Abstract We propose a new scheme of lensed fiber employing a quadrangular-pyramid-shaped fiber endface (QPSFE) for the coupling high-power 980nm laser diodes and single-mode fibers. The quadrangular-pyramid-shaped fiber was accomplished by first grinding and polishing a flat surface to the center of fiber at the desired inclination angle of £c, rotating the fiber to £p and polishing to the center of fiber, repeating the same process on the other sides of the fiber by rotating the fiber to £k-£p and £p. Then the QPSFE was fabricated by heating the tip of quadrangular-pyramid-shaped fiber in a fusing splicer to form an elliptical microlens endface. A coupling efficiency of 85% has been demonstrated. This higher coupling efficiency of the QPSFE lensed fiber is attributed to the better matching of the elliptical Gaussian field distribution between the laser source and the fiber.

In recent years, even though the light output of GaN-related LED continues to increase, the brightness is still low compared to conventional lighting systems and it is necessary to further improve the light extraction of LEDs. In this study, the characteristics of LPD-SiO2 film and Al/SiO2/GaN MOS diode were investigated in advance of the formation of SiO2 micro structure for improving the oxide quality and controlling the deposition parameters. Temperature-difference method, post-annealing treatment, photochemical treatment, sulfurated treatment and etc. were used for the purposes of better properties of the MOS structure and the LED. To obtain higher light extraction efficiency of GaN LED, hemispherical SiO2 microlens was formed on the conventional and the flip-chip LEDs. The deposition mechanism had been developed to obtain the further improvements on the electrical and optical properties. The influences of epoxy encapsulation on the LEDs without and with microlens were also studied. Considering the refractive index of SiO2 is close to that of the epoxy, the enhancements of light extraction efficiency and angular optical distribution of GaN LED by using SiO2 microlens will be degraded after encapsulating. Therefore, we also tried to deposit ZnO film and rod on GaN LED by LPD method to maintain or further enhance the light extraction efficiency of GaN LEDs by the combining the micro structure and the epoxy encapsulation.

Integrated microlens array on a transparent film, called an optical film, provides interesting applications for various fields. In a FPD (Flat Panel Display), the optical films are the more important components to improve the efficiency and quality. In this dissertation, a diffuser film which consisted of two different microlens arrays on the two surfaces of a film was developed and used to enhance the brightness and uniformity of a light source. There were also several microlens arrays developed, such as a hexagonal microlens array with gap and gapless, a gapless dual-curvature microlens array and a diffuser film. A process called polygonal microlens array process had been used to manufacture them. It had advantages of mass production, various polygonal shapes and 100% fill-factor. A softer mold of PDMS and a metal mold of NiCo alloy were utilized to replicate the MLAs. In this dissertation, several replication processes were applied to mass product and to find out which one is more suitable for the diffuser film. In this dissertation, the results of different shapes and dimensions of microlens arrays showed various light distribution. Therefore, for searching a more suitable and novel layout of a diffuser, Taguchi Method with simulation was used to design the layout of a diffuser film before fabrication process. Finally, a diffuser film was measured and demonstrated its optical effects. According to the results of measurement and simulation, the average intensity and the S/N ratios were shown. The trend of simulation and measurement was also similar.

Semiconductor quantum dots (QDs) are prime candidates for single and entangled photon sources in quantum information technologies due to their unique optical properties. This thesis investigates the development of QD sources operating at the telecom C-band ---around 1550 nm---, a critical aspect for long-distance applications in optical fibers. The research focuses on the design and optimization of InAs/GaAs QDs for efficient single photon emission within the telecom C-band. This thesis delves into the optimization of the quantum dot environment, by etching its matrix as a microlens (ML). The design process utilizes both simulations and lab fabrication techniques to achieve a source with high single photon throughput, a key requirement for quantum key distribution (QKD). To achieve this, the design optimizes factors such as material growth techniques, device structures, and microlens array configuration to enhance light collection efficiency by a microscope objective and Purcell effect for higher single-photon emission rate. The optimized microlens geometries, particularly the Gaussian and hemispherical shapes, significantly enhanced light extraction efficiency by the objective, achieving up to 40\% and 35\% respectively. The combined fabrication techniques of FIB milling, photolithography, and dry etching resulted in upgraded optical properties and minimal scattering in the microlenses. Furthermore, this work builds upon previous research conducted at the Royal Institute of Technology (KTH). The Quantum Nano Photonics (QNP) group successfully employed QDs to generate entangled photon states. This thesis extends this research by focusing on the design and optimization of a telecom C-band QD source suitable for long-distance transmission through existing fiber optic infrastructure over the Greater Stockholm Metropolitan Area, i.e. between the QNP-group lab at KTH AlbaNova campus and Ericsson HQ, in Kista, Stockholm. The feasibility of such transmission is explored by demonstrating the transmission of single photons from a QD source in the QNP lab at KTH to Ericsson's lab. This thesis contributes to the advancement of QD-based telecom C-band photon sources for future quantum communication networks, with a specific focus on microlens design and fabrication for enhanced single-photon emission efficiency. / Halvledarkvantprickar (QD) är utmärkta kandidater för enstaka och sammanflätade fotonkällor i kvantinformationsteknik på grund av deras unika optiska egenskaper. Denna avhandling undersöker utvecklingen av QD-källor som strålar på telekom C-band ---cirka 1550 nm---, en kritisk aspekt för långdistansapplikationer i optiska fiber. Forskningen fokuserar på design och optimering av InAs/GaAs QDs för effektiv emission av enstaka fotoner inom telekom C-bandet. Denna avhandling fördjupar sig i utformningen av kvantprickarkällan, med hjälp av en mikrolins (ML) array. Designprocessen använder både simuleringar och tillverkningstekniker för att uppnå en källa med hög enfotonrenhet, ett viktigt krav för kvantnyckeldistribution (QKD). För att uppnå detta optimerar designen faktorer som materialtillväxttekniker, enhetsstrukturer och mikrolinskonfiguration för att förbättra ljusinsamlingseffektiviteten och Purcell-effekten för ljusare och snabbare emission av enstaka fotoner. De optimerade mikrolinsgeometrierna, särskilt de gaussiska och halvsfäriska formerna, förbättrade avsevärt ljusextraktionseffektiviteten och nådde upp till 40\% respektive 35\%. De kombinerade tillverkningsteknikerna FIB-fräsning, fotolitografi och torretsning resulterade i uppgraderade optiska egenskaper och minimal spridning i de mikrolinserna. Vidare bygger detta arbete på tidigare forskning som bedrivits vid Kungliga Tekniska Högskolan (KTH). Quantum Nano Photonics-gruppen (QNP) använde framgångsrikt QD för att generera sammanflätade fotontillstånd. Denna avhandling utvidgar denna forskning genom att fokusera på design och optimering av en telekom C-band QD-källa lämplig för långdistansöverföring genom befintlig fiberoptisk infrastruktur över Storstockholmsområdet, dvs. mellan QNP-gruppens labb på KTH AlbaNova campus och Ericssons huvudkontor i Kista, Stockholm. Genomförbarheten av sådan överföring undersöks genom att demonstrera överföringen av enstaka fotoner från en QD-källa i QNP-labbet på KTH till Ericssons labb. Denna avhandling bidrar till utvecklingen av QD-baserade C-bandsfotonkällor för framtida kvantkommunikationsnätverk, med ett specifikt fokus på mikrolinsarraydesign för förbättrad renhet och emissionseffektivitet för enskilda fotoner. Arbetet bygger på tidigare forskning om generering av kvantsammanflätning och banar väg för säkra kvantkommunikationsnätverk över långa avstånd.

This aim of this dissertation is to fabrication microlens arrays (MLA) by silicon mold using dry etching technique and imprint on the PET substrate by direct imprinting microlens structures on Polyethylene terephthalate (PET) substrates using Si molds.The MLA on PET substrates can be used to increase light emitting efficiency from OLED. The MLA was formed by first etching the silicon wafers using SF6 process gas in an RIE/ECR system using isotropic etching technique.The concave undercuts obtained after the dry etching was removed by wet-etching the wafer in HF and HNO3 solutions.Finally,the fabricated silicon mold was used to imprint the microlens structure on the PET substrates.The microlens array with 10 £gm and 25 £gm radius on PET substrate were successfully fabricated using the technique.The surface coverage of the MLA of beter than 90% was obtained. In addition,the outcoupling efficiency of an OLED can be increased using the MLA.The brightness enhancement factor of 1.67 was achieved using in the MLA comparision to the simulation result of 1.73.

This research reports a simple and novel method to fabricate microlens arrays by soft stamping the unexposed SU-8 photoresist. A SU-8 based stamp composed of micro-nozzle arrays with a reservoir structure on a glass substrate is first fabricated using a process of dosage control exposure. The unexposed SU-8 is then encapsulated in the cross-linked SU-8 shell and was used as the ¡§ink¡¨ for the stamping process. The proposed SU-8 microlens array is then formed by stamping the formed SU-8 structure on a bare glass substrate at a temperature higher than the glass transition temperature (Tg) of the unexposed SU-8 microlens array. Lenses with various radii of curvature can be formed by controlling the working temperature during the stamping process. In addition, this work also employed a simple electric static pulling scheme to manipulate the fabricated lenses profiles. Aspherical SU-8 microlens arrays with a wide range of tunable focal lengths were fabricated with this approach. Furthermore, we develop an advanced localize E-field control technique to fabricate microlenses with various focus length and microlenses with different tilt angle in a single lens array sheet. A novel grayscale mask fabrication technique is also proposed first. This low cost and rapid method is applied on stepwise and continuous tilt plane fabrication for produces a gradually changed E-field. Hetero axes and focus lengths microlenses are fabricated with this approach. In order to farther understand the real E-field distribution, a novel PCF based E-field sensor fabrication technique is also proposed. This technique also shows the potential on various PCF based devices fabrications.

Brightness enhancement film (BEF) has been manufactured in foreign factories for backlight module of liquid crystal display (LCD), then it only have some interior factories to put in exploitation. Because of this, the study presents a precision machining and new step-imprint hot embossing process to fabricate pyramid-shaped microlens array. First, a tungsten (W) steel material is manufactured by precision machining. The dimension of a pyramid-shaped microlens on the W steel are about 300 £gm in the base line of three side, 222 £gm in bevel edge of three side, 139 £gm in height of bottom to top, 180 £gm in pitch of the left and right sides between two pyramid-shaped microlens tips, and 85 degree in top angle of three bevel. The W steel mold is used as the first mold. Second, the pyramid peaks of first mold pattern are transferred on bulk metallic glass (BMG) using step-imprint hot embossing method with position adjustable mechanism to form a smaller concave pyramid-shaped microlens array, it can avoid arc radius of cutting tools which is used as the second mold. Another the pyramid peaks are transferred on PMMA (Polymethylmethacrylate) for concave pyramid-shaped microlens array of optical film in the hot embossing system. Finally, the second mold is fabricated to emboss convex pyramid-shaped microlens array of optical film on PMMA. The foregoing method is provided for backlight module of optical films process.

This study utilizes a modified LIGA process to fabricate a high aspect ratio aspherical micro lens array, which improves low light output of OLED due to its intrinsic total internal reflection. Presently typical OLED extraction efficiency is not high. How to increase OLED extraction efficiency is a valuable topic to discuss. This study analyzes related parameters that influence the formation of micro lenses, for example, the influence of variation of diametric dimension, dry etching parameters and electroforming rate. The experimental results indicate that the tolerance of dimensional variation of the diameter is about 5% during the thermal reflow and dry etching stage. The oxygen content and the photoresist surface during dry etching influence the result. A high electroforming rate is helpful for covering the surface defects on photoresist. An undercut caused by dry etching will discontinue the initial electroformed layers. A apherical microens array can raise the luminance to a maximum of 15 times higher.

Organic light-emitting diodes (OLEDs) are regarded as next-generation light sources. The enhancement of external quantum efficiency of OLEDs has been investigated widely. It is an effective method of improving the external quantum efficiency, which destroys the phenomenon of total internal reflection inside the OLEDs by attaching microlens array to the surface of the glass substrate of the OLEDs. In this thesis, a multi-level aspherical gapless microlens array was designed and manufactured, and it was applied to OLEDs. In contrast with a spherical microlens array, the multi-level aspherical gapless microlens array can achieve a form of high aspect ratio and high fill factor, and they can enhance the external quantum efficiency of OLEDs. At first, aspherical microlens arrays with different parameters, including shapes of curved surface, layouts and feature dimensions, were simulated by optical simulation software, FRED. The aspherical microlens arrays which were attached to an OLED were simulated with a ray tracing method. Then, an optimal geometry and layout were found out. After simulation, a film with multi-level aspherical microlens array was fabricated by a LIGA-like process, including lithography, electroforming, PDMS (Polydimethylsiloxane) micro-molding and UV (Ultraviolet) -cured techniques. The characteristic in this process was to use multi-lithography to fabricate a microlens array with multi-level and high aspect ratio. The shape of multi-level was similar to the design, and the process can achieve the advantage of batch manufacture. Finally, the films with different multi-level aspherical microlens array were attached to an OLED to measure the optical-electric properties. The measured results were compared with simulation and confirmed them.

Gravitational microlenses are stellar- or planetary-mass objects which cause a transient amplification when passing in the foreground of a distant source. We study microlenses that consist of three point masses. Such a model can represent a triple star, a binary star with a planet, a star with two planets, or a star + planet + moon system. Up to date, four planetary systems have been discovered in triple-lens microlensing events. We aim to expand the theory of triple lenses in order to simplify the interpretation of observed data and enable correct analysis in more complex cases. We focus mainly on the classification of triple-lens models with respect to their caustics. For a given source trajectory, the caustic determines prominent features on the light curve and thus its knowledge is essential for the analysis of microlensing events. We map the topology of the critical curve (the main caustic image) and the number of cusps of the caustic in the lens-model parameter space. We introduce methods for the classification of general $n$-point-mass microlenses. The methods are then demonstrated on four two- parameter and three three-parameter models. Furthermore, we study amplification maps for both point sources and extended sources, with an emphasis on new features appearing in triple and general $n$-point-mass...