An optomechanical system consists of an optical cavity coupled to a mechanical oscillator. The system used for this work was a silica microsphere. In a silica microsphere, the optical cavity is formed by light that is confined by total internal reflection while circulating around the equator of the sphere. The mechanical oscillator is the mechanical breathing motion of the sphere itself. The optical cavity and mechanical oscillator are coupled by radiation pressure and by the mechanical oscillator physically changing the length of the optical cavity. The optomechanical analog to electromagnetically induced transparency (EIT), known as optomechanically induced transparency (OMIT), has previously been studied in its steady state. One topic of this dissertation is an experimental study of OMIT in the time domain. The results of these experimental demonstrations continue comparisons between EIT and OMIT, while also building a foundation for optomechanical light storage. In OMIT, an off-resonance control laser controls the interaction between on-resonance light and the mechanical oscillator. Optomechanical light storage makes use of this arrangement to store an optical signal as a mechanical excitation, which is then retrieved at a later time as an optical signal. This is done by using two temporally separated off-resonance control laser pulses. This technique is extremely flexible in frequency and displays a storage lifetime on the order of microseconds. Use of optomechanical systems for quantum mechanical applications is hindered by the thermal background noise of the mechanical oscillator. Addressing this issue by first cooling the mechanical oscillator is costly and fraught with difficulties. The final topic presented in this dissertation deals with this issue through the use of an optomechanical dark mode. Two optical modes can interact with the same mechanical mode. The dark mode is a state that couples the two optical modes but is decoupled from the mechanical oscillator. While our specific optomechanical system is limited by its somewhat modest optomechanical cooperativity, this conversion process can, in principle, preserve the quantum state of the signal, even at room temperature, opening the possibility for this technique to be applied in quantum information processing.

Les méta-surfaces permettent de contrôler efficacement es rayonnements électromagnétiques en manipulant la phase, l'amplitude et la polarisation des ondes. Pour de nombreuses applications, telles que des fonctions d’agilité, de commutations et de détection, des surfaces de haute performance sont nécessaires. L’objectif de cette thèse est d'explorer des méthodes innovantes permettant d'améliorer les facteurs de qualité des méta-surfaces dans les domaines micro-ondes et optique. La limitation des méta-surfaces est généralement liée aux pertes par rayonnement et à l'absorption non radiative. L'étude se concentre sur des solutions permettant la suppression des pertes de rayonnement en utilisant des concepts de mode sombre et de résonance de Fano. Un mécanisme d'excitation direct de mode sombre dans un résonateur individuel basé sur l’adaptation de symétrie est proposé. La possibilité d'améliorer l'efficacité de la réponse magnétique en optique est présentée. L'analyse de l'excitation par résonance de Fano dans un système de résonateurs couplés identiques est également réalisée sur la base du formalisme de la théorie des modes couplés. Deux configurations générales correspondant à l'arrangement spatial symétrique et énantiomères des résonateurs sont considérées. Dans le premier cas, le système de cavité formé par les méta-surfaces très proches fournit des caractéristiques spectrales très étroites et une sensibilité efficace élevée par rapport aux cavités Fabry-Perot conventionnelles. Dans le second cas, les caractéristiques de conception permettent de contrôler la suppression des pertes de rayonnement, permettant d'augmenter considérablement le facteur de qualité de la résonance de Fano. / Metasurfaces allows an effective control of electromagnetic radiation by manipulating phase, amplitude and polarization of electromagnetic waves. For numerous applications including tunable, switchable and sensing functionalities, high performance metasurfaces are required. The goal of this thesis is to explore innovative methods enabling to improve the quality factors of metasurfaces in microwave and optical domains. The limitation of metasurfaces is generally related to radiation losses and non-radiative absorption. The study is focused on solutions allowing the suppression of radiative losses by using concepts of dark mode and Fano resonance. A direct dark mode excitation mechanism in individual resonator based on symmetry matching is proposed. The possibility to enhance magnetic response efficiency in optical frequency range is presented. Analysis of Fano resonance excitation in a system of identical coupled resonators is also performed on the basis of coupled mode theory formalism. Two general configurations are considered corresponding to symmetric and enantiomeric space arrangement of resonators. In the first case, cavity system formed by near-field coupled metasurfaces provides sharp spectral characteristics and high efficient sensitivity compared to conventional Fabry-Perot cavities. In the second case the design features enables to control suppression of radiation losses, allowing to considerably increase Fano resonance quality factor.

Mörkt läge är ett digitalt gränssnittsläge där text eller annan viktig information visas i ljusa färger mot en mörk bakgrund. Detta är i kontrast till ljust läge – mörk text på vit bakgrund – som ofta anses som standard. Läsförståelse är förmågan att få en förståelse av en text, och är viktig på grund av den stora användningen av skriftlig information i samhället samt för inhämtningen av ny kunskap. Denna förmåga är särskilt viktig för personer i högre former av utbildning, såsom universitet och högskolor. Denna studie undersöker mörkt läges effekt på läsförståelse. Effekten testades genom att låta deltagarna göra en kortare version av läsförståelsedelen av ett högskoleprov i både mörkt och ljust läge. Totalt deltog 15 personer, och alla var studenter från EECS – skolan för elektroteknik och datavetenskap – på KTH. Denna studie finner endast en obetydlig skillnad mellan läsförståelse i ljust eller mörkt läge, då till fördel för ljust läge. Det måste dock noteras att studien varit mycket liten när det gäller antalet testdeltagare, vilket innebär att resultaten inte är särskilt robusta och kan knappast generaliseras till andra grupper. / Dark mode is a display setting where text or other important information is displayed in light colors on a dark background. This is in contrast to light mode, where dark text is displayed on a white background, which is often considered to be the standard. Reading comprehension is the ability to gain a deeper understanding of a text, and is important for the utilization of written information in society as well as the acquisition of new knowledge. This ability is especially important for people in higher levels of education, such as universities and colleges. This study investigates the effect of dark mode on reading comprehension. The effect was tested by letting participants perform a shorter version of the reading comprehension part of an older Swedish Scholastic Aptitude Test in both dark and light mode. In total 15 people participated, and all were students from the School of Electrical Engineering and Computer Science at KTH. This study finds only an insignificant difference between reading comprehension in light or dark mode, with the difference being in favor of light mode. It should be noted that the study has been very small in regards to the number of participants, meaning that the results are not very robust and can hardly be generalized for other groups of people.

Det har blivit vanligare att ge användare val mellan dark mode och light mode, en undersökning görs över hur det påverkar användaren att ha val mellan olika teman samt val av andra aspekter av en webbsidas design. Hur dessa val kan förbättra tillgängligheten för användare med funktionsvariation undersöks och diskuteras. Studien fokuserar på hur dessa val påverkar användare men också den tekniska aspekten av att ha användaralternativ. Två hypoteser kom upp, att version utan val skulle ha snabbast laddningstid och att användare finner det viktigt att ha med användaralternativ. Resultaten visar att den första hypotesen motbevisas medan den andra hypotesen bevisas. Inför framtiden så önskas mer fördjupning och utveckling speciellt då funktionsvariationer alltid kommer att finnas kvar. / <p>Det finns övrigt digitalt material (t.ex. film-, bild- eller ljudfiler) eller modeller/artefakter tillhörande examensarbetet som ska skickas till arkivet.</p>

Purpose – As screen time per individual increases, more users of digital devices experience ocular related diseases. The purpose of this study is to gather reasons for the vast popularity Dark Mode gained in contemporary society, by investigating previous design eras. As a general lack of trend analysis within user interface design has been identified, the goal of the study is to lay the foundation for further research in the field of user interface design. Method – The study relies on a qualitative literature review. Publications related to Dark Mode, light-on-dark color schemes and digital trends were analyzed for topic-specific content that was then elaborated to give a critically viewed framework of the emerging trend. Findings – The results of our study indicate that various factors led to creation of the hyped trend, known as Dark Mode. It was first and foremost practicality of the light-on-dark color scheme that paved the way for Dark Mode. All operating systems, many apps, platforms and even websites incorporated it in their design. Being an optional feature, Dark Mode makes it more comfortable for users to use their devices outside the light hours or in environments with bad lighting conditions. With Dark Mode users get a far-reaching personalization tool, that visually changes essentially the whole OS or app. From a psychological point of view this improves user satisfaction, as humans naturally are seeking way to be in control. Being in control of own devices is undoubtedly an important aspect of it. Besides that, Dark Mode houses potential to lower energy consumption of devices and provides users with longer battery times. This, however, only applies to devices with display technology like OLED, where backlighting is at least divided into zones, that can be turned off when not in use. Devices with conventional LED displays cannot benefit from lower energy consumption. Implications – The study indicates that individuals use Dark Mode for a more satisfying user experience as they feel e.g. less eye strain with a dark themed user interface. Editing and coding software is mostly designed in a light-on-dark color scheme, as users often work for long continuous hours on screen, surrounded by dark environment. As screen time per individual increases, more users are experiencing ocular diseases. In counteraction, society demanded dark themed interfaces for operating systems, websites, and apps. As individuals were already using unofficial dark themes on different interfaces, tech companies started releasing system updates to make Dark Mode a choice. As Apple released their user interface update just in 2019, Dark Mode is still a relevant trend discussed in the industry and society. Experts indicate that Dark Mode is here to stay, as it satisfies preferences of many users and makes current OLED screens and future digital devices with appropriate display technology more sustainable. Limitations – The time frame of the study, as well as the Covid-19 pandemic greatly limited the possibilities of conducting the study. Due to the novelty of the trend, there is lack of previous research, which limited the view on the subject to only work available. Keywords – Dark Mode, dark-on-light color scheme, retro trends, user interface design, user experience, digital trends, display, screen, screen time, eye strain