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.

The use of steel fiber reinforced concrete (SFRC hereafter) is becoming more and more common. Building codes and recommendations are gradually including the positive effect of fibers on mechanical properties of concrete. How to take advantage of the higher ductility and energy absorption capacity of SFRC to reduce anchorage lengths when using fibers is not a straightforward issue. Fibers improve bond performance because they confine reinforcement (playing a similar role to that of transverse reinforcement). Their impact on bond performance of concrete is really important in terms of toughness/ductility. The study of previous literature has revealed important points of ongoing discussion regarding different issues, especially the following: a) whether the effect of fibers on bond strength is negligible or not, b) whether the effect of fibers on bond strength is dependent on any other factors such as concrete compressive strength or concrete cover, c) quantifying the effect of fibers on the ductility of bond failure (bond toughness). These issues have defined the objectives of this thesis. A modified version of the Pull Out Test (POT hereafter) has been selected as the most appropriate test for the purposes of this research. The effect of a number of factors on bond stress¿slip curves has been analyzed. The factors considered are: concrete compressive strength (between 30 MPa and 50 MPa), rebar diameter (between 8 mm and 20 mm), concrete cover (between 30 mm and 5 times rebar diameter), fiber content (up to 70 kg/m3), and fiber slenderness and length. The experimental program has been designed relying on the principles of statistical Design Of Experiments. This has allowed to select a reduced number of combinations to be tested without any bias or loss of accuracy. A total of 81 POT specimens have been produced and tested. An accurate model for predicting the mode of bond failure has been developed. It relates splitting probability to the factors considered. It has been proved that increasing fiber content restrains the risk of splitting failure. The favorable effect of fibers when preventing splitting failures has been revealed to be more important for higher concrete compressive strength values. Higher compressive strength values require higher concrete cover/diameter ratios for splitting failure to be prevented. Fiber slenderness and fiber length modify the effect of fiber content on splitting probability and therefore on minimum cover/diameter ratios required to prevent splitting failures. Two charts have been developed for estimating the minimum cover/ diameter ratio required to prevent splitting. Predictive equations have been obtained for estimating bond strength and areas under the bond stress¿slip curve as a function of the factors considered. Increasing fiber content has a slightly positive impact on bond strength, which is mainly determined by concrete compressive strength. On the contrary, fibers have a very important effect on the ductility of bond failure, just as well as concrete cover, as long as no splitting occurs. Multivariate analysis has proved that bond stress corresponding to the onset of slippage behaves independently from the rest of the bond stress¿slip curve. The effect of fibers and concrete compressive strength on bond stress values corresponding to the onset of slips is mainly attributable to their influence on the material mechanical properties. On the contrary, the effect of fibers and concrete cover on the rest of the bond stress¿slip curve is due to their structural role. / García Taengua, EJ. (2013). Bond of Reinforcing Bars to Steel Fiber Reinforced Concrete (SFRC) [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/32952

A spinning apparatus was built for the investigation of the phase-separation technique as applied to the production of polypropylene fibers from naphthalene solutions. The solutions were spun through a single 2.00 millimeter spinneret at compositions of 15 and 22 per cent polymer and at temperatures of 145 and 160°C. Linear velocities in the spinneret and draw ratios ranged from 0.125 to 0.277 meters per minute and from 759 to 2198, respectively. It was found that naphthalene could be extracted from the fibers by diethyl ether in less than one minute; however, this extraction was not necessary prior to properties testing because all of the naphthalene in the fibers exposed to air was lost by sublimation. Deniers of 14 selected fiber samples varied inversely with draw ratio and directly with solution composition in a range from 2.5 to 8.0. After the samples were cold-drawn 3:1, tests with a Scott Tensilgraph showed that tenacities, per cent elongations at break, and secant moduli varied directly with draw ratio in ranges from 0.9 to 1.6 grams per denier, from 50 to 150 per cent, and from 17 to 30 grams per denier, respectively. Per cent elongations at break also varied directly with solution composition. The fibers, in general, exhibited good hand, bulk, tangling, and self-crimping characteristics. Photographs of four of the fiber samples were made to show the tangling and crimp qualities. / Master of Science

The polarization-maintaining properties of single crystal sapphire fibers are investigated and a polarimetric optical sensor for high temperature measurements is designed. The polarization-maintaining properties of single crystal sapphire fibers are investigated experimentally for different modal power distributions and different fiber lengths. Experimental results indicate that linearly polarized light launched along one of the principal axes of the birefringence can be partially maintained. The polarization-maintaining ability (PMA) has been measured to be 6 dB and 3 dB for 7 cm and 32 cm long sapphire fibers, respectively. The temperature coefficient of the differential phase delay between the orthogonal polarization modes has been measured to be 0.0208 rad / °C m. A resolution of 2 °C has been obtained over the measurement range of 25 °C to 800 °C. It is also observed that the PMA is strongly dependent on the mode-coupling parameter. The design of the polarimetric sapphire fiber sensor for high temperature measurements is based on the properties of withstanding high temperatures, polarization preservation and temperature dependence of phase delay. Since the temperature dependence of phase delay is proportional to the fiber length, consideration of a similar strain sensor is expected in the near future. / Master of Science

Fiber optic sensors offer many advantages over conventional sensors, including; small size, low weight, high strength and durability. Standard silica optical fibers are limited by the material properties of silica. Temperatures above 700°C and other harsh environments are incompatible with standard optical fiber sensors. Sapphire fiber sensors offer another option for fiber optic sensing. Sapphire fibers are limited by the material properties of sapphire, which include high melting point, extreme hardness and imperviousness to chemical reactions and radiation. These properties coupled with the advantages of conventional fiber optic sensing make sapphire optical fiber sensors a good candidate for sensing requirements in harsh environments. We investigate the potential for the use of sapphire fibers as sensors. Two sensors are developed based on widely different techniques. Results from preliminary tests of each are given. / Master of Science

The polarimetric behavior of conventional dual mode, elliptical-core, optical fiber sensors is investigated. To compliment the experimental results, a novel linearly polarized modal analysis of elliptical-core geometries is performed. The method numerically finds solutions of a waveguide equation described by Mathieu differential equations. To move beyond conventional dual mode fiber sensing applications, selected placement of the dual mode fiber endpoints upon a flexible structure is investigated. Modal filtering behavior will result if the endpoints are chosen to span two antinodes of the underlying structure. To truly achieve signal processing capabilities, spatially weighting the sensitivity of the sensor becomes necessary. Experimental results are described and future applications are proposed. / Master of Science

A survey of research in nonlinear optical fibers is given. Important background concepts are introduced and explained. Present and future applications of nonlinear optical fibers arc reviewed. A mathematical model of a nonlinear optical fiber is developed using a coupled-mode theory approach, and methods of solving nonlinear partial differential equations arc discussed. A detailed history of research in the field is given, and recommendations for future research are made. / Master of Science

A novel coupler measurement station and technique for manufacturing fused biconical tapered multi-port multimode couplers with improved uniformity among ports is presented. Improvement in the uniformity of the couplers is achieved by diffusion of the minimum taper region of the coupler. The phenomenon of dopant transport from the core to the cladding (or from the cladding to the core) at high temperatures is known as diffusion. Diffusion of a germanium-doped core results in the germanium dopants migrating from the core into the cladding thus increasing the effective diameter of the core which is accompanied by a decrease in the refractive index. The cores of individual fibers in the minimum taper region are a few micrometers apart. Diffusion thus results in a minimum taper region that has approximately uniform refractive index leading to better uniformity among ports. The experimental setup and results of diffusion tests on multimode fiber with different core/cladding ratios are presented. A coupler station that is capable of making bi- directional measurements of the coupler is demonstrated successfully. The coupler station also enables a user to dynamically monitor the ports of the coupler during manufacture, and can be adapted to manufacture star couplers ranging in size from two to sixteen fibers. / Master of Science

Microbends are axial distortions on the optical fiber that have a spatial wavelength small enough to effect coupling between guided and radiation or cladding modes. The magnitude of this wavelength-dependent coupling is a function of the nature and the number of microdefonnations. Since these periodic perturbations lead to an attenuation in signal level, they are avoided in fiber-based communication systems. However, controlled induction and signal processing of microbending losses has led to the fabrication of novel optical fiber~based sensors, devices, and components. A systematic study of microbending effects in singlemode optical fibers is presented in this thesis. The theoretical analysis is based on the coupling between the fundamental LP₀₁ mode to discrete cladding modes. An algorithm is developed to characterize optical attenuation as a function of the spatial period of the microbend defonnation. Optical attenuation peaks are described in terms of central wavelength, amplitude and spectral width. An excellent correlation is shown between the experimental results and the theoretical predictions, with nominal errors less than 2.5%. The algorithm developed may be used with any commercially available singlemode fiber, and any kind of microbend de former apparatus, provided the microbend defonnation function â ±(z) is known accurately. Based on the above analysis, a wavelength-tunable fiber polarizer is proposed and demonstrated. The polarizer is fabricated by inducing a periodic perturbation on a high birefringence singlemode optical fiber. The fiber thus exhibits polarization· selective attenuation characteristics. The operating wavelength is shown to be tunable by changing the spatial period of the defonnation. A polarization extinction ratio of 25 dB is obtained with an attenuation of 1.3 dB, at an operating wave length of 1177 nm. / Master of Science

Load testing was performed on a one-third scale model steel fiber reinforced concrete post-tensioned flat plate. The specimen had nine 10ft x 10ft x 3in. bays along with a 2ft-6in. overhang. Distributed loading was applied with a whiffle tree loading system at each bay and overhang section. Throughout the test, crack widths, crack locations, deflections, concrete strains, and reinforcing bar strains were monitored. The post-tensioned flat plate was designed to just meet the maximum allowable stress requirements of ACI 318. Minimal quantities of hairline cracks were observed after stressing the slab, and up through service-level loads, the cracks grew slightly in length and width. The slab behaved elastically through service-level loading. As factored-level loading was approached, the slab began to behave inelastically as indicated by both the load-deflection plots and the load-strain plots. A total ultimate load of 282psf (174psf of applied load) was reached when concrete crushing occurred. A 0.20in. wide full-length crack was observed running on the bottom surface of the slab between column lines 1 and 2, and a full-length crack was observed at column line 2 on the top surface of the slab. These two cracks were the leading contributors to the slab's failure. The performance of the SFRC post-tensioned flat plate indicated that considerations should be made to remove requirements for negative moment reinforcement in post-tensioned flat plates when SFRC is used. Also, the requirements for positive moment reinforcement should be modified. Additionally, the SFRC post-tensioned flat plate exhibited excellent levels of ductility. More experimentation should be conducted to determine if the maximum tensile stress in ACI 318 can be increased for post-tensioned flat plates with SFRC. / Master of Science / Load testing was performed on a one-third scale model steel fiber reinforced concrete (SFRC) post-tensioned flat plate. Post-tensioned flat plates are a type of concrete structural system typically used as flooring. This system typically employs high-strength steel strands, which are stretched to introduce compression into the concrete, which helps prevent the onset of cracking. The specimen had nine 10ft x 10ft x 3in. bays along with a 2ft-6in. overhang. Distributed loading was applied with a whiffle tree loading system at each bay and overhang section. The whiffle tree loading system was used to allow actuators to spread out the vertical loading on the slab. During the test, crack widths, crack locations, deflections, concrete strains, and reinforcing bar strains were monitored. The post-tensioned flat plate was designed to just meet the maximum allowable stress requirements of the governing standard, ACI 318. Minimal quantities of hairline cracks were observed after stressing the slab, and up through service-level loads, the cracks grew slightly in length and width. As larger loads were applied, the cracks grew and the effects of these cracks on the slab were evidenced in the deflection and strain measurements. A total ultimate load of 282psf (174psf of applied load) was reached when concrete crushing occurred. A 0.20in. wide full-length crack was observed running on the bottom surface of the slab between column lines 1 and 2, and a full-length crack was observed at column line 2 on the top surface of the slab. These two cracks were a driving force in the slab’s failure. The performance of the SFRC post-tensioned flat plate indicated that considerations should be made to change the requirements for negative and positive moment reinforcement in post-tensioned flat plates when SFRC is used. Additionally, the SFRC post-tensioned flat plate exhibited great performance after significant cracking was present. More experimentation should be conducted to determine if the maximum allowable tensile stress in ACI 318 can be increased for post-tensioned flat plates with SFRC.