Dissertations / Theses on the topic 'Fiber optic instrument'

Polarimetry, as applied to chemical analysis, deals with the determination of the extent and direction that an optically active chemical species will rotate incident linearly polarized light. Although well developed for physical sensing, the technique of fiber optic polarimetry for chemical sensing remains in its infancy. This thesis is concerned with the design and development of an optical fiber polarimeter which measures the optical rotation of linearly polarized light that occurs in a sensing region between two multi-mode optical fibers. Over short distances, the polarization preserving capabilities of large-core multi-mode optical fibers were investigated. Polarimetric analyses were performed using sucrose and quinine hydrochloride. The instrument has a resolution of O.O8·, and is an excellent platform for an LC or FIA detector. Its more intriguing future lies in evanescent field sensor applications and studies of chiroptical surface interactions.
Master of Science

Laser ultrasonics is an all-optical non-destructive testing technique which employs ultrasonic waves as a means of ascertaining the internal part of an opaque material (for light). The difference from a conventional ultrasonics testing technique relies on the generation and detection of these waves which, in the laser ultrasonics technique, is performed by a laser pulse and an optical detector of ultrasound, respectively. This technique is employed in the aerospace and aeronautics industry for flaw detection or material characterization, since it is couplant free, non-contact and remote from the inspected object. The high cost and complexity of a commercial laser ultrasonics system, however, led to the development in this work, of an intensity-modulated fiber optic sensor to be employed as the optical detector of a laser ultrasonics system. This fiber optic sensor is capable to detect angular displacement in the range of microradians and presents high sensitivity, optical fiber compatibility, wide bandwidth and, furthermore, is simple to assembly and low cost. The fiber optic sensor comprises two optical fibers, a positive lens, a reflective surface, a laser, and a photodetector. A mathematical model was developed to determine and simulate the static characteristic curve of the sensor and to analyze the influence of geometrical parameters in its performance. Different sensor configurations were assembled and experimental static characteristic curves were acquired to validate the mathematical model. The normalized sensitivity, for the configurations tested, ranges from (0.25×Vmax) to (2.40×Vmax) mV/?rad and the linear range, from 194 to 1840 ?rad. Regarding an specific sensor configuration (the sensor 4/4) with reflective surface of 100% of reflectivity, the sensor presented an unnormalized sensitivity of 7.7 mV/?rad, an estimated resolution of approximately 1 ?rad and signal-to-noise ratio of 32 dB. The sensor was tested on the dynamic operation for sound and ultrasound detection and, finally as the optical detector of the complete laser ultrasonics system developed in this work. The sensor also proved to be suitable for time-of-flight measurements and nondestructive testing, being an alternative to the piezoelectric or the interferometric detectors.

Дисертація присвячена вирішенню наукової проблеми підвищення ефективності незображуючих волоконно-оптичних систем (НВОС) для мінімально інвазивної клінічної медицини. Розроблено узагальнені принципи структурно-функціональної організації незображуючих волоконно-оптичних систем для мінімально інвазивної клінічної медицини, в основі яких лежать узагальнені класифікації НВОС та волоконно- оптичного інструменту (ВОІ); оригінальну математичну модель розповсюдження оптичного випромінювання всередині біотанини та математичну модель флуоресцентного сигналу від неї; нові математичні моделі та технічні рішення побудови оригінальних базових функціональних модулів з оцінюванням і оптимізацією їх ефективності за запропонованими кількісними показниками з метою цілеспрямованого створення діагностичних та лікувальних систем і наступним їх впровадженням у виробництво та клінічну практику.

Orientador: José Antonio Siqueira Dias
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação
Made available in DSpace on 2018-08-21T18:07:20Z (GMT). No. of bitstreams: 1 BiazonFilho_AlcinoJose_D.pdf: 3212736 bytes, checksum: 5eb7bde925a233493806c588f3c39cfe (MD5) Previous issue date: 2012
Resumo: Sensores de fibra óptica são imunes à interferência eletromagnética (EMI), e são uma excelente escolha para ser usado em ambientes eletricamente ruidosos aplicações em sensoriamento remoto, incluindo aeroespacial, ferroviário equipamentos de segurança militar e em linhas de alta tensão. Outras vantagens incluem o fato de que eles são compactos, leves e os sinais de medição podem ser transmitidos a distâncias muito grandes (da ordem de km). Os interrogadores convencionais para redes de Bragg (FBG) do sensor são equipamentos de custo elevado e não pode ser utilizado em aplicações de baixo custo. Neste trabalho é apresentada uma nova técnica de interrogação robusta e de baixo custo que apresenta uma boa precisão. A técnica, que utiliza um circuito de retroalimentação eletrônico para estabilizar o ponto de operação DC das grades de Bragg, permite a medição simultânea de ambos sinais AC e DC. Um protótipo do interrogador proposto foi projetado e implementado. A técnica exige apenas três componentes ópticos: um laser distribuído, um acoplador óptico e um fotodiodo. O interrogador foi testado com sucesso em uma aplicação de DC (medição de temperatura) e uma aplicação AC (medição de corrente elétrica). Os resultados experimentais mostraram que o controle eletrônico em malha fechada pode controlar o ponto de operação da FBG com uma precisão de ± 2 ppm
Abstract: Fiber optic sensors are immune to electromagnetic interference (EMI), and are an excellent choice for being used in electrically noisy environments sensing applications, including aerospace, rail, military security equipment and in high voltage power lines. Other advantages include the fact that they are compact, lightweight and the measured signals can be transmitted at very large distances (of the order of kilometers). The conventional interrogators for Fiber Bragg Gratings (FBG) sensor are high cost equipment and cannot be used in low cost applications. In this work it is presented a novel robust and low cost interrogation technique that presents good accuracy. The technique, which uses an electronic feedback loop to stabilize the DC operating point of the Bragg gratings, allows the simultaneous measurement of both AC and DC signals. A prototype of the proposed interrogator was designed and implemented. The technique requires only three optical components: a Distributed Feedback Laser, an optical coupler and one photodiode. The interrogator has been successfully tested in a DC application (temperature measurement) and an AC application (electrical current measurement). Experimental results showed that the electronic feedback loop can control the operation point of the FBG with a precision of ±2 ppm
Doutorado
Eletrônica, Microeletrônica e Optoeletrônica
Doutor em Engenharia Elétrica

High-order wavefront correction is not only beneficial for high-contrast imaging, but also spectroscopy. The size of a spectrograph can be decoupled from the size of the telescope aperture by moving to the diffraction limit which has strong implications for ELT based instrument design. Here we present the construction and characterization of an extremely efficient single-mode fiber feed behind an extreme adaptive optics system (SCExAO). We show that this feed can indeed be utilized to great success by photonic-based spectrographs. We present metrics to quantify the system performance and some preliminary spectra delivered by the compact spectrograph.

L'interférométrie visible longue base est une technique d'observation en astronomie permettant de sonder les objets avec une résolution spatiale qu'il est impossible d'atteindre avec un télescope seul. La mise en œuvre au sol de cette méthode est limitée en sensibilité et précision de mesure à cause de la turbulence atmosphérique. Or les nouveaux besoins scientifiques, tels que la détermination des paramètres fondamentaux, l'étude de l'environnement proche ou de la surface des étoiles, requièrent la capacité d'observer des objets de moins en moins brillants et de faire des mesures de plus en plus précises, en interférométrie visible. Pour s'affranchir de la turbulence, l'interférométrie multimode a été développée en reprenant le concept de l'interférométrie des tavelures utilisée sur un seul télescope. Aujourd'hui, pour améliorer davantage les performances des futurs instruments, cette instrumentation évolue vers l'utilisation de la nouvelle génération de détecteur, l'Electron Multiplying Charge-Coupled Device (EMCCD), et de l'emploi des fibres optiques interfacées avec des optiques adaptatives. Cette avancée est motivée par le succès de l'utilisation conjointe de l'optique adaptative et du suivi de franges pour s'affranchir partiellement de la turbulence en interférométrie infrarouge, en 2017 avec l'instrument GRAVITY (Gravity Collaboration et al. 2017). Le prototype FRIEND (Fibered and spectrally Resolved Interferometer - New Design) a été conçu pour caractériser et évaluer les performances de la combinaison de ces éléments, dans le domaine visible. L'amélioration de la précision des instruments interférométriques est apportée par les fibres optiques et par la dynamique du signal délivré par une EMCCD. L'inconvénient de l'emploi des fibres dans le visible est une perte de la sensibilité du fait que le taux d'injection du flux dans celles-ci est très faible à cause de la turbulence atmosphérique. Mais il se trouve que l'optique adaptative et l'EMCCD permettent d'améliorer la sensibilité. En effet, l'optique adaptative maximise l'injection en réduisant l'influence de la turbulence atmosphérique, et l'EMCCD est capable de détecteur de faibles flux. FRIEND prépare ainsi le développement du futur instrument SPICA, recombinant jusqu'à six télescopes (Mourard et al. 2017, 2018). Celui-ci devra explorer la stabilisation des interférences grâce au suivi de franges. Cet aspect n'est pas abordé dans cette thèse. Je présente dans cette thèse le prototype FRIEND, capable de recombiner jusqu'à trois télescopes, opérant dans la bande R en franges dispersées. Il est doté de fibres optiques gaussiennes monomodes à maintien de polarisation et d'une EMCCD. Il est installé sur l'interféromètre visible Center for High Angular Resolution Astronomy (CHARA), au Mount Wilson, en Californie, qui est en train de s'équiper d'optiques adaptatives. J'ai développé des estimateurs de visibilité et de clôture de phase, la méthode de réduction des données de ce prototype et une stratégie d'observation. Grâce à ces outils, j'ai montré que les optiques adaptatives améliorent le taux d'injection dans les fibres. Il est alors apparu que la stabilisation de l'injection est importante pour maximiser le rapport signal-à-bruit dans chaque image. La biréfringence des fibres dégrade les performances de l'instrument mais elle a pu être compensée. J'ai montré qu'un instrument, basé sur la conception de FRIEND, permet d'accéder à des mesures de visibilité faibles avec une précision, inatteignable avec la génération actuelle, grâce au développement et l'utilisation d'un modèle de rapport signal-à-bruit. L'instrument a enfin été testé dans son intégralité sur le système binaire connu ζ Ori A. Cette observation montre la fiabilité et la précision des mesures interférométriques obtenues avec ce prototype, montrant l'intérêt de cette association de technologies pour les futurs interféromètres visibles
Long baseline visible interferometry in astronomy is an observing technique which allows to get insights of an object with an outstanding angular resolution, unreachable with single-dish telescope. Interferometric measurements with ground-based instrumentation are currently limited in sensitivity and precision due to atmospheric turbulence. However, the new astrophysical needs, particularly the determination of fundamental parameters or the study of the closed environment and the surface of the stars, require to observe fainter objects with a better precision than now in visible interferometry. Ought to overcome the atmospheric turbulence, multispeckle interferometry has been developed by adapting speckle imaging technics used on single-dish telescope. Today, in order to improve the performance of the future combiners, instrumentation progresses to the use of a new generation detector called EMCCD, and the use of optical fibers which are coupled with adaptive optics. This path is chosen thank to the success of the use of the adaptive optics with the fringe tracking in the infrared interferometry in 2017 (Gravity Collaboration et al. 2017), in order to compensate turbulence. FRIEND prototype (Fibered and spectrally Resolved Interferometer - New Design) has been designed to characterize and estimate the performance of such a combination of technologies, in the visible spectral band. The improvement of the precision of the measurements from interferometric instruments is due to optical fibers and the dynamical range of the EMCCD. The counterpart of using the optical fibers is a loss in sensitivity due to a low injection rate of flux into the fibers because of the atmospheric turbulence. On the other hand, sensitivity is improved thanks to adaptive optics and EMCCDs. Indeed, adaptive optics increases the injection rate and EMCCDs can measure low fluxes. Lastly, FRIEND is a pathfinder for the future instrument SPICA which should recombine up to 6 telescopes (Mourard et al. 2017, 2018). Fringe-tracking aspects will have to be studied for SPICA; this topic is not dealt with in this thesis. In this work, I present the FRIEND prototype, which can recombine up to three telescopes and operates in the R band with dispersed fringes. It has Gaussian polarization-maintaining single mode optical fibers and an EMCCD. It is set up at the Center for High Angular Resolution Astronomy (CHARA), at Mount Wilson, in California. CHARA is currently being equipped with adaptive optics. I develop estimators of visibility modulus and closure phase, the data reduction software and an observing strategy. Thanks to that, I am able to show that adaptive optics improves the injection rate. I also demonstrate how important the stabilization of injection is to maximize the signal-to-noise ratio (SNR) per frame. Birefringence of the fibers decreases the performance of the instrument but we manage to compensate it. I show how such an instrument can measure low visibility with a better precision than now by developing and using a SNR model of FRIEND. Finally, FRIEND has entirely been tested on the known binary system ζ Ori A. These observations demonstrate how reliable and accurate the measurements of FRIEND are

The nuclear industry shows an increasing interest in the fiber optic technology for both data communication and sensing applications in nuclear plants. The optical fibers offer several advantages and the sensors based on this technology do not need any electrical power at the sensing point, they have a quick response and they can be easily multiplexed: in the case of a temperature sensor, several thermocouples can be substituted by a single fiber, resulting in a decrease of the waste material. The fission reactors are a very harsh environment: it is characterized by the highest dose of gamma-rays, of the order of magnitude of GGy, besides a high flux of neutrons and high operating temperature (300°C for the current reactors, known as generation III). This work has been carried out in collaboration with AREVA, a French industrial conglomerate active in the energy domain, with the aim of realizing a temperature sensor resistant to the environment of nuclear reactor of generation IV, in particular a Sodium-cooled Fast Reactor. The currently used technology, the thermocouples, presents a drift of the measurement due to irradiation, that needs a calibration, and a long response time on the order of seconds. In order to remove the drift, to reduce the response time and to increase the precision, a Fiber Bragg Grating temperature sensor was chosen, in regard to all the advantages of the optical fibers. To understand the behavior of such system in a harsh environment, as the nuclear reactor core, we used an experimental approach based on complementary techniques such as radiation-induced attenuation, photoluminescence, electron paramagnetic resonance and Raman spectroscopies

Orientador: Jose Antonio Siqueira Dias
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação
Made available in DSpace on 2018-08-07T11:11:31Z (GMT). No. of bitstreams: 1 Leite_RogerioLara_D.pdf: 18262113 bytes, checksum: 8c49a719bdf98e92810c4c7275e7da78 (MD5) Previous issue date: 2006
Resumo: Os sensores a fibra óptica são especialmente indicados para operarem em ambientes eletricamente ruidosos, uma vez que são imunes aos efeitos da interferência eletromagnética (EMI) encontrados nestes ambientes. Tal característica faz com que os sensores ópticos sejam altamente vantajosos para as aplicações nos sistemas de sensoreamento utilizados pelas empresas de energia elétrica. Este trabalho apresenta o desenvolvimento de um protótipo de baixo custo de um sensor óptico de alta tensão com alta confiabilidade, que pode ser usado para monitorar o estado ou limiares de tensão em uma rede elétrica. Uma técnica de detecção do sinal através do sensoreamento com grades de Bragg é apresentada, fabricada e avaliada. Os resultados mostram que a técnica de detecção empregada, onde a amplitude ac do sinal da luz refletido é medida em um fotodiodo, mostra-se adequada para a aplicação em sensores de alta tensão. As medidas realizadas em um protótipo de sensor de alta tensão com fibra óptica com grade de Bragg indicam que o esquema de detecção desenvolvido é promissor, e pode ser usado para medir outros sinais dinâmicos que respondam a um esforço de pequena amplitude aplicado à fibra óptica. O protótipo desenvolvido permitiu a detecção de tensões variando na faixa de 143 V -60kY. É também apresentada uma nova técnica para estabilizar termicamente grades de Bragg com a temperatura, utilizando o sinal uma fibra extra, casada com a fibra do sensor, que através de um circuito de realimentação atua no elemento aquecedor/resfriador do laser semicondutor(thenno electrical cooler), para fazer com que o comprimento de onda do laser siga as variações da sintonia da grade de Bragg sensora, causadas por variações da temperatura. Esta técnica inovadora poderá ser utilizada para a compensação térmica de outros tipos de sensores com grade de Bragg, permitindo a fabricação de sensores de baixo custo e grande simplicidade de implementação
Abstract: Fiber optics sensors are specially indicated to operate in noisy electrical environments because they are immune to the effects of electromagnetic interference (EM!) found in these environrnents. Such characteristic makes these sensors highly advantageous to the applications in the measurement systems used by electrical energy companies. This work presents the development of a prototype of a high-voltage and a low cost optical sensor which is used to monitor the state or voltage threshold with a high reliability. A technique for the detection of fiber Bragg grating sensors signals was developed, presented and tested. The experimental results showed that the developed detection technique, where the ac amplitude of the signal result from the light reflection is measured with a photodiode is adequate for high voltage sensing applications. The prototype of the high voltage fiber Bragg sensor was tested and the measured results indicate that the technique can be used to detect any other dynarnic measurand which induces a small strain amplitude when applied to the fiber Bragg grating. The developed prototype detected voltages in the range from 143 V to 60 kV. It is also presented a new technique for obtaining temperature independent fiber Bragg gratings, using a feedback circuit which uses the signal detected from a matched fiber and generates a signal which actuates on the thermo electrical cooler of the semiconductor laser, modifying the laser' s output wavelength, in orer to accurate track the Bragg wavelength shifts caused by temperature variations. This novel technique can be used for the fabrication of simple and low-cost temperature compensated fiber Bragg grating sensors
Doutorado
Eletrônica, Microeletrônica e Optoeletrônica
Doutor em Engenharia Elétrica

The majority of structural studies on DNA have been carried out using fibre diffraction, while studies of its dynamics and thermal behaviour have been mainly performed in solution. When the DNA double helix is heated, it exhibits local separation of the two strands that grow in size with temperature and lead to their complete separation. This work has investigated various aspects of this phenomenon. The experiments reported in this thesis were carried out on films of oriented fibres of DNA prepared with the Wet Spinning Apparatus. Thus, sample preparation and characterisation are essential parts of the research. The structures of two forms of DNA, A and B, have been explored as a function of relative humidity at fixed ionic conditions. A method to eliminate traces of ever-present B-form contamination in A-form samples was established. The high orientation of the DNA molecules within the samples allowed us to investigate dynamical fluctuations and the melting transition of DNA using neutron scattering, which can provide the spatial information crucial to understand a phase transition, probing the static correlation length along the molecule as a function of temperature. The transition has been investigated for A and B-forms in order to understand its dependence on molecular configuration.Furthermore, after the first melting, denatured DNA films show typical glass behaviour. Their thermal relaxation has been explored using calorimetry.Neutron and X-ray inelastic scattering (INS and IXS) were used in the past to measure longitudinal phonons in fibre DNA, and the results shown disagreement. Recent INS measurements supported with phonon simulations have been crucial to understand the different dispersion curves reported to date. Experiments using INS and IXS have been carried out to continue with this investigation. Attempts to observe the transverse fluctuations associated to the thermal denaturing of DNA, never experimentally investigated before, have been made.

碩士
國立虎尾科技大學
機械與機電工程研究所
101
Large diameter (0.4~1.0mm) fiber termination is widely used in the gum related cares. However, cost-effective shaped fiber is not yet developed for high power (~5W) laser. In this study, we have demonstrated the feasibility of using two stepping motors with a patented axial movement (0.005mm increments) method. The key parameters are investigated using finite element modeling. The results show that larger fiber diameter with less number of feeding increments can damage the fiber during polishing process.

Acquiring the motions of the inner ear sensory tissues provides insight to how the cochlea works. For this purpose, Spectral Domain Optical Coherence Tomography (SDOCT) is an ideal tool as it has a penetration depth of several millimeters. SDOCT can not only image inside the cochlear partition, but also measure the sample structures’ simultaneous displacements. We customized a commercial Spectral Domain Optical Coherence Tomography system for such functions and detailed the software and hardware steps so this powerful system could be more accessible to auditory researchers. The cochlea is surrounded by bones and tissues, and damage to it would make it passive. For this reason, cochlear vibrometry measuring locations have been limited to either the basal or apical regions. That is why I fabricated a two-dimensional scanning SDOCT-based probe, to access more cochlear locations through a small hand-drilled hole. What is exciting about the probe is that an electrode can be attached to its side to acquire spatially and temporally coincident voltage and displacement data. This would help us better understand the cochlear mechano-electrical feedback process. Lastly, I investigated how the SDPM-reported displacement could be influenced by its neighboring signals and demonstrated this signal competition phenomenon experimentally and theoretically.

M.Ing.
The aim of this project is to research the feasibility of an all-fibre laser distance measurement device that utilises a figure-eight fibre laser (F8L), in the nonlinear amplifying loop mirror (NALM) configuration, as a light source and implements pulse compression to improve the accuracy and signal-to-noise ratio of the system. A figure-eight fibre laser in the NALM configuration for use in a laser distance measurement device is described. The theory of fibre lasers is discussed, including mode-locking and Qswitching, and the characteristics of a NALM loop are analysed. By varying the length of the NALM loop from 500 m to 2000 m or inserting highly nonlinear dispersion shifted fibre, a variety of pulses in the picosecond to nanosecond range can be produced. The lengths of the pulses depend on the length of the NALM loop, the pump power and the setting of the polarisation controllers. The figure-eight fibre laser is pumped with a 980 nm laser diode up to 550 mA, which corresponds to 320 mW. Distance measurements are done with short unmodulated and long modulated pulses. Distance measurement with short unmodulated pulses is discussed only briefly and tested with a simple experiment. The focus of this project is distance measurement with long modulated pulses. A low autocorrelated binary sequence is modulated onto one of the long pulses produced by the figure-eight fibre laser by an electro-optic amplitude modulator. The long pulse gives the proposed system a good signal-to-noise ratio (SNR), while the modulation improves the accuracy. A Barker code of length 13 is proposed as modulation code because of its good autocorrelation properties. The Barker code will improve the accuracy 13-fold, with a corresponding increase in SNR. An electro-optic amplitude modulator is used to implement the modulation. The modulated long pulse is then sent to a target. After reflection, the signal is detected and cross-correlated to obtain the time-of-flight for the pulse. The code generation and cross-correlation are implemented with an FPGA via VHDL programming. The distance to a target can be calculated by knowing the time-of-flight and the speed of light in the propagation medium. In this project the resolution, single-shot precision, accuracy, linearity, repeatability and maximum unambiguous distance of the proposed all-fibre laser distance measurement device are examined.

Optics are a powerful probe of chemical structure that can often be linked to theoretical predictions, providing robustness as a measurement tool. Not only do optical interactions like second harmonic generation (SHG), single and two-photon excited fluorescence (TPEF), and infrared absorption provide chemical specificity at the molecular and macromolecular scale, but the ability to image enables mapping heterogeneous behavior across complex systems such as biological tissue. This thesis will discuss nonlinear and linear optics, leveraging theoretical predictions to provide frameworks for interpreting analytical measurement. In turn, the causal mechanistic understanding provided by these frameworks will enable structurally specific quantitative tools with a special emphasis on application in biological imaging. The thesis will begin with an introduction to 2nd order nonlinear optics and the polarization analysis thereof, covering both the Jones framework for polarization analysis and the design of experiment. Novel experimental architectures aimed at reducing 1/f noise in polarization analysis will be discussed, leveraging both rapid modulation in time through electro-optic modulators (Chapter 2), as well as fixed-optic spatial modulation approaches (Chapter 3). In addition, challenges in polarization-dependent imaging within turbid systems will be addressed with the discussion of a theoretical framework to model SHG occurring from unpolarized light (Chapter 4). The application of this framework to thick tissue imaging for analysis of collagen local structure can provide a method for characterizing changes in tissue morphology associated with some common cancers (Chapter 5). In addition to discussion of nonlinear optical phenomena, a novel mechanism for electric dipole allowed fluorescence-detected circular dichroism will be introduced (Chapter 6). Tackling challenges associated with label-free chemically specific imaging, the construction of a novel infrared hyperspectral microscope for chemical classification in complex mixtures will be presented (Chapter 7). The thesis will conclude with a discussion of the inherent disadvantages in taking the traditional paradigm of modeling and measuring chemistry separately and provide the multi-agent consensus equilibrium (MACE) framework as an alternative to the classic meet-in-the-middle approach (Chapter 8). Spanning topics from pure theoretical descriptions of light-matter interaction to full experimental work, this thesis aims to unify these two fronts.