Thesis (M.S. in Computer Science and M.S. in Electrical Engineering)--Naval Postgraduate School, March 2004. / Thesis advisor(s): Gilbert M. Lundy, Roberto Cristi. Includes bibliographical references (p. 95-97). Also available online.

This thesis explores the application of coiled sapphire multimode optical fibers for evanescent wave chemical sensing in both the visible spectrum and the near infrared. As has been suggested in the literature pertaining to silica fibers, bending converts low-order modes to high order ones, which leads to more evanescent absorption and thus a more sensitive chemical detector. By coiling the fiber many times, it was expected that even greater sensitivity would be attained. Experiments were performed to investigate the sensor response to different solutions and to characterize this response. In the first of three experiments, the large absorption peak of water at 3μm was examined in order to compare the sensitivity of a straight fiber versus a coiled one. In the second experiment, the effect of increasing the number of coils was investigated, as was the response of the sensor to varying concentrations of water in heavy water. In the third experiment, methylene blue dye was used to investigate the extent of adsorption of dye molecules on the sapphire fiber and its persistence

The hierarchical assembly of mass, wherein smaller clumps of dark matter, stars, gas, and dust buildup over time to form the galaxies we see today in the local Universe through accretion events with other clumps, is a central tenet of galaxy formation theory. Supported by theoretically motivated simulations, and observations of the distribution of galaxies over a large range of redshift, the theory of hierarchical growth is now well established. However, on the scales of individual galaxies, hierarchical growth struggles to explain a number of observations involving the amount and distribution of dark matter in galaxies, and the timescale of both the formation of stars, and the assembly of those stars into galaxies. In this dissertation I attempt to address some of the central issues of galaxy formation. My work focuses on massive elliptical galaxies and employs the orbit-based, axisymmetric dynamical modeling technique of Schwarzschild to constrain the total mass of a galaxy to large radii. From this starting point a determination of the extent and shape of the dark matter halo profile is possible and can then be compared to the results of simulations of the formation of galaxies. These dynamical models include information on the stellar orbital structure of the galaxy, and can be used as a further point of comparison with N-body simulations and observations from other groups. Dynamical modeling results for both M49 and M87, the first and second rank galaxies in the Virgo Cluster, are presented and compared in Chapters 4 and 2 respectively. Although both galaxies are similar in mass, a closer analysis shows they exhibit very different dark matter halo profiles and stellar orbital structure, and likely followed very different formation pathways. My primary dataset comes from observations carried out on the Mitchell Spectrograph (formally VIRUS-P) at McDonald Observatory.\footnote{The instrument's name was changed over the last year. As some of this work was originally written when the instrument was named VIRUS-P, I have elected to use that name in those sections of this dissertation (Chapters 2 and 5). In Chapters 3, 4, and 6, I use the current name.} The Mitchell Spectrograph is a fiber-fed integral field spectrograph, and allows one to collect spectra at many positions on a galaxy simultaneously. With spectroscopy one is able to not only constrain the kinematics of the stars, but also their integrated chemical abundances. In the introduction I describe recent work I have carried out with my collaborators using the Mitchell Spectrograph to add further constraints to our picture of galaxy formation. In that work we find that the cores of massive elliptical galaxies have been in place for many billions of years, and had their star formation truncated at early times. The stars comprising their outer halos, however, come from less massive systems. Yet unlike the stars of present day, low-mass galaxies, whose star formation is typically extended, these accreted systems had their star formation shut off at high redshift. Although our current sample is relatively small, these observations place a rigid constraint on the timescale of galaxy assembly and indicate the important role of minor mergers in the buildup of the diffuse outer halos of these systems. All of these advances in our understanding of the Universe are driven, in large part, by advances in the instrumentation used to collect the data. The Mitchell Spectrograph is a wonderful example of such an advance, as the instrument has allowed for observations of the outer halo of M87 to unprecedented radial distances (Chapter 3). A significant component of my dissertation research has been focused on characterizing the fiber optics of both the Mitchell Spectrograph and the fiber optics for the VIRUS spectrograph. I cover the results of the work on the Mitchell Spectrograph optical fibers in Chapter 5. The affects of stress and motion on a fiber bundle, critical to the VIRUS spectrograph, are explored in Chapter 6. / text

This thesis studies frequency-shifted interferometry (FSI), a useful and versatile technique for fiber-optic sensing. I first present FSI theory by describing practical FSI configurations and discussing the parameters that affect system performance. Then, I demonstrate the capabilities of FSI in fiber-optic sensor multiplexing and high sensitivity chemical analysis. We implemented a cryogenic liquid level sensing system in which an array of 3 fiber Bragg grating (FBG) based sensors was interrogated by FSI. Despite sensors' spectral overlap, FSI is able to separate sensor signals according to their spatial locations and to measure their spectra, from which whether a sensor is in liquid or air can be unambiguously determined. I showed that a broadband source paired with a fast tunable filter can be used in FSI systems as the light source. An array of 9 spectrally overlapping FBGs was successfully measured by such a system, indicating the potential of system cost reduction as well as measurement speed improvement. I invented the the FSI-CRD technique, a highly sensitive FSI-based fiber cavity ring-down (CRD) method capable of deducing minuscule loss change in a fiber cavity from the intensity decay rate of continuous-wave light circulating in the cavity. As a proof-of-principle experiment, I successfully measured the fiber bend loss introduced in the fiber cavity with FSI-CRD, which was found to be 0.172 dB/m at a bend radius of 12.5 mm. We then applied FSI-CRD to evanescent-field sensing. We incorporated fiber tapers as the sensor head in the system and measured the concentration of 1-octyne solutions. A minimum detectable 1-octyne concentration of 0.29% was achieved with measurement sensitivity of 0.0094 dB/% 1-octyne. The same system also accurately detected the concentration change of sodium chloride (NaCl) and glucose solutions. Refractive index sensitivity of 1 dB/RIU with a measurement error of 1*10^-4 dB was attined for NaCl solutions. Finally, I proposed a theoretical model to study the polarization effects in FSI systems. Preliminary results show that the model can already explain the experimental observations. It not only provides insight into how to improve system performance but also suggests potential new applications of the technique.

This thesis studies frequency-shifted interferometry (FSI), a useful and versatile technique for fiber-optic sensing. I first present FSI theory by describing practical FSI configurations and discussing the parameters that affect system performance. Then, I demonstrate the capabilities of FSI in fiber-optic sensor multiplexing and high sensitivity chemical analysis. We implemented a cryogenic liquid level sensing system in which an array of 3 fiber Bragg grating (FBG) based sensors was interrogated by FSI. Despite sensors' spectral overlap, FSI is able to separate sensor signals according to their spatial locations and to measure their spectra, from which whether a sensor is in liquid or air can be unambiguously determined. I showed that a broadband source paired with a fast tunable filter can be used in FSI systems as the light source. An array of 9 spectrally overlapping FBGs was successfully measured by such a system, indicating the potential of system cost reduction as well as measurement speed improvement. I invented the the FSI-CRD technique, a highly sensitive FSI-based fiber cavity ring-down (CRD) method capable of deducing minuscule loss change in a fiber cavity from the intensity decay rate of continuous-wave light circulating in the cavity. As a proof-of-principle experiment, I successfully measured the fiber bend loss introduced in the fiber cavity with FSI-CRD, which was found to be 0.172 dB/m at a bend radius of 12.5 mm. We then applied FSI-CRD to evanescent-field sensing. We incorporated fiber tapers as the sensor head in the system and measured the concentration of 1-octyne solutions. A minimum detectable 1-octyne concentration of 0.29% was achieved with measurement sensitivity of 0.0094 dB/% 1-octyne. The same system also accurately detected the concentration change of sodium chloride (NaCl) and glucose solutions. Refractive index sensitivity of 1 dB/RIU with a measurement error of 1*10^-4 dB was attined for NaCl solutions. Finally, I proposed a theoretical model to study the polarization effects in FSI systems. Preliminary results show that the model can already explain the experimental observations. It not only provides insight into how to improve system performance but also suggests potential new applications of the technique.

STARNET is a fiber optic based network which facilitates the interconnection of distributed Local Area Networks. Configured as a sixteen pointed star topology with a multiprocessor based controller at the center of the star (named the Central Switch). STARNET is capable of scheduling calls from users connected to User Access Nodes located at the points of the star. Messages are passed from one node to another through the Central Switch via duplex fiber optic lines connecting each node to the center. / This paper presents a multiprocessor based design of the User Access Node. The hardware and software structure is examined in depth, providing solid guidelines for the physical construction of the unit. The performances of statistical STARNET models using parameters obtained from the design (and three different Central Switch models) are plotted and compared for five different examples of external traffic. The model analysis gives an indication of the expected message delays, supporting the feasibility of the design.

I examine two methods for modeling the temporal dynamics of optical communication networks that rapidly and accurately simulate the statistics of unlikely but physically significant system configurations. First, I implement a fiber emulator based upon a random uniform walk over the Poincaré sphere that reproduces the expected polarization temporal autocorrelation statistics with a small number of emulator sections. While easy to implement numerically, the increased computational efficiency afforded by this approach allow simulations of the PMD temporal dynamics to be preferentially biased towards regions of low probability using standard multicanonical methods for the first time. Then, in a subsequent study, I present a general transition matrix formalism that additionally applies to other time-dependent communication systems. I compare the numerical accuracy of several transition matrix sampling techniques and show that straightforward modifications of the acceptance rule can significantly increase computational efficiency if the numerical parameters are chosen to ensure a small self-transition probability within each discretized histogram bin. The general applicability of the transition matrix method is then demonstrated by calculating the outage dynamics associated with the hinge model of polarization evolution and, separately, fading in wireless communication channels. Further, I develop a Magnus expansion formalism for the rapid and accurate estimation of the frequency dynamics of optical polarization that extends the work of Ref.[94] to systems with PMD and PDL. My approach reproduces the power-series expansion and differential equation solution techniques of previous authors while also preserving the required symmetries of the exact solution in every expansion order. This significantly improves the bandwidth of high estimation accuracy, making this method well-suited to the stochastic analysis of PMD and PDL induced system penalty while also yielding physically realizable operator expansions applicable to the joint compensation of PMD and PDL. Finally, I employ high-speed polarimetery to demonstrate experimentally that low-amplitude mechanical excitations of commercially available dispersion compensation modules can excite high-frequency, > 75,000 rotations/s, polarization transients that are nearly invariant between successive measurements. I extend this procedure to measurements of the transient evolution of PMD.

Thesis (M.Eng.)--University of Wollongong, 2006. / Typescript. Includes bibliographical references: leaf 101-106.

Thesis (M.App.Sc.) - Carleton University, 2006. / Includes bibliographical references (p. 192-196). Also available in electronic format on the Internet.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 67-68). Also available via the Internet.