Fraunhofer-Publica
The Fraunhofer-Publica has been successfully documenting the research results of the Fraunhofer-Gesellschaft for over 30 years. The platform enables the collaborative linking of research-relevant objects and disseminates within the international scientific community.
The Fraunhofer-Publica thus fulfils its responsibility to promote the transfer of knowledge and know-how to industry and society.
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Research outputs
As an application-oriented research organisation, Fraunhofer aims to conduct highly innovative and solution-oriented research - for the benefit of society and to strengthen the German and European economy.
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Projects
Fraunhofer is tackling the current challenges facing industry head on. By pooling their expertise and involving industrial partners at an early stage, the Fraunhofer Institutes involved in the projects aim to turn original scientific ideas into marketable products as quickly as possible.
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Researchers
Scientific achievement and practical relevance are not opposites - at Fraunhofer they are mutually dependent. Thanks to the close organisational links between Fraunhofer Institutes and universities, science at Fraunhofer is conducted at an internationally first-class level.
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Institutes
The Fraunhofer-Gesellschaft is the leading organisation for applied research in Europe. Institutes and research facilities work under its umbrella at various locations throughout Germany.
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PublicationUnlocking the potential of extreme hyperchromats - Pushing the limits of axial color splitting( 2024)In contrast to conventional optical systems, which are optimized for wavelength-independent imaging, hyperchromats aim for strongly wavelength-dependent focal lengths. In this contribution, the design parameters of hyperchromatic two-lens optical systems were derived that provide strong axial color splitting expressed by extremely low equivalent Abbe numbers. These systems have been investigated for compositions of either pure refractive or all diffractive lenses, as well as hybrid configurations thereof. First, lens doublets made of cemented elements are considered and the variables affecting the equivalent Abbe number of the system are investigated. In particular, the influence of the focal lengths of the individual lenses and the Abbe numbers of the selected lens materials are taken into account. The best parameter-sets were determined by paraxial numerical simulations for different cemented configurations. To ensure a simple implementation, especially to avoid exotic or potentially harmful materials, only readily available inorganic standard glasses were considered. In the next phase of this investigation an air gap was inserted between the two lenses, which is an additional influence parameter on the equivalent Abbe number. Following the paraxial considerations, selected two-lens configurations were transferred to the non-paraxial domain and refined using optical design software, also taking aberrations into account. To further reduce achievable equivalent Abbe numbers, an aspherical surface was introduced to compensate for spherical aberrations. Finally, for the refractive doublets an equivalent Abbe number of 2.4 was achieved, which corresponds to only 12% of the smallest Abbe number of the selected materials. This result was even surpassed by the hybrid hyperchromat, resulting in an extraordinary minimum equivalent Abbe number of -0.6 that is more than five times smaller than the Abbe number of diffractive lenses.
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PublicationCladding light handling in thulium-doped fiber amplifiers for kW-class spectral beam combination( 2024)Power scaling of fiber lasers has always been pursued, being limited by nonlinear effects and heat generation in the active fiber and various components. Among the most critical components are cladding light strippers (CLS) between amplifier chains, removing light from leaked higher order modes, the unabsorbed pump or losses from splices and components. Polymer-based CLS work sufficiently well for the near-IR including the pump wavelength at 793 nm but suffer from high absorption at the signal wavelength near 2 µm and have not been evaluated in detail in this regime. Therefore, it is necessary to examine different acrylates and siloxanes at both the pump and signal wavelengths individually concerning their performance as CLS and test their limits. We present a CLS with an improved design which can withstand 7.5 W at 2039 nm while stripping >46 dB. For higher powers to >800 W, we examine CO2-laser inscribed CLS at the pump wavelength, reaching 21 dB stripping efficiency within only 15 mm of length.
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PublicationAccurate experimental analysis and theoretical representation of OLED emission zone profiles( 2024)A model for characterizing emission zone profiles (EMZ) in organic LEDs is introduced. Considering limits for resolving EMZ features yields a characterization by two parameters only. This enables to compare different EMZ results numerically and to define optimization targets that can be observed experimentally. Exemplary data on current-dependent EMZ shift illustrate the application of the method.
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PublicationEntwicklung, Auslegung und Aufbau eines kontinuierlich betriebenen Hochdruck-Hochtemperatur-Reaktorsystems zur Herstellung von Benzin-und Dieselkaftstoff durch die Hydrierung von TCR-Öl aus biogenen ReststoffenDie vorliegende Dissertation befasst sich mit der Hydrierung von Pyrolyseölen, die durch das Thermo-Catalytische-Reforming(TCR®)-Verfahren hergestellt werden. Es wurde eine kontinuierliche Hydrieranlage geplant, gebaut und betrieben. Hierfür wurden die passenden Prozessparameter für die optimale Ausbeute und Entfernung von Heteroatomen gesucht, wie beispielsweise Stickstoff, Sauer-stoff und Schwefel. Es ist wichtig, sich mit dem Themenbereich zu befassen, da Pyrolyseöle aus dem TCR®-Verfahren mit fossilem Rohöl gemischt und gemeinsam in Raffinerien aufbereitet werden kön-nen. Durch den Austausch von fossilem Öl durch Pyrolyseöl aus dem TCR®-Verfahren kann eine Reduktion der CO2-Emissionen in der petrochemischen Industrie und dem Verkehrssektor erreicht werden. Die bisherigen Untersuchungen haben ergeben, dass die erforderliche Stabilität der Pyrolyseöle aus anderen Pyrolyse-Prozessen, wie beispielsweise der schnellen Pyrolyse, nicht vorhanden ist. Das TCR®-Verfahren ermöglicht es nun, thermisch-stabile Pyrolyseöle herzustellen und für Downstream-Pro-zesse zu nutzen, wodurch ein Einsatz in Raffinerien möglich ist. Die Erkenntnisse konnten gewonnen werden, indem Untersuchungen für die Hydrierung an Modellsystemen, die verschiedene Pyrolyseöle simuliert haben, durchgeführt wurden. Durch die Verwendung von Modellsystemen konnten die Fragen nicht beantwortet werden, ob reale Pyrolyseöle hydriert und welche kommerziell erhältlichen Hydrierkatalysatoren hierfür verwendet werden können. Die erzielten Ergebnisse wurden durch Experimente in einem kontinuierlichen Hydrierreaktor erlangt. In dem kontinuierlichen Reaktorsystem werden bis 3 kg Pyrolyseöl pro Stunde umgesetzt. Getestet wurden verschiedene Prozessparameter und Katalysatoren. Durch den kontinu-ierlichen Betrieb ist die Übertragung auf Prozesse in der Raffinerie möglich. Ergebnisse der Experimente sind, dass Downstream-Prozesse mit den Bedingungen 10 MPa und 380 °C möglich sind, um eine optimale Ausbeute und Qualität der hydrierten Pyrolyseöle zu erlangen. Durch die erzielten Ergebnisse kann der Schluss gezogen werden, dass Pyrolyseöle aus dem TCR®-Prozess für den kontinuierlichen Downstream-Prozess geeignet sind. Außerdem lassen sich diese Ergebnisse in eine Vision für eine CO2-Neutralität von China übertragen, da durch den TCR®-Prozess und die anschlie-ßende Hydrierung von TCR®-Öl sich biogene Reststoffe in nachhaltige Chemikalien und Kraftstoffe um-wandeln lassen.
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PublicationImpact of parasitic wire resistance on accuracy and size of resistive crossbars( 2021)The size of crossbar-like resistive multiplication accumulation (MAC) accelerators is restricted by parasitic interconnect resistances limiting the computation efficiency. In order to understand the impact of the interconnect (wire) resistance on the computation accuracy, this work proposes a modelling methodology for adapting the neural network weights regarding the weight error caused by wire resistance. Even more, this work investigates the maximal achievable crossbar size based on the proposed design variable âthe minimal allowed weight error ratio Ron/Reqvâ instead of using an iterative numerical method. Using the proposed method this work investigate the computation accuracy improvement through splitting the layer computation into multiple small crossbars. The result indicates that simply separating the computation into multiple small crossbar does not improve the accuracy always. Considering the minimal Ron/Reqv can more easily result in a proper crossbar siz e.
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