TY - JOUR A1 - Kefer, Stefan A1 - Sauer, Theresia A1 - Hessler, Steffen A1 - Kaloudis, Michael A1 - Schmauss, Bernhard A1 - Hellmann, Ralf T1 - Robust Polymer Planar Bragg Grating Sensors Embedded in Commercial-Grade Composites JF - Polymers N2 - This contribution demonstrates the functionality of polymer planar Bragg grating (PPBG) sensors integrated into commercial-grade carbon fiber reinforced polymer (CFRP) components. Multiple CFRP specimens are generated by curing a stack of pre-impregnated fibers inside of a heated mechanical press, exposing the polymer sensor to a pressure of 7 bar and a temperature of 120 °C for 2 h. After integration, the sensor still exhibits a strong and evaluable signal. Subsequent flexural experiments reveal a linear response of the integrated sensor’s Bragg wavelength to the CFRP specimen’s maximum deflection. Additional findings demonstrate that the embedded PPBG can be used to detect plastic deformations of a CFRP workpiece, whereas a linear correlation of plastic deformation to the resulting Bragg signal offset is determined. A plausibility check of the obtained results is delivered by a comparison of three-point flexural experiments on bulk CFRP workpieces, without integrated sensors and additional specimens featuring external optical sensors affixed to their surface. It is found that PPBGs based on cyclic olefin copolymers are able to overcome the temperature-related limitations of traditional polymer-based optical sensors and can thus be directly integrated into commercial-grade composites during production. KW - Bragg grating sensors KW - carbon fiber reinforced polymers KW - cyclic olefin copolymers KW - Bragg-Reflektor KW - Optischer Sensor Y1 - 2020 UR - https://www.mdpi.com/2073-4360/12/3/715/htm U6 - https://doi.org/10.3390/polym12030715 VL - 12 IS - 3 SP - 715 EP - 715 ER - TY - CHAP A1 - Kefer, Stefan A1 - Rosenberger, Manuel A1 - Hessler, Steffen A1 - Girschikofsky, Maiko A1 - Belle, Stefan A1 - Roth, Gian-Luca A1 - Schmauss, Bernhard A1 - Hellmann, Ralf T1 - Fabrication and Applications of Polymer Planar Bragg Grating Sensors based on Cyclic Olefin Copolymers T2 - 2019 Photonics & Electromagnetics Research Symposium - Fall (PIERS - Fall) N2 - This contribution reviews recent advancements, current research and possible applications of polymer planar Bragg grating (PPBG) sensors with a focus on the utilization of cyclic olefin copolymer (COC) substrates. COC-PPBGs can be handled and fabricated efficiently by employing a single writing step procedure which features simultaneous generation of waveguide and Bragg grating structure within an injection molded substrate. The resulting photonic structures exhibit an attenuation as low as 1.2 dB cm-1 and a reflectivity up to 99 %. The potential of COC-PPBGs for high-temperature applications is proven by demonstrating temperature measurements up to 160 °C. Moreover, it is possible to employ single PPBGs for multidimensional stress and strain sensing or even three-dimensional shape reconstruction. Due to their excellent properties, it is feasible to integrate COC-PPBGs into commercial-grade carbon fiber reinforced polymer workpieces for structural health monitoring. Furthermore, utilization of appropriate coatings enables functionalization of PPBGs for refractive index sensing and thus biochemical applications. Beside the fabrication and characterization of COC-based PPBGs, this contribution exemplifies and reviews such applications. KW - Bragg gratings , Gratings , Optical waveguides , Temperature sensors , Substrates KW - Optischer Sensor KW - Bragg-Reflektor Y1 - 2020 UR - https://ieeexplore.ieee.org/document/9021801 SN - 978-1-7281-5304-9 U6 - https://doi.org/10.1109/PIERS-Fall48861.2019.9021801 SP - 647 EP - 655 PB - Institute of Electrical and Electronics Engineers ER - TY - JOUR A1 - Kefer, Stefan A1 - Dai, Jixiang A1 - Yang, Minghong A1 - Schmauss, Bernhard A1 - Hellmann, Ralf T1 - Hypersensitive H2 sensor based on polymer planar Bragg gratings coated with Pt-loaded WO3-SiO2 JF - Optics Letters N2 - This letter demonstrates a novel hydrogen sensor based on a polymer planar Bragg grating coated with Pt-loaded WO3-SiO2. The reflected Bragg signal shows a distinct peak splitting correlated to substrate anisotropies originating from the injection molding process. Especially at low H2 concentrations, both sensing peaks exhibit an outstanding response to the heat generated by the exothermic reaction between hydrogen molecules and coating. Thereby, a hydrogen volume ratio of 50 ppm leads to a Bragg wavelength shift of -37 pm, which yields an outstandingly low detection limit of only 5 ppm H2 in air. Thus, functionalized polymer planar Bragg gratings are eminently suitable for H2 leak detection applications. KW - Bragg Grating Sensors KW - Hydrogen Detection KW - Cyclic Olefin Copolymers KW - Gassensor KW - Wasserstoff KW - Bragg-Reflektor Y1 - 2020 UR - https://www.osapublishing.org/ol/abstract.cfm?uri=ol-45-13-3601 U6 - https://doi.org/https://doi.org/10.1364/OL.395341 VL - 45 IS - 13 SP - 3601 EP - 3604 ER - TY - GEN A1 - Kefer, Stefan A1 - Dai, Jixiang A1 - Yang, Minghong A1 - Schmauss, Bernhard A1 - Hellmann, Ralf T1 - Hypersensitive H2 sensor based on polymer planar Bragg gratings coated with Pt-loaded WO3–SiO2: erratum N2 - We present an erratum to our Letter [Opt. Lett. 45, 3601 (2020)]. Labeling errors in two figures and an incorrect sentence are revised. The corrections have no influence on the conclusions of the original Letter. N2 - Erratum KW - Bragg Grating, Hydrogen Detection, Functionalization KW - Gassensor KW - Wasserstoff KW - Bragg-Reflektor Y1 - 2020 UR - https://www.osapublishing.org/ol/abstract.cfm?uri=ol-45-16-4498 U6 - https://doi.org/https://doi.org/10.1364/OL.401819 VL - 45 IS - 16 SP - 4498 EP - 4498 ER - TY - JOUR A1 - Kefer, Stefan A1 - Bischoff, Kay A1 - Roth, Gian-Luca A1 - Haubner, Julian A1 - Schmauss, Bernhard A1 - Hellmann, Ralf T1 - Tunable Bulk Polymer Planar Bragg Gratings Electrified via Femtosecond Laser Reductive Sintering of CuO Nanoparticles JF - Advanced Optical Materials N2 - This contribution demonstrates and discusses electrically tunable polymer planar Bragg gratings based on bulk cyclic olefin copolymers. A lithographic single-writing-step method and femtosecond laser reductive sintering of copper(II) oxide nanoparticles are subsequently employed in order to generate buried photonic structures and copper conducting paths on top of the polymer substrate. This way, the necessary number of process steps for fabricating a planar polymer-based electro-optical device is greatly reduced. The response of a fully electrified grating structure follows temperature changes, induced by the copper conducting path, with sensitivities up to −31 pm K−1. Dilatometric measurements show that the specimen's behavior is correlated to the situationally reduced thermal expansion of the bulk polymer substrate. In consequence, the tuning response of the photonic platform follows a second order polynomial, whereas a direct current of 30 mA, which correlates to a power consumption of 18.3 mW, leads to a local temperature increase and a residual Bragg wavelength shift of 19.6 K and −547 pm, respectively. Moreover, the outstanding flexibility of the proposed fabrication concept is underlined by demonstrating alternative conducting path geometries, whereas one of the additional designs is adapted to control the spectral width of the Bragg grating's reflection peak. KW - Bragg gratings KW - CuO nanoparticles KW - cyclic olefin copolymers KW - electro-optic tuning KW - integrated photonics KW - Femtosekundenlaser KW - Bragg-Reflektor Y1 - 2021 UR - https://onlinelibrary.wiley.com/doi/10.1002/adom.202002203 U6 - https://doi.org/https://doi.org/10.1002/adom.202002203 VL - 9 IS - 13 SP - 2002203 EP - 2002203 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 - JOUR A1 - Kefer, Stefan A1 - Pape, Dominik A1 - Roth, Gian-Luca A1 - Hessler, Steffen A1 - Schmauss, Bernhard A1 - Hellmann, Ralf T1 - Micromilling-assisted fabrication of monolithic polymer ridge-type waveguides with integrated photonic sensing structures JF - Optical Materials Express N2 - This study demonstrates and discusses a novel approach for the fabrication and rapid prototyping of monolithic photonic platforms comprising a ridge-type waveguide with integrated sensing structures. First, the bulk injection-molded cyclic olefin copolymer substrates are micromilled in order to define the physical extension of the ridge structure. Cross-sections down to 30 × 30 µm2, exhibiting a mean surface roughness of 300 nm, are achieved with this process. Subsequently, UV radiation is used to modify the ridge structure’s refractive index, which leads to the formation of an optical waveguide. By employing a phase mask, it is possible to equip the photonic platform with a Bragg grating suitable for temperature measurements with a sensitivity of −5.1 pm K-1. Furthermore, an integrated Fabry-Pérot cavity, generated during the micromilling step as well, enables refractive index measurements with sensitivities up to 1154 nm RIU-1. KW - Cyclic Olefin Copolymers KW - Micromilling KW - Bragg Grating KW - Fabry-Pérot Etalon KW - Bragg-Reflektor KW - Optischer Sensor Y1 - 2021 UR - https://www.osapublishing.org/ome/fulltext.cfm?uri=ome-11-8-2389&id=453071 U6 - https://doi.org/https://doi.org/10.1364/OME.425778 VL - 11 IS - 8 SP - 2389 EP - 2400 ER - TY - GEN A1 - Kefer, Stefan A1 - Bischoff, Kay A1 - Roth, Gian-Luca A1 - Haubner, Julian A1 - Schmauss, Bernhard A1 - Hellmann, Ralf T1 - Tunable Bulk Polymer Planar Bragg Gratings Electrified via Femtosecond Laser Reductive Sintering of CuO Nanoparticles (Advanced Optical Materials 13/2021) N2 - This cover image outlines the fabrication method of a polymer planar Bragg grating electrified via femtosecond laser reductive sintering of CuO nanoparticles (see article number 2002203 by Stefan Kefer and co-workers). Based on this sophisticated methodology, bulk cyclic olefin copolymer substrates can be equipped with integrated photonic structures comprising a waveguide as well as a Bragg grating. Its reflective characteristics can be efficiently tuned by means of the subsequently generated Cu conducting path, whereas the applied femtosecond laser process enables an almost limitless degree of freedom towards conducting path geometries. N2 - Cover zum zugehörigen Artikel KW - Femtosekundenlaser KW - Bragg-Reflektor Y1 - 2021 UR - https://onlinelibrary.wiley.com/doi/10.1002/adom.202170048 U6 - https://doi.org/https://doi.org/10.1002/adom.202170048 ER - TY - CHAP A1 - Kefer, Stefan A1 - Roth, Frederick A1 - Kaloudis, Michael A1 - Schmauss, Bernhard A1 - Hellmann, Ralf T1 - Monitoring of Composite Bicycle Components using Polymer Planar Bragg Gratings T2 - SMSI 2021 - Sensors and Instrumentation N2 - This study demonstrates mobile load monitoring of a composite bicycle component using an application- customized polymer planar Bragg grating sensor, evaluated by a mobile interrogation unit. After a referencing procedure, the mechanical load of a seat post is monitored while cycling through a test track. KW - Bragg Grating KW - Composites KW - Cyclic Olefin Copolymers KW - Micromilling KW - Load Monitoring KW - Bragg-Reflektor KW - Verbundwerkstoff KW - Fahrrad Y1 - 2021 UR - https://www.ama-science.org/proceedings/details/3992 SN - 978-3-9819376-4-0 U6 - https://doi.org/10.5162/SMSI2021/B9.2 SP - 161 EP - 162 PB - AMA Service GmbH CY - Wunstorf, Germany ER - TY - JOUR A1 - Kefer, Stefan A1 - Limbach, Tobias A1 - Pape, Natalie A1 - Klamt, Kathrin A1 - Schmauss, Bernhard A1 - Hellmann, Ralf T1 - Birefringence in Injection-Molded Cyclic Olefin Copolymer Substrates and Its Impact on Integrated Photonic Structures JF - Polymers N2 - This contribution quantifies the birefringence within injection-molded cyclic olefin copolymer plates and discusses its impact on the mechanical properties of the plates. It also focuses on the impact of birefringence on integrated waveguides and Bragg gratings and provides fabrication guidelines for such structures. The anisotropy in all three dimensions of the workpiece is examined by means of polarimetry and a prism coupler. It is found that the birefringence is inhomogenously distributed within the workpieces, whereas the maximum birefringence not only varies locally, but also depends on the observation direction. Overall, a maximum birefringence of 10 × 10−4 is found at the plate’s surface near the injection gate. The anisotropy then reduces exponentially towards the center of the workpiece and saturates at 1.8 × 10−4, in a depth of 0.4 mm. Thus, the birefringence strongly affects near-surface photonic structures. It is found that, depending on their orientation and the local birefringence of the substrate, waveguides and Bragg gratings fabricated with comparable parameters behave completely differently in terms of polarization-dependent optical attenuation, cross-sectional intensity distribution and Bragg reflection signal. For example, the support of the TM mode can vary between total loss and an optical attenuation of 0.9 dB × cm−1. In consequence, this study underlines the importance of quantifying the birefringent state of an injection-molded cyclic olefin copolymer workpiece if it is supposed to serve as a substrate for integrated photonic structures. The study furthermore demonstrates that birefringence effects can be omitted by burying the photonic structures deeper into the volume of the thermoplastic. KW - cyclic olefin copolymer KW - birefringence KW - integrated photonics KW - Bragg grating KW - injection molding KW - Bragg-Reflektor KW - Wellenleiter KW - Doppelbrechung Y1 - 2024 UR - https://www.mdpi.com/2073-4360/16/2/168 U6 - https://doi.org/10.3390/polym16020168 VL - 16 IS - 2 SP - 168 EP - 168 ER -