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1
Pham, Thi Nhung. "Fabry-Perot interferometer based on end-of-fiber polymer microtip for chemical sensing." Electronic Thesis or Diss., Bordeaux, 2024. http://www.theses.fr/2024BORD0006.
Анотація:
Les interféromètres Fabry-Perot (FPI) ont reçu un grand intérêt pour leur utilisation en tant que capteurs. Les FPI sont constitués d'une cavité optique avec des surfaces parallèles qui réfléchissent la lumière incidente, produisant un signal interférométrique optique. Ce signal dépend de la distance entre les surfaces réfléchissantes et de l'indice de réfraction de la cavité, qui sont sensibles aux variations d’humidité, de température, de pression et du matériau. Les FPI peuvent être attachés à des fibres optiques, qui fonctionnent comme un guide d'ondes pour le signal incident et le signal réfléchi, et former ainsi des capteurs compacts. Cette thèse présente des capteurs chimiques à base de FPI incorporant une micropointe en polymère structurée à l'extrémité d'une fibre optique, étudiés pour la détection d'humidité, d'eau et de cibles chimiques.Tout d'abord, nous développons une pointe de triacrylate de pentaérythritol (PETA) sur la facette d'une fibre optique par photopolymérisation autoguidée. Une extrémité de la fibre est placée dans une goutte de PETA et la photopolymérisation est activée par un laser de 375 nm injecté à l'autre extrémité de la fibre. Les conditions optimales pour former une pointe PETA mécaniquement stable sont 1μW de puissance laser × 1s de temps d'exposition. Cependant, les chaînes PETA ne sont pas complètement polymérisées lors de cette étape, ce qui entraîne une fréquence de résonance instable de la pointe. La pointe doit donc être post-polymérisée sous une lampe UV de 365nm pour obtenir une caractéristique dynamique stable, avant leur application en tant que capteur.Deuxièmement, nous démontrons que la pointe PETA est un capteur efficace pour détecter l'humidité. Elle fonctionne comme une cavité optique formée entre le cœur de la fibre/PETA et l'interface PETA/environnement, ce qui permet d'obtenir un signal interférométrique clair. Le signal FPI de la pointe est très sensible à l'humidité de l'air grâce aux groupes hydroxyles du PETA, qui absorbent les molécules d'eau dans l'air humide, induisant un gonflement de la pointe. La longueur et/ou l'indice de réfraction sont donc modifiés, ce qui entraîne une variation du signal interférométrique. La pointe présente une sensibilité constante de 90 pm/%RH, équivalent à une sensibilité relative de 104 ppm/%RH pour une plage d'humidité de 30 à 80 %. La détection est hautement reproductible et stable. En outre, l'effet de la température est négligeable, favorisant leur potentiel d’application.Ensuite, nous appliquons les pointes PETA basées sur le FPI pour déterminer la teneur en eau de solutions de glycérol et d'éthylène glycol. Le signal FPI de la pointe PETA varie de manière non linéaire lorsque la teneur en eau passe de 0 à 100% en poids. La variation du signal FPI est due à la contraction de la pointe, qui est liée à la perte d'eau à l'intérieur de la structure PETA. Lorsque la contamination par l'eau est inférieure à 10%, la pointe présente une sensibilité de 394 pm/wt.% et 226 pm/wt.% pour les solutions de glycérol et d'éthylène glycol, respectivement. Ainsi, la pointe PETA basée sur le FPI présente un grand potentiel pour la détermination de la teneur en eau de solutions aqueuses, y compris les hydrocarbures.Enfin, une pointe constituée d'un cœur PETA et d'une enveloppe de polymères à empreintes moléculaires (MIP) a été mise au point pour détecter la Dansyl-L-phénylalanine. La pointe PETA est initialement fabriquée en utilisant la polymérisation autoguidée et les MIP sont ensuite copolymérisés pour former une fine couche d'enveloppe autour de la pointe PETA. Lors de la détection sélective de la Dansyl-L-phénylalanine, l'indice de réfraction de la couche de MIP change, ce qui entraîne une modification du signal FPI de l'ensemble de la pointe PETA/MIP. Cette méthode simple offre de nouvelles possibilités pour créer des capteurs à fibre optique MIP à base de FPI applicables à une large gamme d'analytes, qu’ils soient fluorescents ou nonFabry−Perot interferometers (FPIs) have received a significant attention for their use in sensor applications. FPIs consist of an optical cavity with separate parallel reflecting surfaces which reflect incident light, resulting in an optical interferometric signal. The FPI signal depends on the distance between the reflecting surfaces and the refractive index of the cavity medium, which are sensitive to variation of environment humidity, temperature, pressure, and material. FPIs can be attached to optical fibers to form compact fiber optic FPI-based sensors in which the optical fiber works as a waveguide for both incident and reflected signal. This thesis presents FPI-based chemical sensors incorporating a polymer microtip located at the end of an optical fiber and characterizes their sensing capabilities for humidity, water, and chemical targets.Firstly, we develop a pentaerythritol triacrylate (PETA) tip on the facet of an optical fiber by a self-guiding photopolymerization. One end of the optical fiber is placed inside a PETA droplet and the self-guiding photopolymerization of PETA is actuated by a 375 nm laser injected to the other end of the fiber. The optimal conditions to form a straight and mechanically stable PETA tip are 1.0 μW of laser power × 1.0 second of exposure time. However, the PETA chains do not completely polymerize during this self-polymerization, leading to an unstable dynamic resonant frequency of the tip. Thus, the tip needs a post-polymerization under a UV 365 nm lamp to achieve a stable dynamic characteristic, which is applicable for further sensing applications.Secondly, we demonstrate the PETA tip as an effective sensor to detect humidity. The PETA tip acts as an optical cavity formed between the fiber-core/PETA and the PETA/environment interface, resulting in a clear interferometric signal. The FPI signal of the tip is highly sensitive to humidity in the air. This is due to hydroxyl groups within the PETA structure, which strongly absorb water molecules in the humid air and significantly swell the tip. The length and/or the refractive index of the tip are therefore changed, resulting in a FPI shift. The tip exhibits a consistent sensitivity of 90pm/%RH, equivalent to a relative sensitivity of 104 ppm/%RH in the humidity range from 30 to 80%. The sensing performance is highly reproducible and stable. Furthermore, the cross effect of the temperature is negligible, indicating a great practical potential for the devices.Next, we apply the FPI-based PETA tips to determine the water content in glycerol and ethylene glycol solutions. The FPI signal of the PETA tip shifts nonlinearly towards longer wavelengths as the water content increases from 0 to 100 wt.%. The shift in the FPI signal occurs due to the contraction in the tip length, which is linked to the loss of water inside the PETA structure caused by the hydrophilic solutions. When the water contamination is below 10 wt.%, the tip shows a sensitivity of 394 pm/wt.% and 226 pm/wt.% for glycerol and ethylene glycol solutions, respectively. Therefore, the FPI-based PETA tip shows a great potential in determining water content in hydrophilic aqueous solutions, including hydrocarbons.Finally, a tip consisting of a PETA core and a shell of molecularly imprinted polymers (MIPs) is developed for detecting Dansyl-L-phenylalanine. The PETA tip is initially fabricated using the self-guiding polymerization and MIPs are then copolymerized to form a thin shell layer around the PETA tip. Upon the selective binding of Dansyl-L-phenylalanine, the refractive index of the MIP layer changes, leading to the change in the FPI signal of the whole PETA/MIP tip. This straightforward and affordable method offers new innovative possibilities for creating FPI-based MIP fiber optic sensors, which can be applied for a wide range of analytes, including both non-fluorescent and fluorescent targets
2
Andrews, Jeffrey Pratt. "Longitudinal misalignment based strain sensor." Thesis, Virginia Tech, 1989. http://hdl.handle.net/10919/43283.
Анотація:
A practical fiber optic strain sensor has been developed to measure strains in the range of 0.0 to 2.0 percent strain with a resolution ranging between 10 and 100 microstrain depending on sensor design choices. This intensity based sensor measures strain by monitoring strain induced longitudinal misalignment in a novel fiber interconnection. This interconnection is created by aligning fibers within a segment of hollow core fiber. Related splice loss mechanisms are investigated for their effect on resolution. The effect of gauge length and launch conditions are also investigated.
Master of Science
3
Lee, Shiao-Chiu. "Axial offset effects upon optical fiber sensor and splice performance." Thesis, Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/91128.
Анотація:
A kind of intensity modulated fiber sensor utilizing axial offset parameter is proposed. The theoretical analysis and experimental characteristics of this sensor are described.
All the theoretical results derived in this thesis are based on assuming a uniform power distribution in the fibers. An expression of coupling efficiency of central dipped parabolic graded index fibers due to axial offset is derived. The results show less sensitivity to axial offset for the central dipped fibers than for the parabolic profile fibers without a dip. Expressions of coupling efficiency of graded index fibers due to axial offset for several different values of a are also derived. The results show that sensitivity increases as the value of a decreases. A general expression of coupling efficiency which is valid for small values of axial offset is derived. This expression exhibits a linear relationship between coupling efficiency and small axial offset.
Coupling efficiencies versus fiber end separation and axial offset of step index fibers have been measured. The measurements show that coupling efficiency is much more sensitive to axial offset than end separation. A simple construction of the axial offset fiber sensor is described. An approximate linear relationship between the output power and the mechanical loading has been obtained for this sensor. Several ways of increasing the sensitivity of this sensor are discussed.M.S.
4
Bronk, Karen Srour. "Imaging based sensor arrays /." Thesis, Connect to Dissertations & Theses @ Tufts University, 1996.
Анотація:
Thesis (Ph.D.)--Tufts University, 1996.Adviser: David R. Walt. Submitted to the Dept. of Chemistry. Includes bibliographical references. Access restricted to members of the Tufts University community. Also available via the World Wide Web;
5
Kominsky, Daniel. "Development of Random Hole Optical Fiber and Crucible Technique Optical Fibers." Diss., Virginia Tech, 2005. http://hdl.handle.net/10919/28949.
Анотація:
This dissertation reports the development of two new categories of optical fibers. These are the Random Hole Optical Fiber (RHOF) and the Crucible Technique Hybrid Fiber (CTF). The RHOF is a new class of microstructure fiber which possesses air holes which vary in diameter and location along the length of the fiber. Unlike all prior microstructure fibers, these RHOF do not have continuous air holes which extend throughout the fiber. The CTF is a method for incorporating glasses with vastly differing thermal properties into a single optical fiber. Each of these two classes of fiber brings a new set of optical characteristics into being. The RHOF exhibit many of the same guidance properties as the previously researched microstructure fibers, such as reduced mode counts in a large area core. CTF fibers show great promise for integrating core materials with extremely high levels of nonlinearity or gain. The initial goal of this work was to combine the two techniques to form a fiber with exceedingly high efficiency of nonlinear interactions.
Numerous methods have been endeavored in the attempt to achieve the fabrication of the RHOF. Some of the methods include the use of sol-gel glass, microbubbles, various silica powders, and silica powders with the incorporation of gas producing agents. Through careful balancing of the competing forces of surface tension and internal pressure it has been possible to produce an optical fiber which guides light successfully.
The optical loss of these fibers depends strongly on the geometrical arrangement of the air holes. Fibers with a higher number of smaller holes possess a markedly lower attenuation. RHOF also possess, to at least some degree the reduced mode number which has been extensively reported in the past for ordered hole fibers. Remarkably, the RHOF are also inherently pressure sensitive. When force is applied to an RHOF either isotropically, or on an axis perpendicular to the length of the fiber, a wavelength dependent loss is observed. This loss does not come with a corresponding response to temperature, rendering the RHOF highly anomalous in the area of fiber optic sensing techniques. Furthermore an ordered hole fiber was also tested to determine that this was not merely a hitherto undisclosed property of all microstructure fibers.
Crucible technique fibers have also been fabricated by constructing an extremely thick walled silica tube, which is sealed at the bottom. A piece of the glass that is desired for the core (such as Lead Indium Phosphate) is inserted into the hole which is in the center of the tube. The preform is then drawn on an fiber draw tower, resulting in a fiber with a core consisting of a material which has a coefficient of thermal expansion (CTE) or a melting temperature (Tm) which is not commonly compatible with those of silica.Ph. D.
6
Wavering, Thomas A. "Optical Path Length Multiplexing of Optical Fiber Sensors." Thesis, Virginia Tech, 1998. http://hdl.handle.net/10919/36037.
Анотація:
Optical fiber sensor multiplexing reduces cost per sensor by designing a system that minimizes the expensive system components (sources, spectrometers, etc.) needed for a set number of sensors. The market for multiplexed optical sensors is growing as fiberoptic sensors are finding application in automated factories, mines, offshore platforms, air, sea, land, and space vehicles, energy distribution systems, medical patient surveillance systems, etc. Optical path length multiplexing (OPLM) is a modification to traditional white-light interferometry techniques to multiplex extrinsic Fabry-Perot interferometers and optical path length two-mode sensors. Additionally, OPLM techniques can be used to design an optical fiber sensor to detect pressure/force/acceleration and temperature simultaneously at a single point. While power losses and operating range restrictions limit the broadscale applicability of OPLM, it provides a way to easily double or quadruple the number of sensors by modifying the demodulation algorithm. The exciting aspect of OPLM is that no additional hardware is needed to multiplex a few sensors. In this way OPLM works with conventional technology and algorithms to drastically increase their efficiency. [1]Master of Science
7
Fan, Chenjun. "Fiber optic sensor based on dual ring resonator system /." Online version of thesis, 1992. http://hdl.handle.net/1850/11070.
8
Utou, Frumence E. "Fiber optic sensors ensuring structural integrity." Thesis, Cape Peninsula University of Technology, 2005. http://hdl.handle.net/20.500.11838/1300.
Анотація:
Thesis (DTech (Mechnical Engineering))--Cape Peninsula University of Technology, 2005Among the issues that are taken into consideration for many years by Engineers and Technologists is the integrity of the servicing elements in structures and mechanisms. It is a documented phenomenon that after a certain period of time, in service, engineering components tend to change their original state, and begin to develop faults and defects. This includes the original shape distortion due to effects such as bending, twisting, and cracks. The above-sited effects may be caused by the sudden or accumulative effect of overloading, thermal shocks, corrosion etc, which eventually lead to malfunction of these engineering components. The occurrence of the cracks may be as a result of stress variation in excess of different or similar materials; thermal shocks, vibration, etc. A system of structural health monitoring using optical fiber sensors to track down a crack occurrence and its propagation is considered to be a promising method in warning of catastrophic events. Taking advantage of optical fibers' properties and behavior, such as easy interaction with other materials, small size, low weight, corrosion resistance, geometrical flexibility and an inherent immunity to electromagnetic interference, there is potential in adopting the Fiber Optic Sensors (FOS) for structural health monitoring systems. Structural integrity does not confine itself to crack detection only. For example there are many instances where unwanted or excessive displacement may occur. Optical fibers play an important role in proximity sensing as evidenced in the literature [49] to [54] and available commercial systems. However it is felt that FOS displacement sensors may suffer in measurement accuracy due to in situ conditions.
9
Haskell, Adam Benjamin. "A Durability and Utility Analysis of EFPI Fiber Optic Strain Sensors Embedded in Composite Materials for Structural Health Monitoring." Fogler Library, University of Maine, 2006. http://www.library.umaine.edu/theses/pdf/HaskellAB2006.pdf.
10
Xiao, Hai. "Self-Calibrated Interferometric/Intensity-Based Fiber Optic Pressure Sensors." Diss., Virginia Tech, 2000. http://hdl.handle.net/10919/28845.
Анотація:
To fulfill the objective of providing robust and reliable fiber optic pressure sensors capable of operating in harsh environments, this dissertation presents the detailed research work on the design, modeling, implementation, analysis, and performance evaluation of the novel fiber optic self-calibrated interferometric/intensity-based (SCIIB) pressure sensor system.
By self-referencing its two channels outputs, for the first time to our knowledge, the developed SCIIB technology can fully compensate for the fluctuation of source power and the variations of fiber losses. Based on the SCIIB principle, both multimode and single-mode fiber-based SCIIB sensor systems were designed and successfully implemented. To achieve all the potential advantages of the SCIIB technology, the novel controlled thermal bonding method was proposed, designed, and developed to fabricate high performance fiber optic Fabry-Perot sensor probes with excellent mechanical strength and temperature stability. Mathematical models of the sensor in response to the pressure and temperature are studied to provide a guideline for optimal design of the sensor probe. The solid and detailed noise analysis is also presented to provide a better understanding of the performance limitation of the SCIIB system. Based on the system noise analysis results, optimization measures are proposed to improve the system performance. Extensive experiments have also been conducted to systematically evaluate the performance of the instrumentation systems and the sensor probes. The major test results give us the confidence to believe that the development of the fiber optic SCIIB pressure sensor system provides a reliable pressure measurement tool capable of operating in high pressure, high temperature harsh environments.Ph. D.
11
Peterson, Brian James. "Wireless sensor interrogator design for passive, resonant frequency sensors using frequency modulation spectroscopy." Thesis, Montana State University, 2009. http://etd.lib.montana.edu/etd/2009/peterson/PetersonB0509.pdf.
Анотація:
The lack of passive, wireless, chemical and biological sensor systems is a significant impediment to sensor system applications. While active sensors with a wireless communications link continue to decrease in power consumption, they still require a power source, such as a battery. This active power consumption limits the useful life of the sensor and its applications. A more attractive solution would be a passive, wireless, chemical and biological sensor integrated with a wireless interrogation platform to monitor the sensor. The focus of this thesis is the realization of a wireless sensor interrogator capable of monitoring multiple, passive, resonant-frequency sensors. It is demonstrated, using Frequency Modulation Spectroscopy techniques, that the resonant frequency of a passive sensor can be detected and tracked over time. Simulated results are presented that verify the functionality of the proposed wireless sensor interrogator. In addition, an experimental hardware setup and subsequent experimental results are presented that verify the simulation results. Considerations for the design of the wireless sensor interrogator and opportunities for future research are discussed.
12
Ipson, Benjamin L. "Polarimetric Temperature Sensor Using Core-replaced Fiber." Diss., CLICK HERE for online access, 2004. http://contentdm.lib.byu.edu/ETD/image/etd606.pdf.
13
Wang, Xingwei. "Optical Fiber Tip Pressure Sensor." Thesis, Virginia Tech, 2004. http://hdl.handle.net/10919/35490.
Анотація:
Miniature pressure sensors which can endure harsh environments are a highly sought after goal in industrial, medical and research fields. Microelectromechanical systems (MEMS) are the current methods to fabricate such small sensors. However, they suffer from low sensitivity and poor mechanical properties.
To fulfill the need for robust and reliable miniature pressure sensors that can operate under high temperatures, a novel type of optical fiber tip sensor only 125μm in diameter is presented in this thesis. The essential element is a piece of hollow fiber which connects the fiber end and a diaphragm to form a Fabry-Pérot cavity. The all-fused-silica structure fabricated directly on a fiber tip has little temperature dependence and can function very well with high resolution and accuracy at temperatures up to 600ï °C. In addition to its miniature size, its advantages include superior mechanical properties, biocompatibility, immunity to electromagnetic interference, disposability and cost-effective fabrication.
The principle of operation, design analysis, fabrication implementation and performance evaluation of the sensor are discussed in detail in the following chapters.
Master of Science
14
Brady, Geoffrey Phillip. "Fibre Bragg grating sensors : interrogation and multiplexing techniques." Thesis, University of Kent, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.309781.
15
Feth, Shari. "Sapphire optical fiber sensors." Thesis, This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-12232009-020350/.
16
Silva, Muñoz Rodrigo. "Structural Health Monitoring Using Embedded Fiber Optic Strain Sensors." Fogler Library, University of Maine, 2008. http://www.library.umaine.edu/theses/pdf/SilvaMunozR2008.pdf.
17
Chen, Qiao. "ESA based fiber optical humidity sensor." Thesis, Virginia Tech, 2002. http://hdl.handle.net/10919/10134.
Анотація:
Several techniques for measuring humidity are presented. The goal of the study is to use the electrostatic self-assembled monolayer synthesis process to fabricate a Fabry-Parot Cavity based optical fiber humidity sensor. The sensing scheme bases on the refractive index change with relative humidity of the film applied to the end of optical fiber. That is, the change in reflected optical power indicates certain humidity. To achieve this, some chemicals induce on specific coating materials were applied at the end of optical fiber. In this thesis, experimental results are given to prove that the humidity sensor has high sensitive and fast response time. Furthermore, we investigate the potential for the use of human breathing monitoring and air flow rate detection. Results from preliminary tests of each are given.Master of Science
18
Miller, Mark S. "Optical fiber-based corrosion sensor systems." Diss., This resource online, 1995. http://scholar.lib.vt.edu/theses/available/etd-03042009-041455/.
19
Gaikwad, Parikshit S. "Chemically deposited optical fiber humidity sensor." Master's thesis, Mississippi State : Mississippi State University, 2003. http://library.msstate.edu/etd/show.asp?etd=etd-06092003-141607.
20
Ren, Yundong. "Specially Shaped Optical Fiber Probes: Understanding and Their Applications in Integrated Photonics, Sensing, and Microfluidics." Digital WPI, 2019. https://digitalcommons.wpi.edu/etd-dissertations/569.
Анотація:
Thanks to their capability of transmitting light with low loss, optical fibers have found a wide range of applications in illumination, imaging, and telecommunication. However, since the light guided in a regular optical fiber is well confined in the core and effectively isolated from the environment, the fiber does not allow the interactions between the light and matters around it, which are critical for many sensing and actuation applications. Specially shaped optical fibers endow the guided light in optical fibers with the capability of interacting with the environment by modifying part of the fiber into a special shape, while still preserving the regular fiber’s benefit of low-loss light delivering. However, the existing specially shaped fibers have the following limitations: 1) limited light coupling efficiency between the regular optical fiber and the specially shaped optical fiber, 2) lack special shape designs that can facilitate the light-matter interactions, 3) inadequate material selections for different applications, 4) the existing fabrication setups for the specially shaped fibers have poor accessibility, repeatability, and controllability. The overall goal of this dissertation is to further the fundamental understanding of specially shaped fibers and to develop novel specially shaped fibers for different applications. In addition, the final part of this dissertation work proposed a microfluidic platform that can potentially improve the light-matter interactions of the specially shaped fibers in fluidic environments. The contributions of this dissertation work are summarized as follows: 1) An enhanced fiber tapering system for highly repeatable adiabatic tapered fiber fabrications. An enhanced fiber tapering system based on a novel heat source and an innovative monitoring method have been developed. The novel heat source is a low-cost ceramic housed electric furnace (CHEF). The innovative monitoring method is based on the frequency-domain optical transmission signal from the fiber that is being tapered. The enhanced fiber tapering system can allow highly repeatable fabrication of adiabatically tapered fibers. 2) A lossy mode resonance (LMR) sensor enabled by SnO2 coating on a novel specially shaped fiber design has been developed. The developed LMR sensor has a D-shape fiber tip with SnO2 coating. It has the capability of relative humidity and moisture sensing. The fiber-tip form factor can allow the sensor to be used like a probe and be inserted into/removed from a tight space. 3) Specially shaped tapered fibers with novel designs have been developed for integrated photonic and microfluidic applications. Two novel specially tapered fibers, the tapered fiber loop and the tapered fiber helix have been developed. The tapered fiber loop developed in this work has two superiority that differentiated itself from previous works: a) the mechanical stability of the tapered fiber loop in this work is significantly better. b) the tapered fiber loops in this work can achieve a diameter as small as 15 ?m while still have a high intrinsic optical quality factor of 32,500. The tapered fiber helix developed in this work has a 3D structure that allows it to efficiently deliver light to locations out of the plane defined by its two regular fiber arms. Applications of the tapered fiber helices in both integrated photonic device characterizations and microparticle manipulations have been demonstrated. 4) Developed an acrylic-tape hybrid microfluidic platform that can allow function reconfiguration and optical fiber integration. A low-cost, versatile microfluidic platform based on reconfigurable acrylic-tape hybrid microfluidic devices has been developed. To the best of the author’s knowledge, this is the first time that the fabrication method of sealing the acrylic channel with a reconfigurable functional tape has been demonstrated. The tape-sealing method is compatible with specially shaped fiber integrations.
21
Vošček, Jakub. "Optické vlákno jako distribuovaný teplotní senzor." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2020. http://www.nusl.cz/ntk/nusl-433164.
Анотація:
The financial requirements between fiber optic sensors and conventional sensors are gradually declining, which, despite many advatages and wide range of applicationas, has slowed down the demand for these sensors. With the demand for fiber optic sensors also grow the requirements for the parameters of these sensors. This thesis deals with distributed temperature fiber optic sensors. Non--linear phenomen in optical fibers, such as Raman scattering is used for measuring with these sensors. This scatterin was used to obtain information about temperature, which effected the optical cable under the test.
22
Holmberg, Patrik. "Laser processing of Silica based glass." Doctoral thesis, KTH, Laserfysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-173929.
Анотація:
The main topic of this thesis work is photosensitivity and photo-structuring of optical fibers and bulk glass. Although research in the field of photosensitivity in glass and optical fibers has been ongoing for more than three decades, the underlying mechanisms are still not well understood. The objective was to gain a better understanding of the photo-response by studying photosensitivity from a thermodynamic perspective, as opposed to established research focusing on point defects and structural changes, and strain and stress in optical fibers. Optical fibers was mainly used for experimental studies for two reasons; first, photosensitivity in fibers is more pronounced and more elusive compared to its bulk counterpart, and secondly, fibers provide a simplified structure to study as they experimentally can be seen as one-dimensional.Initially, ablation experiments on bulk glass were performed using picosecond infrared pulses. With a design cross section of 40x40 μm, straight channels were fabricated on the top (facing incident light) and bottom side of the sample and the resulting geometries were analyzed. The results show a higher sensitivity to experimental parameters for bottom side ablation which was ascribed to material incubation effects. Moreover, on the top side, the resulting geometry has a V-shape, independent of experimental parameters, related to the numerical aperture of the focusing lens, which was ascribed to shadowing effects.After this work, the focus shifted towards optical fibers, UV-induced fiber Bragg gratings (FBGs) and thermal processing with conventional oven and with a CO2 laser as a source of radiant heat.First, a system for CO2 laser heating of optical fibers was constructed. For measuring the temperature of the processed fibers, a special type of FBG with high temperature stability, referred to as "Chemical Composition Grating" (CCG) was used. A thorough characterization and temperature calibration was performed and the results show the temperature dynamics with a temporal resolution of less than one millisecond. The temperature profile of the fiber and the laser beam intensity profile could be measured with a spatial resolution limited by the grating length and diameter of the fiber. Temperatures as high as ~ 1750 °C could be measured with corresponding heating and cooling rates of 10.500 K/s and 6.500 K/s.Subsequently, a thorough investigation of annealing and thermal regeneration of FBGs in standard telecommunication fibers was performed. The results show that thermal grating regeneration involves several mechanisms. For strong regeneration, an optimum annealing temperature near 900 C was found. Two different activation energies could be extracted from an Arrhenius of index modulation and Braggv iwavelength, having a crossing point also around 900 °C, indication a balance of two opposing mechanisms.Finally, the thermal dynamics and spectral evolution during formation of long period fiber gratings (LPGs) were investigated. The gratings were fabricated using the CO2 laser system by periodically grooving the fibers by thermal ablation. Transmission losses were reduced by carefully selecting the proper processing conditions. These parameters were identified by mapping groove depth and transmission loss to laser intensity and exposure time.Huvudtemana i denna avhandling är fotokänslighet och fotostrukturering av optiska fibrer och bulk glas. Trots att forskning inom fotokänslighet i glas och optiska fibrer har pågått under mer än tre decennier är de bakomliggande mekanismerna ännu inte klarlagda. Syftet var att få en bättre förståelse för fotoresponsen genom att studera fotokäsligheten ur ett termodynamiskt perspektiv, i motsats till etablerad forskning med fokus på punktdefekter och strukturförändringar, samt mekaniska spännings effekter i optiska fibrer. Optiska fibrer användes för flertalet av de experimentella studierna av två skäl; för det första är fotokänsligheten i fibrer större och dessutom vet man mindre om bakomliggande mekanismer jämfört med motsvarande bulk glas, och för det andra kan fibrer vara enklare att studera eftersom de experimentellt kan ses som en endimensionell struktur.Inledningsvis utfördes ablaherings experiment på bulk glas med en infraröd laser med pikosekund pulser. Raka kanaler med ett designtvärsnitt på 40x40 μm tillverkades på ovansidan (mot infallande ljus) och bottensidan av provet och de resulterande geometrierna analyserades. Resultaten visar en högre känslighet för variationer i experimentella parametrar vid ablahering på undersidan vilket kan förklaras av inkubations effekter i materialet. Dessutom är den resulterande geometrin på ovansidan V-formad, oavsett experimentella parametrar, vilket kunde relateras till den numeriska aperturen hos den fokuserande linsen, vilket förklaras av skuggningseffekter.Efter detta arbete flyttades fokus mot optiska fibrer, UV inducerade fiber Bragg gitter (FBG), och termisk bearbetning med konventionell ugn samt även med en CO2-laser som källa för strålningsvärme.Först konstruerades ett system för CO2-laservärmning av fibrer. För mätning av temperaturen hos bearbetade fibrer användes en speciell sorts FBG med hög temperaturstabilitet, kallade ”Chemical Composition Gratings” (CCG). En grundlig karaktärisering och temperaturkalibrering utfördes och temperaturdynamiken mättes med en tidsupplösning på under en millisekund. Temperaturprofilen i fibern, och laserns strålprofil, kunde mätas med en spatiell upplösning begränsad av gitterlängden och fiberns diameter. Temperaturer upp till ~1750 °C, vilket är högre än mjukpunktstemperaturen, kunde mätas med korresponderande uppvärmnings- och avsvalningshastighet på 10.500 K/s och 6.500 K/s.Därefter gjordes en omfattande undersökning av värmebearbetning och termisk regenerering av FBG:er i telekomfiber. Resultaten visar att termisk gitter-regenerering aktiveras av flera olika mekanismer. Värmebearbetning vid en temperatur omkring 900 °C resulterade i starka gitter efter en regenerering vid en temperatur på 1100 °C. Två olika aktiveringsenergier kunde extraheras från en Arrhenius plot avseende brytningsindexmodulation och Braggvåglängd, med en skärningspunkt tillika runt 900 °C, vilket indikerar en avvägning mellan två motverkande mekanismer vid denna temperatur.Slutligen undersöktes temperaturdynamiken och de spektrala egenskaperna under tillverkning av långperiodiga fibergitter (LPG). Gittren tillverkades med CO2-vi iilasersystemet genom att skapa en periodisk urgröpning medelst termisk ablahering. Transmissionsförluster kunde reduceras med noggrant valda processparametrar. Dessa parametrar identifierades genom mätningar av ablaherat djup och transmissionsförlust som funktion av laserintensitet och exponeringstid.
QC 20150924
23
Beadle, Brad Michael. "Fiber optic sensor for ultrasound." Diss., Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/17869.
24
Beadle, Brad Michael. "Fiber optic sensor for ultrasound." Thesis, Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/19173.
25
Shih, Jessica Chu-Huei. "Concentric-core optical fiber sensors." Thesis, Virginia Polytechnic Institute and State University, 1986. http://hdl.handle.net/10919/91069.
Анотація:
This thesis describes the implementation of a mechanical strain sensor which uses concentric core optical fiber waveguide as the sensing element. When this particular type of fiber is strained, a transfer of optical power occurs between propagating modes in the two concentric cylindrical cores of the fiber. This strain-induced redistribution of optical power may be detected at the output end of the fiber using either two separated optical detectors or a two dimensional detector array. The calibrated strain sensitivity of the sensor is reported and suggestions for continuing research are discussed.M.S.
26
Barnes, Adam. "Sapphire fiber in optical sensors." Thesis, This resource online, 1995. http://scholar.lib.vt.edu/theses/available/etd-09052009-041053/.
27
CASALICCHIO, MARIA LUISA. "Innovative Plastic Optical Fiber Sensors." Doctoral thesis, Politecnico di Torino, 2012. http://hdl.handle.net/11583/2497120.
Анотація:
This thesis describes the development of new types of fiber optic sensors for the measurement of
mechanical quantities such as displacement, vibration and acceleration.
Also, it describes the realization of specific acquisition systems designed to interrogate the developed
sensors.
Since optical fibers have been historically associated with high speed telecommunication links
because of their very large bandwidth and low attenuation, there is a great interest for their employment
in sensor applications.
Fiber sensors represent a promising solution in many fields since fibers can be used for the measurement
of several quantities, not only mechanical as those investigated in this work, but also
chemical with the possibility to detect specific chemical or bio-chemical molecules.
Among the physical quantities to be detected, the displacement measurement is required in some
applications, especially in structural civil and mechanical fields, where it is possible to evaluate
the cracks evolution, providing information about the safety of the structure under monitoring in
order to detect eventually risky situations.
All the developed sensors are able to measure the displacement along one or two axis, that can
be employed also during vibration tests especially at high frequencies, and also acceleration sensors
to monitor acceleration at low frequencies.
The developed sensors are based on plastic optical fibers instead of the traditional glass fibers,
which are traditionally employed in optical communications.
This change is related to the aim of realizing sensors maintaining the excellent typical characteristics
of the fibers, such as electromagnetic immunity, intrinsically fire safety and flexibility of
applications, but with costs comparable to those of commercial electromechanical sensors.
Indeed, nowadays, the commercial fiber optic sensors are based on glass fibers because they have
very good performance.
However, they find limited applications due to the high costs of their complex interrogation systems
and also for the procedure required to splice the fibers.
On the other hand, plastic optical fibers represent a promising alternative because of their geometrical
and optical properties that allow employing low-cost non coherent sources such as LED
and also simplifying the procedure for the sensor connection and installation.
Therefore, the design of the proposed plastic optical fiber displacement sensors is described
with the sensor practical arrangement and the realized prototypes. An acquisition system has
been designed and realized to characterize the sensors and the characterization results are also
provided. Moreover, the development and the characterization of a plastic optical fiber sensor able
to measure the displacement in two directions have been described.
The main drawback of the developed sensors are stability issues and for this reason laboratory
and in situ-tests have been carried out in order to verify the sensor performance over the time.
I
The results obtained with the stability tests have highlighted the necessity to develop displacement
sensors with increased stability. To this aim, a compensation technique based on two different
wavelengths has been developed.
The same working principle of the developed displacement sensor has been exploited to realize
a fiber vibrometer to be employed during the vibration monitoring for measuring without contact
the vibrations of the device under test.
The sensor development, a suitable calibration procedure developed to overcome the problem of
real targets with a non uniform reflectivity, and the experimental tests have been described.
Furthermore, the preliminary results concerning the feasibility study of a plastic optical fiber
accelerometer are reported.
28
Biazon, Filho Alcino José. "Nova técnica de malha fechada para estabilização do ponto de operação de interrogadores de sensores com grade de bragg em fibras ópticas." [s.n.], 2012. http://repositorio.unicamp.br/jspui/handle/REPOSIP/260881.
Анотація:
Orientador: José Antonio Siqueira DiasTese (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
29
Shreeve, Bryson J. "Magnetic Field Sensing with Slab Coupled Optical Fiber Sensors." BYU ScholarsArchive, 2011. https://scholarsarchive.byu.edu/etd/2774.
Анотація:
This thesis reports an in-fiber magnetic field sensor that is able to detect magnetic fields as low as 2 A/m at a spatial resolution of 1 mm. The small sensor consists of a magneto-optic slab waveguide, bismuth-doped rare earth iron garnet (Bi-RIG) that is coupled to an optical fiber. By coupling light from the fiber to the slab waveguide, it becomes an in-fiber magnetic field sensor. This is due to the Magneto-Optic Kerr effect; a change in refractive index is proportional to the applied magnetic field. When an AC field is applied, an AC component in the output power can be detected by a spectrum analyzer. The novelties of Magneto-Optic Slab Coupled Optical Sensor (MO-SCOS) devices include their small compact nature and a dielectric structure allowing low electromagnetic interference. Due to their compact size they are capable of placement within devices to measure interior electromagnetic fields immeasurable by other sensors that are either too large for internal placement or disruptive of the internal fields due to metallic structure. This work also reports progress on EO SCOS development. The EO sensor has found application in new environments including the electromagnetic rail gun, and a dual-axis sensor.
30
Kahn, Mohammed Tariq Ekeramodien. "Development of a non-monochromatic lightwave sensor for applications in smart structures research." Thesis, Peninsula Technikon, 1998. http://hdl.handle.net/20.500.11838/888.
Анотація:
Thesis (MTech (Electrical Engineering))--Peninsula Technikon, Cape Town, 1998The purpose of this study was to perform an investigation into advances in the field of opto-electronics and to develop a suitable lightwave sensor, for application in smart structures research. Included in the scope of this research was the theoretical development and analysis of an appropriate technology to lead to an implementation of such sensors. This project forms part of an overall plan to gain experience in optoelectronic (photonic) sensor design. In research done previously in smart structure monitoring, piezo-electric techniques with the usual electrical interconnections was used. In a highly distributed sensor system the problems of electromagnetic interference, the tribo-electric effect and noise could be problematic. In this research, opto electronic techniques were thoroughly researched and an improvement on laser based fibre-optic interferometers was made. A non monochromatic lightwave interferometer was developed from theory and a prototype tested. The results suggests that an interferometric sensor can be operated with a non monochromatic source by using a second interferometer to modulate the frequency spectrum of the light before it is detected by a photodetector. Various test and measurement circuits for improved photodetector performance were evaluated, as well as a study of signal processing techniques that would be of use for an upgrade of the project where specific feature detection and analysis using the sensor is envisaged. A specification for a computer based data acquisition system was developed to do initial tests. The project should continue, with the sensor head being improved and all the necessary signal processing routines programmed into a Labview based data acquisition system.
31
Burford, Mary Kathleen. "Material process monitoring with optical fiber sensors." Thesis, Virginia Tech, 1996. http://hdl.handle.net/10919/45077.
Анотація:
Our motivation for this work is based on the need to rnom tor the cure and inservice
health of composite materials. We describe the continuation of an effort to design a multi-functional fiber optic sensor which can be embedded in polymeric composite laminates for monitoring the degree of cure during its fabrication, as well as internal composite strains occurring post-cure.3 In short, this dual-purpose sensor combines the characteristics of a Fresnel reflectometer with those of the extrinsic Fabry-Perot interferometer. For monitoring cure, a broadband source is used so the output intensity of the sensor is amplitude-modulated as the refractive index of the conlposite is increased during the polymerization process. Post-cure, a coherent light source is implernented so a. sinusoidal variation of the output signal occurs when strains within the
composite cause the sensor output to be phase-modulated. We demonstrate the
measurement of refractive index with the Fresnel reflectometer/EFPL and test it as an embedded refractive index monitor. Our experimental results demonstrate that the refractive index of 5-nlinute epoxy increases by approximately 2 % during the cure process. In addition, the sensor can be used as an interferometer to measure intenlal composite strains, where the phase difference between consecutive fringe peaks is one-half the wavelength of the source.Master of Science
32
Noren, Jonathan Robert. "Electric Field Sensing in a Railgun Using Slab Coupled Optical Fiber Sensors." BYU ScholarsArchive, 2012. https://scholarsarchive.byu.edu/etd/3482.
Анотація:
This thesis discusses the application of Slab Coupled Optical Fiber Sensors (SCOS) in a railgun. The specific goal of these sensors is to create an electric field profile at a specific point in the gun as the armature passes. The thesis explores the theory that powers the railgun as well as the principles of the SCOS sensors. It also elaborates on the various noise sources found throughout the detection system and concludes with a summary of the various field tests that were performed throughout this project. There are many benefits to using a railgun over traditional weapons in the field. These benefits not only include both safety and cost, but also greater overall defense capabilities. Unfortunately, the velocity skin effect (VSE) causes the current railgun designs to have limited life span through wear on the rails. In order to develop superior railguns and railgun armatures, the accurate detection of the VSE through measuring the electric field is of great interest. We used a SCOS, a small directionally precise dielectric sensor, as a small sensing area is required to be able to measure the electric fields inside of the rail gun. The actual usage of the SCOS within the railgun produced an additional set of problems that are not commonly encountered in the lab. The chief amongst these was noise from strain, RF pickup, and phase noise. This thesis also reports various methods used to reduce each of these noise sources.
33
Allsop, Thomas David Paul. "A fibre optical strain sensor." Thesis, University of Plymouth, 1999. http://hdl.handle.net/10026.1/2779.
Анотація:
Strain-sensing elements, fabricated in standard communications-grade single mode optical fibre, are increasingly being considered for application in structural health monitoring. The reason for this is the numerous advantages demonstrated by these devices compared with traditional indicators. This thesis describes work carried out on optical sensors at the University of Plymouth. The aim of this work was to achieve an optical fibre strain sensing system capable of measuring absolute strain with good resolution and having wide dynamic range, without bulky optical equipment and not susceptible to misalignment due to handling. Earlier work was devoted to study on an intrinsic Fabry-Perot interferometric sensor and an optical phase-shift detection technique. The sensing element investigated relied on the end face of an optical fibre as one mirror and the second mirror being a layer of Titanium Dioxide (TO2). Although some results are included, it was soon realised that this sensor had a number of problems, particularly with fabrication. As no simple solution presented itself, consideration was given to a sensor that made use of the change in reflectance of an intra-core fibre Bragg grating when the grating was subjected to strain. The bulk of work described in this thesis is concerned with this type of sensing element. The grating structure is inherently flexible and a number of structural formats were studied and investigated. The first and simplest grating considered was two linearly chirped Bragg gratings used in a Fabry-Perot configuration (a grating resonator). The sensor was tested using the sensing detection system and although the fabrication problems were overcome absolute strain measurement was unattainable. To achieve this end, a theoretical study of a number of grating structures was carried out using the T-matrix Formalism. Confidence in using this approach was gained by comparing the spectral behaviour of a proposed grating with results, which were given by another theoretical model for the same proposed grating. The outcome of this study was that two structures in particular showed promise with regard to absolutism (the measure of true strain) and linearity. Discussions held with the department of Applied Physics at Aston University about fabrication resulted in one of the proposed designs being abandoned due to difficulties of fabrication. The second structure showed more promise and fabrication attempts were put in hand. This grating is linearly-chirped with a Top-hat function and a sinusoidal perturbation as a taper function of the refractive index modulation. Experiments were performed, data were acquired and system performance for this sensor is presented. The thesis concludes that using such a fibre Bragg grating as the sensing element of a strain sensing system enables it to measure absolute strain without using bulky optical equipment. At present, the resolution of strain is limited by the quality of the grating being fabricated (anomalies on profile), this should improve once the fabrication technique is refined.
34
Ludden, Brendan Patrick. "A distributed optical fibre sensor." Thesis, University of Cambridge, 1997. https://www.repository.cam.ac.uk/handle/1810/272327.
35
Gibson, Richard S. "Slab-Coupled Optical Fiber Sensors for Electric Field Sensing Applications." Diss., CLICK HERE for online access, 2009. http://contentdm.lib.byu.edu/ETD/image/etd3248.pdf.
36
Kinney, Stuart. "The development of an optical position sensor." Virtual Press, 1998. http://liblink.bsu.edu/uhtbin/catkey/1115421.
Анотація:
A theoretical study of an electrically passive, loss-compensated, optical position sensor is the goal of this project. Optical fiber sensors exploit light as the information carrier. Fiber-optic sensors consist of a constant light source launched into an optical fiber and transmitted to another point at which a measurement is made.In the proposed optical position sensor, a Light Emitting Diode (LED) produces a constant beam of light, which is channeled through an optical fiber to a Graded Index (GRIN) lens. This lens makes all the light rays parallel to one another, a process called collimation. The light then enters a polarizer which is a lens that further orders the light rays in a process called polarization.Then the light enters a chamber in which a doubly refracting (birefringent) crystal is situated. The crystal is a wedge, and thus has a varying thickness throughout its length. The light beam strikes the crystal, sending a spectrum, or spectral signature, that is distinct to the particular thickness of the crystal. That signature goes directly from the chamber housing the crystal into a lens called an analyzer which orders the light again through polarization. Then the light goes into another GRIN lens, and this GRIN lens focuses the light onto an optical fiber, which transmits the particular spectral signature of this light to an optical spectrum analyzer (OSA). The OSA uses a Photodiode Array to accept the incoming light, a device that takes in light and redistributes it to a monitor for display by the user. Such a device is called a detector. The thickness of the crystal that the light travels through is determined by the crystal's position.If the crystal rests on a platform which is connected to an object whose position must always be monitored, then the crystal will move as the object moves. The different spectral signatures shown on a monitor reveal different thicknesses of the crystal, which reveal different positions of the monitored object. The object whose position is measured is the measurand.The selected crystal is quartz. It has a 12.5-mm length, a width of 10.8-mm at its thinnest end, and a taper angle to the thickest end of only 0.008 degrees, which corresponds to a 0.17-micron difference between the two. This angle is called the polishing angle of the quartz. The quartz itself is called the active cell. The Photodiode Array Detector receives the spectral signature from the optical fiber, and that signature is projected on an OSA, which is software built-in to the computer. A mathematical program is used to evaluate the signature, and the position of the measurand is thereby revealed. How accurate the measurement is can be revealed by use of a control device. If the quartz crystal is moved by a measuring device, such as a micrometer, the distance that the crystal moved may be measured by the micrometer, as well as by the OSA. By comparing the two, the accuracy of the spectrograph, and the position it reveals, can be known.Department of Physics and Astronomy
37
Murphy, Kent A. "Novel phase-modulated optical fiber sensors." Diss., Virginia Tech, 1992. http://hdl.handle.net/10919/39712.
38
Park, William Heuywon. "Fluorescence lifetime sensor using optical fiber and optical signal processing." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0009/MQ34107.pdf.
39
DeWolf, Scott. "Optical and mechanical behavior of the optical fiber infrasound sensor." Diss., [La Jolla] : University of California, San Diego, 2009. http://wwwlib.umi.com/cr/ucsd/fullcit?p1469578.
Анотація:
Thesis (M.S.)--University of California, San Diego, 2009.Title from first page of PDF file (viewed October 22, 2009). Available via ProQuest Digital Dissertations. Includes bibliographical references (p. 46-48).
40
Garcia, Mina Diego Felipe. "Bi-tapered Fiber Sensor Using a Supercontinuum Light Source for a Broad Spectral Range." University of Dayton / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1492001857501804.
41
Cameron, Alexander John. "A Bayesian approach to optimal sensor placement." Thesis, University of Oxford, 1989. http://ora.ox.ac.uk/objects/uuid:ad201132-d418-4ee4-a9d5-3d79bd4876a7.
Анотація:
By "intelligently" locating a sensor with respect to its environment it is possible to minimize the number of sensing operations required to perform many tasks. This is particularly important for sensing media which provide only "sparse" data, such as tactile sensors and sonar. In this thesis, a system is described which uses the principles of statistical decision theory to determine the optimal sensing locations to perform recognition and localization operations. The system uses a Bayesian approach to utilize any prior object information (including object models or previously-acquired sensory data) in choosing the sensing locations.
42
Chadderdon, Spencer L. "Application Improvements of Slab-Coupled Optical Fiber Sensors." BYU ScholarsArchive, 2014. https://scholarsarchive.byu.edu/etd/3976.
Анотація:
This dissertation explores techniques for improving slab-coupled optical fiber sensor (SCOS) technology for use in specific applications and sensing configurations. SCOS are advantageous for their small size and all-dielectric composition which permit non-intrusive measurement of electric fields within compact environments; however, their small size also limits their sensitivity. This work performs a thorough analysis of the factors contributing to the performance of SCOS and demonstrates methods which improve SCOS, while maintaining its small dimensions and high level of directional sensitivity. These improvements include increasing the sensitivity by 9x, improving the frequency response to include sub 300 kHz frequencies, and developing a method to tune the resonances. The analysis shows that the best material for the slab waveguide is an electro-optic polymer because of its low RF permittivity combined with high electro-optic coefficient. Additional improvements are based on changing the crystal orientation to a transverse configuration, which enhances the sensitivity due to a combined increase in the effective electro-optic coefficient and electric field penetration into the slab. The transverse SCOS configuration not only improves the overall sensitivity but increases the directional sensitivity of the SCOS. Lithium niobate and electro-optic polymer are both experimentally shown to exhibit minimal frequency dependent sensitivity making them suitable for broad frequency applications. Simultaneous interrogation of multiple SCOS with a single tunable laser is achieved by tuning the resonant wavelengths of KTP SCOS so their resonances overlap.
43
Kahn, Mohammed Tariq Ekeramodien. "Miniaturised dedicated application opto-electronic sensors in the evolution of smart systems." Thesis, Peninsula Technikon, 2002. http://hdl.handle.net/20.500.11838/1196.
Анотація:
Thesis (DTech (Electrical Engineering))--Peninsula Technikon, Cape Town, 2002In the last decade, the South Amcan Electricity Supply Commission would have had their ability to serve an ever demanding public severely tested. With the dilemma of providing electricity supply through hazardous environmental conditions, and with prospects of supplying power even beyond South Afiican borders, the need for a comprehensive damage and power delivery assessment strategy becomes all the more relevant. The rapid growth being made in the evolution of so called "intelligent" structures, with inherent sensor, actuator and control mechanisms built in can have direct influence on a power distribution network. At least in the foreseeable future, the impact ofphotonic sensors with inherent miniaturization, a foremost candidate in Smart System technology, can play a vital role in damage assessment of a potentially large network such as that found in the supply ofelectricity. Smart systems are nonliving systems that integrate the functions of sensing, actuation, logic and control, to respond adaptively to changes in their condition or environment to which they are exposed, in a useful and usually repetitive manner. Sensors are a fundamental part of the evolution of such systems and form the basis for the topic of this dissertation. The use ofoptical fiber sensors is increasing widely mainly due to their (a) miniature size, (b) remote signal processing ability, and (c) multiplexing capabilities. Because of the above features a variety of optical fiber sensing techniques has evolved over the years having potential for a myriad of applications. In this work a systems model and equations was developed for modeling the propagation of light in a optical waveguide, in order to study a Fabry Perrot sensor topology for application as a miniaturised sensor in a new type of smart structure, namely a smart electrical power system.
44
Harold, Douglas A. "An Evaluation of Optical Fiber Strain Sensing for Engineering Applications." Thesis, Virginia Tech, 2012. http://hdl.handle.net/10919/41239.
Анотація:
A fatigue test has been performed on 7075-T651 aluminum specimens which were bonded with polyimide coated optical fibers with discrete Bragg gratings. These fibers were bonded with AE-10 strain gage adhesive. The results indicate that lower strain amplitudes do not produce cause for concern, but that larger strain amplitudes (on the order of 3500 μ) may cause some sensors to become unreliable.
The strain response of acrylate coated optical fiber strain sensors bonded to aluminum specimens with AE-10 and M-Bond 200 strain gage adhesives was investigated with both axial and cantilever beam tests. These results were compared to both the strain response of conventional strain gages and to model predictions. The results indicate that only about 82.6% of the strain in the specimen was transferred through the glue line and fiber coating into the fiber. Thus, multiplying by a strain transfer factor of approximately 1.21 was sufficient to correct the optical fiber strain output. This effect was found to be independent of the adhesive used and independent of the three-dimensional profile of the glue line used to attach the fiber. Finally, this effect did not depend on whether the fiber had a polyimide or an acrylate coating.
Further investigation was conducted on the feasibility of using optical fiber strain sensors for monitoring subcritical damage (such as matrix cracks) in fiber reinforced composite materials. These results indicate that an array of optical fibers which monitor the strain profile on both sides of a composite panel may be sufficient for these purposesMaster of Science
45
Maier, Eric William. "Buried fiber optic intrusion sensor." Thesis, Texas A&M University, 2004. http://hdl.handle.net/1969.1/425.
Анотація:
A distributed fiber optic intrusion sensor capable of detecting intruders from the pressure of their weight on the earth's surface was investigated in the laboratory and in field tests. The presence of an intruder above or in proximity to the buried sensor induces a phase shift in light propagating along the fiber which allows for the detection and localization of intrusions. Through the use of an ultra-stable erbium-doped fiber laser and phase sensitive optical time domain reflectometry, disturbances were monitored in long (several km) lengths of optical fiber. Narrow linewidth and low frequency drift in the laser were achieved through a combination of optical feedback and insulation of the laser cavity against environmental effects. The frequency drift of the laser, characterized using an all-fiber Mach Zehnder interferometer, was found to be less than 1 MHz/min, as required for operation of the intrusion detection system. Intrusions were simulated in a laboratory setting using a piezoelectric transducer to produce a controllable optical phase shift at the 2 km point of a 12 km path length. Interrogation of the distributed sensor was accomplished by repetitively gating light pulses from the stable laser into the sensing fiber. By monitoring the Rayleigh backscattered light with a photodetector and comparing traces with and without an induced phase shift, the phase disturbances were detected and located. Once the feasibility of such a sensor was proven in the laboratory, the experimental set up was transferred to Texas A&M's Riverside Campus. At the test site, approximately 40 meters of fiber optic cable were buried in a triangle perimeter and then spliced into the 12 km path length which was housed inside the test facility. Field tests were conducted producing results comparable to those found in the laboratory. Intrusions over this buried fiber were detectable on the φ-OTDR trace and could be localized to the intrusion point. This type of sensor has the potential benefits of heightened sensitivity, covertness, and greatly reduced cost over the conventional seismic, acoustic, infrared, magnetic, and fiber optic sensors for monitoring long (multi-km) perimeters.
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Alfeeli, Bassam. "Ionizing Radiation Resistance of Random Hole Optical Fiber for Nuclear Instrumentation and Control Applications." Thesis, Virginia Tech, 2009. http://hdl.handle.net/10919/32661.
Анотація:
Random hole optical fibers (RHOF) offer advantages over other types of microstructured optical fibers (MOFs). They are inexpensive and easy-to-make when compared to the high cost of ordered hole MOFs. They also have unique characteristics since they contain open and closed holes. The open holes contain ambient air under normal conditions and the closed holes contain residual gases from the fabrication process at certain pressure. The objective of this research work was to investigate the radiation resistance of Random Hole Optical Fibers (RHOF) for possible use as both sensing element and data transmission medium in nuclear reactor instrumentation and control applications.
This work is motivated by the demand for efficient, cost effective, and safe operation of nuclear power plants, which accounts for more than 14% of the worldâ s electricity production.
This work has studied the effect of gamma irradiation on RHOF fibers by comparing their performance to that of standard solid telecommunication fibers and commercially available specialty solid fiber designed to be radiations hardened fiber. The fibers were evaluated at different absorbed dose levels: 12 mGy(Si), 350 mGy(Si), and 7200 Gy(Si) by measuring their radiation induced absorption (RIA) on-line. In the low dose test, the maximum RIA measured in untreated RHOF was approximately 8 dB while the RIA in the untreated MMF fibers reached a maximum at about 28 dB. In the high dose test, the maximum RIA measured in untreated RHOF was 36 dB while RIA in the methanol washed RHOF was only 9 dB. RHOF also demonstrated superior radiation damage recovery time over all of the other fibers tested. Based on the experimental evaluations, it was deduced that RHOFs used in this work are resistant to gamma radiation. and recover from radiation damage at a faster rate compared to other fibers tested. The radiation induced absorption (RIA) at the 1550 nm window in the RHOF fibers could be attributed to the OH absorption band tail. However, the existence of other mechanisms responsible for RIA is also postulated. Some of these mechanisms include bulk and surface defects which are related to the fabrication process and the influence of the gases confined within the RHOF microstructure.
Gamma radiation resistance of RHOFs can be attributed to the lack of dopants and also possibly the inherent OH and nitrogen content. The behavior of thermally annealed RHOF and their fast recovery is in favor of this hypothesis.Master of Science
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Luanje, Appolinaire Tifang. "INTEGRATED OPTICAL FIBER RAMAN SENSOR FOR CRYOGENIC APPLICATION." MSSTATE, 2008. http://sun.library.msstate.edu/ETD-db/theses/available/etd-04042008-155057/.
Анотація:
An integrated fiber optical Raman sensor was designed for real-time, non intrusive detection of liquid and gaseous mixtures at high pressure and high flow rates. The integrated sensor employs a high-power solid-state pumped Nd:YAG frequency doubled (532nm) laser (3W), a modified In Photonics Raman probe which has built-in Raman signal filter optics, and two high-resolution spectrometers and photomultiplier tubes (PMT) with selected bandpass filters to collect both N2 and O2 Raman signals. The detection unit was also integrated with Lab View software interfaced PMT modules for fast data acquisition.
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Wang, Yongxin. "High Speed Fiber Optic Spectrometer." Diss., Virginia Tech, 2007. http://hdl.handle.net/10919/30126.
Анотація:
This dissertation presents the structure, operational principle and mathematical model of a novel high speed fiber optic spectrometer (HSFOS). In addition, the performance analysis is conducted and preliminary experimental results are listed and discussed. Such a spectrometer is highly desired by the ever-increasing applications of fiber optic sensors.
In the recent decades, a variety of fiber optic sensors have been proposed, built and tested. Compared to their electronic counterparts, fiber optic sensors although still under development, are preferred more by certain industrial and medical applications which benefit from their unique properties such as immunity to electromagnetic interference, ability to withstand harsh environments and composition of purely dielectric materials. In recent years, new fiber optic sensors have been designed for applications where high response frequency up to a few hundred KHz is required while advantages of high accuracy and large dynamic range must be maintained. The bottle neck then emerged in the signal demodulation part of the sensor system. The quadrature phase detection could achieve high demodulation speed but with small dynamic range, medium accuracy and measurement ambiguity. The white light interferometry could provide a solution for high accuracy and large dynamic range measurement without ambiguity because of its absolute measurement nature. However the signal demodulation speed is limited due to the low spectrum acquisition rate of the existing spectrometers.
The new HSFOS utilizes time domain dispersion of the sampled incoming light by dispersive fiber rather than the spatial dispersion employed by traditional spectrometers. In addition the signal that represents the spectrum of the light is naturally a serial signal which can be detected by a single detector and recorded by a high speed data acquisition device. Theoretical study of the operation principle is made and a mathematical model for the spectrometer is developed based on Marcuse's previous work. One major difference of the new derivation is that the propagation constant is expanded about the center circular frequency of each monochromatic light pulse instead of the center frequency of the chromatic light pulse which makes the physical picture of the chromatic light pulse evolution in a dispersive fiber clearer and facilitates both the analytical and numerical analysis. The profile of the dispersed chromatic light pulse could be treated as the superposition of all the dispersed monochromatic light pulses. Another major difference is the Taylor's series of the propagation constant is not truncated as it is in those previous work, which improves the accuracy of the model. Moreover, an approximate model is made which could further reduce the computation tasks in numerical simulations. Performance analysis for accuracy, resolution, speed and noise are conducted through numerical simulations based on the model and the experimental results. The sources of two different errors and their effects on accuracy are discussed respectively. The effects on spectral resolution by the properties of the modulation pulse and the fiber dispersion are studied. The results indicate that by using a rectangle modulation pulse under certain conditions, the resolution can be improved. The speed analysis gives that the spectrum acquisition rate can reach 1 million frames per second when the spectral width is less than 100 nm. In the noise analysis, the erbium-doped fiber amplifier (EDFA) is determined to be the dominant noise source. But by using two EDFAs, the overall signal to noise ratio is improved by 9.2 dB. The preliminary experimental results for FP sensor and FBG sensor signal demodulation are presented. The HSFOS for FP sensor signal demodulation achieves 15 nm resolution. By using the oversampling method, the HSFOS for FBG sensor signal demodulation achieves 0.05 nm spectral positioning resolution.Ph. D.
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Juarez, Juan C. "Distributed fiber optic intrusion sensor system for monitoring long perimeters." Thesis, [College Station, Tex. : Texas A&M University, 2005. http://hdl.handle.net/1969.1/ETD-TAMU-1702.
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MacLean, Alistair. "A distributed fibre optic water sensor." Thesis, University of Strathclyde, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.248853.