a large, panoramic field of view (FOV) infinite depth of field and multiple imaging functionalities including focusing and inversion. We have also fabricated lattices inspired by natural arthropodal compound eyes, which comprise a radial distribution of waveguide and in turn impart a continuous, enhanced FOV. We demonstrate the application of these films in controlling the beam profiles of LEDs including their divergence and convergence. Finally, we show that thin films patterned with a periodic array of planar waveguides serve as effective beam steering coatings, which deflect light away from the metallic front contacts of commercially available solar cells and in this way, increase their efficiency. / Thesis / Doctor of Philosophy (PhD)

Topological states in photonic systems are described by qualitative discrete quantum numbers and feature unique combinations of properties such as robustness to perturbations and dissipationless surface transport of energy and information. Due to the many easily accessible platforms in photonics, topological photonics is one of the spearheads of topological physics that has offered exciting possibilities for investigations of novel topological phenomena and numerous promising technological uses. This master thesis aims at investigating from a theoretical and experimental perspective the properties of topological states of interacting light modes in arrays of coupled waveguides. First, we present a review of recent advances in the recently emerged field of topological physics. Then we review recent work on lattice models that feature topological edge states, and subsequently, we identify the existence of robust corner states on the edge of honeycomb lattices. These states display, similarly to the corner states known in 1D SSH and 2D Kagome lattices, exponential localisation with naturally occurring total destructive interference. Additionally, the corner states share properties with the dynamic transport modes of photonic Floquet topological insulators. However, the origin of the corner localisation is different from the previously studied examples: instead of dimerised coupling strength, the asymmetric and dimerised number of neighbours in the direction of the corner generates the intensity gradient. Motivated by our numerical study, we outline an experimental realisation of the novel honeycomb corner states, by means of waveguide lattices written in glass. The waveguides are 3D written in the bulk of a glass sample, with the lattice pattern orthogonal to the main direction of propagation which acts as a time coordinate in the experiments. Femtosecond direct laser writing enables fabricating truly 3D waveguides. Our experimental preparations cover a study of the effects of fabrication parameters for the relevant structures. We discuss how the localisation and robustness properties of the honeycomb corner states would next be investigated in the prepared experimental setting. / Topologiska tillstånd i fotoniska system beskrivs av särskilda topologiska diskreta kvanttal och har unika kombinationer av egenskaper såsom robusthet mot fluktuationer och förlustfri yttransport av energi och information. Tack vare de många lättillgängliga plattformarna inom fotonik är topologisk fotonik en av spjutspetsarna inom topologisk fysik och har erbjudit unika möjligheter för undersökningar av nya topologiska fenomen och med många lovande tekniska användningsområden. Denna masteruppsats syftar till att undersöka, ur ett teoretiskt och experimentellt perspektiv, egenskaperna hos topologiska tillstånd av interagerande ljusmoder i gitter av kopplade vågledare. Först presenterar vi en översikt av de senaste framstegen inom det nyligen uppkomna området topologisk fysik. Sedan sammanfattar vi det senaste arbetet med gittermodeller som har topologiska kanttillstånd, och därefter identifierar vi förekomsten av robusta hörntillstånd på kanten av bikakegitter. Dessa tillstånd uppvisar, på samma sätt som hörntillstånden som är kända i 1D SSH- och 2D Kagome-gitter, hög kantlokalisering med naturligt förekommande total destruktiv interferens. Dessutom delar hörntillstånden egenskaper med de kända fotoniska Floquet-topologiska isolatorerna som uppvisar topologisk transport. Ursprunget till hörnlokaliseringen skiljer sig dock från de tidigare studerade exemplen: istället för en dimeriserad kopplingsstyrka genererar det asymmetriska och dimeriserade antalet grannar i hörnets riktning intensitetsgradienten. Med motivering i den numeriska studien inleder vi en experimentell realisering av de nya bikakehörntillstånden, med hjälp av vågledargitter skrivna i glas. Vågledarna är 3D-skrivna på insidan av ett glasprov, med gittermönstret ortogonalt mot huvudutbredningsriktningen som fungerar som en tidskoordinat i experimenten. Direkt laserskrivning med femtosekundlaser gör det möjligt att tillverka vågledare i tre dimensioner. Våra experimentella förberedelser omfattar en studie av effekterna av tillverkningsparametrar för de relevanta strukturerna. Vi diskuterar hur lokaliserings- och robusthetsegenskaperna för bikakehörntillstånden sedan skulle undersökas med den experimentella metoden.