D.Ing. / This work comprises a study of reflective interferometric fibre optic sensors. The use of Bragg gratings, multilayer quarter-wave stacks, and rugate mirrors for fibre optic sensing applications is discussed in this work. Rugate mirrors are presented in more detail since they form an important part of the research. The control system for an electron cyclotron resonance plasma enhanced chemical vapour deposition reactor was developed for the growth of inhomogeneous dielectric filters. The system is intended to control the growth of films of the required refractive index profile for optical applications on different substrates including fibre ends. The system also includes an automatic microwave tuner. Rugate mirrors deposited directly on optical fibre were used in a dual cavity Fabry- Perot interferometric strain sensor. It was found by computer simulation that reflectances of 40% for the two outer mirrors and 68% for the centre mirror allow the interferometer to have maximum fringe amplitude. The sensor was evaluated experimentally as a strain gauge. The maximum strain applied to the sample was about 0.12% and the corresponding phase change was about 800 radians. The discrepancy between the readings of this sensor and those of a resistive strain gauge, applied to the same structure, did not exceed 5%. Two novel fibre optic sensors were developed during this work: a merged Sagnac- Michelson interferometric sensor for distributed disturbance detection, and a disturbance location sensor using modified Sagnac and Mach-Zehnder interferometers. Both are intended for distributed impact location along the fibre. The magnitude of impact can also be measured with these sensors. The merged Sagnac-Michelson interferometric sensor uses two light sources and a frequency selective mirror to separate the Michelson and Sagnac signals. Birefringence in the fibre was used to bias the Sagnac interferometer to have a sine response. Computer simulations yielded the optimal biasing conditions: the state of linear polarisation of the input light should be rotated by r/4 with respect to the horizontal axis; birefringence in the Sagnac loop must provide retardation of ff/2 with the optical axes rotated by K/4 with respect to the horizontal axis. We verified the sensor concept experimentally. The discrepancy between measured and actual locations of disturbances applied to the fibre did not exceed 2.5 m for a 200 m long sensing loop. The sensor using the modified Sagnac and Mach-Zehnder interferometers makes use of phase modulation and synchronous detection to obtain the sine-biased Sagnac signal. A modified Sagnac interferometer configuration that incorporates an additional coupler and a mirror, allows separation of the Sagnac and Mach-Zehnder signals. Operation of the new configuration was verified experimentally in the system with a sensing fibre of 100 m long. The discrepancy between measured and actual locations of disturbances applied to the fibre did not exceed 2 m.

A class of low nonlinearity dispersion-shifted and dispersion-flattened fibers for broadband and long haul applications is presented. The refractive index profiles of these fibers assume a depressed-core multi-clad geometry in order to achieve effective-areas much larger than those in conventional optical fibers. A systematic approach for designing large effective-area dispersion-shifted fibers, using a reference W-index profile to initiate the design, is presented. Transmission properties, including effective-area, mode-field-diameter, dispersion, dispersion slope, cutoff wavelength, and bending, microbending and splice losses are evaluated for several design examples. To ascertain that the proposed fibers can be practically fabricated, the effects of varying fiber dimensions and indices on effective-area, mode-field-diameter and dispersion are assessed. It is shown that there is a trade-off between effective-area and mode-field-diameter and, generally, larger effective-areas are associated with larger mode-field-diameters. In other words, less signal distortion due to fiber nonlinearity (larger effective-area) is associated with higher power loss due to bending of fiber (larger mode-field-diameter). Thus, a large effective-area and low bending loss are conflicting requirements. A parameter Q is defined as a performance indicator, considering effective-area and mode-field-diameter. Dispersion-shifted single-mode fiber designs with effective-areas of 78 μm² to 210 μm² and the corresponding mode-field-diameter of 8.94 μm to 14.94 μm, dispersion less than 0.07 ps/nm.km, and dispersion slope of about 0.05 ps/ nm².km are presented. Numerical simulations for propagation of pulses in few designed fibers are performed.Designs of large effective-area dispersion-flattened fibers are also presented, for the first time we believe. These fibers provide large effective-area and low dispersion over an extended range of wavelengths. For our design, over the wavelength range of 1.48 μm < λ < 1.58 μm, the effective-area is 75 μm² to 100 μm², while the dispersion remains below 0.7 ps/nm.km. / Ph. D.

By adding annealed plain carbon steel fibers and stainless steel fibers into Ultra-High Performance Concrete (UHPC), we have increased UHPC’s toughness through optimized thermal processing and alloy selection of steel fiber reinforcements. Currently, steel fiber reinforcements used in UHPCs are extremely brittle and have limited energy dissipation mainly through debonding due to matrix crumbling with some pullout. Implementing optimized heat treatments and selecting proper alternative alloys can drastically improve the post-yield carrying capacity of UHPCs for static and dynamic applications through plastic deformations, phase transformations, and fiber pullout. By using a phase transformable stainless steel, the ultimate flexural strength increased from 32.0 MPa to 42.5 MPa (33%) and decreased the post-impact or residual projectile velocity measurements an average of 31.5 m/s for 2.54 cm and 5.08 cm thick dynamic impact panels.

We combine the evanescent field (EF) sensing mechanism with the fiber loop ringdown (FLRD) sensing scheme to create FLRD-EF sensors. The EF sensor heads are fabricated by etching the cladding of a single-mode fiber (SMF), while monitoring the etching process by the FLRD technique in real-time, on-line with high control precision. The effect of the sensor head dimensions on the sensors' detection sensitivity and response time are investigated. The EF scattering (EFS) sensing mechanism is combined with the FLRD detection scheme to create a new type of fiber optic index sensor. The detection limit for an optical index change is 3.2×10-5. This is the highest sensitivity for a fiber optic index sensor so far, without using any chemical-coating or optical components at the sensor head. A new type of index-based biosensor using high sensitivity FLRDEFS technique to sense deoxyribonucleic acid (DNA) and bacteria (Escherichia coli) is created.

No description available.

In this dissertation, various analytical models to characterize fiber nonlinearities have been applied, and the ranges of validity of the models are determined by comparing with numerical results. First, the perturbation approach is used to solve the nonlinear Schrödinger equation, and its range of validity is determined by comparing to the split-step Fourier method. In addition, it is shown mathematically that the perturbation approach is equivalent to the Volterra series approach. Secondly, root-mean-square (RMS) widths both in the time domain and in the frequency domain are modeled. It is shown that there exists an optimal input pulse width to minimize output pulse width based on the derived RMS models, and the functional form of the minimum output pulse width is derived. The response of a fiber to a sinusoidally modulated input which models an alternating bit sequence is studied to see its utility in measuring system performance in the presence of the fiber nonlinearities. In a single channel system, the sinusoidal response shows a strong correlation with eye-opening penalty in the normal dispersion region over a wide range of parameters, but over a more limited range in the anomalous dispersion region. The cross-phase modulation (CPM) penalty in a multi-channel system is also studied using the sinusoidally modulated input signal. The derived expression shows good agreement with numerical results in conventional fiber systems over a wide range of channel spacing, ∆<i>f</i>, and in dispersion-shifted fiber systems when ∆<i>f</i> > 100GHz. It is also shown that the effect of fiber nonlinearities may be characterized with stochastic input signals using noise-loading analysis. In a dense wavelength division multiplexed (DWDM) system where channels are spaced very closely, the broadened spectrum due to various nonlinear effects like SPM (self-phase modulation), CPM, and FWM (four-wave mixing) is in practice indistinguishable. In such a system, the noise-loading analysis could be useful in assessing the effects of broadened spectrum due to fiber nonlinearities on system performance. Finally, it is shown numerically how fiber nonlinearities can be utilized to improve system performance of a spectrum-sliced WDM system. The major limiting factors of utilizing fiber nonlinearities are also discussed. / Ph. D.

Distributed sensing has been an attractive alternative to the traditional single-point sensing technology when measurement at multiple locations is required. Traditional distributed sensing methods based on silica optical fiber and electric coaxial cables have some limitations for specific applications, such as in smart textiles and wearable sensors. By adopting the fiber thermal drawing technique, we have designed and fabricated multi-material electrode-embedded polymer fibers with distributed sensing capabilities. Polymers sensitive to temperature and pressure have been incorporated into the fiber structure, and thin metal electrodes placed inside fiber by convergence drawing have enabled detection of local impedance change with electrical reflectometry. We have demonstrated that these fibers can detect temperature and pressure change with high spatial resolution. We have also explored the possibility of using polymer optical fiber in a Raman scattering based distributed temperature sensing system. Stokes and Anti-Stokes signals of a PMMA fiber illuminated by a 532 nm pulsed laser was recorded, and the ratio was used to indicate local temperature change. We have also developed a unique way to fabricate porous polymer by thermal drawing polymer materials with controlled water content in the polymer. The porous fibers were loaded with a fluorescent dye, and its release in tissue phantoms and murine tumors was observed. The work has broadened the scope of multi-material, multi-functional fiber and may shed light on the development of novel smart textile devices. / PHD / In recent years smart textiles and wearable gadgets have already changed the way we live. There has been increasing industrial interest to develop novel flexible, stretchable devices that can interact with human and the environment. Thermal drawing technique originally invented for manufacturing telecommunication optical fiber has been used by researchers to fabricate fibers with more functionality. In this work, we report the progress made on the fabrication of multi-material fiber. Soft polymer fibers capable of measuring temperature and pressure were designed and made by the thermal drawing technique. Submillimeter fibers with thin copper electrodes have shown potential to be readily embedded in a smart fabric to provide 1D information in one direction or woven into a 2D pattern for area monitoring. We have also explored another temperature measurement scheme using polymer optical fibers with a pulsed laser. Compared with the electronic fibers, it is less susceptible to electrical noise and more robust. Lastly, we have shown a unique way to generate porosity in thermally drawn polymer fibers. The elongated pores in the fibers come from water escaping the fiber during the fabrication process. The three aspects of the project expand the scope of multi-material, multi-functional fiber and can shed light on the future development of electronic textile devices.

International Telemetering Conference Proceedings / October 23-26, 2000 / Town & Country Hotel and Conference Center, San Diego, California / This paper discusses the conversion of an existing telemetry system to the use of fiber optic communications. The change was implemented to provide expanded capabilities of existing capital assets with a minimum of investment. The paper reviews the design constraints and options considered for a specific flight test program. The different options, such as fiber type, connector type, wavelength, bit rate, and encoding method, are compared and discussed as to their applicability, reliability, and cost effectiveness in a telemetry environment. The paper discusses the solution selected and the capabilities of the final design, as compared to the initial system.

This study focuses on the processing, structure, and properties of gel spun polyacrylonitrile (PAN) and polyacrylonitrile/carbon nanotube (PAN/CNT) carbon fibers. Gel spun PAN based carbon fibers are manufactured beginning with a study of PAN dissolution in an organic solvent (dimethylformamide, DMF). Homogeneity of the PAN/DMF solution is determined through dynamic shear rheology, and the slope of the Han Plot (log G’ vs log G’’). Solutions were then extruded into gel spun fibers using a 100 filament fiber spinning apparatus in a class 1000 cleanroom. Fibers were then subjected to fiber drawing, stabilization, and carbonization, to convert the PAN precursor fiber into carbon fiber. Carbon fiber tensile strength was shown to scale with the homogeneity of the PAN/DMF solution, as determined by the slope of the log G’ vs log G’’ plot. After the development of the understanding between the homogeneity of the PAN/DMF solutions on the gel spun PAN based carbon fiber tensile properties, the effect of altering the fiber spinning processing conditions on the gel spun PAN based carbon fiber structure and properties is pursued. Cross-sectional shape of the gel spun PAN precursor fiber, characterized with a stereomicroscope, was found to become more circular in cross-section as the gelation bath temperature was increased, the amount of solvent in the gelation bath was increased, and when the solvent was switched from DMF to dimethylacetamide (DMAc). Gel spun fibers were then subjected to fiber drawing, stabilization, and carbonization to manufacture the carbon fiber. Carbon fibers were characterized to determine single filament tensile properties and fiber structure using wide-angle x-ray diffraction (WAXD) and high resolution transmission electron microscopy (HRTEM). It was found that the carbon fiber tensile properties decreased as the carbon fiber circularity increased, as a result of the differences in microstructure of the carbon fiber that result from differences in fiber spinning conditions. In the second half of this study, the addition of CNT into the PAN precursor and carbon fiber is investigated. CNT addition occurs during the solution processing phase, prior to gel spinning. As a first study, Raman spectroscopy is employed to investigate the bundling behavior of the CNT after gel spinning and drawing of the PAN/CNT fibers. By monitoring the peak intensity of the (12,1) chirality in the as-received CNT powder, and in differently processed PAN/CNT fibers, the quality of CNT dispersion can be quickly monitored. PAN/CNT fibers were then subject to single filament straining, with Raman spectra collected as a function of PAN/CNT filament strain. As a result of the PAN/CNT strain, stress induced G’ Raman band shifts were observed in the CNT, indicating successful stress transfer from the surrounding PAN matrix to the dispersed CNT. Utilization of the shear lag theory allows for the calculation of the interfacial shear strength between the PAN and incorporated CNT, which is found to increase as the quality of CNT (higher aspect ratio, increased graphitic perfection, and reduced impurity content), quality of CNT dispersion, and fiber drawing increase. PAN/CNT fibers were then subjected to stabilization and carbonization for the manufacture of gel spun PAN/CNT based carbon fibers. These fibers were then characterized to investigate the effect of CNT incorporation on the structure and properties of the carbonized fibers. The gel spun PAN/CNT based carbon fibers were compared to commercially produced T300 (Toray) and IM7 (Hexcel) carbon fibers, and gel spun PAN based carbon fiber. Fiber structure was determined from WAXD and HRTEM. Carbon fibers properties investigated include tensile properties, and electrical and thermal conductivity. PAN/CNT based carbon fibers exhibited a 103% increase in room temperature thermal conductivity as compared to commercially available IM7, and a 24% increase in electrical conductivity as compared to IM7. These studies provide a further understanding of the processing, structure, property relationships in PAN and PAN/CNT based carbon fibers, beginning at the solution processing phase. Through the manufacture of more homogeneous PAN/DMF solutions and investigations of the fiber spinning process, gel spun PAN based carbon fibers with a tensile strength and modulus of 5.8 GPa and 375 GPa, respectively, were successfully manufactured in a continuous carbonization facility. Gel spun PAN/CNT based carbon fibers exhibit room temperature electrical and thermal conductivities as high as 74.2 kS/m and 33.5 W/m-K.

No description available.