Search
Now showing items 1-10 of 368
Resource Allocation in OFDMA Wireless Networks
(University of Waterloo, 2008-12-23)
Orthogonal frequency division multiple access (OFDMA) is becoming a widely deployed mechanism in broadband wireless networks due to its capability to combat the channel impairments and support high data rate. Besides, ...
Cooperative Models of Particle Swarm Optimizers
(University of Waterloo, 2008-09-04)
Particle Swarm Optimization (PSO) is one of the most effFective optimization tools, which
emerged in the last decade. Although, the original aim was to simulate the behavior of a group of birds or a school of fish looking ...
Transparent Oxide Semiconductors: Fabrication, Properties, and Applications
(University of Waterloo, 2008-05-14)
Transparent oxide semiconductors (TOSs) are materials that exhibit electrical conduction and optical transparency. The traditional applications of these materials are transparent conducting oxides in flat-panel displays, ...
Analog Signal Processor for Adaptive Antenna Arrays
(University of Waterloo, 2008-01-04)
An analog circuit for beamforming in a mobile Ku band satellite TV antenna array has been implemented. The circuit performs continuous-time gradient descent using simultaneous perturbation gradient estimation. Simulations ...
Credit-Based User Authentication for Delay Tolerant Mobile Wireless Networks
(University of Waterloo, 2008-01-21)
Wireless Internet has become increasingly popular due to anywhere anytime access feature. The Internet architecture was designed underlying the existing of the end-to-end path connection. The promise of wireless Internet ...
CDM Robust & Low Noise ESD protection circuits
(University of Waterloo, 2009-01-20)
In spite of significant progress during last couple of decades, ESD still affects production yields, manufacturing costs, product quality, product reliability and profitability. The objective of an ESD protection circuit ...
Spherical Silicon Photovoltaics: Material Characterization and Novel Device Structure
(University of Waterloo, 2008-08-28)
Single crystalline silicon spheres have been used as alternative material for solar cell fabrication. This innovative technology has several advantages over traditional wafer technology. However, the material, process ...
CDMA Channel Selection Using Switched Capacitor Technique
(University of Waterloo, 2001)
CDMA channel selection requires sharp as well as wide-band Filtering. SAW Filters which have been used for this purpose are only available in IF range. In direct conversion receivers this has to be done at low frequencies. ...
Electrostatic discharge protection circuit for high-speed mixed-signal circuits
(University of Waterloo, 2007-05-10)
ESD, the discharge of electrostatically generated charges into an IC, is one of the most important reliability problems for ultra-scaled devices. This electrostatic charge can generate voltages of up to tens of kilovolts. ...
Design and Characterization of Silicon-on-Insulator Passive Polarization Converter with Finite-Element Analysis
(University of Waterloo, 2005)
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 μm, 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....