(This thesis consists of two parts.) Part I Comparison of Traveling Wave and Gain-Clamped Semiconductor Optical Amplifiers. Today's Wavelength Division Multiplexing (WDM) optical networks are getting dynamic light-path reconfigurable and optical transparent. Optical amplification without optoelectronic conversion is a key technology in all-optical networks. semiconductor optical amplifier (SOA) is a very potential device in this field. Besides the linear amplification, the nonlinear features of SOA make it has a broad application in wavelength conversion, tunable wavelength filter, optical switching and optical logic. The simple structure and very compact size of SOA indicate the essential low-cost and compatibility of integration. Resonant cavity is the basic structure of conventional SOAs, while gain-clamped SOAs (GC-SOAs) provide a constant gain which raises a lot of interests in applications. SOA with Distributed Bragg Reflectors (DBR) is one of the structures to realize the clamped gain. In this thesis the performances of traveling wave SOA (TW-SOA) and DBR-SOA are compared through a dynamic model. This model consists of a distributed feedback wave equation, a carrier rate equation and a material gain model, thereby can be used to simulate both of the two SOAs. To balance the time cost of simulation and the accuracy of the result, three important non-physical parameters, simulated bandwidth, cavity discritization and frequency discretizaiton, are investigated. The simulation results show that DBR-SOA has a very stable device gain which is independent on input optical power. From a noise level point of view DBR-SOA and TW-SOA have different characteristics. These comparison is conducted with both large signal input and small signal input. In addition, a desirable application, SOA in a multi-channel WDM system, is also simulated with GC-SOA and TW-SOA. The Bit Error Rate (BER) of TW-SOA increases greatly due to inter-channel cross talk, while the BER of GC-SOA is virtually constant with the variation of WDM channel number. Another application, wavelength converter, shows TW-SOA is very useful in non-linear application. Part II Impact of Dispersion on Hybrid of Frequency-Hopped Optical CDMA and WDMA Networks. A new analytical formula for analysis of the system performance of the Hybrid of Wavelength Division Multiple Access (WDMA) and Code Division Multiple Access (CDMA) is developed and presented. The effects of fiber dispersion and inter-channel crosstalk are considered and their impact on system performance is analyzed in terms of power penalty. Finally, methods to overcome the effects of the fiber dispersion are discussed. / Thesis / Master of Applied Science (MASc)

Surface modification of electrodes becomes a powerful process to improve the performance of organic electronic devices such as organic light emitting diodes (OLEDs) and organic photovoltaic cells (OPVs), boosting their further commercialization. Effective improvement can be achieved by introducing several types of nanoparticles onto the electrodes. Magnetic fields also have influence in the organic electronics, due to charge transport mechanisms of organic semiconducting materials. Therefore, magnetic nanoparticles are of particular interest. Magnetic γ-Fe2O3 nanoparticles have been produced using diblock copolymer reverse micelles method. The processes were elucidated in detail by Raman spectroscopy to reveal the iron oxide evolution. Compositional and structural information of individual γ-Fe2O3 nanoparticles were also characterized thoroughly by transmission electron microscopy (TEM) equipped with energy-dispersive X-ray spectroscopy (EDX) and electron energy loss spectroscopy (EELS), while their magnetic properties of the nanoparticles arrays were also evaluated by superconducting quantum interference device (SQUID) magnetometer. The low temperature annealing process was developed to facilitate the incorporation of γ-Fe2O3 nanoparticles in practical devices. Introducing γ-Fe2O3 nanoparticles onto the anode of basic OPV devices showed a positive effect on performance during the preliminary test. By using several methods, dispersion of γ-Fe2O3 nanoparticles can be tuned, examined by disLocate which is a comprehensive suite of tools for quantitative dispersion analysis. Additionally, the size of the nanoparticles can be changed simply by changing the loading ratio of FeCl3 below the maximum loading which was determined by quantum mechanical mapping using atomic force microscopy (AFM-QNM). With high control in terms of size and dispersion, the magnetic γ-Fe2O3 nanoparticles are ready to be employed to study the surface modification and magnetic effect on organic electronic devices. / Thesis / Master of Applied Science (MASc)

Fatigue and dispersion strengthening are reviewed generally. Experiments are described in which thin film transmission electron microscopy, as well as optical and electron fractography were employed to elucidate the mechanism of fatigue failure in dispersion strengthened nickel. It was found that whereas fatigue crack initiation occurs as in conventional materials, the propagation of both fatigue and tensile cracks is abnormal. The material fails in shear wherever possible although this is prevented where triaxial tensile stresses exist. Particle-matrix detachment does not occur during either tensile or fatigue stressing. / Thesis / Master of Science (MS)

This thesis investigates Stochastic Separated Flow (SSF) models for particle dispersion in turbulent shear flows. A new model is presented that accounts for anisotropy and incorporates a temporal and a spatial autocorrelation in the description of the fluctuating component of the turbulent gas-phase velocity. This model and three SSF models available in the literature are evaluated by comparing predictions with the shear layer experiments of Lazaro and Lasheras (1989), Hishida et al (1992) and the turbulent round jet experiment of Yuu et al (1978). Results are discussed and deficiencies in the models explored. The new model of Evinou and Lightstone compensates for the crossing trajectory effect with the inclusion of a spatial correlation based on the relative velocity of the particle and the time step employed. / Thesis / Master of Applied Science (MASc)

Optical coherent techniques are used to eliminate the power fading found in optical subcarrier multiplexed systems. In a double-side band optical subcarrier system the signal experiences a periodic power fading that is dependent on the fiber dispersion and subcarrier frequency. This power fading is manifested during the direct detection of the subcarrier system using a square-law photodetector. Using a modified optical local oscillator to coherently detect the subcarrier channel this power fading can be eliminated. An optical local oscillator is centered at the optical carrier in order to perform homodyne detection. However, the local oscillator is modulated by a term equal the subcarrier frequency of interest. This is then a dual-frequency optical local oscillator. By controlling the phases of the local oscillator and the local subcarrier oscillator independently in the homodyne detection scheme, both the phase error and power fading of the detected subcarrier channel can be eliminated. This technique also allows the subcarrier to be selected optically, before the optical-to-electrical conversion. Analytical and simulation results are given to show the benefits of optical coherent detection in double-sideband subcarrier systems. By eliminating the periodic power loss found in the double-sideband subcarrier system the signal becomes dispersion limited and not power limited. A comparison of double-sideband and single-sideband subcarrier systems is presented. Multiple subcarriers and subcarrier spacing are also investigated for both double sideband and single sideband subcarrier systems. Optical phase and modulator noise are also considered in the analysis and simulation of coherent detection using a dual frequency optical local oscillator. Since the implementation used to eliminate the power fading is a phase correction based process, the phase noise of both the source and local oscillator lasers must be considered and the technique compared to typical direct and coherent detection techniques. Also, the effects of modulator nonlinearity are simulated for multichannel subcarrier multiplexed systems and comparisons made between the performance of using the dual-frequency local oscillator and typical detection techniques. It is shown that the advantages of the dual-frequency LO are retained in the presence of both phase noise and modulator nonlinearity. / Ph. D.

Success in geotechnical analysis, design, and construction invariably requires that we have proper knowledge and understanding of (1) the strength, (2) the fluid flow properties, and (3) the stress-deformation behavior of the earth materials. These important engineering properties are primarily determined by the components and structure of a soil, which also dictate the soil's responses in an electromagnetic field. As a nondestructive technique, the electromagnetic property measurement offers a promising approach to characterize earth materials and identify the effects of changes in environments. However, despite many investigations in the last several decades, the relationship between the frequency-dependent electromagnetic properties of soils and their components and structure are still not well understood. Hence, estimation of engineering properties of a soil in a quantitative way from electromagnetic measurements can be uncertain. In this research several tasks have been accomplished: (1) Development of a physically based model that provides a means of investigating the coupled effects of important polarization mechanisms on soil electromagnetic properties, and a means of relating the electromagnetic properties of a soil to its fines content, clay mineralogy, anisotropy, degree of flocculation and pore fluid chemistry; (2) Proposal of a practically applicable method to determine the volumetric water content, specific surface area and pore fluid salt concentration simultaneously from the dielectric spectrum; (3) Deduction of the wide-frequency electromagnetic properties of a soil by measuring its responses to a step pulse voltage using time domain reflectometry (TDR); (4) Establishment of the relationships between the specific surface area and compressibility, residual shear strength and hydraulic conductivity. This study establishes a framework for quantifying soil engineering properties from their electromagnetic properties. If properly determined and interpreted, the electromagnetic properties can also provide insights into the causes of soil property changes over time and can be very useful in studying the effects of biological factors in geotechnical engineering, a field that may offer great potential for future advances. / Ph. D.

In fiber optic communication systems, the main linear phenomenon that causes optical pulse broadening is called dispersion, which limits the transmission data rate and distance. The principle nonlinear effect, called self-phase modulation, can also limit the system performance by causing spectral broadening. Hence, to achieve the optimal system performance, high data rate and low bandwidth occupancy, those effects must be overcome or compensated. In a nonlinear dispersive fiber, properties of a transmitting pulse: width, chirp, and spectra, are changed along the way and are complicated to predict. Although there is a well-known differential equation, called the Nonlinear Schrodinger Equation, which describes the complex envelope of the optical pulse subject to the nonlinear and dispersion effects, the equation cannot generally be solved in closed form. Although, the split-step Fourier method can be used to numerically determine pulse properties from this nonlinear equation, numerical results are time consuming to obtain and provide limited insight into functional relationships and how to design input pulses. One technique, called the Variational Method, is an approximate but accurate way to solve the nonlinear Schrodinger equation in closed form. This method is exploited throughout this thesis to study the pulse properties in a nonlinear dispersive fiber, and to explore ways to compensate dispersion for both single link and concatenated link systems. In a single link system, dispersion compensation can be achieved by appropriately pre-chirping the input pulse. In this thesis, the variational method is then used to calculate the optimal values of pre-chirping, in which: (i) the initial pulse and spectral width are restored at the output, (ii) output pulse width is minimized, (iii) the output pulse is transform limited, and (iv) the output time-bandwidth product is minimized. For a concatenated link system, the variational calculation is used to (i) show the symmetry of pulse width around the chirp-free point in the plot of pulse width versus distance, (ii) find the optimal dispersion constant of the dispersion compensation fiber in the nonlinear dispersive regime, and (iii) suggest the dispersion maps for two and four link systems in which initial conditions (or parameters) are restored at the output end. The accuracy of the variational approximation is confirmed by split-step Fourier simulation throughout this thesis. In addition, the comparisons show that the accuracy of the variational method improves as the nonlinear effects become small. / Master of Science

A time domain chromatic dispersion measurement system for single-mode optical fibers is presented for easy measurements in both the laboratory and the field. This technique uses a relative group delay of a band of light at slightly different wavelengths from a single pulsed laser diode to determine chromatic dispersion and the zero chromatic dispersion (ZCD) wavelength of the fiber. Time domain dispersion measurements find the group delay directly, eliminating the need for a vector voltmeter and the added phase calibration and group delay calculations needed in most frequency (phase) domain techniques. With the use of a monochromator as a bandpass filter, a number of group delay data points can be taken throughout the spectral width of a single laser diode. Since the group delay data are relative measurements, access is needed only to the output of a length of fiber. This makes this time domain technique especially well suited for field use. Using the modified Sellmeier equation, only three group delay measurements need to be taken to find the zero chromatic dispersion (ZCD) wavelength and a highly accurate approximation to the chromatic dispersion curve. The modified Sellmeier equation coefficients are found by a simple BASIC program, eliminating the need for curve-fitting and numerical differentiation routines. The desired chromatic dispersion curve and ZCD wavelength are found by straightforward differentiation. / M.S.

Acoustic Frequency Domain Reflectometry (AFDR) is a novel technique employing frequency modulated continuous wave (FMCW) methods in solid acoustic waveguide reflectometry. It is particularly suited to dispersion compensation and phase compensation due to the measurement domain being the frequency domain. This work rigorously analyzes, develops, and experimentally demonstrates AFDR, alongside various compensation methods and demodulation techniques. Distributed measurement of temperature is tested using several novel signal processing algorithms for strain determination and is estimated to have a resolution of 0.58 °C over a 20 cm gauge length. An error correction algorithm to improve SNR in the measurement of strain is proposed and validated. The sensing system has a theoretical spatial resolution of 2 mm and an estimated sensing resolution limit of about 1 cm. AFDR and the associated signal processing developments are positioned to be transformative across many areas of acoustics, with significant potential for distributed sensing along an acoustic waveguide. / Doctor of Philosophy / Acoustic Frequency Domain Reflectometry (AFDR) is demonstrated as a novel method for using acoustic waves to sense different material parameters. Acoustic waves can be guided down various structures, such as a metal wire. Rather than sending out a short burst of acoustic power and analyzing its echoes in the metal wire, this technique uses a constant source of acoustic waves with varying frequency, instead recording how the electrical characteristics of the acoustic source change as frequency changes. Since the measurement is made across frequency, this method is particularly suited to correct for various aspects of the acoustic wave that change with frequency in an otherwise undesirable way. The ability to compensate for acoustic wave speeds that change with frequency as well as imperfections intrinsic to the tuning itself using multiple new methods is demonstrated. Distributed measurement of temperature is tested using various signal processing algorithms, and estimated to have a resolution of 0.58 °C for a 20 cm sensing length. The validated sensing system theoretically has the ability to resolve changes over 2 mm, and the resolution over which sensing may be possible is estimated to be 1 cm. AFDR and the associated signal processing developments are positioned to be transformative across many areas of acoustics, with significant potential for distributed sensing along an acoustic waveguide.

The dielectric-dispersion, curve of cellulose nitrate may be obtained over a 1ow frequency range in h-butyl acetate. The parallel resistance method is used for capacitance measurements is a nickel cell. Comparison of the distribution curve and the dispersion curve above a distinct similarity between the two curves. A relationship of the log frequency to intrinsic viscosity has been derived and appears to be acceptable with ±10% of the values obtained from fractional precipitation. Thus the distribution curve of cellulose nitrate may be determined from the dielectric dispersion curve. / Master of Science