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Sensitivity to differential motion components, shearing and compressive (opposed) motion, was examined. The hypothesis that the visual system contains local mechanisms specifically sensitive to these types of motion was tested. Stimuli consisted of two moving sinusoidal gratings. Sensitivity to shear and compression was compared with sensitivity for linear motion. Lower thresholds of motion and contrast sensitivities were obtained. Subjects were more sensitive to opposed than to non-opposed motion for a range of grating orientations and different grating spatial frequencies. However sensitivity for opposed motion decreased in the presence of a second added linear motion. The hypothesis of local shear and compression mechanisms was rejected in favour of antagonistic (opponent) interactions between local motion mechanisms. Motion capture was examined. Stimuli were made up of a circular test grating surrounded by another grating. Subjects were required to judge the direction of motion of the test grating. Experiments examined the effects on motion capture of: centre grating size; orientation of surround; relative contrast of centre and surround; plaids in the surround. Conditions favouring motion capture were: with the smallest centre grating; with surround and centre orientations within thirty degrees; with surround had higher contrast than the centre; and only when a plaid surround contained a component of similar orientation as the centre. For conditions of motion capture relative to those of no-capture, increased velocity thresholds for judging the centre direction were found. This was associated with a shift in the bias point between opposed directions with no change in overall sensitivity to motion. It is suggested that a cooperative network of local motion mechanisms featuring centre-surround opponency can account for all the results of this study.

This thesis reports the research and industry-related works carried out from the development of a fibre-optic strain sensor system for Civil Engineering applications. A sensor system consists of a number of core components, including the sensing element, interrogation/demodulation, multiplexing, signal processing and hardware equipment. In the process of development, a number of issues have been identified and investigated, which resulted in the improvement of the system performance, as well as the proposal of new techniques for the sensor system. First, an improved demodulation technique for a type of sensor, namely the fibre Fizeau interferometer (FFI), is presented. The technique is based on the improvement of the Fourier transform peak detection method, which suffers severely from the poor resolution and accuracy of finding the sensor cavity length. The improvement over the original method has been compared and verified through simulations and experiments. Second, a simultaneous demodulation technique for multiplexed FFI and fibre Bragg grating (FBG) sensors using the discrete wavelet transform (DWT) is proposed. Third, a multiplexing technique using amplitude-modulated chirped FBGs and the DWT is proposed. These two proposed techniques have been demonstrated experimentally through strain measurements. The strain resolution, crosstalk and limitations are investigated. In addition, simultaneous quasi-static strain and temperature sensing of different metal plates are performed. Fibre-optic sensors have found numerous applications in different areas. In this thesis, the use of FBG sensors in Civil Engineering applications is demonstrated in four experimental studies, including: (i) long-term measurement of drying shrinkage and creep of structural grade concrete; (ii) simultaneous measurement of shrinkage and temperature of reactive powder concrete (RPC) at early-age; (iii) measurement of coefficients of thermal expansion of cement mortar and RPC; and (iv) field-trial on the strain monitoring of the world?s first RPC road bridge. In addition, the experimental and practical issues of using FBG sensors are considered.

Thesis (MS )--Montana State University--Bozeman, 2008. / Typescript. Chairperson, Graduate Committee: Douglas S. Cairns. Includes bibliographical references (leaves 142-147).

Thesis (M.App.Sc.) - Carleton University, 2007. / Includes bibliographical references (p. 80-92). Also available in electronic format on the Internet.

Thesis (M.S.)--Rochester Institute of Technology, 2006. / Typescript. Includes bibliographical references (leaves 111-114).

Fiber optical temperature and strain sensors have been extensively investigated for applications in the civil structures to ensure safety and prevent disasters in advance. Most of the demonstrated fiber sensors are based on the silica fibers to form an interferometer by measuring the spectrum wavelength shift caused by the change of the refractive index and fiber length, and the sensitivities, defined as the rate of wavelength shift with respect to temperature or strain, are limited by the small values of thermal-expansion coefficient and thermo-optic effect of the silica materials. To improve the sensitivity, we designed the dual-core As2Se3-PMMA fiber with the PMMA cladding diameter 56.5 times larger than that of the As2Se3 cores, which brings out many interesting sensing applications. Nonlinear devices have a variety of practical applications including parametric amplification, all-optical switching, super-continuum generation, and sensing applications. Tapered chalcogenide-polymer fiber structures composed of an As2Se3 core and a polymethyl methacrylate (PMMA) cladding are a promising platform for nonlinear applications because the As2Se3 core provides high nonlinearity over the near- and mid-infrared spectral ranges for compact nonlinear devices with low power consumption and the PMMA cladding provides high mechanical strength for easy handling. Advanced As2Se3-PMMA fiber structures such as dual-core fibers that support guided propagation of an even mode and an odd mode will open the way for a variety of novel devices in the near- and mid-IR wavelength range. In my work I utilized two As2Se3 fibers and a polymethyl methacrylate (PMMA) tube for the fabrication of dual-core As2Se3-PMMA tapers and demonstration of the sensing applications and nonlinear optical effects. The thesis mainly consists of three parts: the fabrication process, the sensing applications, and the nonlinear applications in the tapered dual-core As2Se3-PMMA fiber. In the first part, the fabrication process of the tapered dual-core As2Se3-PMMA fiber is introduced. The dual-core As2Se3-PMMA fibers are fabricated using a rod-in-tube method. The images of the setups and fibers in process are listed. In the second part, a theoretical model for temperature and strain measurement and four sensing applications are introduced. Firstly, we demonstrate an approach for high-sensitivity simultaneous temperature and strain measurement in a dual-core As2Se3-PMMA taper with As2Se3 core diameter of 0.55 μm. High measurement sensitivities are observed for both principal polarization axes of the tapered dual-core As2Se3-PMMA fiber with temperature sensitivities of -115 pm/ºC for axis-1, -35.5 pm/ºC for axis-2, and strain sensitivities of -4.21 pm/με for axis-1 and -3.16 pm/με for axis-2. Secondly, the thermal forces in a dual-core As2Se3-PMMA taper are investigated. A temperature-insensitive strain sensor is proposed and demonstrated based on the thermal forces. Finally, two approaches for temperature and strain sensitivity enhancement are investigated. The first approach is by reducing the value of the variation of the difference between phases of the even and odd modes with respect to wavelength (∂ϕd(λ)/∂λ) and increasing thermal-forces in a dual-core As2Se3-PMMA taper with As2Se3 core diameter of 2.5 μm. The value of ∂ϕd(λ)/∂λ decreases with the As2Se3 core diameter and thermal-forces on the As2Se3 cores are enhanced in the fibers with large PMMA cladding, which work together to enhance the measurement sensitivity. The second approach is based on effective group-velocity matching between the even and odd modes of a dual-core As2Se3-PMMA taper on which an antisymmetric long-period grating is inscribed. The variation of the difference between phases of the even and odd modes with respect to wavelength tends to 0 (∂ϕd(λ)/∂λ→0) near the resonance wavelength of the grating due to the effective group-velocity matching between the two modes, and consequently, thermally-induced change of the difference between phases of the two modes ϕd (λ) leads to a large wavelength shift indicating enhancement of the temperature measurement sensitivity. In the third part, I study the nonlinear optical effects in the hybrid fibers. Firstly, I demonstrate modulation instability within the normal-dispersion regime in a dual-core As2Se3-PMMA fiber. Then I review the work about the forward stimulated Brillouin scattering and its sensing applications. The radial and torsional-radial guided acoustic modes of silica fibers and tapered dual-core As2Se3-PMMA fibers are investigated experimentally and the preliminary results are presented.

[pt] O objetivo principal deste trabalho foi o de estudar as redes de Bragg em fibras ópticas e suas principais aplicações, com especial interesse na compensação de dispersão de pulsos ópticos em sistemas de telecomunicações, onde uma implementação original foi construída. Faz-se uma revisão geral das técnicas existentes para fabricá-las e caracterizá-las, além de suas principais aplicações, não somente na área de telecomunicações mas também na área sensoriamento óptico. São mostrados os resultados experimentais obtidos nas montagem realizadas para escrever redes de Bragg em fibras ópticas e para caracterizá-las. Algumas experiências usando redes de Bragg para o controle do comprimento de onda de emissão de um laser de semicondutor e para medição de força aplicada numa estrutura são mostradas. São mostrados também os resultados experimentais inéditos obtidos com a compensação de dispersão de pulsos ópticos em enlaces de telecomunicações, onde várias montagens foram realizadas para comprovar a superioridade da utilização da redes de Bragg para esse fim. Demonstra-se também um sistema para gerar pulsos solitônicos sintonizável em comprimento de onde numa faixa de MHZ. Finalmente são mostrados os resultados obtidos com a utilização de fibras ópticas para chaveamento interferométrico de luz. Neste sistema são utilização como elemento óptico não linear fibras tipo D, com e sem redes de Bragg, revestidas com filme de materiais semicondutores amorfos. / [en] Bragg grating in optical fibers are used to compensate the dispersion of optical pulses in telecommunication systems. Initially, an overview is presented of the existing fabrication techniques of such gratings, as well as the techniques used for characterization. Some useful applecations in telecommunications and sensing are also shown. The results obtained in the set-up to write and to characterize Bragg gratings are presented. Some measurements were also done with typical applications such as controlling the emitting wavelength in semiconductors lasers, and monitoring the applied pressure in an optical fiber. Some new results are described on dispersion compensation in fibers. Using specially chirped Bragg gratings to pre- compensatedispersion of an optical pulse in a 80 km fiber link, we demonstrated that the poor quality of the input laser pulses has little impact on the duration of the pulses recovered after transmission. Finally, an interferometric switching arrangement using a semiconductor coated D fiber as nonlinear control element, is presented. The configuration uses infrared optical pulses to control a continuous wave light signal. It is also shown that the original reflected wavelength of a semiconductor coated D-fiber with Bragg grating can be shited with an external optical control signal.

Neste trabalho é apresentado um sistema de leitura de redes de Bragg derivado da técnica por filtro Fabry-Perot sintonizável. A técnica apresentada é implementada através de um sistema atuador piezelétrico que modula mecanicamente uma rede de Bragg de referência, com seu espectro de reflexão convoluido com o espectro de reflexão de uma rede sensora. A técnica desenvolvida apresenta vantagens em relação ao processo original por ter implementação mais simples, menor custo e melhor discriminação de posição espectral. / This work presents a process to detect Bragg grating spectra based on the tunable Fabry Perot filter technique. The apparatus is assembled with a piezoelectric actuator that mechanically modulates a reference Bragg grating. The spectrum of that grating is convoluted with the spectrum of the sensor during a sweep. The device presents some advantages as, eg., simplicity, lower cost and better discrimination for the spectral position of the reflected band.

[pt] A utilização de redes de Bragg com chirp em fibra, para compensação dos efeitos da dispersão cromática, é uma técnica promissora que permite o aumento progressivo da capacidade de canalização dos sistemas ópticos. Dentre as diversas técnicas para a compensação da dispersão, sendo propostas nos tempos correntes, o emprego da rede de Bragg em fibra tem se mostrado o mais exequível em virtude de serem passivas, relativamente fáceis de fabricar, de boa reprodutibilidade e alto grau de integrabilidade aos sistemas. Este trabalho mostra a aplicação desse dispositivo em experimentos de compensação de dispersão com o emprego de modulação direta e externa em diferentes taxas de transmissão. / [en] The use of in-fibre Bragg gratings with dispersion compensating purposes, is a promissing technique for the increasing optical systems bitrate pace development. Among the various dispersion compensation techniques, in-fibre Bragg gratings had proven, to be the most feasible. They are passive, higly reproducible, relatively easy to fabricate at reasonable costs and have a good degree of integrability. This dissertation exploits significant aspects of the Bragg fibre grating fabrication and its employment as dispersion compensation device.