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.

Orb weavers intercept insects using non-hardening bioadhesive droplets, supported by two flagelliform fibers. Droplets contain an adhesive glycoprotein core and aqueous layer that confers hygroscopicity. The first study investigates the durability of these droplets to cycling, or repeatedly adhering, extending, and pulling off. Droplets of four species proved resilient, cycling 40 times. Cycling, coupled with droplet humidity responsiveness, qualifies them as smart materials. However, thread adhesion is complex, relying on an integrated performance of multiple droplets and the flagelliform fibers. As insects struggle, the flagelliform fibers bow and the droplets extend, forming a suspension bridge configuration whose biomechanics sum the adhesion of droplets and dissipate the energy of struggling insects. Given this performance, the second study predicts that the material properties of both thread components have evolved in a complementary way. Comparative phylogenetics of 14 study species revealed that their elastic moduli are correlated, with glycoproteins being six times more elastic than flagelliform fibers. Spider mass affects the amount of each material, but not their properties. Since glycoprotein performance changes with humidity, we hypothesized that orb weavers generate greater adhesion at their foraging humidity. After delimiting low and high humidity species groups (eight and six species, respectively), bridge force was determined as total contributing droplet adhesion at three humidities. Only three spiders generated greater adhesion outside of their foraging humidity. The distribution of force along a suspension bridge differed from a previously reported pattern. We also characterize the sheet configuration, which generates force similar to suspension bridges. / Master of Science / In nature, adhesives are used for a variety of functions. Many animals use adhesives use adhesives when climbing. Examples include toe pads of geckos, tarsal pads of ants, and tube feet of and sea urchins. Here, adhesion is repeatedly generated and released as the animal moves. However, some animals depend on permanent adhesives to anchor to surfaces. Marine mussels and barnacles, whose adult forms are sessile, use adhesives to resist the powerful action of waves and currents. Adhesion also plays a critical role in prey capture, where it prevents prey from escaping. The sticky droplets of a sundew plants and the adhesive capture threads of spider orb webs trap flies. Biologists and engineers study these bioadiehsives in search of inspiration and principles that will guide the development of new materials, including adhesives that function underwater, harden rapidly, or remaining pliable after adhering. This study investigated the material properties of capture threads spun by orb weaving spiders, which rely on non-hardening sticky droplets, supported by two protein fibers to capture insects. Inside each droplet is an adhesive core allows droplets to adhere to an insect and to extend as it struggles to escape. Surrounding this core is an aqueous layer that attracts atmospheric water, causing droplets to track changes in ambient humidity. A study of the cycling (or reusability) of four species' droplets repeatedly adhered a droplet to a surface and extending it to pull-off. These droplets were very resilient, cycling 40 times. Cycling, coupled with droplet humidity responsiveness, qualifies them as smart materials. However, prey capture is more complex, relying on the integration of multiple droplets and their supporting flagelliform fibers. As insects struggle, these fibers bow and the droplets extend, forming a suspension bridge configuration whose biomechanics sum the adhesion of droplets to resist an insect escape. The threads of 14 species were examined to test the hypothesis that material properties of both thread components have evolved in a complementary way to optimize adhesive performance. This revealed that the elasticities of the two capture thread components were correlated, with support fiber elasticity being greater. Capture threads generated the greatest adhesion at humidities during times that a spider feeds, although the distribution of this force across a suspension bridge showed different patterns among the species. The functional integration of a capture thread's components and its ability to respond to environmental humidity gives it exciting biomimicry potential.

The biosensing field has grown in importance and research efforts over the last few years for many reasons including point of care sensing devices and possible early detection of diseases in the body. Dopamine sensing is discussed in this paper and the development of a dopamine sensing platform would lead to early detection of diseases linked to its abundance or lack thereof in the brain such as Parkinson's disease. This work focuses on the electrochemical methods of biosensing, specifically dopamine sensing, and this method involves the use of electrodes as its sensing component. Multimaterial electrode-embedded fibers are used as the sensing electrode and the electrode material presented is platinum (Pt). Platinum is employed because of its biocompatibility property. The electrodes are placed in the fiber by the method of convergence fiber drawing and the fiber ends are stripped to expose the electrode for application. To make the proposed sensing platform more cost-effective, the platinum is electrodeposited onto the multimaterial fiber's embedded electrode. We discuss the use of a W/Pt modified electrode and a pure platinum wire in dopamine sensing and demonstrate that Pt is indeed a good candidate for dopamine sensing. The results show that the sensitivity of the W/Pt modified electrode to dopamine is higher than that of a pure Pt wire. This work has shown the promising application of electrodeposition in developing a cheaper flexible biosensing platform and opens up the possibility of the development of wearable flexible smart textile sensors because of the use of flexible multimaterial fibers. / Master of Science / The idea of sensing is important to our world and various scientific developments in this area have improved our way of life as humans. Biological sensing, which is what this thesis focuses on, detects the presence of various substances in the body, and developments in the area of biosensing have led to the creation of devices that can detect diseases or gather general information about a person's anatomical state. There has been increased interest in the detection of dopamine as more studies show that some diseases such as Parkinson's disease are related to the amounts of dopamine present in the brain. In this work, we present a potential platform for sensing dopamine in vitro using electrochemistry. Multimaterial fibers with embedded electrodes capable of measuring dopamine were fabricated using a thermal drawing technique. The electrode material in this fiber is the most important part of the sensing platform as it is what determines how sensitive the fiber is to an analyte. The two main topics discussed in this work are the modification of the electrode material using an electrodeposition technique and the sensing of dopamine with the modified electrode using the electrochemical methods of cyclic voltammetry and differential pulse voltammetry. The material involved in the electrodeposition process is Platinum (Pt) and the results show that platinum is a suitable material for dopamine sensing.

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.