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The fiber-to-the-x (FTTX) has been widely investigated as a leading access technology to meet the ever growing demand for bandwidth in the last mile. The passive optical network (PON) provides a cost-effective and durable solution. In this thesis, we investigate different aspects of the PON, in the search for cost-effective and high-performance designs of link system and devices. In Chapter 2, we propose a novel upstream link scheme for optical orthogonal frequency division multiplexing (OOFDM)-PON. The colorless laser diodes are used at the optical network units (ONUs), and the overlapped channel spectrum of orthogonal subcarrier multiplexing provides high spectral efficiency. At the optical line terminal (OLT), optical switch and all optical fast Fourier transform (OFFT) are adopted for high speed demultiplexing. The deterioration caused by the laser perturbation is also investigated. In Chapter 3, we design a novel polarization beam splitter (PBS), which is one of the most important components in polarization-controlled optical systems, e.g. the next-generation PON utilizing polarization multiplexing. Our PBS is built on a slab waveguide platform where the light is vertically confined. Planar lenses are formed to collimate and refocus light beam by converting the phase front of the beam. A planar subwavelength grating of a wedge shape induces the form birefringence, where the transverse electric (TE) and transverse magnetic (TM) waves have different effective refractive indices, and are steered to distinct directions. This design provides low insertion loss (< 0.9 dB) and low crosstalk (< -30 dB) for a bandwidth of 100 nm in a compact size, and can be realized by different material systems for easy fabrication and/or monolithic integration with other optical components. In Chapter 4, we study the mode partition noise (MPN) characteristics of the Fabry-Perot (FP) laser diode using the time-domain simulation of noise-driven multi-mode laser, Doctor of Philosophy (PhD)

Mitchella is a small genus of the Rubiaceae with only two species. It is the only herbaceous semishrub of the family showing a disjunct distribution in eastern Asia and eastern North America, extending to Central America. Its phylogeny and biogeographical diversification remain poorly understood. In this study, we conducted phylogenetic and biogeographical analyses for Mitchella and its close relative Damnacanthus based on sequences of the nuclear internal transcribed spacer (ITS) and four plastid markers (rbcL, atpB-rbcL, rps16 and trnL-F). Mitchella is monophyletic, consisting of an eastern Asian M. undulata clade and a New World M. repens clade. Our results also support Michella as the closest relative to the eastern Asian Damnacanthus. The divergence time between the two intercontinental disjunct Mitchella species was dated to 7.73 Mya, with a 95% highest posterior density (HPD) of 3.14-12.53 Mya, using the Bayesian relaxed clock estimation. Ancestral area reconstructions suggest that the genus originated in eastern Asia. The semishrub Mitchella appears to have arisen from its woody ancestor in eastern Asia and then migrated to North America via the Bering land bridge in the late Miocene., AuthorCount:6

This thesis presents the methods to extract modal parameters of semiconductor laser diodes based on a general zero-dimensional rate equation model. Three experiments, namely: the steady-state power versus injection current, small signal intensity modulation response and measurement of small signal response through dispersive optical fiber have been introduced, performed and analyzed under a sample space of 20 Multiple Quantum Well (MQW) Distributed feedback (DFB) laser of the same specification and from the same manufacturer. Testing software has been developed to perform the experiments , collect and analyze the data. The test results display an interesting Gaussian distributions that can be used to enhance further extraction process. An new method to extract the line-width enhancement factor has been purposed, which introduce a new way to extract rate equation parameters for laser lasing at the wave length for zero dispersion in optical fiber (1310nm). The new method circumvent the difficulty for measurement of small signal response through dispersive optical fiber method will not work due to the low fiber dispersion around this wavelength. This method has been validated and published at OSA conference., Master of Applied Science (MASc)

New types of laser using the basic structure of FP cavity are designed and modeled, to achieve high SMSR single-mode lasing that can be immune to high level of optical feedbacks for optical network communication applications. The work includes design of asymmetric Bragg reflection waveguide laser that employs wavelength selective Bragg reflectors as the claddings to confine and filter desired FP longitudinal modes for amplification and lasing. Si-rich SiO2 single-mode laser based on this structure is also proposed and analyzed. To optimize a recent design of discrete mode laser that is re-growth free and feedback-perturbation insensitive, a comprehensive implementation of the time domain transfer matrix method, including temperature and feedback effects, is carried out. The model helps to obtain a optimized DM structure that is balanced between high SMSR and low feedback sensitivity., Doctor of Science (PhD)

Wavelength division multiplexing (WDM) is the key technology of the current generation fiber-optics network. To build agile and intelligent next generation optical networks, optical wavelength conversion and signal regeneration are crucial new functions under intense research and development. These new functions call for innovative, low cost and high performance optoelectronic devices. One of such enabling devices is quantum-well electroabsorption modulators (EAM) that are appealing in terms of structural simplicity and low noise and are potentially advantageous on high-speed operation and low power consumption. The goal of this thesis is to systematically study EAM for optical signal functions in optical networks from various perspectives, including fundamental device physics, comprehensive models, innovative design, and experimental prototyping. After the first chapter of introduction, Chapter 2 and 3 are devoted to device models. In Chapter 2, a self-consistent and physics-based model has been developed for two key nonlinear optical mechanisms in quantum-well EAM: exciton saturation and electric field screening. Presented in Chapter 3 is a simplified but efficient model for EAM with a feature of handling strong electric field. Next, the fundamental physics relevant to nonlinear EAM are studied in Chapter 4 and 5. Exciton state mixing effects on intersubband transitions in quantum well have been investigated in Chapter 4 and a drastic different picture from that of the previous studies has been revealed. Studies have also been done in Chapter 5 on valence band mixing effects in exciton capture and escape in quantum well structures. And it is found that much faster capture and escape processes can be resulted from the band mixing effects. Then, the two key design issues of nonlinear EAM have been addressed. In Chapter 6, different saturation dynamics of electrons and holes in quantum wells have been thoroughly analyzed and utilized to achiev, Doctor of Philosophy (PhD)

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