<p>Developing a hybrid platform that combines nanophotonic circuits and atomic physic may provide new chip-scale devices for quantum application or versatile tools for exploring photon-mediated long-range quantum systems. However, this challenging project demands the excellent integration of cold atom trapping and manipulation technology with cutting-edge nanophotonics circuit design and fabrication. In this thesis project, we aim to develop a novel suspended membrane platform that serves as a quantum interface between laser-cooled, trapped atoms in an ultrahigh vacuum and the photons guided in the nanophotonic circuits based on high-quality silicon nitride microring resonators fabricated on a transparent membrane substrate. </p> <p><br></p> <p>The proposed platform meets the stringent performance requirements imposed by nanofabrication and optical physics in an ultra-high vacuum. These include a high yield rate for mm-scale suspended dielectric photonic devices, minimization of the surface roughness to achieve ultrahigh-optical quality, complete control of optical loss/in-coupling rate to achieve critical photon coupling to a microring resonator, and high-efficiency waveguide optical input/output coupler in an ultrahigh vacuum environment. This platform is compatible with laser-cooled and trapped cold atoms. The experimental demonstration of trapping and imaging single atoms on a photonic resonator circuit using optical tweezers has been demonstrated. Our circuit design can potentially reach a record-high cooperativity parameter C$>$500 for single atom-photon coupling, which is of high importance in realizing a coherent quantum nonlinear optical platform and holds great promise as an on-chip atom-cavity QED platform.</p>

In this paper, we present the design guidelines for a tunable optical isolator in an SOI-based ring resonator with two small time-modulated regions. By considering a physical model, the proper geometrical and modulation parameters are designed, based on a standard CMOS foundry process. The effect of the variation of the key parameters on the performance of the isolator is explained by two counter-acting mechanisms, namely the separation between the resonance frequencies of counter-rotating modes and energy transfer to the side harmonic. We show that there is a trade-off between these parameters to obtain maximum isolation. Consequently, by applying the quadrature phase difference one can obtain the maximum separation between the resonance frequencies and hence the minimum insertion loss, while the maximum isolation is obtained at the modulation phase difference of −0.78π , which leads to a higher insertion loss. Robustness of the design is investigated through a sensitivity analysis for the fabrication variations in the distance and width of the modulated regions. We demonstrate that there is a trade-off between isolation and insertion loss, and by varying the modulation parameters, we can achieve isolation of 18 (5) dB with 7 (1.8) dB insertion loss.

The main goals of this thesis are to design and examine heterogeneous antennas for different wireless applications of a wide variety of EM spectrum requirements: which includes WLAN 5.0 GHz, WLAN (2.45 GHz), UMTS (1.92-2.17 GHz), 2G, UMTS, LTE, ultra-wideband (UWB) applications, and MBAN applications (2.4 GHz). Various techniques for expanding bandwidth, enhancing performance, and balancing the operation have been examined through comprehensive simulated and physically fabricated models. Thereafter, a compact DRA, for UWB applications is examined. The combined resultant effects of asymmetric positioning of DRs (2, 3 and 4 Cylindrical elements), defected ground technique, dimensions, and profile of the aperture give RF designers detailed scope of the optimization process. More resonances are achieved, and the bandwidth is improved. The obtained results show that, an impedance bandwidth of 133.0%, which covers the Ultra­ Wideband band (3.6GHz - 18.0GHz), with a maximum power gain of 9dBi attained. In addition, a compact conformal wearable CPW antenna using EBG-FSS for MBAN applications at 2.4GHz is proposed. They are designed using fabric materials suitable for daily clothing. The performance of the antenna is investigated in free space, on a layered biological tissue model, and on a real human body to evaluate SAR. When the antenna is combined with an EBG-FSS structure, isolation between the antenna and the human body is introduced. The results show that the FBR is enhanced by 13 dB, the gain by 6.55dBi, and the SAR is lowered by more than 94%. The CPW antenna demonstrated here is appropriate for future MBAN wearable systems. The design, investigation, and application of water level monitoring utilizing subsurface wireless sensor are covered in this thesis. A wideband double inverted-F antenna is designed and examined to overcome signal attenuation issues. The obtained result is feasible, which has an operating bandwidth of 0.8 to 2.17GHz, with a reflection coefficient better than 10 dB. Moreover, a field trial is conducted to evaluate the robustness of the antenna under extreme conditions. A very good efficiency was also demonstrated, with losses of under 20%. Further, the results from the field experiment established that the antenna is a reliable contender for wireless communication in such challenging environments. / Libyan Ministry of Higher Education / The full text will be available at the end of the embargo: 19th June 2025

The reliable quantitative detection of biomarkers and pathogens at picomolar or even lower concentration would be a great help in point-of-care testing but is not readily available today. Integrated optical waveguides, which interact with the biochemical species to be monitored, are promising candidates for the detection of such ultra-low concentrations. The focus of this thesis is on optical waveguides in the shape of micro-ring or micro-racetrack resonators that are manufactured by UV-assisted nanoimprint lithography. This replica manufacturing technology is analyzed using analytical and numerical models in order to identify and quantify the main influence factors that determine the limit of detection of such biosensors. Potential biosensor applications are evaluated and general design rules are derived. The resulting measurements confirm the high potential of the chosen approach with respect to excellent sensitivity, low limit of detection and high dynamic range. With suitable optimization of the sensor layout, a further improvement of the performance by one to two orders of magnitude is possible.:Editor’s Preface Variables and constants Abbreviations 1 Introductions 1.1 Medical laboratory diagnostics 1.2 Biosensor technologies for point-of-care testing 1.3 Integrated optical waveguides and microresonators 1.4 Outline of the thesis 2 Basics 2.1 Guided waves in planar optical waveguides 2.1.1 Planar optical waveguides 2.1.2 Propagation of optical waves 2.1.3 Coupled modes in waveguides 2.2 Planar optical microresonators 2.2.1 Basic layouts and parameters 2.2.2 Manufacturing 2.2.3 Biosensing 2.3 Functionalization and biofunctionalization 3 UV-NIL Polymer Microresonator Biosensor Design 3.1 UV-assisted nanoimprint lithography 3.2 Waveguide cross-sections and refractive indices 3.2.1 Analytical waveguide modeling 3.2.2 Mode diagrams 3.2.3 Conclusions 3.3 Waveguide coupling 3.4 Waveguide losses 3.4.1 Absorption loss 3.4.2 Roughness loss 3.4..3 Substrate loss 3.4.4 Radiation loss due to bending 3.5 Sensitivity of the effective index to analyte binding 3.6 Overall sensitivity and detection limit 3.7 Generic design guidelines 3.8 Parameter selection for UV-NIL polymer waveguides 3.9 Comparison of polymer and silicon-based waveguides 3.9.1 Waveguide geometry 3.9.2 Radiation loss due to bending 3.9.3 Material damping 3.9.4 Surface roughness 3.9.5 Coupling channel widths and coupling coefficients 3.9.6 Conclusions 4 Characterization and Proof of Concept 4.1 Manufacturing-based design limits and chosen designs 4.2 Measurement setup and characterization process 4.3 Optical properties of UV-NIL polymer microresonators 4.4 Proof of concept 4.4.1 Sensitivity to bulk solutions 4.4.2 Reproducibility and drift 4.4.3 Comparison with theory 4.4.4 Comparison with literature 4.4.5 Sensitivity improvement 4.5 Asymmetry of the resonance curves 4.5.1 Cavity lifetime 4.5.2 Thermal influence 4.5.3 Summary 4.6 Conclusions 5 Integration into a biosensor platform 5.1 Chemical functionalization by oxygen plasma 5.2 Preparation of a biosensor characterization assay 5.2.1 Binding of fluorescent nanoparticles onto polymer surfaces 5.3 Microfluidic system 5.3.1 Programmable microfluidic system 5.3.2 System evaluation and improvement 5.4 Conclusions 6 Conclusions Declaration of authorship Acknowledgements Publications and awards / Der zuverlässige quantitative Nachweis von Biomarkern und Krankheitserregern in pikomolarer oder noch niedrigerer Konzentration wäre eine große Hilfe bei Tests am Point-of-Care, ist aber heute nicht ohne weiteres verfügbar. Integrierte optische Wellenleiter, die mit den zu überwachenden biochemischen Spezies interagieren, sind vielversprechende Kandidaten für den Nachweis solcher ultraniedriger Konzentrationen. Der Schwerpunkt dieser Arbeit liegt auf optischen Wellenleitern in Form von Mikro-Ring- oder Mikro-Spur-Resonatoren, die durch UV-unterstützte Nanoimprint-Lithographie hergestellt werden. Diese Replika-Herstellungstechnologie wird mit Hilfe analytischer und numerischer Modelle analysiert, um die wichtigsten Einflussfaktoren zu identifizieren und zu quantifizieren, die die Nachweisgrenze solcher Biosensoren bestimmen. Potenzielle Biosensoranwendungen werden bewertet und allgemeine Designregeln abgeleitet. Die daraus resultierenden Messungen bestätigen das hohe Potenzial des gewählten Ansatzes in Bezug auf ausgezeichnete Empfindlichkeit, niedrige Nachweisgrenze und hohen Dynamikbereich. Bei geeigneter Optimierung des Sensorlayouts ist eine weitere Verbesserung der Leistung um ein bis zwei Größenordnungen möglich.:Editor’s Preface Variables and constants Abbreviations 1 Introductions 1.1 Medical laboratory diagnostics 1.2 Biosensor technologies for point-of-care testing 1.3 Integrated optical waveguides and microresonators 1.4 Outline of the thesis 2 Basics 2.1 Guided waves in planar optical waveguides 2.1.1 Planar optical waveguides 2.1.2 Propagation of optical waves 2.1.3 Coupled modes in waveguides 2.2 Planar optical microresonators 2.2.1 Basic layouts and parameters 2.2.2 Manufacturing 2.2.3 Biosensing 2.3 Functionalization and biofunctionalization 3 UV-NIL Polymer Microresonator Biosensor Design 3.1 UV-assisted nanoimprint lithography 3.2 Waveguide cross-sections and refractive indices 3.2.1 Analytical waveguide modeling 3.2.2 Mode diagrams 3.2.3 Conclusions 3.3 Waveguide coupling 3.4 Waveguide losses 3.4.1 Absorption loss 3.4.2 Roughness loss 3.4..3 Substrate loss 3.4.4 Radiation loss due to bending 3.5 Sensitivity of the effective index to analyte binding 3.6 Overall sensitivity and detection limit 3.7 Generic design guidelines 3.8 Parameter selection for UV-NIL polymer waveguides 3.9 Comparison of polymer and silicon-based waveguides 3.9.1 Waveguide geometry 3.9.2 Radiation loss due to bending 3.9.3 Material damping 3.9.4 Surface roughness 3.9.5 Coupling channel widths and coupling coefficients 3.9.6 Conclusions 4 Characterization and Proof of Concept 4.1 Manufacturing-based design limits and chosen designs 4.2 Measurement setup and characterization process 4.3 Optical properties of UV-NIL polymer microresonators 4.4 Proof of concept 4.4.1 Sensitivity to bulk solutions 4.4.2 Reproducibility and drift 4.4.3 Comparison with theory 4.4.4 Comparison with literature 4.4.5 Sensitivity improvement 4.5 Asymmetry of the resonance curves 4.5.1 Cavity lifetime 4.5.2 Thermal influence 4.5.3 Summary 4.6 Conclusions 5 Integration into a biosensor platform 5.1 Chemical functionalization by oxygen plasma 5.2 Preparation of a biosensor characterization assay 5.2.1 Binding of fluorescent nanoparticles onto polymer surfaces 5.3 Microfluidic system 5.3.1 Programmable microfluidic system 5.3.2 System evaluation and improvement 5.4 Conclusions 6 Conclusions Declaration of authorship Acknowledgements Publications and awards

Silicon photonics (SiP) has become a cornerstone technology of the modern age by leveraging the mature fabrication processes and infrastructure of the microelectronics industry for the cost-effective and high-volume production of compact and power-efficient photonic integrated circuits (PICs). The impact that silicon (Si)-based PICs have had on data communications, particularly data center interconnection and optical transceiver technologies, has encouraged SiP chip development and their use in other applications such as artificial intelligence, biomedical sensing and engineering, displays for augmented/virtual reality, free-space communications, light detection and ranging, medical diagnostics, optical spectroscopy, and quantum computing and optics. To expand the functionality and improve the performance of SiP circuits for these surging applications, subwavelength grating (SWG) metamaterials have been thoroughly investigated and implemented in various passive integrated photonic components fabricated on the silicon-on-insulator (SOI) platform. SWG metamaterials are periodic structures composed of two materials with different permittivities that exhibit unnatural properties by using a period shorter than the guided wavelength of light propagating through them. The ability to synthesize the constituent SiP materials without any need to alter standard fabrication procedures enables precise, flexible control over the electromagnetic field and sophisticated selectively over anisotropy, dispersion, polarization, and the mode effective index in these metastructures. This provides significant benefits to SOI devices, such as low loss mode conversion and propagation, greater coupling efficiencies and alignment tolerances for fiber-chip interfaces, ultrabroadband operation in on-chip couplers, and improved sensitivities and limits of detection in integrated photonic sensors. Parallel to the rise of SiP technology is the development of other materials compatible with mature PIC fabrication methods both in the foundry (e.g., silicon nitride (Si3N4)) and outside the foundry (e.g., high-index oxide glasses such as aluminum oxide (Al2O3) and tellurium oxide (TeO2)). Si3N4 offsets the pitfalls of Si as a passive waveguiding material, providing lower scattering and polarization-dependent losses, optical transparency throughout the visible spectrum, increased tolerance to fabrication error, and better handling of high-power optical signals. Meanwhile, Al2O3 and TeO2 both serve as excellent host materials for rare-earth ions, and TeO2 possesses strong nonlinear optical properties. Using a single-step post-fabrication thin film deposition process, these materials can be monolithically integrated onto Si PICs at a wafer scale, enabling the realization of complementary-metal-oxide-semiconductor (CMOS)-compatible, hybrid SiP devices for linear, nonlinear, and active functionalities in integrated optics. While SWG metamaterials have widely impacted the design space and applicability of integrated photonic devices in SOI, they have not yet made their mark in other material systems outside of Si. Furthermore, demonstrations of their capabilities in active processes, including optical amplification, are still missing. In this thesis, we present a process for developing various SWG metamaterial-engineered integrated photonic devices in different material systems both within and beyond SOI. The demonstrations in this thesis emphasize the benefits of SWG metamaterials in these devices and realize their potential for enhancing functionality in applications such as sensing and optical amplification. The objective of the thesis is to highlight the prospects of SWG metamaterial implementation in different media used in integrated optics. This is accomplished by experimentally demonstrating SWG metamaterial waveguides, ring resonators and other components composed of different hybrid core-cladding material systems, including Si-TeO2 and Si3N4-Al2O3. Chapter 1 introduces the background and motivation for integrated optics and SWG metamaterials and provides an overview and comparison of the different materials explored in this work. Chapter 2 presents an initial experimental demonstration of TeO2-coated SOI SWG metamaterial waveguides and mode converters. It also details the design of fishbone-style SWG waveguides aimed at lowering loss and enhancing mode overlap with the active TeO2 cladding material in the hybrid SiP platform. Chapter 3 details an open-access Canadian foundry process for rapid prototyping of Si3N4 PICs, emphasizing the Si3N4 material and waveguide fabrication methods, as well as the design and characterization of various integrated photonic components included in a process design kit. The platform is compared against other Si3N4 foundries, and plans for further development are also discussed. Chapter 4 reports the first demonstration of SWG metamaterial waveguides and ring resonators fabricated using a Si3N4 foundry platform. The measured devices have a propagation loss of ∼1.5 dB/cm, an internal quality factor of 2.11·10^5, and a bulk sensitivity of ∼285 nm/RIU in the C-band, showcasing competitive metrics with conventional Si3N4 waveguides and SWG ring resonators and sensors reported in SOI. Chapter 5 presents work towards an SWG metamaterial-engineered waveguide amplifier. The fabricated device, based in Si3N4 and functionalized by an atomic layer deposited, erbium-doped Al2O3 thin film cladding, exhibited a signal enhancement of ∼8.6 dB, highlighting its potential for on-chip optical amplification. Methods to reduce the loss within the material system are proposed to achieve net gain in future devices. Chapter 6 summarizes the thesis and discusses pathways for optimizing the current devices as well as avenues for exploring new and intriguing materials and devices for future applications in integrated photonics. / Thesis / Doctor of Philosophy (PhD)

Die vorliegende Arbeit beschreibt die Entwicklung und Charakterisierung eines mikromechanischen kraftgekoppelten Schwingsystems für die resonante Detektion niederfrequenter Schwingungen. Es wird ein neuartiges Prinzip vorgestellt, das es ermöglicht, niederfrequente Vibrationen frequenzselektiv zu erfassen. Mittels Amplitudenmodulation wird das niederfrequente Signal in einen höheren Frequenzbereich umgesetzt. Durch Ausnutzung der mechanischen Resonanzüberhöhung wird aus dem breitbandigen Signal ein schmales Band herausgefiltert, die anderen Frequenzbereiche werden unterdrückt. Auf diese Weise wird direkt die spektrale Information des niederfrequenten Signals gewonnen. Eine Fourier-Transformation ist hierbei nicht notwendig. Die Abstimmung des Sensors erfolgt über eine Wechselspannung und führt dadurch zu einer einfachen Auswertung. Die Schwerpunkte der Arbeit liegen in den theoretischen Untersuchungen zum neuartigen Sensorprinzip, in der Entwicklung einer mikromechanischen Sensorstruktur zum Einsatz des neuen Prinzips sowie in der Entwicklung und Charakterisierung eines Messsystems zur Detektion niederfrequenter mechanischer Schwingungen mit dem neuen Sensor. / This thesis describes the development and characterization of a micromechanical force coupled oscillator system for the resonant detection of low frequency vibrations. It presents a novel working principle that enables spectral measurements of low frequency vibrations. The low frequency spectral content is converted into a higher frequency range by means of amplitude modulation. Due to the mechanical resonance a narrow band is filtered out of the wide band vibration signal. The remaining frequency content is suppressed. Hence, the spectral information is directly obtained with the sensor system without a fast Fourier transform. The tuning is done with an AC voltage resulting in a simple analysis. The main focuses of the work are the theoretical analysis of this novel sensor principle, the development of the micromechanical sensor structure for the use of the novel principle as well as the development and characterization of a measurement system for the spectral detection of low frequency mechanical vibrations with the developed sensor system.

Frequency reference oscillator is a critical component of modern radio transceivers. Currently, most reference oscillators are based on low-frequency quartz crystals that are inherently bulky and incompatible with standard micro-fabrication processes. Moreover, their frequency limitation (<200MHz) requires large up-conversion ratio in multigigahertz frequency synthesizers, which in turn, degrades the phase-noise. Recent advances in MEMS technology have made realization of high-frequency on-chip low phase-noise MEMS oscillators possible. Although significant research has been directed toward replacing quartz crystal oscillators with integrated micromechanical oscillators, their phase-noise performance is not well modeled. In addition, little attention has been paid to developing electronic frequency tuning techniques to compensate for temperature/process variation and improve the absolute frequency accuracy. The objective of this dissertation was to realize high-frequency temperature-compensated high-frequency (>100MHz) micromechanical oscillators and study their phase-noise performance. To this end, low-power low-noise CMOS transimpedance amplifiers (TIA) that employ novel gain and bandwidth enhancement techniques are interfaced with high frequency (>100MHz) micromechanical resonators. The oscillation frequency is varied by a tuning network that uses frequency tuning enhancement techniques to increase the tuning range with minimal effect on the phase-noise performance. Taking advantage of extended frequency tuning range, and on-chip temperature-compensation circuitry is embedded with the sustaining circuitry to electronically temperature-compensate the oscillator. Finally, detailed study of the phase-noise in micromechanical oscillators is performed and analytical phase-noise models are derived.

By implementing the rolled-up microfabrication method based on strain engineering, several systems are investigated within the contents of this thesis. The structural morphing of planar geometries into three-dimensional structures opens up many doors for the creation of unique material configurations and devices. An exploration into several novel microsystems, encompassing various scientific subjects, is made and methods for on-chip integration of these devices are presented. The roll-up of a metal and oxide allows for a cylindrical hollow-core structure with a cladding layer composed of a multilayer stack, plasmonic metamaterial. This structure can be used as a platform for a number of optical metamaterial devices. By guiding light radially through this structure, a theoretical investigation into the system makeup of a rolled-up hyperlens, is given. Using the same design, but rather propagating light parallel to the cylinder, a novel device known as a metamaterial optical fiber is defined. This fiber allows light to be guided classically and plasmonically within a single device. These fibers are developed experimentally and are integrated into preexisting on-chip structures and characterized. A system known as lab-in-a-tube is introduced. The idea of lab-in-a-tube combines various rolled-up components into a single all-encompassing biosensor that can be used to detect and monitor single bio-organisms. The first device specifically tailored to this system is developed, flexible split-wall microtube resonator sensors. A method for the capturing of embryonic mouse cells into on-chip optical resonators is introduced. The sensor can optically detect, via photoluminescence, living cells confined within the resonator through the compression and expansion of a nanogap built within its walls. The rolled-up fabrication method is not limited to the well-investigated systems based on the roll-up from semiconductor material or from a photoresist layer. A new approach, relying on the delamination of polymers, is presented. This offers never-before-realized microscale structures and configurations. This includes novel magnetic configurations and flexible fluidic sensors which can be designed for on-chip and roving detector applications.

With the advent of micro and nano electromechanical systems (MEMS/NEMS), there has been rapid development in the design and fabrication of sensitive resonant sensors. Sensitivity of such devices depends on the resonant frequency and the quality factor (Q). The Q of these devices are dependent on process induced prestress in the structural geometry, interaction with the external environment, and the encapsulation method. For high frequency sensors operating in air and under encapsulation condition, the Q is dominated by structural and fluid-structure interaction losses. In this thesis, we set out to study the dominant energy dissipative mechanisms that are constituent of the experimentally observed loss (Q-factor) in two specific test geometries—uncapped and capped circular MEMS drumhead resonators. Considering the importance of various factors, we consider four important problems pertaining to the uncapped as well as capped resonators. In the first problem, the most important factors perhaps are the acoustic radiation losses emanating from the annular plate, and the effect of added mass effect on the natural frequencies of the annular plate. The second problem is to investigate the dominant contribution of squeeze film losses and acoustic radiation losses with respect to various natural frequencies of the annular plate. The third problem is to consider the effect of prestress on the natural frequencies of the annular plate and its associated fluid-structure interaction losses (quality factors due to squeeze film damping and acoustic radiation losses). The fourth problem is to study the dominant fluid-structure interaction losses and structural losses that are constituent of experimentally measured Q-factors of the encapsulated annular plate (conceptual representation of MEMS device under packaged conditions). In the first problem, we study the mode dependent acoustic radiation losses in an uncapped drumhead microresonator which is represented by a annular circular plate fixed at its outer edge, suspended over a fixed substrate. There are two main effects which are associated with such systems due to the fluid-structure interaction. First is the “added mass effect,” which reduces the effective resonance frequency of the structure. The second is the acoustic radiation loss from the top side of the resonator, that affects the quality factor of the vibrating structure. In deriving the analytical solution, we first obtain the exact mode shapes of the structure ignoring any effect of the surrounding fluid (air) on the mode shape. Subsequently, we use these mode shapes to study the effect of the surrounding fluid on the associated natural frequencies and the Q-factor. The effect of “added mass” on the frequencies of the structure is found to be negligible. However, the acoustic radiation losses found to be significant. Additionally, we found that the variation in Qac over the first few modes (< 40 MHz) is marked with a local maximum and a minimum. Beyond this range, Qac increases monotonically over the higher frequency modes. It is also found that such kind of variation can be described using different acoustics parameters. Finally, comparing the acoustics radiation loss based quality factor with the experimental results for the uncapped drumhead resonator, the acoustic damping dominates only at higher modes. Therefore, our second problem forms the basis of finding other fluid-related damping. In the second problem, we explore the fluid losses due to squeeze film damping in the uncapped drumhead micro resonator. In this case, the squeeze film loss is due to the flow of the fluid film between the bottom surface of the annular plate and the fixed substrate. Based on the literature survey, it is found that the squeeze film damping reduces with increase in the air-gap thickness and the operating frequencies respectively. However, the squeeze film effect can not be ignored at lower frequencies. In order to investigate the contribution of squeeze film damping in uncapped resonator, we determine squeeze-film damping based quality factor Qsq corresponding to different modes of the resonators using FEM based software, ANSYS. On comparing Qsq with the experiments, we found that Qsq matches well with the experiments corresponding to the lower modes. Therefore, it is found that Qsq dominates at low frequencies (< 20 MHz) and Qac plays significant role at high frequencies (> 40 MHz). Both types of damping should be considered while modeling the fluid damping in uncapped resonator. In the next study, we discuss the effects of prestress on the resonant frequencies and quality factor. In the third study, we discuss the applicability of thin-plate theory with prestress and membrane theory in computing the frequencies and quality factor due to acoustic and squeeze film losses in the uncapped drumhead resonator. In the first two studies, although the quality factor due to acoustic losses and the squeeze film captures the correct trend of the experimental results, there is a mismatch between the experimental and theoretical frequencies computed with added mass effect. In order to improve the computation of frequencies corresponding to measured modes, we first used membrane theory to predict the frequencies, and finally we quantify that there exists discrepancy between computed and the corresponding experimental frequencies with error of about 8–55%. Since, both the membrane as well as thin plate theory without prestress do not correctly model the frequencies, we used the thin plate theory with prestress. For a prestress level of 96 MPa, we found the match between the computed frequencies and the corresponding quality factors with the measured values. However, we also found that there exists strong dependence of prestress on the acoustic radiation loss, with decrease in the acoustic loss based quality factors with increase in the prestress level. In the subsequent problem, we focus on the computation of losses in capped drumhead resonator which leads to a design possibility of improving the quality factor by containing the acoustic radiation losses. In the fourth problem, we study the structural and fluid-structure interaction losses which are dominant constituent of net Q-factor observed in experiments due to encapsulation of uncapped drumhead resonator. Essentially, the geometry of the capped resonator constitutes upper and lower cavities subjected to fluid-structure interaction losses on both sides of the annular plate. The dominant fluid-structure interaction loss is found to be due to squeezing action acting simultaneously in the upper and lower cavities. However, as we go to the higher modes, squeeze film damping become very small and the damping due to structure related losses such as clamping and thermoelastic losses becomes significant. We found the thermoelastic damping to be the dominant source of structural damping at higher resonant modes, whereas, the clamping losses are found to be relatively smaller. Finally, on comparing the net quality factor with the experimental results, we observed that the squeeze film losses are dominant at lower frequencies, and thermoelastic losses dominate at the higher frequencies. However, there remains some discrepancy between theoretical and experimental Q-factors particularly over higher frequency range. Such discrepancy may be due to some unaccounted factors which may be explored to improve the modeling of damping in capped resonators. The emphasis of this work has been towards developing a comprehensive understanding of different dominant dissipative mechanisms, classified into the fluid-structure interaction and the structural losses, that are constituent of the Q-factor at various resonant modes of uncapped and capped drumhead resonators.

Die verlässliche Erzeugung einzelner Photonen mit wohldefinierten Eigenschaften in allen Freiheitsgraden ist entscheidend für die Entwicklung photonischer Quantentechnologien. Derzeit basieren die wichtigsten Einzelphotonenquellen auf dem Prozess der spontanen parameterischen Fluoreszenz (SPF), bei dem ein Pumpphoton in einem nichtlinearen Medium spontan in ein Paar aus Signal und Idlerphotonen zerfällt. Resonator-überhöhte SPF, also das Plazieren des nichtlinearen Mediums in einem optischen Resonator, ist ein weit verbreitetes Verfahren, um Einzelphotonenquellen mit erhöhter Helligkeit und angepassten spektralen Eigenschaften zu konstruieren. Das Anpassen der spektralen Eigenschaften durch gezielte Auswahl der Resonatoreigenschaften ist besonders für hybride Quantentechnologienvon Bedeutung, welche darauf abzielen, unterschiedliche Quntensysteme so zu kombinieren, dass sich deren Vorteile ergänzen. Diese Arbeit stellt eine umfassende theoretische und experimentelle Analyse der dreifach resonanten SPF vor. Das aus der Literatur bekannte theoretische Modell wird diesbezüglich verbessert, dass der Einfluss sämtlicher Eigenschaften des Resonators auf die wichtigen experimentellen Größen (z.B. die Erzeugungsrate) gezielt ausgewertet werden kann. Dieses verbesserte und hoch genaue Modell stellt eine wichtige Grundlage für die Entwicklung und Optimierung neuartiger Photonenpaarquellen dar. Im experimentellen Teil dieser Arbeit wird der Aufbau und die Charakterisierung einer dreifach resonanten Photonenpaarquellen präsentiert. Die neu entwickelte digitale Regelelektronik sowie ein hochstabiler, schmalbandiger Monochromator welcher auf monolitischen, polarisationsunabhängigen Fabry-Pérot Resonatoren basiert, werden vorgestellt. Indem diese temperaturstabilisierten Resonatoren als Spetrumanalysator verwendet werden, wird zum ersten Mal die Frequenzkammstruktur des Spektrums der erzeugten Signal- und Idlerphotonen nachgewiesen. Des Weiteren wird der Einfluss der Pumpresonanz auf die Korrelationsfunktion und die Zweiphotoneninterferenz von Signal- und Idlerphotonen simuliert und vermessen. Abschließend werden Experimente aus dem Bereich der hybriden Quantennetzwerke präsentiert, in welchen Quantenfrequenzkonversion verwendet wird um die erzeugten Signalphotonen in das Telekommunikationsband zu transferieren. Dabei wird nachgewiesen, dass das temporale Wellenpaket durch die Konversion nicht beeinflusst wird und aufgezeigt, wie Quantennetzwerke von kommerziellen Telekommunikationstechnologien profitieren können. / The consistent generation of single photons with well-defined properties in all degrees of freedom is crucial for the development of photonic quantum technologies. Today, the most prominent sources of single photons are based on the process of spontaneous parametric down-conversion (SPDC) where a pump photon spontaneously decays into a pair of signal and idler photons inside a nonlinear medium. Cavity-enhanced SPDC, i.e., placing the nonlinear medium inside an optical cavity, is widely used to build photon-pair sources with increased brightness and tailored spectral properties. This spectral tailoring by selective adjustment of the cavity parameters is of particular importance for hybrid quantum technologies which seek to combine dissimilar quantum systems in a way that their advantages complement each other. This thesis provides a comprehensive theoretical and experimental analysis of triply-resonant cavity-enhanced SPDC. We improve the theoretical model found in the literature such that the influence of all resonator properties on the important experimental parameters (e.g., the generation rate) can be analyzed in detail. This convenient and highly accurate model of cavity-enhanced SPDC represents an important basis for the design and optimization of novel photonpair sources. The experimental part of this thesis presents the setup and characterization of a triply-resonant photon-pair source. We describe the digital control system used to operate this source over days without manual intervention, and we present a highly stable, narrow-linewidth monochromator based on cascaded, polarization-independent monolithic Fabry-Pérot cavities. Utilizing these temperature-stabilized cavities as a spectrum analyzer, we verify, for the first time, the frequency comb spectral structure of photons generated by cavity-enhanced SPDC. We further simulate and measure the impact of the pump resonance on the temporal wave-packets and the two-photon interference of signal and idler photons. Finally, we present a series of experiments in the context of hybrid quantum networks where we employ quantum frequency conversion (QFC) to transfer the generated signal photons into the telecommunication band. We verify the preservation of the temporal wave-packet upon QFC and highlight how quantum networks can benefit from advanced commercial telecommunication technologies.