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Femtosecond Pulsed Laser Direct Writing System for Photomask FabricationNgoi, Kok Ann Bryan, Venkatakrishnan, K., Stanley, P., Lim, L.E.N. 01 1900 (has links)
Photomasks are the backbone of microfabrication industries. Currently they are fabricated by lithographic process, which is very expensive and time consuming since it is a several step process. These issues can be addressed by fabricating photomask by direct femtosecond laser writing, which is a single step process and comparatively cheaper and faster than lithography. In this paper we discuss about our investigations on the effect of two types of laser writing techniques, namely, front and rear side laser writing with regard to the feature size and the edge quality of the feature. It is proved conclusively that for the patterning of mask, front side laser writing is a better technique than rear side laser writing with regard to smaller feature size and better edge quality. Moreover the energy required for front side laser writing is considerably lower than that for rear side laser writing. / Singapore-MIT Alliance (SMA)
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Exploration du traitement au laser femtoseconde de supports transparents de nouveaux composants laser / Exploring femtosecond laser processing of transparent media for novel laser componentsGebremichael, Wendwesen 06 June 2019 (has links)
L’inscription par laser femtoseconde directe dans les cristaux laser offre une nouvelle opportunité de conception et développement de sources laser intégrées. Elle conduit à un prototypage rapide et à un bon rapport coût-efficacité, conformément aux futures feuilles de route de la photonique. Cependant, les défis liés au dépôt d’énergie d’un laser intense dans des milieux transparents et les modifications qui s’ensuivent restent encore des questions ouvertes. Ces défis ont été relevés en partie grâce à une étude minutieuse et systématique des zones modifiées par laser femtoseconde dans les matériaux transparents. Le fluorure de calcium (CaF2), en raison de sa symétrie cubique et de ses excellentes propriétés de luminescence en tant que cristal laser, a été choisi comme matériaux de référence dans cette thèse. L’inscription laser en régime femtoseconde de guides d’ondes à l’intérieur de ce cristal a été réalisée pour une conception future de source laser intégrée. Pour la première fois, des écritures laser « lisses » et non réciproques ont été observées à l’intérieur de certains échantillons « coupés spécialement » de cristaux de CaF2. De plus, un guidage de la lumière dépendant de la polarisation a été identifié et est présenté. Un modèle et une méthode ont été développés pour caractériser quantitativement et qualitativement ces guides d’ondes, en particulier pour les mesures de perte de transmission, ainsi que les cartographies tridimensionnelles de l’indice de réfraction des zones modifiées. / Femtosecond laser micromachining inside laser crystals offers a new platform to miniaturize highly compact laser sources. It leads to rapid prototyping and cost-effectiveness in line with the future photonics roadmaps. However, the challenges in relation to an intense laser pulse energy deposition within transparent media and the modifications that follow still remain open-ended questions. These challenges have been addressed with a careful and systematic study of femtosecond modified zones inside transparent materials. Due to its cubic symmetry and excellent luminescence properties as laser crystal, Calcium Fluoride (CaF2) was selected, and ultrafast laser inscription of waveguides inside this crystal was realized. Smooth and non-reciprocal writings were observed inside certain “specially cut” samples of the CaF2 crystals for the first time. Additionally, polarization dependent guiding is identified and presented. Furthermore, an authentic model and concept was engaged for the quantitative and qualitative characterization of the waveguides, particularly for the transmission loss measurements and the three-dimensional refractive index mappings of the modified zones.
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Topological States in Waveguide Lattices / Topologiska tillstånd i vågledargitterFransén, Daniel January 2022 (has links)
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.
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