As the use of polymer matrix composites for structures increases, there is a growing need for monitoring these structures. Distributed strain sensing using optical fibers shows promise for monitoring composite structures due to optical fiber's small size, light weight, and ability to obtain continuously distributed strain data. This study investigates the feasibility of using embedded optical fibers using two case studies: embedding the fibers in the adhesive layer of double lap shear composite specimens, and within composite end-notched flexure specimens to locate a growing crack front. To establish a repeatable fabrication methodology, manufacturing techniques for embedding the optical fibers were investigated. The measured strain distribution from the optical fibers compares well with data obtained from finite element analyses for both the double lap shear and end-notch flexure specimens. Additionally, the embedded optical fibers do not seem to impact the failure loads or fracture behavior of the specimens.

A blackbody optical fiber thermometer consists of an optical fiber whose sensing tip is given a metallic coating. The sensing tip of the fiber forms an isothermal cavity, and the emission from this cavity is approximately equal to the emission from a blackbody. Standard two-color optical fiber thermometry involves measuring the spectral intensity at the end of the fiber at two wavelengths. The temperature at the sensing tip of the fiber can then be inferred using Planck's law and the ratio of the spectral intensities. If, however, the length of the optical fiber is exposed to elevated temperatures, erroneous temperature measurements will occur due to emission by the fiber. This thesis presents a method to account for emission by the fiber and accurately infer the temperature at the tip of the optical fiber. Additionally, an estimate of the temperature profile along the fiber may be obtained. A mathematical relation for radiation transfer down the optical fiber is developed. The radiation exiting the fiber and the temperature profile along the fiber are related to the detector signal by a signal measurement equation. Since the temperature profile cannot be solved for directly using the signal measurement equation, two inverse minimization techniques are developed to find the temperature profile. Simulated temperature profile reconstructions show the techniques produce valid and unique results. Tip temperatures are reconstructed to within 1.0%. Experimental results are also presented. Due to the limitations of the detection system and the optical fiber probe, the uncertainty in the signal measurement equation is high. Also, due to the limitations of the laboratory furnace and the optical detector, the measurement uncertainty is also high. This leads to reconstructions that are not always accurate. Even though the temperature profiles are not completely accurate, the tip-temperatures are reconstructed to within 1%—a significant improvement over the standard two-color technique under the same conditions. Improvements are recommended that will lead to decreased measurement and signal measurement equation uncertainty. This decreased uncertainty will lead to the development of a reliable and accurate temperature measurement device.

Optical fibers are increasingly being used to create sensing devices. The D-fiber has an elliptical core and exhibits birefringence. This birefringence can be used to create a polarimetric sensor. The elliptical core supports two orthogonal modes that have separate effective indices of refraction. The indices of refraction change with a change in temperature. Since the effective indices of refraction change differently for the two modes, the birefringence also changes. This change in birefringence can be seen as a change in detected power through the fiber through the use of polarizers. The fiber then becomes a temperature sensor. The sensitivity of the fiber can be enhanced by replacing a section of the core of the fiber with a sensing material. With the sensing material in the core of the fiber, it has direct interaction with the light and strongly affects it. A polarimetric temperature sensor is created by replacing a section of the core with a polymer, which is sensitive to temperature. The core-replaced fiber in a polarimetric sensing configuration is compared to a a unetched fiber set up in the same way. The core-replaced fiber sensor is five times as sensitive to temperature as an unetched fiber.

This paper describes optical fiber and cable evaluation carried out at Bell-Northern Research during the summer period of May- August, 1980. Contemporary fibers and cables designed for telecommunications use were evaluated and the results on the following three areas are reported: (1) Resistance of fiber optics cables to temperature extremes and mechanical abuse. (2) Fiber tensile strength, both fast-fracture and fatigue, and a test method to predict longevity of the fibers. (3) Pulse broadening, measured as a function of link lengths in order to establish engineering rules which can predict performance for 10km lengths (typical repeater spacing) from the individual fiber characteristics. / Thesis / Master of Engineering (MEngr)

Hydrogen peroxide is used in various fields, such as food preservative, bleaching, oxidizing, reducing, and chemical reaction reagents. However, inappropriate use may have harmful effects to human health or environment. A number of analytical methods have been developed for the determination of hydrogen peroxide. Herein is described the effort to develop an optical fiber chemical sensor based on the evanescence wave absorbance that can detect the presence of, and measure the concentration of, hydrogen peroxide. For the H2O2 optical fiber sensor, Nafion membrane was coated in the fiber optic. Titanium ions dispersed in a Nafion membrane can form a TiO-H2O2 complex with the H2O2 diffused into the membrane. The complex is shown to absorb light with a maximum absorption near 360 nm. The intensity of the absorbance peak is directly proportional to the concentration of H2O2. At present, this sensor has been tested for detecting H2O2 concentrations ranging from 0.03 ppm to 9 ppm in an aqueous solution at room temperature. Additionally, coating polydimethylsiloxiane (PDMS) outside the fiber optic can detect H2O2 in high concentration 300ppm and high temperature 70oC. Finally, the use of the developed optical fiber chemical sensor allows the direct determination of H2O2 in milk.

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