TY - CHAP A1 - Kefer, Stefan A1 - Pape, Natalie A1 - Schmauss, Bernhard A1 - Hellmann, Ralf T1 - Fabrication of Lattice-Like Waveguides in Planar Cyclic Olefin Copolymers T2 - 28th International Conference on Optical Fiber Sensors N2 - This work demonstrates the femtosecond laser-based fabrication of lattice-like waveguides in planar cyclic olefin copolymers. An overview of the fabrication process is provided and waveguiding in the C-band is proven via optical near-field analysis. KW - Wellenleiter KW - Femtosekundenlaser Y1 - 2023 SN - 978-1-957171-30-2 U6 - https://doi.org/10.1364/OFS.2023.Th6.69 ER - TY - CHAP A1 - Kefer, Stefan A1 - Schmauss, Bernhard A1 - Hellmann, Ralf T1 - Sapphire-Based Planar Bragg Grating Devices T2 - 28th International Conference on Optical Fiber Sensors N2 - This study reports on the long-term stability and the high-temperature capability of sapphire-based photonic crystal waveguides with integrated Bragg gratings. Furthermore, their Bragg grating reflectivity as well as their temperature sensitivity is quantified. KW - Bragg-Reflektor KW - Wellenleiter Y1 - 2023 SN - 978-1-957171-30-2 U6 - https://doi.org/10.1364/OFS.2023.W2.4 ER - TY - CHAP A1 - Kefer, Stefan A1 - Zettl, Julian A1 - Schmauss, Bernhard A1 - Esen, Cemal A1 - Hellmann, Ralf ED - Kling, Rainer ED - Pfleging, Wilhelm ED - Watanabe, Akira T1 - High-Precision Micromachining of Sapphire Towards Optical Waveguiding Structures using Femtosecond Lasers T2 - Laser-based Micro- and Nanoprocessing XVII N2 - While sapphire is one of the most durable materials, its properties entail that high-precision machining, especially in the sub-millimeter regime, is still challenging. This contribution demonstrates and discusses novel femtosecond laser-based micromachining approaches for the fabrication of rotational-symmetric sapphire workpieces, specifically the generation of optical fibers by means of laser lathe of sapphire rods and the practical realization of windmill fibers. In addition, volume refractive index modification in planar sapphire substrates is presented to induce photonic crystal waveguides. The micromachined structures are comprehensively examined with respect to geometric fidelity, surface roughness, refractive index modification, and potential optical waveguiding properties. All micromachining approaches are done by means of frequency-doubled or frequency-tripled femtosecond laser radiation. Different laser optical setups including laser scanning head, spatial beam profilers including a spatial light modulator and axial rotatory movement of the specimen are employed for micro structuring and in-depth refractive index modifications. In particular for laser lathe, a sophisticated scanning pattern, in combination with an incremental axial rotatory movement of the specimen, allows for the precise diameter reduction of sapphire rods with 250 µm diameter to fibers with outer diameters of 25 µm. By supporting the workpiece with a V-groove fixture, multi-mode fibers with lengths up to 20 cm can be processed with an average surface roughness of 250 nm. Additionally, an adapted ablation scanning sequence enables the first practical demonstration of sapphire windmill fibers. Furthermore, using a spatial light modulator allows for the adaption of the laser propagation properties as to enable volume refractive index modifications with free-form arrangement. Hexagonal patterns of refractive index modifications surrounding a pristine waveguide core are fabricated and single-mode waveguiding at 1550 nm is verified. Finally, the possibility of integrating Bragg gratings into this photonic waveguide type is demonstrated KW - sapphire KW - femtosecond laser KW - micromachining KW - laser lathe KW - rod-to-fiber KW - Femtosekundenlaser KW - Saphir Y1 - 2023 SN - 9781510659230 U6 - https://doi.org/10.1117/12.2648758 SP - 3 EP - 11 ER - TY - CHAP A1 - Kefer, Stefan A1 - Pape, Natalie A1 - Gries, Nikola A1 - Roth, Gian-Luca A1 - Schmauss, Bernhard A1 - Hellmann, Ralf T1 - Towards Pressure Sensors Based on Polymer Planar Bragg Gratings T2 - Organic Photonic Materials and Devices XXV N2 - While Bragg grating-based optical devices have shown promising performances for pressure sensing applications, their sensitivity, especially in the low-pressure regime, is unsatisfying and needs to be optimized by elaborate designs, such as cantilevers or other extrinsic mechanical transducers. This contribution demonstrates and discusses a novel concept for optical pressure sensors based on polymer planar Bragg gratings. Waveguide and Bragg grating are fabricated underneath the surface of a temperature-stable and humidity-insensitive cyclic olefin copolymer substrate by means of a femtosecond laser. Based on the employed direct-writing procedure, in combination with adaptive, in-situ beam shaping with a spatial light modulator, writing depth, i.e., location of the photonic structures within the substrate, as well as Bragg grating periodicity and positioning can be deliberately chosen. Afterwards, the polymer substrate is post-processed with a high-precision micro mill, so a diaphragm comprising the integrated photonic structures is generated. The resulting diaphragm exhibits a thickness of 300 µm and a diameter of 10 mm. Finally, the optical sensor is packaged and sealed to form an air-filled gas pocket underneath the diaphragm. Deformations of the diaphragm by external pressure changes translate to strain variations along the waveguide axis and thus perturb the Bragg grating period. This leads to changes in the grating’s wavelength of main reflection, which can be evaluated in order to quantify the relative external pressure. With this straightforward optical sensor concept, pressure sensitivities up to 39 pm kPa-1, within relative pressures ranges from 78 kPa to 372 kPa, are achieved. KW - Bragg grating KW - pressure sensor KW - integrated photonics KW - cyclic olefin copolymers KW - femtosecond laser KW - Bragg-Reflektor KW - Drucksensor Y1 - 2023 SN - 9781510659414 U6 - https://doi.org/10.1117/12.2648723 ER - TY - CHAP A1 - Kefer, Stefan A1 - Schmauss, Bernhard A1 - Hellmann, Ralf T1 - POLYMER PLANAR BRAGG GRATINGS BASED ON BULK CYCLIC OLEFIN COPOLYMERS: FABRICATION AND FUNCTIONALIZATION T2 - Proceedings of Student Conference on Sensors, Systems and Measurement 2021 KW - Bragg-Reflektor Y1 - 2021 UR - https://scssm.fel.cvut.cz/wp-content/uploads/2021/07/Proceedings-SCSSM-2021.pdf SN - 978-80-01-06822-9 ER -