the presented work demonstrates the fabrication process of the master for nano-imprint lithography (NIL) stamp for multi-mode waveguide (MM-WG) with μ-mirror using hybrid-lithography, which includes a 2-photon-polymerization direct laser writing process (2PP-DLW) for μ-mirror surface and UV-photo lithography for MM-WGs. For the definition of the mirror surface at either end of waveguides in the master stamp, the 2PP-DLW process was used. It offers a lower surface roughness (< 0.1 λ) with fewer processing steps, alignment accuracy of ± 1 μm, prints fine and sharp contours, and relatively faster scanning for a specific material, which makes it the foremost technology over the traditional micro-mirror processes such as the dicing process, moving mask lithography, laser ablation, wet etching, and dry etching. For the fabrication of the waveguide core with rectangular cross-sections in the master stamp, UV mask exposure with SU-8 was used. It is a mass-production and low-cost technique. It gives a smooth structure with 90-degree sidewalls compared to other processes like dry etching, wet etching, mosquito method, and E-beam writing. We demonstrated the design and process of a master pattern with a density range from 0.04 to 0.2 to maintain equal pressure over the stamp in the NIL step for an almost uniform residual thickness layer.:Abstract Introduction Design of Experiments Experimental Results and Discussions Conclusion

The advancement in demand for high bandwidth energy-efficient communication in the data centre and edge cloud servers needs a viable optical interconnection solution to cope with the demands. Therefore, the presented study describes the concept of flexible multi-mode waveguides (MM-WGs) as an optical link for co-packaged optics. It evaluates three lithography technologies; UV-lithography, 2 photon polymerization direct laser writing process (2PP-DLW), and nano-imprint lithography (NIL) for the fabrication of flexible MM-WGs. The UV-lithography and 2PP-DLW process were evaluated for the fabrication of MM-WGs and micro-mirrors, respectively, for the master pattern of the NIL stamp. The NIL evaluates the imprinting of the MM-WGs with micro-mirrors at either end on the flexible and transparent PEN substrates with a low-loss OrmoClad lower cladding layer. There are five different cross-sections from 10×10 µm 2 to 50×50 µm 2 of MM-WGs with micro-mirrors were imprinted. Additionally, it presents the importance of integrating multi-lithography technologies to fabricate flexible optical links where a 2PP-DLW process shows the best results for printing µm-scale optical components. On the other side, UV-lithography with SU-8 gives the foremost definition of the master for the polymeric MM-WGs. Furthermore, NIL offers the industrial mass-production option alongside prototyping.:Abstract Introduction Introduction to the Concept of Multi-Lithography Technologies for Flexible Optical Link Experimental Results and Discussion Conclusion and Future Outlook

Nature-inspired surfaces provide an endless potential for innovations and exploitations in material science and engineering for a broad range of applications. Particularly, significant progress has been achieved in the fields of ice formation and wetting phenomena on metallic surfaces. One of the most relevant wetting states is superhydrophobicity, which is characterized by the complete repellency of water droplets upon impinging on a surface. A superhydrophobic surface can be accompanied by additional functions such as anti- icing, corrosion-resistance or self-cleaning. A particularly attractive material to implement functional surfaces is aluminum, due to its outstanding mechanical properties such as lightweight and high strength combined with an excellent electrical conductivity and affordable price. Functionalized aluminum surfaces can further increase the added value of technical aluminum products which are used in the automotive, aerospace and life science industry among others. A promising strategy to achieve multifunctionalities is by fabricating micrometer and submicrometer features on the material’s surface. Thus, surface texturing of aluminum components is an extremely relevant topic in science and engineering which affects all facets of our lives. Until now, micropatterned aluminum surfaces, that combine water- repellent, self-cleaning and icephobic properties, have not yet been completely explored. The present doctoral thesis focuses on structuring aluminum substrates to fabricate multifunctional surfaces with superhydrophobic, self-cleaning and anti-icing properties. To accomplish this goal, scanner-based direct laser writing (DLW) and two- and four-beam direct laser interference patterning (DLIP) are applied to pattern micrometer and sub- micrometer features on aluminum. They are employed separately to fabricate single-scale textures, as well as in combination in order to obtain multi-scale geometries and complex patterns. The laser texturing parameters are optimized to maximize the addressed functionalities and their influence on the microstructure are studied. In order to explain the wetting and freezing behavior of the functional surfaces, numerical heat transfer simulation models are applied. The most promising textures are then selected and tested under realistic icing conditions simulating the freezing behavior of water droplets on aircraft parts during flight. Moreover, a new method to characterize the self-cleaning efficiency of laser-patterned aluminum is developed. The textured aluminum surfaces attained a water-repellent functionality with a static water contact angle of up to 163° and a sliding angle of 12° without chemical post-processing. This functionality permitted a self-cleaning property where the DLIP and DLW+DLIP structures provided a maximum self-cleaning efficiency with remaining contamination as low as 1 %. The ice-repellent characterization at a temperature of -20°C revealed that in all investigated laser-structured surfaces the freezing time of 8 μl droplets increased up to three times compared to an unstructured reference. Moreover, it was demonstrated, that optimized surface textures led to a reduction of the ice adhesion strength by up to 90 %.:Selbstständigkeitserklärung Kurzfassung Abstract Acknowledgements Table of content List of abbreviations and symbols 1 Motivation 2 Theoretical principles and definitions 3 State of the art 4 Materials and methods 5 Results and discussion 6 Conclusions 7 Outlook Literature Curriculum vitae of the author List of publications / Von der Natur inspirierte Oberflächen bergen ein endloses Potential für Innovationen auf den Gebieten der Materialwissenschaft und demonstrieren ein breites Anwendungsfeld. Insbesondere in den Bereichen der Eisbildung und der Benetzungsphänomene auf Metalloberflächen wurde ein bedeutender Fortschritt erzielt. Einer der relevantesten Benetzungszustände ist der der Superhydrophobizität, welcher sich durch die vollständige Abweisung von Wassertropfen auszeichnet, sobald diese auf eine Oberfläche auftreffen. Eine superhydrophobe Oberfläche kann von zusätzlichen Funktionen wie Vereisungsschutz, Korrosionsbeständigkeit oder Selbstreinigung begleitet werden. Dabei ist besonders der Werkstoff Aluminium zur Realisierung funktionaler Oberflächen attraktiv, aufgrund seiner mechanischen Eigenschaften wie etwa ein geringes Gewicht und eine hohe Festigkeit bei gleichzeitig hervorragender elektrischer Leitfähigkeit ergänzt durch einen günstigen Preis. Funktionalisierte Aluminiumoberflächen können die Wertschöpfung von technischen Aluminiumprodukten deutlich erhöhen. Diese werden u.a. im Automobilsektor, in der Luft- und Raumfahrtindustrie oder im Life-Science-Bereich eingesetzt. Ein vielversprechender Ansatz zur Realisierung multifunktionaler Eigenschaften basiert auf der Herstellung von Mikrometer- und Submikrometer-Strukturen auf der Oberfläche. Daher stellt die Texturierung von Aluminiumkomponenten ein äußerst relevantes Thema in der Wissenschaft und Technik dar, da sie sämtliche Facetten unseres täglichen Lebens tangiert. Bis heute sind laser-strukturierte Aluminiumoberflächen, die wasserabweisende, selbstreinigende und eisabweisende Eigenschaften vereinen, noch nicht vollständig erforscht. Die zugrunde liegende Dissertation thematisiert die Strukturierung von Aluminiumsubstraten zur Herstellung multifunktionaler Oberflächen mit superhydrophoben, selbstreinigenden und vereisungsmindernden Eigenschaften. Dafür, werden direktes Laserschreiben (engl. Direct laser writing, DLW) sowie die direkte Laserinterferenzstrukturierung (engl. Direct laser interference patternin, DLIP) auf Aluminium angewendet. Die Verfahren werden sowohl separat zur Herstellung von einskaligen Texturen als auch in Kombination eingesetzt, um mehrskalige komplexe Muster zu fertigen. Die Strukturierungsparameter werden zur Maximierung der erwähnten Eigenschaften hin optimiert, und ihr Einfluß auf die Mikrostruktur wird untersucht. Um das Benetzungs- und Vereisungsverhalten der funktionalisierten Oberflächen zu erklären, werden numerische Simulationsmodelle eingesetzt. Die vielversprechendsten Texturen werden unter realistischen Vereisungsbedingungen getestet, welche das Gefrierverhalten von Wassertropfen auf Flugzeugbauteilen während des Fluges simulieren. Darüber hinaus wird eine neue Methode zur Charakterisierung der Selbstreinigungseffizienz von laserstrukturiertem Aluminium entwickelt und angewendet. Die texturierten Aluminiumoberflächen erhielten ohne chemische Nachbearbeitung eine wasserabweisende Funktionalität mit einem statischen Wasserkontaktwinkel von bis zu 163° und einem Gleitwinkel von 12°. Diese Funktionalität ermöglichte eine Selbstreinigungseigenschaft, bei der die DLIP- und DLW+DLIP-Strukturen die höchste Effizienz mit einer Restverunreinigung von bis zu 1 % erzielten. Die eisabweisende Charakterisierung bei einer Temperatur von -20°C offenbarte, dass bei allen untersuchten laserstrukturierten Oberflächen die Vereisungszeit von 8 μl Wassertropfen bis um das Dreifache anstieg, im Vergleich zur unstrukturierten Referenz. Darüber hinaus konnte demonstriert werden, dass optimierte Oberflächentexturen zu einer Reduzierung der Eis- Adhäsionskraft um bis zu 90 % führten.:Selbstständigkeitserklärung Kurzfassung Abstract Acknowledgements Table of content List of abbreviations and symbols 1 Motivation 2 Theoretical principles and definitions 3 State of the art 4 Materials and methods 5 Results and discussion 6 Conclusions 7 Outlook Literature Curriculum vitae of the author List of publications

This paper describes technology and process development for a hybrid lithography approach pairing UV-lithography for planar single mode waveguides with 2-photon-polymerization direct-laser-writing for out-of-plane coupling mirrors. Improvements to multi-layer direct patterning of OrmoCore/-Clad material system using UV-lithography are presented. Near square core cross sections are achieved. Minimum alignment accuracy at ≈ 3 μm is observed. Cut-back measurement on single mode waveguides shows attenuation of 0.64 dB cm −1 and 1.5 dB cm −1 at 1310 nm and 1550 nm respectively. Up to 2.5-times increase of shear-strength after thermal exposure up to 300 ◦ C is found using shear tests and compared for various surface treatments. Mechanical compatibility to reflow soldering is derived. An extensive study on the pattering of ORMOCER® using 2-photon-polymerization is performed. Flat 45 ◦ -micro mirrors with sub-10 μm dimensions are 3D-printed both in OrmoCore and OrmoComp. Outlook to further research on hybrid lithography integration approach is given.

This paper describes design and advances in process development for UV-lithography of planar single mode waveguides with openings for out-of-plane coupling µ-mirrors. Improvements to multi-layer direct patterning of OrmoCore/-Clad material system using UV-lithography are presented. Near square core cross sections are achieved. However, non uniformity across 4” wafer is shown due to varying proximity and UV-intensity. Openings in full stack with steep sidewalls without residual layer are patterned. Reduction in stack thickness for very small exposure doses due to inhibition even under inert atmosphere is shown. 45° -µ-mirrors are integrated in these openings to manufacture a U-link via a single mode waveguide and two adjacent micro-mirrors. Optical characterization of U-link demonstrates the feasibility of hybrid lithography approach. However, non-uniformity of core cross-section leads to cross coupling of planar waveguides. Outlook to further research on UV-lithography of multi-layer waveguide stack and alignment with µ-mirror printing is given.

Laser patterning techniques have shown in the last decades to be capable of producing functional surfaces on a large variety of materials. A particular challenge for these techniques is the treatment of additively manufactured parts with high roughness levels. The presented study reports on the surface modification of additive-manufactured components of Ti64 and Al–Mg–Sc (Scalmalloy), with the aim of implementing water- and ice-repellent properties. Different laser-based microstructuring techniques, using nanosecond and picosecond pulses, are combined to create multiscale textures with feature sizes between ≈800 nm and 21 μm. The wettability could be set to static water contact angles between 141° and 153° for Ti64 and Al–Mg–Sc, respectively. In addition, surface free energy is analyzed for different surface conditions.

This paper describes advances in hybrid-lithography process, combining UV-lithography for planar, single mode redistribution layer (RDL) and 2-photon-polymerization direct-laser-writing (2PP-DLW) for micro-mirrors inside RDL-opening. Improvements to multi-layer direct patterning of OrmoCore/-Clad material system using UV-lithography and need for broadband UV-LED source are presented. Near square core cross sections and smooth sidewalls are achieved. Openings in full stack with steep sidewalls without residual layer are patterned. To optimize 2PP-DLW-process processing window for both OrmoComp and IP-DIP is thoroughly characterized. Roughness measurements prove feasibility even of coarsely printed structure as reflective μ-mirror for 1550 nm wavelength. Finally these results are applied to periscope probe for wafer-level-testing of edge emitting lasers and proof of concept is shown. Outlook to further research on UV-lithography of multi-layer waveguide stack and alignment with μ-mirror printing is given.