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Theses 2016

Statistical Signal Processing Method for Sleep Analysis in Infants

Abstract: Sleep is a natural periodic state of rest for mind and body taking about one third of lifetime of humans. It is essential for their well-being, efficiency and long-term health. During infancy and early childhood, the role of sleep is even more crucial as human infants spend more time asleep than awake and optimal conditions in this stage are necessary for their physiological, mental and social development. This has stimulated numerous conventional researches about infant sleep which have investigated qualitatively the role of sleep on infant development. However, such studies have not included experimental manipulations designed to evaluate the underlying relation between the disposable diaper, as one of multiple factors affecting the sleep of infants, and the quality of sleep.

In this thesis, a new method for monitoring and quantitatively analyzing the sleep of infants was developed; depending only on the body movement signal measured usin an accelerometer. For this, a sleep study involving 36 healthy infants aged 28+/-6 weeks was performed over 18 nights. The analysis of the activity signals was carried out by an in-depth signal processing method. To support the preprocessing of the measured data, daily sleep diaries and questionnaire were also used. After extracting multiple local and global features from the processed signals, the output is then used to build a randomized comparative analysis. Its main purpose is to evaluate quantitatively if there is an influence of using either a weakly or highly absorbent disposable diapers, as one of multiple factors on the quality of infant sleep and in which features of the activity signal variations can be observed.

The developed algorithm allows for detecting and analyzing high-activity peaks in the signal. The number of extracted peaks correlated highly with the number of awakenings reported in the sleep diaries. We also found that even though the sleep duration was comparable between the two groups of nights using different products, there were measurable variances in both the level of activity and the sleep fragmentation. The differences were observed in the global features of the signal, while no significant changes were detected when comparing the local features within the night. Furthermore, the study showed a higher level of activity in boys compared to girls, and a higher sleep fragmentation for breastfed infants compared to those who relied on formula milk for nutrition. Finally positive influences and limitations of the study are discussed. 

Obtaining Bright Squeezed Vacuum in Orbital Angular Momentum Modes Using a Non-Linear Interferometer

Summary: Light beams with helical or spiral wavefronts carry orbital angular momentum (OAM). OAM beams can be used in a large range of applications. Beyond the optical range, for instance, there is the possibility to generate bright x-rays carrying OAM components and helical wavefronts can be sued in radio frequency communications or in astronomy, where an antenna array can be used to detect them. In optical trapping, the transfer of OAM is used for the optical manipulation of particles. The OAM beams also have applications in the communications field. Superpositions of helical beams have been used to perform information encoding over large distances. The OAM modes can also be used to realize multidimensional entanglement in quantum key distribution (QKD).

The bright squeezed vacuum (BSV) is a state of light which presents non-classical correlations and manifests macroscopic entanglement. This light is characterized by its large number of photons per mode. Hence, the BSV is a promising source for the information encoding in the quantum domain. The BSV can be generated by means of a strongly pumped non-linear crystal in a process called parametric down-conversion (PDC).

Because of the fundamental features of the OAM modes and the BSV light mentioned above, it is interesting to prepare the BSV in OAM modes. The quantum information encoding can be performed using the orthogonality of the OAM modes prepared in the BSV state. It is also interesting to generate a mode of BSV carrying a single value of OAM.

In this project, the generation of BSV radiation in OA; modes is performed by means of two identical non-linear crystals. The constructive and destructive interference of the radiation from the two crystals provides OAM-types modes. By separating the crystals, the interference pattern changes and therefore, the generated modes change. However, the radiation can always be decomposed in terms of OAM modes. The main objective in this work is to study the OAM characteristics of this light under the described conditions. For this purpose, two different methods are used to measure the OAM components of the BSV radiation. In the first method, the measurement of the auto-correlation function provides the effective number of modes. In the second method, the diffraction of the beam with the phase modulated by means of a spatial light modulator (SLM) is used to measure the content of each mode in the superposition or mixture of OAM modes.

From the measurements performed in this project, the most important observations are summarized as follows: The effective number of modes is recued with the increase of the pump power for both measurements. As the pump power increases from 40mW to 90mW, the effective number of modes reduces from 10.11 to 3.338. The modal decomposition showed that all the modes have ring-shape but different azimuthal components. Having those results, the next step is to filter the modes without losing the non-classical features of the BSV. This can be performed by the use of additional refractive optical elements which convert OAM states into transvers momentum states. In recent experiments, these elements have been used and the losses were not too high for the applications considered. For this work, the loses should be carefully calibrated and reduced as much as possible. An evaluation of the performance of this method will be done in future experiments. 

Optical Investigation of Interplay of Mie and Diffraction Resonances in Planar Non-Closely Packed Hybrid Metal-dielectric Photonic Crystals

Summary: In this experimental work, optical properties of monolayers of organic (polystyrene) sphere have been investigated with two sets of samples. Samples which consisted of monolayer of spheres (i) assembled on dielectric substrate and (ii) gold coated glass substrate. Spheres size distribution was from ~550 nm to ~1060 nm to work in the VIS-NIR range of light spectrum.

System of monolayer-glass samples were studied in first order approximation as photonic crystal slabs supporting wave guided modes and guided resonances. Spectral position of resonances were controlled by varying the filling fraction of spheres in overall volume the ordered monolayer lattice. Centre-to-center distance remained preserved while filling fraction was varied by plasma etching of spheres in our samples. Energy losses via dielectric substrate are concluded to be the main reason which limits the capability of controlling the resonances of 2D monolayer of spheres through the geometry of the lattice. It has been demonstrated that the analogy of 2D colloidal lattice of spheres with photonic crystal slab can only qualitatively explain the optical response of the system. Strong departure of resonance positions were found between the spectral positions predicted by effective medium theory and experimental values when effective refractive index of monolayer was reduced below 1.28 in our samples. Dispersion of resonances has been studied by angle resolved spectroscopy with s- and p-linearly polarized light.

Resonances provided by hybrid photonic plasmonic structure in ML-gold-glass samples have been observed and studied. Hybrid structure has been understood at its different architectural levels, capable of supporting wave guided modes, surface plasmon polariton modes, hybrid modes, and strong Mie. However, there was no persuasive evidence for the existence of SPPs found or observed in the transmission spectrum. Periodicity introduced by the ordered arrangement of spheres was confirmed in the well-defined resonant structure in the transmission spectra of the samples. It has been shown that the hybrid photonic plasmonic structure due to the inclusion of metallic character in system provides an extra degree of freedom in order to tune the optical response of structure through manipulating the geometry of colloidal monolayer. A large improvement in light confinement and the quality of resonances has been observed in ML-Au-glass samples in comparison to the similar samples with glass substrate. Using Mie plot software, Mie resonances has been traced, and strong Mie resonances are confirmed in ML-Au-glass sample in comparison to the ML-glass samples. 

Mueller Matrix Analysis for Light Interacting with Dense Particulate Films

Abstract: Mueller ellipsometric technique is a complete means of description of polarized light which is used for studying optical properties of materials. In this work, a method of Mueller matrix elements extraction and filtering from multiple polarization inputs was developed and applied to study disorder in dense particulate thin films. Films made of two different sorts of particles, namely spherical SiO2 and nanorod ZnO, were studied. It is found that order induced anisotropy is the most reliable indicator of particulate film quality. Severa figures of merit relying on Mueller matrix elements, ellipsometric parameters and degree of light polarization werde developed to quantify disorder in the particle positions and orientations on the film surface.

Laser Processing of Thin Borosilicate Glass with UV Nanosecond Laser Radiation for Display and Interposer Applications

Abstract: The application of thin and ultra thin borosilicate glass as smartphone and tablet cover or interposer material in microelectronic devices requires methods for separation and drilling. Laser processing with short and ultra-short laser pulses have proven to enable high quality cuts by either direct ablation or internal glass modification and cleavage. A recently developed high power UV nanosecond laser source allows for pulse shaping of individual laser pulses and bursts. Thus, the pulse duration, pulse bursts and the repetition rate can be set individually at a maximum output power of up to 60 W. In this study, the novel pulsed UV laser system was used to study the laser ablation and drilling process on 400 μm and 50 μm thick borosilicate glass at different pulse durations ranging from 2 – 10 ns and a pulse burst with two 10 ns laser pulses with a separation of 10 ns. Single line scan and multiscan experiments were performed to correlate the process parameters and the laser pulse shape with the ablation depth and cutting edge chipping. Increasing the pulse duration within the single pulse experiments from 2 ns to longer pulse durations led to a moderate increase in ablation depth and a significant increase in chipping. The highest material removal was achieved with the 2×10 ns pulse burst. Experimental data also suggest that chipping could be reduced while maintaining a high ablation depth by selecting an adequate pulse overlap. In addition, the real-time combination of different pulse patterns during drilling thin borosilicate glass produced holes with low overall chipping at a high throughput rate. Finally, a temperature characterization was conducted with a thermographic camera while hole arrays were drilled in borosilicate glass at different repetition rates, in order to identify a damage generation threshold.

Raman Spectroscopy and Multiphoton Endomicroscopy for Labelfree Optical Diagnostics of Colon Cancer

Abstract: A successful diagnosis at the earliest, cellular stage of colon cancer is the key to combat this deadly disease. In this regard, the two labelfree optical technologies multiphoton endo-microscopy and Raman spectroscopy offer an immense potential. Multiphoton endo-microscopy uses autofluorescence and second harmonic generation in the samples for imaging tissue through histology like optional sectioning. The prototype of such an endoscope with a custom scan softwre was developed at the Institute of Bio-medical Technologies. in this master thesis, this scan softwre has been reworked and upgraded by new function, such as line averaging, a two-layer scan or the export as TIFF-files. Furthermore, a study on the bio-chemical changes during tumor development induces by ulcerative colitis in mice was performed using Raman spectroscopy. This technique is based on the inelastic scattering by molecules with certain rotational and vibrational energy bonds. It is molecule-specific but requires sophisticated processing algorithms to subtract the unwanted fluorescence background. A new measuring setup, a data processing algorithm and a complete statistical model were built and can be sued for more elaborate studies. The preliminary results suggest that the Raman signal is reliable and that the detected peaks match very well to the results of comparable studies. Unfortunately, the spectral differences between cancerous inflammatory and healthy tissue are not sufficient to enable an automatic differentiation. Finally the concept of a hybrid system is presented, combining multiphoton imaging with Raman spectroscopy to one single endoscope. Based on the exiting setups, the realization of such a hybrid system is feasible and might overcome most of the limitations preventing automatic cancer detection. 

Towards Octave-Spanning Low-Power Microresonator Frequency Combs: Optical Characteriazation of Silicon Nitride Chips

Abstract: Optical microresonators with small modal volumes and high quality factors (Q) are ideal platforms for the research on nonlinear optics and quantum opto-mechanics. Among the multitude of materials used for microresonators, silicon nitride (SiN) with its high Kerr nonlinearity, low mechanical loss, wide transparency window from the visible to the mid-IR, absence of nonlinear (e.g. two or three photon) absorption and access with CMOS-compatible fabrication techniques, becomes one of the most promising materials for this research. Benefiting from such advantages, SiN microresonators can be used for microresonator frequency comb generation through four-wave mixing via Kerr nonlinearity. Up-to-date, fabricated SiN photonic chip-based microresonators can generate broadband microresonator frequency combs with 100 GHz – 1 THz mode spacings to spectrally cover more than the telecommunication bands of 1270 – 1640 nm from a single input laser wavelength, opening a new pathway to highly compatible optical communication systems.

However, currently the performance of SiN photonic chip-based microresonators is still limited by their high power requirement, determined by the low input power coupling efficiency from optical fibers to SiN waveguides and the low quality factor Q of the microresonators. The coupling efficiency is typically around 15% and improving it requires deliberate designs and fabrication

techniques. The Q of SiN microresonators is typically around 10^6, and improving the Q is presently hindered by the absorption and scattering induced by the material interfaces and the gases trapped in the material during the deposition. The improvements of the coupling efficiency and Q will reduce the power requirement for microresonator frequency comb generation and enables packaging SiN chip-scale frequency combs into integrated systems.

Anomalous group velocity dispersion is required for the microresonator frequency comb generation and the bright Kerr dissipative soliton formation. In addition, a broadband frequency comb can be achieved with a proper dispersion profile. Recently an important advancement to achieve broadband coherent frequency combs is the observation of the dispersive wave emission in SiN microresonators. To generate such dispersive waves in microresonators, the higher order dispersion needs to be precisely tailored and experimentally characterized.

This master thesis addresses the issues mentioned above. It aims to achieve broadband microresonator frequency combs with

low power requirement. To realize such a goal, three milestones have been achieved: (1) the optimization of the input power coupling efficiency from optical fibers to SiN waveguides is investigated with simulations, and >40% coupling efficiency is achieved experimentally; (2) the waveguide-ring resonator coupling and the coupling ideality describing the practical resonator Q are investigated with theoretical models, simulations and experimental characterization; (3) an experimental setup to characterize the microresonator dispersion up to the fourth order is established. With the three milestones mentioned above, a standard routine combining theoretical models, versatile simulation tools and novel experimental characterization platforms to achieve broadband microresonator frequency combs with low power requirement is demonstrated.

Investigation of Velocity Profiles in Dense GDI Sprays by Phase Doppler Anemometry

The optimization of the commercial Phase Doppler Anemometer (Dantec Dynamics) was performed in order to obtain trustworthy velocity data in dense sprays. A commercially available five-hole injector was used to provide a spray. Optimization of the system parameters and subsequent characterization of the velocity fields were performed considering only one spray stream. For the reliable system optimization, the same operating conditions were provided and the same spatial locations were investigated. Afterward, the optimized experimental setup was applied to measure two component velocity fields at different measurements planes: 5nm, 10 nm, 15 nm, 20 nm, 30 nm and 50 nm away from the nozzle tip. Test conditions were chosen to observe the spray at non-flashing and flashing states. The velocity at the nozzle orifice was extrapolated from the downstream flow. Additionally, we performed the analysis of drop sizes obtained by the PDA system. This analysis found to be an indispensable procedure to provide a better understanding of the velocity data.

The results showed that flash boiling has the potential to increase the droplet velocity and enhance the atomization process. Moreover, the validation rate at flashing conditions was found to be higher, which is also associated with the enhanced atomization of a spray.

 

Self-healing of Bessel Beams

Conclusions:

  • Self-healing effect of Bessel beams is directly measurable and observable in laboratory
  • Due to diffraction the Bessel beam starts to restore its profile even before the geometrical shadow (core shadow) of the obstruction ends -> Diffractioin plays a major role in the self-healing of Bessel beams
  • Off-axis obstructions perturb the Bessel beam more strongly than on-axis obstructions
  • Real (non-ideal) Bessel beams restore their initial intensity profile almost perfectly (within the scope of measurement accuracy) for both, on- and off-axis obstructions
  • The phase of the Bessel beam jumps by π between each lobe of the Bessel beam
  • Unlike for Bessel beams, a clear self-healing effect cannot be observed for Gaussian beams

Development of a New Two Colors Video-Ophthalmoscope for Precise Measuerment of Cardiac Cycle Induced Reflection Changes in the Retina

Abstract: The purpose of this study is to develope components of a new two colors video ophthalmoscope to measure cardiac cycle induced reflection changes in the human retina. These changes occur due to the changing blood volume. These reflection changes can also be measured using one wavelength. However, due to eye and head movements, the light intensity changes during the measurement.

The basic principle of this work is to use two wavelength, one wavelength that is absorbed by blood and another wavelength that is not absorbed by blood and can be used to compensate for intensity changes. The development of the illumination and detection components are described. The function of this principle is shown using the changing blood volume in the finger. Recently it was shown that the waveform of the cardiac cycle induced reflection changes in the eye depends on the intraocular pressure. The main aim is to use two two-color-videoophthalmoscope to measure both eyes simultaneously. Simultaneous measurement of both eyes permits to compare both waveform of the cardiac cycle. If there is an asymmetry in the waveform of reflection signal, it can be possible that an asymmetry will be noticed in the IOP as a sign of beginning glaucoma.

Inversion Problem Based on the Modified Beer-Lambert Law (MBLL) to Reconstruct Oximetry Parameters of Hemoglobin in Cutaneous Phantom

Conclusions:

  • One of the primary goals of this thesis is to introduce light attenuating chromophores of blood other than hemoglobin, such as fat and water. This goal is achieved by introducing abosrbance of light by these chromophores in the modified Beer Lambert Law (MBLL) equations. Experimentally, the chromophores are inserted in the skin phantom in order to make the skin phantoms mimic skin optical properties more properly.
  • There is a strong relation between partial lenght factor (PPF) and hemoglobin concentration. PPF of the aforemention chromosphores are calculated.
  • PPF of various chromophores are used for recovering the absoltue values of hemoglobin concentration. Several known concentrations of hemoglobin are rcovered by means of their individual PPF values.
  • The MATLAB codes are modified to make the scanning procedure and the calculation faster. The scanning speed became twice as fast as before. And also, an ergonomic shell structure for the scanning module is deisgned and constructed.
  • In this thesis, several low concentration hemoglobin solutions were made to validate this method of recovering hemoglobin concentration. A stockpile of PPF data of various blood chromophores can be particularly useful for recovering oxygenation information of real human blood.

Fabrication of Optical Phantoms with Specific Oxygenation Levels

Abstract: By making use of optical technologies, much about the human body can be understood and treated. In the near-infrared part of the spectrum, hemoglobin is the most important absorber of light, acting as a bio-marker or indicator of tissue health in many photonic diagnostic techniques, like photoacoustic imaging, hyperspectral imaging and near-infrared spectroscopy (NIRS).

In order to calibrate the photonic devices, simulate light distributions in a medium and set a reference to optical properties, ‘Optical Phantoms’ are constructed. Fabricating phantoms that mimic the absorption properties of oxy- and deoxyhemoglobin – which determine the oxygen saturation in blood – over a wide spectral range present a challenge.

In this project, 11 different biocompatible silicon-soluble color pastes have their optical properties characterized. To achieve that, thin phantoms made of biocompatible silicone containing the individual colors are case and evaluated, with the help of a spectrometer. Concentration independent optical coefficients of these colors are then defined.

Knowing the individual absorption and scattering coefficients of each color allowed for the programming of a user interface, which allows one to create a recipe of a silicone phantom, with selected optical properties.

Finally, this user interface is put to proof by creating an optical phantom with a specific oxygen saturation.

Tailoring the Optomechanical Coupling in Multimode Photonic Crystal Resonators

Abstract: In this thesis, I describe the design, fabrication and characterization of a quasi-twodimensional photonic crystal multi-mode optomechanical resonator formed from thin film silicon. This cavity optomechanical device consists of a dielectric membrane patterned with a triangular lattice of holes, in which three line defect nanoscale slots creating a so-called zipper-style double nanobeam [1] in between photonic crystal slabs. The coupled fundamental optical modes localized in the slots can be designed to form three high-Q optical resonances that can achieve large couplings to the mechanical modes of the zipper beam.

In general, cavity optomechanics examines the interaction between light and the mechanical motion of nano to macro scale oscillators. The coupling is typically mediated by generalized radiation pressure forces. Cavity optomechanics adresses various fundamental and technological challenges in physics and engineering such as force sensing, wavelength conversion, generation of quantum states of motion, squeezing of light and mechanical motion, state transfer between light and mechanics and gravitational wave detection. Recently, a particular class of devices based on photonic crystals have shown their ability to confine optical and mechanical modes to exceptionally small mode volumes, thus boosting heir coupling strength while maintaining high quality factors. These so-called optomechanical-crystals hold great promise towards the realization of strong optomechanical coupling, which remains a key challenge in the field. Recently, some theoretical works proposed multi-mode optomechanical systems to achieve a large ratio between the optomechanical coupling g0 and cavity decay rate . Motivated by this theoretical prediction [2] and by recent achievements in the development of membrane membrane-in-the-middle setup on an optomechanical crystal basis [3], the goal of this work is to push the idea even further by introducing more optical and mechanical modes to approach regimes of larger optomechanical coupling strengths.

The first chapter of this thesis introduces the cavity optomechanics. The following chapter describes the realization of cavity optomechanics employing photonic crystals. In addition, the computational design and numerical modeling tools to obtain a photonic crystal optomechanical cavity are introduced. The third chapter is an indepth analysis of the triple- slotted photonic crystal optomechanical cavity design.

This chapter details the optimization of the multimode optomechanical cavity and the impact of the geometry on the coupling strength. The fourth chapter presents the nanofabrication process used for these devices. The following chapter gives an overview of the device characterization. Lastly, the results and future perspectives for this work are summarized.

Determination of Binary Diffusion Coefficients of Molecular Gas Mixtures by Using a Lochschmidt-Cell Combined with Holographic Iinterferometry

Summary and outlook: During this thesis the gaeous binary diffusion coefficients of the CH4-C3H2 system were investigated in a Lochschmidt cell combined with a holographic interferometry at 5 bar and 293.15 K using pure gases as well as corresponding mixtures resulting in different average propane mole fractions 1/6, 1/3, 1/2, 2/3 and 5/6. Preparation of the experimental set-up was carried out in order to be able to investigate the flammable gases and their mixtures, where in particular the sealing material had to be exchanged. In addition, the set-up peripheral gas piping system was modified to be able to fill, empty, and flush the cell in a convenient and safe way. The previous data evaluation procedure was implemented in MATLAB. This allows performing measurements and analyzing the measurement data at the same time, since the old software for data evaluation was not usable during the measurement runs. Furthermore, the new software allows for a standard evaluation of measurements where mixtures are used prior to the diffusion process.

The obtained results for the investigated system show that the overall average D12ρmix value does not depend significantly on the initial concentration gradients and the propane mode fraction. This is caused by a corresponding high estimated uncertainty, in particular for the overall average D12ρmix values for the high average propane mole fractions. This issue will need further analysis in upcoming work.

In the future, the system CH4-C3H8 will be investigated at pressures of 1 bar and 2 bar and at temperatures of 293.15 K and 313.15 K to access information on the temperature and pressure dependency, which is important in context with the ab initio calculation performed in a related project at Rostock university. For the same purpose, the investigation of the system CO2C3H8 is planned to performed at pressures of 1, 2, 5 and 10 bar and temperatures of 293.15 K and 313.15 K. Currently the data evaluation is based on the assumption that D12ρmix  is constant over whole investigating mole fraction. However, investigating the concentration dependency of the binary diffusion coefficient based on the mentioned assumption can be criticized. The newly implemented data evaluation can be used to examine any new proposed possible sources for the observed irregularities since it brings more freedom for data processing in comparison to the old software. 

Characterization of the Interaction of Gas Free Jets under Static Conditions

Abstract: In the present thesis, the interaction of methane jets emerged from various multi-hole injectors is studied. A constant volume chamber and two optical measurement techniques are employed for the investigation. Schlieren photography is used to visualize gas injections, which are recorded by means of a high-speed camera. Images are processed in order to calculate penetration depth and cone angle. Besides, particle image velocimetry is applied for the measurement of velocity fields. The entrainment rate if the surrounding medium is evaluated for selected nozzle designs. Entrainment rate, penetration depth and cone angle are important parameters which jointly contribute to the characterization of jet interaction. A significant discovery is made while observing injections at high fuel and low chamber pressures. As a result of rapid entrainment, jets issued by some symmetrical six-hole injectors strongly attracted each other and merged. It is revealed that the interjection velocity decreases during the merging process and increases when a single jet is formed.

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