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

Interferometric fiber optic sensors have been extensively used to measure a large variety of physical, chemical and biomedical parameters due to their superior performance. At the Center for Photonics Technology of Virginia Tech, a variety of interferometric fiber optic sensors have been developed in recent years, for efficient oil recovery, partial discharge detection in high voltage transformers, pressure sensing in gas turbine engines, and temperature measurements in gasifiers and boilers. However, interrogating an interferometric sensor involves accurate recovery of a measurand from the phase-modulated lightwaves, and has been a challenge for high performance, high speed, and low-cost, to current white-light interferometry (WLI) techniques, such as the widely used scanning WLI (S-WLI) and spectral-domain WLI (SD-WLI). The performance of a white-light interferometric sensing system depends not only on the design of the probes, but also, to a great extent, on the interrogation strategy to be used. In this Ph.D. research, a tunable optical filter based WLI (TOF-WLI) is proposed and validated as a low cost, yet high performance, solution to the interrogation of various types of interferometric sensors. In addition to the capability of linear/quadrature demodulation, TOF-WLI retains all the features of WLI, is compatible with the SD-WLI, and can be tailored for both static and wideband signals. It also has great potential in surface metrology and biomedical imaging as well as optical spectroscopy. The key, to the success of this new approach in competition with the other available WLI techniques, is that the tunable optical filter (TOF) must be specially designed for sensing and extremely low cost. Therefore, two novel TOFs, a diffraction grating tunable filter (DG-TOF) and an extrinsic Fabry-Perot tunable filter (EFP-TF), are proposed and demonstrated. Laboratory and field test results on using the DG-TOF WLI for partial discharge and thermal fault detection in high voltage power transformers, and the EFP-TF WLI in temperature sensor systems and a turbine engine monitoring system will also be presented to demonstrate the feasibility for efficient sensor interrogation. / Ph. D.

The reason of the essay research find position of leakage point, and design a fiber optical leakage detection system. The research of fiber optical detection system in past year, because property of structure produce SNR smaller, quality of detection system is too bed. The essay brings to a hybrid Mach-Zehnder & Sagnac interferomtric can improve the SNR to 10dB. Therefore, it provides the better SNR. The experiment is added to signal process, such as PTL, PGC structure. To provide the systematic characteristic, such as dynamic range(60dB), percentage error(0.025%). The focal of the essay provide leak detection systematic characteristics how we make use of signal process.

The main frame of the distributed fiber optic leak detection system adopted the hybrid Mach-Zehnder & Sagnac interferomtric. We use the sensing fiber of In-Line frame to detect leak physical field. We can measure the position of the leak physical field through our sensing system and signal process system. In the cause of improving detective ability of leak detection system, we modify three elements of the system, including (1) the choice of the acoustic response of sensing fiber, (2) modification of the PZT phase modulator, and (3) modification of the PGC demodulator. The frame of our experiment is composed of the distributed fiber optic leak detection system and leak system of the fluid pipes. In which leak system of fluid pipes is designed the leaky frame of high-pressure fluid pipes. The main of experiment introduce the leak detection system to measure the leak acoustics of the fluid pipes. Then we can discuss the experimental result. The measurable minimum range of our distributed fiber optic leak detection system is3.3x10^-4(rad/¡ÔHz), and the dynamic range is above 75 dB. The dynamic range of this system can improve the original system to above 15 dB.

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. / <p>QC 20150924</p>

[pt] Nesta dissertação são relatadas as etapas que resultam na construção do protótipo de um receptor acústico a Fibra Óptica (RAFO). O trabalho faz parte de um projeto mais amplo visando o desenvolvimento de um medidor de vazão sônico baseado em fibras ópticas. Nesta fase inicial, os esforços foram voltados para a concepção, construção e testes do protótipo do transdutor, responsável pela deteção dos sinais sônicos emitidos por uma fonte, baseado em tecnologia de fibras ópticas. O uso de um sensor extrínseco foi a solução aqui empregada, que adota uma proposta de medição diferente da utilizada em medidores de vazão sônicos convencionais. O sistema de medição de vazão proposto na linha de pesquisa na qual este trabalho está inserido, baseia-se em medidas de tempo de transito para daí inferir a vazão volumétrica do fluido que escoa pelo duto. O sistema foi concebido para operar apenas numa banda estreita de frequências, casada com o sinal senoidal emitido pela fonte sonora. Neste trabalho um receptor acústico a fibra óptica foi projetado, montado e testado, tendo seu funcionamento sido demonstrado para freqüências de operação em torno de 3,2 kHz. A escolha desta faixa de frequências deveu-se basicamente a limitações do sistema de leitura optoeletronico utilizado nos testes de medição. Entretanto, uma vez que o princípio de funcionamento foi demonstrado com sucesso, não existem limitações para o re-dimensionamento do sensor de forma que este possa vir a operar em bandas de freqüência mais elevadas. / [en] This thesis reports the steps that have led to the assemblage and testing of na optical fiber microphone. This is part of a greater effort directed towards the development a sonic flowmeter based on optical fiber technology. In this first phase of the project, focus has been placed on the conception, construction, and testing, of the acoustic receiver first prototype. This transducer will be responsible for capturing the acouustical signails sent by an emitter, also based on optical fiber technology, and which is yet to be developed. In constrast with conventional sonic flowmeters, in which time of flight of acoustical pulses is the measured quantity related to flow rate, we are proposing a system based on measurement of phase difference between emitted and received sinusoidal signals.Hence, the acoustic receiver has been conceived to operate in a narrow frequency band. In particular, the developed prototype has been designed to operate in a frequency band centered at 3.2 kHz. This choice has been dictated by the response of the optoeletronic circuit employed in tests performed with the receiver operating in air and water. Nevertheless, since the principle of operation has been measurement of acoustical signails in higher frequency bands.

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The use of optical fiber sensors is increasing widely in civil, industrial, and military applications mainly due to their, (a) miniature size, (b) high sensitivity, (c) immunity from electro-magnetic interference, (d) resistance to harsh environments, (e) remote signal processing ability, and, (f) multiplexing capabilities. Because of these advantages a variety of optical fiber sensing techniques have evolved over the years having potentials for myriad of applications. One very challenging job, for any of these optical fiber sensing techniques, is to implement a stand alone system with the design and development of all the signal processing models along with the necessary hardware, firmware, and software satisfying the real-time signal processing requirements. In this work we first develop the equations for the system model of the wavelength modulated extrinsic Fabry-Perot interferometric (EFPI) optical fiber sensor, and then design and build all the hardware and software necessary to implement a stand-a / Ph. D.

Structural health monitoring (SHM) has become a strong national interest because of the need of reliable and accurate damage detection methods for aerospace, civil and mechanical engineering infrastructure. Health monitoring of these structures usually requires the sensors to have such features as large area coverage, maintenance free or minimum maintenance, ultra-low cost per measurement point, and capability of operation in harsh environments. Fiber Bragg grating (FBG) has attracted considerable interest for this application because of its compactness, electromagnetic immunity, and excellent multiplexing capability. Several FBG multiplexing techniques have been developed to increase the multiplexing number and further reduce the unit cost. To the author's best knowledge, the current demonstrated maximum multiplexing number are 800 FBG sensors in a single array using optical frequency domain reflectometry (OFDR), whose maximum fiber span is limited by the coherence length of light source. In this work, we proposed and demonstrated a wavelength-scanning time-division multiplexing (WSTDM) of 1000 ultra-weak FBGs for distributed temperature sensing. In comparison with the OFDR method, the WSTDM method distinguishes the sensors by different time delays, and its maximum operation distance, which is limited by the transmission loss of the fiber, can be as high as tens of kilometers. The strong multiplexing capability and low crosstalk of the ultra-weak FBG sensors was investigated through both theoretical analysis and experiment. An automated FBG fabrication system was developed for fast FBG fabrication. With this WSTDM method, we multiplexed 1000 ultra-weak FBGs for distributed temperature sensing. Besides the demonstrated temperature measurement, the reported method can also be applied to measure other parameters, such as strain, pressure. / Ph. D.