Thesis (doctoral)--University of Oulu, 2004. / Includes bibliographical references (p. 147-171). Also available on the World Wide Web.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 77-79). Also available via the Internet.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 62-63). Also available via the Internet.

M.Ing. / Over the past few years, fibre Bragg gratings have emerged as very important components in the photonics environment. Their discovery has greatly revolutionised the design of many complex devices, introducing simplicity and cost effectiveness. Extensive research has been invested into identifying possible areas of application for fibre Bragg gratings. This has resulted in fibre Bragg gratings finding a comfortable niche in the fields of sensors and optical communication systems. This study focuses on the possible application of fibre Bragg gratings in wireless local area networks. Wireless local area networks are rapidly becoming a market of great potential for the investor. To sustain the impressive image of this market, research initiatives should strive to secure cost-effective solutions for the implementation of wireless local area networks. With reduced costs on wireless local area network products, the demand for these products is expected to escalate. Research conducted at the COBRA Institute, has produced a novel concept of optically distributing data signals across a network, and later transmitting them at radio frequencies between antenna sites. This concept, earmarked for wireless local area networks, uses a fast tuneable laser source, graded index polymer optical fibre and a periodic optical filter to generate the radio frequency microwave signals. The periodic filter in this network system serves to up-convert the frequency of the signal to radio-frequency levels. The filter is an important component of the network and it is situated at the antenna site. For wireless local area networks that require broad coverage, the number of periodic optical filters deployed for the system can be high. This can have a negative impact on the cost of the network. This research proposes a low-cost Fabry-Perot filter designed from fibre Bragg gratings, to replace the optical periodic filter discussed in the network mentioned above. The work presented in this study consolidates the design theories of Fabry-Perot filters and fibre Bragg gratings. The grating-based Fabry-Perot filter is modelled using coupled-mode theory, simulated using the transfer matrix method and fabricated via the strain controlled phase mask technique. The figures of merit that describe the spectral performance of the Fabry-Perot filter (i.e. free spectral range, minimum resolvable bandwidth, finesse and contrast factor) are compared to calculations associated with classical designs. The final part of this study presents experimental measurements of the generated radio frequency microwave signal. The purpose of these measurements is firstly to demonstrate the feasibility of the entire concept of generating radio frequency microwave signals using optical frequency multiplication. The second goal for the measurements is to benchmark the performance of the new grating-based Fabry-Perot filter against expected results approximated through calculations. Both goals were achieved with encouraging observations.

No description available.

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This dissertation focuses on developing new technologies for ultra-low-cost sapphire fiber-optic high-temperature sensors. The research is divided into three major parts, the souceless sensor, the simple Fabry-Perot (F-P) interrogator, and the sensor system. Chapter 1 briefly reviews the background of thermal radiation, fiber optic F-P sensors, and F-P signal demodulation. The research goal is highlighted. In Chapter 2, a temperature sensing system is introduced. The environmental thermal radiation was used as the broadband light source. A sapphire wafer F-P temperature sensor head was fabricated, with an alumina cap designed to generate a stable thermal radiation field. The radiation-induced optical interference pattern was observed. We demodulated the temperature sensor by white-light-interferometry (WLI). Temperature resolution better than 1°C was achieved. Chapter 3 discusses a novel approach to demodulate an optical F-P cavity at low-cost. A simple interrogator is demonstrated, which is based on the scanning-white-light-interferometry (S-WLI). The interrogator includes a piece of fused silica wafer, and a linear CCD array, to transform the F-P demodulation from the optical frequency domain to the spatial domain. By using the light divergence of an optical fiber, we projected a tunable reference F-P cavity onto an intensity distribution along a CCD array. A model for S-WLI demodulation was established. Performance of the new S-WLI interrogator was investigated. We got a good resolution similar to the well-known traditional WLI. At last, we were able to combine the above two technologies to a sapphire-wafer-based temperature sensor. The simple silica wafer F-P interrogator was optimized by focusing light to the image sensor. This approach improves the signal to noise ratio, hence allows the new integrator to work with the relatively weak thermal radiation field. We, therefore, proved in the experiment, the feasibility of the low-cost sourceless optical Fabry-Perot temperature sensor with a simple demodulation system. / PHD

Narrowband spectral filters find important applications in optical fiber communication systems, particularly in wavelength demultiplexers and single-frequency semiconductor lasers. Conventional Fabry-Perot resonators provide a narrow spectral width but lack the capability of mode discrimination. A new coupled-waveguide Fabry-Perot resonator made of two parallel waveguides with reflecting mirrors at the ends is proposed for application as narrowband tuned spectral filter in single-mode diode lasers and wavelength demultiplexers. The interference of counter propagating waves from reflection by end mirrors and the coupling of waves between the two parallel guides contribute to the operation of this resonator structure. Thus, the device exhibits the attributes of both Fabry-Perot resonator and directional coupler. The coupled-mode theory of parallel waveguides is employed to analyze the proposed structure. Spectral characteristics are derived from the governing coupled-mode equations and related boundary conditions. Two geometries consisting of identical waveguides, as well as nonidentical waveguides, are examined. The spectral characteristics of the proposed resonator demonstrate that significant improvement in mode discrimination capability and longitudinal mode spacing over the conventional Fabry-Perot resonator is achieved. Numerical results for several example cases are presented and the influence of various parameters on spectral properties are investigated. / Master of Science

A surface acoustic wave sensor based on an extrinsic Fabry-Perot interferometer is described. A single-mode fiber, used as the input/output fiber, and a multimode fiber, used mainly as a reflector, form an air-gap that acts as a low-finesse Fabry-Perot cavity. The Fresnel reference reflection from the glass/air interface at the front of the air-gap interferes with the sensing reflection from the air/glass interface at the far end of the air-gap in the input/output fiber. Strains in the silica tube housing the two fibers change the air-gap length, thereby altering the phase difference between the reference and sensing reflections and modulating the output intensity. A theoretical analysis of the interaction between the strain induced by the acoustic fields and the fiber sensor is presented. Because signal drifting in interferometric sensors is common, a dual optical wavelength stabilization technique is also incorporated into the sensor to minimize the effect. Signal to noise ratios (SNR’s) on the order of 39 dB are obtained with a strain sensitivity of 4°/ μstrain cm⁻¹. / Master of Science

DNA detection technology has developed rapidly due to its extensive application in clinical diagnostics, bioengineering, environmental monitoring, and food science areas. Currently developed methods such as surface Plasmon resonance (SPR) methods, fluorescent dye labeled methods and electrochemical methods, usually have the problems of bulky size, high equipment cost and time-consuming algorithms, so limiting their application for in vivo detection. In this work, an intrinsic Fabry-Perot interferometric (IFPI) based DNA sensor is presented with the intrinsic advantages of small size, low cost and corrosion-tolerance. This sensor has experimentally demonstrated its high sensitivity and selectivity. In theory, DNA detection is realized by interrogating the sensor's optical cavity length variation resulting from hybridization event. First, a microgap structure based IFPI sensor is fabricated with simple etching and splicing technology. Subsequently, considering the sugar phosphate backbone of DNA, layer-by-layer electrostatic self-assembly technique is adopted to attach the single strand capture DNA to the sensor endface. When the target DNA strand binds to the single-stranded DNA successfully, the optical cavity length of sensor will be increased. Finally, by demodulating the sensor spectrum, DNA hybridization event can be judged qualitatively. This sensor can realize DNA detection without attached label, which save the experiment expense and time. Also the hybridization detection is finished within a few minutes. This quick response feature makes it more attractive in diagnose application. Since the sensitivity and specificity are the most widely used statistics to describe a diagnostic test, so these characteristics are used to evaluate this biosensor. Experimental results demonstrate that this sensor has a sensitivity of 6nmol/ml and can identify a 2 bp mismatch. Since this sensor is optical fiber based, it has robust structure and small size ( 125μm ). If extra etching process is applied to the sensor, the size can be further reduced. This promises the sensor potential application of in-cell detection. Further investigation can be focused on the nanofabrication of this DNA sensor, and this is very meaningful topic not only for diagnostic test but also in many other applications such as food industry, environment monitoring. / Master of Science