As optical fiber systems evolve to higher data rates, the importance of polarization control and manipulation steadily increases. Polarization manipulating devices, such as polarization splitters and converters, can be realized by introducing material anisotropy or geometric asymmetry. Compared to active devices, passive polarization converters are more simply fabricated and controlled; therefore they have attracted increasing attention during the past two decades. However, materials employed in previous polarization rotating waveguides are mainly limited to low index-contrast III-V semiconductors such as InP and GaAs. Such III-V devices possess large radiation loss, large curvature loss, and low coupling efficiency to single-mode fibers; in addition, due to the weak optical confinement, the device spacing has to be large, which prevents high-density and large-scale integration in optoelectronic integrated circuits (OEIC) and planar lightwave circuits (PLC). <br /><br /> In this dissertation, the silicon-on-insulator (SOI) technology is introduced to the design and fabrication of passive polarization rotators (PR). Efficient and accurate full-vectorial finite-element eigenmode solvers as well as propagation schemes for characterizing novel SOI PRs are developed because commercial software packages based on finite-difference techniques are inefficient in dealing with arbitrary waveguide geometries. <br /><br /> A set of general design procedures are accordingly developed to design a series of slanted-angle polarization converters, regardless of the material system (SOI or III-V), outer-slab layer configuration (symmetric or asymmetric), and longitudinal loading (single- or multi-section). In particular, our normalized design charts and simple empirical formula for SOI polarization converters are applicable to a wide range of silicon-guiding-film thickness, e. g. , from 1 to 30 &mu;m, enabling fast and accurate polarization rotator design on most commercial SOI wafers. With these procedures, in principle 100% polarization conversion efficiency can be achieved by optimizing waveguide geometric parameters. <br /><br /> A novel configuration with asymmetric external waveguiding layers is proposed, which is advantageous for fabrication procedure, manufacturing tolerance, single-mode region, and conversion efficiency. By etching along the crystallographic plane, the angled-facet can be perfectly fabricated. Completely removing external waveguiding layer beside the sloped sidewall not only simplifies production procedures but also enhances fabrication tolerances. <br /><br /> To accurately and efficiently characterize asymmetric slanted-angle SOI polarization converters, adaptive mesh generation procedures are incorporated into our finite-element method (FEM) analysis. In addition, anisotropic perfectly-matched-layer (PML) boundary condition (BC) is employed in the beam propagation method (BPM) in order to effectively suppress reflections from the edges of the computation window. For the BPM algorithm, the power conservation is strictly monitored, the non-unitarity is thoroughly analyzed, and the inherent numerical dissipation is reduced by adopting the quasi-Crank-Nicholson scheme and adaptive complex reference index. <br /><br /> Advantages of SOI polarization rotators over III-V counterparts are studied through comprehensive research on power exchange, single-mode condition, fabrication tolerance, wavelength stability, bending characteristics, loss and coupling properties. The performance of SOI PRs is stable for wavelengths in the ITU-T C-band and L-band, making such devices quite suitable for DWDM applications. Due to the flexible cross-section of SOI polarization converters, the coupling loss to laser diodes and single mode fibers (SMF) can be designed to be very small and can be further reduced by a tapered waveguide with cross-sections always satisfying the single-mode criteria. Slanted-angle SOI polarization rotators display asymmetric bending characteristics and permit extremely small curvatures with negligible radiation loss when the angled-facet is located at the outer bend radius. Moreover, SOI polarization rotators can be manufactured with low-price processing techniques that are fully compatible with CMOS integrated circuits (IC) technology, and thus can be integrated on both photonic and electronic chips. <br /><br /> Experimental verifications have shown good agreement with theoretical analysis and have confirmed the promising characteristics of our novel asymmetric SOI polarization converters. Similar asymmetric-outer-slab geometry has recently been employed by peer researchers to fabricate high performance III-V polarization rotators. We therefore believe that results in this dissertation will contribute much to related research fields....

Software reliability has not kept pace with computing hardware. Despite the use reliability improvement techniques and methods, faults remain that lead to software errors and failures. Runtime monitoring can improve software reliability by detecting certain errors before failures occur. Monitoring is also useful for online and electronic services, where resource management directly impacts reliability and quality. For example, resource ownership errors can accumulate over time (e. g. , as resource leaks) and result in software aging. Early detection of errors allows more time for corrective action before failures or service outages occur. In addition, the ability to monitor individual software concerns, such as application resource ownership structure, can help support autonomic computing for self-healing, self-adapting and self-optimizing software. <br /><br /> This thesis introduces ResOwn - an application resource ownership ontology for interactive session-oriented services. ResOwn provides software monitoring with enriched concepts of application resource ownership borrowed from real-world legal and ownership ontologies. ResOwn is formally defined in OWL-DL (Web Ontology Language Description Logic), verified using an off-the-shelf reasoner, and tested using the call processing software for a small private branch exchange (PBX). The ResOwn Prime Directive states that every object in an operational software system is a resource, an owner, or both simultaneously. Resources produce benefits. Beneficiary owners may receive resource benefits. Nonbeneficiary owners may only manage resources. This approach distinguishes resource ownership use from management and supports the ability to detect when a resource's role-based runtime capacity has been exceeded. <br /><br /> This thesis also presents a greybox approach to concern-specific, dynamic software structure monitoring including a monitor architecture, greybox interpreter, and algorithms for deriving monitoring model from a monitored target's formal specifications. The target's requirements and design are assumed to be specified in SDL, a formalism based on communicating extended finite state machines. Greybox abstraction, applicable to both behavior and structure, provides direction on what parts, and how much of the target to instrument, and what types of resource errors to detect. <br /><br /> The approach was manually evaluated using a number of resource allocation and ownership scenarios. These scenarios were obtained by collecting actual call traces from an instrumented PBX. The results of an analytical evaluation of ResOwn and the monitoring approach are presented in a discussion of key advantages and known limitations. Conclusions and recommended future work are discussed at the end of the thesis....

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