Refine
Year of publication
Document Type
Conference Type
- Konferenzartikel (10)
Is part of the Bibliography
- yes (15)
Keywords
- Optik (2)
- e-learning (2)
- 3D virtual reality (1)
- E-Learning (1)
- Faseroptik (1)
- Gehirn (1)
- Gewebe (1)
- Kraftstoff (1)
- Krankheit (1)
- Lichtwellenleiter (1)
Institute
- Fakultät Elektrotechnik und Informationstechnik (E+I) (bis 03/2019) (15) (remove)
Open Access
- Open Access (5)
- Closed (4)
- Closed Access (4)
The bandwidth behavior of graded-index multimode fibers (GI-MMFs) for different launching conditions is investigated to understand and characterize the effect of differential mode delay. In order to reduce the launch-power distribution the near field of a single-mode fiber is used to produce a controlled restricted launch. The baseband response is measured by observing the broadening of a narrow input pulse (time-domain measurement). The paper verifies the degradation in bandwidth due to profile distortion by scanning the spot of the single-mode fiber with a transversal offset from the center of the test sample. In addition, the impact of the launch-power distribution tuned by different spot-size diameters is demonstrated. Measurements were taken on ‘older’ 50-μm and 62.5-μm GI-MMFs as well as on laser-performance-optimized fibers more recently developed.
The developed solution enables the presentation of animations and 3D virtual reality (VR) on mobile devices and is well suited for mobile learning, thus creating new possibilities in the area of e-learning worldwide. Difficult relations in physics as well as intricate experiments in optics can be visualised on mobile devices without need for a personal computer.
In short-reach connections, large-diameter multimode fibres allow for robust and easy connections. Unfortunately, their propagation properties depend on the excitation conditions. We propose a launching technique using a fibre stub that can tolerate fabrication tolerances in terms of tilts and off-sets to a large extent. A study of the influence of displaced connectors along the transmission link shows that the power distributions approach a steady-state power distribution very similar to the initial distribution established by the proposed launching scheme.
Für Verbindungen über einige hunderte Meter eignen sich Multimode-Lichtwellenleiter (MM-LWL) durch ihre Robustheit und einfache Handhabung ideal. Zudem erlaubt der große Durchmesser des Faserkerns mit 62,5 µm eine sichere, stabile und relativ verlustfreie Verbindung. Neben diesen Vorteilen sind jedoch im letzten Jahrzehnt durch die Erhöhung der Bitrate auch Nachteile sichtbar geworden. So konnten die für niedrige Übertragungsraten genutzten LEDs noch zur Vollanregung der Übertragungsmoden eingesetzt werden. Für höhere Übertragungsraten ist dies jedoch nicht mehr möglich, da sie optisch zu träge sind und somit der schnellen Modulation nicht mehr folgen können. Schnellere Anregungskomponenten, etwa Laserdioden (LD), müssen eingesetzt werden. Durch die spezifische Ausstrahlungscharakteristik der LDs kann jedoch nicht mehr der gesamte MM-LWL-Kern angeregt werden. Dies führt zu unterschiedlichen Modenlaufzeiten im MMLWL, was sich wiederum negativ auf die Übertragungsrate auswirken kann. Dadurch nimmt die Bandbreite rapide ab.
Mobile learning (m-learning) can be considered as a new paradigm of e-learning. The developed solution enables the presentation of animations and 3D virtual reality (VR) on mobile devices and is well suited for mobile learning. Difficult relations in physics as well as intricate experiments in optics can be visualised on mobile devices without need for a personal computer. By outsourcing the computational power to a server, the coverage is worldwide.
In the brain-cell microenvironment, diffusion plays an important role: apart from delivering glucose and oxygen from the vascular system to brain cells, it also moves informational substances between cells. The brain is an extremely complex structure of interwoven, intercommunicating cells, but recent theoretical and experimental works showed that the classical laws of diffusion, cast in the framework of porous media theory, can deliver an accurate quantitative description of the way molecules are transported through this tissue. The mathematical modeling and the numerical simulations are successfully applied in the investigation of diffusion processes in tissues, replacing the costly laboratory investigations. Nevertheless, modeling must rely on highly accurate information regarding the main parameters (tortuosity, volume fraction) which characterize the tissue, obtained by structural and functional imaging. The usual techniques to measure the diffusion mechanism in brain tissue are the radiotracer method, the real time iontophoretic method and integrative optical imaging using fluorescence microscopy. A promising technique for obtaining the values for characteristic parameters of the transport equation is the direct optical investigation using optical fibers. The analysis of these parameters also reveals how the local geometry of the brain changes with time or under pathological conditions. This paper presents a set of computations concerning the mass transport inside the brain tissue, for different types of cells. By measuring the time evolution of the concentration profile of an injected substance and using suitable fitting procedures, the main parameters characterizing the tissue can be determined. This type of analysis could be an important tool in understanding the functional mechanisms of effective drug delivery in complex structures such as the brain tissue. It also offers possibilities to realize optical imaging methods for in vitro and in vivo measurements using optical fibers. The model also may help in radiotracer biomarker models for the understanding of the mechanism of action of new chemical entities.
The combination of fossil-derived fuels with ethanol and methanol has acquired relevance and attention in several countries in recent years. This trend is strongly affected by market prices, constant geopolitical events, new sustainability policies, new laws and regulations, etc. Besides bio-fuels these materials also include different additives as anti-shock agents and as octane enhancer. Some of the chemical compounds in these additives may have harmful properties for both environment and public health (besides the inherent properties, like volatility). We present detailed Raman spectral information from toluene (C7H8) and ethanol (C2H6O) contained in samples of ElO gasoline-ethanol blends. The spectral information has been extracted by using a robust, high resolution Fourier-Transform Raman spectrometer (FT-Raman) prototype. This spectral information has been also compared with Raman spectra from pure additives and with standard Raman lines in order to validate its accuracy in frequency. The spectral information is presented in the range of 0 cm-1 to 3500 cm-1 with a resolution of 1.66cm-1. This allows resolving tight adjacent Raman lines like the ones observed around 1003cm-1 and 1030cm-1 (characteristic lines of toluene). The Raman spectra obtained show a reduced frequency deviation when compared to standard Raman spectra from different calibration materials. The FT-Raman spectrometer prototype used for the analysis consist basically of a Michelson interferometer and a self-designed photon counter cooled down on a Peltier element arrangement. The light coupling is achieved with conventional62.5/125μm multi-mode fibers. This FT-Raman setup is able to extract high resolution and frequency precise Raman spectra from the additives in the fuels analyzed. The proposed prototype has no additional complex hardware components or costly software modules. The mechanical and thermal disturbances affecting the FT-Raman system are mathematically compensated by accurately extracting the optical path information of the Michelson interferometer. This is accomplished by generating an additional interference pattern with a λ = 632.8 nm Helium-Neon laser (HeNe laser). It enables the FT-Raman system to perform reliable and clean spectral measurements from the materials under observation.