TY - JOUR A1 - Kefer, Stefan A1 - Pape, Natalie A1 - Bischoff, Kay A1 - Schmauss, Bernhard A1 - Hellmann, Ralf T1 - Lattice-Like Waveguides With Integrated Bragg Gratings in Planar Cyclic Olefin Copolymers JF - Journal of Lightwave Technology N2 - This contribution demonstrates femtosecond laser direct writing of lattice-like waveguides in planar cyclic olefin copolymer substrates. Based on numerical simulation and experimental near-field analysis, stable single-mode waveguiding around wavelengths of 1550 nm is demonstrated. The waveguiding mechanism is based on a hexagonal array of laser-induced, positive refractive index modification lines. Thus, the lateral extension of the guided mode can be adapted by varying the fabrication parameters and, in consequence, the resulting cross-sectional arrangement of the refractive index perturbations. With an optical attenuationof 2.2 dB·cm-1 around 1550 nm, the fabricated waveguides are well-suited for on-chip integrated photonic devices. Moreover, the waveguides can also be equipped with Bragg gratings to enable the application of the photonic platform as a sensing device. Dependingon their length, the Bragg grating structures exhibit reflectivities ofup to 99% and spectral widths down to 0.3 nm. The flexibility of the fabrication process and the sensing capabilities of the lattice-like waveguides with integrated Bragg gratings are underlined by an exemplary application study demonstrating a relative pressure sensor. For that, a photonic platform is micromilled to generate a 300 µm thick diaphragm and a reference pressure chamber. The strain introduced to the diaphragm by external pressure changes can then be quantified by the integrated photonic structures.This way, absolute pressure sensitivities of up to 38 pm·kPa-1 can be achieved in a relative pressure range from −60 to 100 kPa. The newly-developed lattice-like waveguides with integrated Bragggratings are therefore well-suited for the realization of novel and adaptable photonic devices and sensors. KW - Bragg grating KW - cyclic olefin copolymers KW - femtosecond laser KW - integrated photonics KW - lattice-like waveguide KW - pressure sensor KW - Wellenleiter KW - Bragg-Reflektor Y1 - 2024 U6 - https://doi.org/10.1109/JLT.2023.3328323 SN - 0733-8724 VL - 42 IS - 18 SP - 6302 EP - 6311 PB - Institute of Electrical and Electronics Engineers (IEEE) ER - TY - JOUR A1 - Bischoff, Kay A1 - Kefer, Stefan A1 - Wienke, Alexander A1 - Overmeyer, Ludger A1 - Kaierle, Stefan A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Integration of Bragg gratings in aerosol-jetted polymer optical waveguides for strain monitoring capabilities JF - Optics Letters N2 - We demonstrate and discuss the integration of Bragg gratings in aerosol-jetted polymer optical waveguides, produced in the optical assembly and connection technology for component-integrated bus systems (OPTAVER) process. By using a femtosecond laser and adaptive beam shaping, an elliptical focal voxel generates different types of single pulse modification by nonlinear absorption in the waveguide material, which are arranged periodically to form Bragg gratings. Integration of a single grating structure or, alternatively, an array of Bragg grating structures in the multimode waveguide yields a pronounced reflection signal with typical multimodal properties, i.e., a number of reflection peaks with non-Gaussian shapes. However, the main wavelength of reflection, located around 1555 nm, is evaluable by means of an appropriate smoothing algorithm. When loaded by mechanical bending, a pronounced Bragg wavelength shift of this reflected peak up to 160 pm is detected. This demonstrates that the additively manufactured waveguides can be used not only for signal transmission but also as a sensor. KW - Bragg-Reflektor KW - Lichtwellenleiter Y1 - 2023 U6 - https://doi.org/https://doi.org/10.1364/OL.481801 VL - 48 IS - 7 SP - 1778 EP - 1781 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 - 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 - 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 - 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 - JOUR A1 - Kefer, Stefan T1 - Sapphire Photonic Crystal Waveguides with Integrated Bragg Grating Structure JF - Photonics N2 - Abstract: This contribution demonstrates photonic crystal waveguides generated within bulk planar sapphire substrates. A femtosecond laser is used to modify the refractive index in a hexagonal pattern around the pristine waveguide core. Near-field measurements reveal single-mode behavior at a wavelength of 1550 nm and the possibility to adapt the mode-field diameter. Based on farfield examinations, the effective refractive index contrast between the pristine waveguide core and depressed cladding is estimated to 3x10-4. Additionally, Bragg gratings are generated within the waveguide core. Due to the inherent birefringence of Al2O3, the gratings exhibit two distinct wavelengths of main reflection. Each reflection peak exhibits a narrow spectral full width at a half maximum of 130 pm and can be selectively addressed by exciting the birefringent waveguide with appropriately polarized light. Furthermore, a waveguide attenuation of 1 dB cm-1 is determined. KW - integrated photonics KW - sapphire KW - Bragg grating KW - femtosecond laser KW - photonic crystal waveguide KW - Wellenleiter KW - Femtosekundenlaser KW - Bragg-Reflektor Y1 - 2022 UR - https://www.mdpi.com/2304-6732/9/4/234 U6 - https://doi.org/https://doi.org/10.3390/photonics9040234 VL - 9 IS - 4 SP - 234 EP - 234 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 - 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 - 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 - THES A1 - Girschikofsky, Maiko T1 - Herstellung und Anwendung planarer Bragg-Gitter-Sensoren KW - Bragg-Reflektor KW - Optischer Sensor KW - Integrierter Sensor Y1 - 2020 SN - 978-3-8440-7561-8 PB - Shaker ER -