M.Ing. (Electrical and Electronic Engineering) / A distributed temperature fiber sensor based on the ratio of the Raman anti-Stokes to Rayleigh backscattered light components is studied. The aim of the study is to propose a method of quantifying the noise exhibited in the Rayleigh backscattered signal and further propose correlation coding techniques to reduce the noise in the Rayleigh and Raman backscattered signals. The noise in the Rayleigh backscattered signal is referred to as “interferometric noise”. When Rayleigh scattering along the length of an optical fiber occurs, some of the scattered light travels in a direction opposite to the direction of propagation, and is called backscattered light. When the coherence length of the optical source permits interactions between the Rayleigh backscattered light, there is a possibility for the interacting backscattered light, within a distance that is half the coherence length, to interfere with each other. Furthermore, when the sensing optical fiber is greater than the coherence length of the optical source, there will be several interference sections along the length of the sensing fiber causing the intensity of the Rayleigh backscattered light at the photo-detectors to vary randomly. The intensity variation gives the Rayleigh backscattered signal a jagged appearance indicating the presence of interferometric noise. The longer the coherence length of the optical sources, the larger the intensity variations in the backscattered light, that is, the more the interferometric noise exhibited. The more the interferometric noise in the Rayleigh backscattered signal, the poorer the temperature accuracy of the distributed temperature sensor based on the ratio of the Raman anti Stokes to Rayleigh backscattered components. To quantify the interferometric noise affecting the Rayleigh backscattered signal, a mathematical model based on well-known scattering and interferometry theories is developed. Using the developed mathematical noise model, noise powers of approximately -52dBm and -40dBm for coherence lengths of 4m and 24m are respectively obtained...

Fiber Bragg grating sensors have been constantly researched for the last ten years and have finally begun to find use in the commercial market. However, one of the major factors limiting their widespread use is their system cost. Their lightweight, flexibility, electromagnetic immunity, and small size make fiber Bragg grating (FBG) sensors feasible in hostile environments where electrical and mechanical sensors may not function effectively. These sensor systems utilize moderately expensive light sources and detectors at telecommunication wavelengths of 1300 nm and 1550 nm. These are the center wavelengths of the mass-produced FBGs and FBG phase masks. This thesis addresses the development of a lower cost short wavelength fiber Bragg grating strain sensor system using gratings written at 790 nm and 850 nm with the modified phase mask method recently developed at Oregon State University. Short wavelength gratings allow the use of less expensive semiconductor sources and silicon detectors, greatly reducing the overall cost of a strain sensor system from approximately $1600 for a 1300 nm system to $1000 for a 790 nm system. First, the fundamental properties and historical background of fiber Bragg gratings were reviewed. Followed by a literature review of the structures, fabrication methods, and applications of FBGs including sensor applications. The design, manufacture, and assembly of the new short wavelength strain sensor system were described including the production of pigtailed super-luminescent edge emitting light emitting diodes (SELED) from commercial laser diodes, a fiber recoater, and multiple attempts to write a fiber Bragg grating in the 750-850 nm wavelength region. Finally, the short wavelength strain sensor system was compared with a 1300 nm strain sensor detailing the potential cost savings with the short wavelength system. / Graduation date: 2003

Thesis (M.S.)--West Virginia University, 2007. / Title from document title page. Document formatted into pages; contains xiii, 97 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 72-74).

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A fiber optic fluorometer utilizing a double-fiber optic probe was constructed. The absolute fluorescence signal and effective collection efficiency are approximately one fifth those of typical cuvette fluorometers and agree with those predicted by theory. A quinine sulfate calibration curve shows linearity from a detection limit of 10 pg/mL to 10 μg/mL. Single- and double-fiber probe configurations were also compared. The double-fiber configuration provided better detection limits due to its superior signal-to-background ratio. A discussion of sensor methodology for the monitoring of reaction intermediates is presented and a simple kinetic model for predicting the time dependent response of such sensors is developed. Two possible mechanisms for the Fujiwara reaction with chloroform are discussed. The effect of pyridine, water, and base concentrations on reaction kinetics was evaluated to develop single-phase Fujiwara reagent mixtures for both fluorometric and spectrophotometric determinations of chloroform. A unique "continuous-exposure" apparatus allowing vapor phase transport of chloroform from an aqueous sample to a conventional cuvette was constructed. The spectrophotometric detection limit for chloroform is 11 ng/mL and the method was shown to be suitable for the analysis of tap water. Two fiber optic chemical sensors (FOCS) for the detection of chloroform were developed. An aliquot of the optimized fluorometric reagent solution is held in contact with the fiber optic probe within a light-tight enclosure and is isolated from a bulk sample by a trapped headspace. One FOCS utilizes 1.3 mL of reagent held in a reservoir and the other utilizes a 10-μL drop of reagent suspended on the sensing tips of the fiber optic probe. Chloroform vapor from the sample migrates into the FOCS and reacts with the reagent to produce a fluorescent reaction intermediate which is monitored at 590 nm; the rate of increase in the fluorescence signal is related to chloroform concentration. Both FOCSs give detection limits better than 0.1 ng/mL. The response and total measurement times are comparable for the two FOCSs, and the duration of the linear response is limited by inner-filter effects. The response to a number of volatile GPHHCs including the trihalomethanes are reported. Analyses of tap water for chloroform with the reservoir FOCS and GC/MS were in excellent agreement. / Graduation date: 1992

Thesis (Ph.D.)--Tufts University, 1996. / Adviser: David R. Walt. Submitted to the Dept. of Chemistry. Includes bibliographical references. Access restricted to members of the Tufts University community. Also available via the World Wide Web;

Thesis (Ph.D.)--Tufts University, 1999. / Adviser: David R. Walt. Submitted to the Dept. of Chemistry. Includes bibliographical references (leaves 233-253). Access restricted to members of the Tufts University community. Also available via the World Wide Web;

Thesis (Ph. D.)--Victoria University (Melbourne, Vic.), 2007. / Includes bibliographical references.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 81-82). Also available via the Internet.

Thesis (M.S.) in Food Science and Human Nutrition--University of Maine, 2008. / Includes vita. Includes bibliographical references (leaves 104-107).