Spectrally-based fiber optic sensors are a rapidly maturing technology capable of sensing several environmental parameters in environments that are unfitting to electrical sensors. However, the sensor interrogation systems for this type of sensors are not yet fit to replace conventional sensor systems. They lack the speed, compact size, and usability necessary to move into mainstream test and measurement. The Fiber Sensor Integrated Monitor (FSIM) technology leverages rapid optical components and parallel hardware architecture to move these sensors across the research threshold into greater mainstream use. By dramatically increasing speed, shrinking size, and targeting an interface that can be used in large-scale industrial interrogation systems, spectrally-based fiber optic sensors can now find more widespread use in both research labs and industrial applications. The technology developed in this thesis was demonstrated by producing two advanced interrogators: one that was one half the size of commercially available systems, and one that accelerated live spectral capture by one thousand times – both of which were operated by non-developers with little training.

This dissertation presents experimental and instrumentation developments that take full advantage of the multidimensional nature of line narrowing spectroscopy at liquid nitrogen (77 K) and liquid helium (4.2 K) temperatures. The inconvenience of sample freezing procedures is eliminated with the aid of cryogenic fiber optic probes. Rapid collection of multidimensional data formats such as wavelength time matrices, excitation emission matrices, time-resolved excitation emission matrices and time resolved excitation emission cubes is made possible with the combination of a pulsed tunable dye laser, a spectrograph and an intensifier-charged coupled device. These data formats provide unique opportunities for processing vibrational luminescence data with second order multivariate calibration algorithms. The use of cryogenic fiber optic probes is extended to commercial instrumentation. An attractive feature of spectrofluorimeters with excitation and emission monochromators is the possibility to record synchronous spectra. The advantages of this approach, which include narrowing of spectral bandwidth and simplification of emission spectra, were demonstrated with the direct analysis of highly toxic dibenzopyrene isomers. The same is true for the collection of steady-state fluorescence excitation-emission matrices. These approaches provide a general solution to unpredictable spectral interference, a ubiquitous problem for the analysis of organic pollutants in environmental samples of unknown composition. Since commercial spectrofluorimeters are readily available in most academic institutions, industrial settings and research institutes, the developments presented here should facilitate the widespread application of line-narrowing spectroscopic techniques to the direct determination, no chromatographic separation, of highly toxic compounds in complex environmental matrixes of unknown composition.

M. Tech. (Department of Process Control and Computer Systems, Faculty of Engineering and Technology), Vaal University of Technology. / The telecommunication and utility cable monitoring system was implemented to protect the cable tampering. Cable tampering occurs despite the fact that methods have been developed, to solve and decrease cable tampering cases such as cable tampering prevention campaigns at the national and international level, organizing security patrols, replacing existing cable with fiber cables and I-Watch system installation. The objective of the research was to design and implement a cable tampering monitoring system which is able to monitor, detect, pinpoint the location and give the distance from the sensor at which the cable tampering took place. The system is an improvement on the traditional cable anti-theft monitoring system, the method of tracking resonance signal frequency was implemented. The system incorporates a sensing circuit which detects a change on the capacitance value of the cable and converts it into an equivalent frequency value, Field-Programable Gate Array (FPGA) board is utilized to convert the frequency into the cable length (the distance from sensor of cable which was taken away), after detecting an anomaly on the cable (tampered with) the output of the system is divided into two parts which are display mode and messaging mode. For display mode, the system uses a Liquid Crystal Display (LCD) which displays the GPS Coordinates of the location where the cable tampering took place and the distance from sensor of the cable which has been tampered with. In the messaging mode, the FPGA activates the GSM module and the module sends alert flag message to the user when the cable is tampered with.

Für den Nachweis dieser Schadstoffe in niedrigen Konzentrationsbereichen sind schnelle und empfindliche Analysemethoden erforderlich. Molekular geprägte Polymere (MIPs) wurden als synthetische Materialien entwickelt, um die molekulare Erkennung von natürlichen Rezeptoren nachzuahmen, aufgrund ihrer Fähigkeit, selektiv eine Vielzahl von Analyten zu erkennen, ihre Stabilität und ihrer einfachen Herstellung. Sie sind zunehmend in der chemischen Sensorik als Rezeptormaterial für den Nachweis bestimmter Analyten bei niedrigen Konzentrationen zu finden, insbesondere in Kombination mit Fluoreszenz aufgrund dessen hoher Empfindlichkeit. Ziel dieser Arbeit war die Entwicklung von optischen Sensormaterialien unter Verwendung von MIPs als Erkennungselemente im Zusammenhang mit Fluoreszenz zum sensitiven Nachweis von Herbiziden und Antibiotika in Wasser- und Lebensmittelproben and deren Kombination mit verschiedenen Vorrichtungsformaten für die zukünftige Detektion einer breiten Palette von wichtigen Analyten. / For the detection of these contaminants in low concentration ranges fast and sensitive analytical tools are required. Molecularly imprinted polymers (MIPs) have been used as synthetic materials mimicking molecular recognition by natural receptors due to their ability to recognize selectively a wide range of analytes, their stability and ease of synthesis. They have gained more and more attention in chemical sensing as receptor material for the detection of suitable groups of analytes at low concentrations especially in combination with fluorescence due to the latter’s high sensitivity. This work aimed the development of optical sensor materials using MIPs as recognition elements connected with fluorescence for the sensitive detection of herbicides and antibiotics in water and food samples and their combination with various device formats for the future detection of a wide range of analytes.

The objective of the paper is to analyze the shrinkage and expansion strain development in thin slabs made of expansive concrete and reinforced with carbon textile reinforcement. The symmetrical textile reinforcement grid provided a biaxial restraint for the concrete shrinkage and expansion. Strains of the slabs were measured with distributed fiber optic sensors (DFOS) in both directions so that a 2D visualization of their distribution can be presented and analyzed. Parallel, standard restrained expansion tests (RET) were conducted to assess the expansive concrete mixture and large-scale beam specimens with uniaxial steel reinforcement were also equipped with DFOS and analyzed. This study aimed to compare the strains in uniaxially restrained elements with steel reinforcement and biaxially restrained textile reinforced concrete elements, in order to assess to what extent the results of the standard RET can be used for evaluation of textile reinforced concrete members.

In this thesis work, a systematic quantitative study has been undertaken, on the performance of etched fiber Bragg Grating (FBG) sensors in the investigation of surface molecular adsorption in real-time; it is shown that the limit of detection (LOD) of FBGs etched below 2 microns diameter, is better compared to prominent optical label-free molecular sensing techniques such as Surface Plasmon Resonance (SPR). Novel fiber optic sensors based on FBG and etched FBG with various nano materials (polyelectrolytes, carbon nanotubes, hydrogel, metals and chalcogenides) coated on the surface of the core or cladding, have been proposed for sensing multi parameters such as pH, protein, humidity, gas, strain, temperature, and light etc. Besides being reproducible and repeatable, the proposed methods are fast, compact, and highly sensitive. A novel optical instrument has also been developed to measure angular deviation, binocular deviation and refractive index of glass slabs, and liquids, based on a shadow casting technique. This method uses the deviation in the geometrical shadow cast by a periodic dot pattern trans-illuminated by a distorted light beam from the transparent test specimen relative to a reference pattern.

A evolução das redes ópticas para atender o crescimento da demanda por largura de banda tem estimulado a busca por uma maior eficiência na utilização da largura de faixa disponível. O sucesso da implementação prática da técnica de acesso múltiplo por divisão de código (CDMA) em sistemas de comunicações móveis também despertou o interesse por aplicações em redes ópticas (OCDMA). Atributos únicos tais como capacidade flexível sob demanda, segurança na comunicação e alta escalabilidade, incentivaram significativamente as pesquisas. Neste contexto, este trabalho apresenta, primeiramente, uma revisão de várias configurações OCDMA propostas na literatura para qualificar e quantificar códigos válidos, com ênfase nas propriedades de correlação. Em seguida, realiza uma modelagem de sistema óptico abrangendo os subsistemas principais de geração, transmissão e recepção de sinal. O impacto das degradações, referentes à fibra óptica e aos diversos dispositivos que constituem o sistema, é então avaliado e sua influência sobre o desempenho de algumas configurações de codificação é investigado. O conhecimento da forma e das condições de manifestação destas degradações poderá servir de base ao processamento de sinal óptico à luz dos esquemas de codificação. Uma discussão sobre qualidade de serviço (QoS) e sobre flexibilização da aplicação OCDMA em sistemas de comunicação óptica também são também abordadas. / The evolution of optical networks verified in the last few years has been characterized by the search for better bandwidth utilization efficiency. The successful implementation of practical code division for multiple access techniques (CDMA) in mobile communications systems has stimulated new investigations on this topic, particularly in the optical domain (optical CDMA). This is justified due to some remarkable attributes of this technology, such flexibility in code design, capacity on demand, safety, and high scalability. In this context, this dissertation presents, initially, a comprehensive review of several code configurations for OCDMA proposed in the literature, with emphasis particularly on the correlation and users availability properties. Next, it describes the modeling of an optical system consisting of the following three subsystems: generation, transmission, and signal detection. The penalties imposed to the optical codes by the propagating medium, as well as by the devices employed in the system, are accounted for and their influence on the performance of some coding configurations is investigated. The knowledge of how and when these penalties will affect the system is crucial in optical signal processing based on codification schemes. Finally, this work also addresses some aspects related to quality of service (QoS) and flexibility of the OCDMA technology in optical communications systems.

Este trabajo de tesis recoge las contribuciones aportadas en el campo de los sensores de fibra óptica en tres ámbitos de trabajo. Un sistema sensor de alta temperatura sin contacto con transductores de fibras ópticas de sílice se ha presentado. Dos topologías de "ojo abierto" y "ojo cerrado" y un algoritmo de decodificación "pirometría de banda dual" propuesto en este trabajo son las novedosas aportaciones presentadas. El sistema ha sido validado en laboratorio y en pruebas de campo de forma exitosa. Para sensores de temperatura con fibras dopadas con Erbio se ha demostrado que su máxima sensibilidad tiene lugar cuando la longitud utilizada es superior a la óptima exigida por el bombeo. Finalmente se ha modelado y validado en laboratorio una red de sensores acústicos basados en interferómetros Fabry-Perot de cavidad larga determinando a partir del modelo obtenido la fase mínima detectable y la visibilidad máxima del sistema. / The thesis collects contributions in the field of optic fibre sensors for three areas. A high temperature sensor system without contact based on silica optic fibre transducers has been submitted. Two topologies "open eye" and "closed eye" and a dual band pyrometer decoding algorithm are the submitted innovative contributions. The system has been validated successful in the laboratory and field tests so. Another contribution has been the demonstration that the maximum sensitivity for temperature sensors based on Er-doped fibres occurs when the used length is more than the optimum required by pumping. Finally a network of acoustic sensors based on Fabry-Perot fibre interferometers has been modelled and validated in the laboratory. The minimum detectable phase and maximum visibility of the system has been obtained from the proposed and validated model

No description available.

Photonics and Optical techniques have advanced recently by a great extend to play an important role in Microwave and Radar applications. Antenna array of modern active phased array radars consist of multiple low power transmit and receive mod- ules. This demands distribution of the various Local Oscillator(LO) signals for up conversion of transmit signals and down conversion of receive signals during various modes of operation of a radar system. Additionally, these receivers require control and clock signals which are digital and low frequency analog, for the synchronization between receive modules. This is normally achieved through RF cables with complex distribution networks which add significantly higher additional weight to the arrays. During radar operations, radio frequency (RF) transmit signal needs to be distributed through the same modules which will in turn get distributed to all antenna elements of the array using RF cables. This makes the system bulky and these large number of cables are prone to Electromagnetic Interference (EMI) and need additional shielding. Therefore it is very desirable to distribute a combination of these RF, analog and digital signals using a distribution network that is less complex, light in weight and immune to EMI. Advancements in Optical and Microwave photonics area have enabled carrying of higher datarate signals on a single fiber due to its higher bandwidth capability including RF signals. This is achieved by employing Wavelength Division Multi- plexing (WDM) that combine high speed channels at different wavelengths. This work proposes, characterizes and evaluates an optical Wavelength Division Multiplexed(WDM) distribution network that will overcome the above mentioned problems in a phased array radar application. The work carries out a feasibility analysis supported with experimental measurements of various physical parameters like am- plitude, delay, frequency and phase variation for various radar waveforms over WDM links. Different configurations of optical distribution network are analyzed for multipoint distribution of both digital and RF signals. These network configurations are modeled and evaluated against various parameters that include power level, loss, cost and component count. A configuration which optimizes these parameters based on the application requirements is investigated. Considerable attention is paid to choose a configuration which does not provide excess loss, which is economically viable, compact and can be realized with minimum component count. After analysing the link configuration, multiplexing density of the WDM link is considered. In this work, since the number of signals to be distributed in radar systems are small, a coarse WDM(CWDM) scheme is considered for evaluation. A comparative study is also performed between coarse and dense WDM (DWDM) links for selection of a suitable multiplexing scheme. These configurations are modeled and evaluated with power budgeting. Even though CWDM scheme does not permit the utilisation of the available bandwidth to the fullest extent, these links have the advantage of having less hardware complexity and easiness of implementation. As the application requires signal distribution to thousands of transmit-receive modules, amplifiers are necessary to compensate for the reduction of signal level due to the high splitting ratio. Introduction of commonly available optical amplifiers like Erbium Doped Fiber Amplifier (EDFA), affect the CWDM channel output powers adversely due to their non-flat gain spectrum. Unlike DWDM systems, the channel separation of CWDM systems are much larger causing significantly high channel gain differences at the EDFA output. So an analysis is carried out for the selection of a suitable wavelength for CWDM channels to minimize the EDFA output power variation. If the gain difference is still significant, separate techniques needs to be implemented to flatten the output power at the antenna end. A CWDM configuration using C-band and L-band EDFAs is proposed and is supported with a feasibility analysis. As a part of evaluation of these links for radar applications, a mathematical model of the WDM link is developed by considering both the RF and digital sig- nals. A generic CWDM system consisting of transmitters, receivers, amplifiers, multiplexers/ demultiplexers and detectors are considered for the modeling. For RF signal transmission, the transmitters with external modulators are considered. Mod- eling is done based on a bottom-top approach where individual component models are initially modeled as a function of input current/power and later cascaded to obtain the link model. These models are then extended to obtain the wavelength dependent model ( spectral response) of the hybrid signal distribution link Further mathematical analysis of the developed link model revealed its variable separable nature in terms of the input power and wavelength. This led to significant reduction in the link equation complexity and development of some approximation techniques to easily represent the link behavior. The reduced form of the link spectral model was very essential as the initially developed wavelength model had a lot of parametric dependency on the component models. This mathematical reduction process led to simplification of the spectral model into a product of two independent functions, the input current and wavelength. It is also noticed that the total link power within specific wavelength range can be obtained by the integrating these functions over a specific link input power. After the mathematical modelling, an experimental prototype physical link is set up and characterized using various radar signals like continuous wave (CW) RF, pulsed RF, non linear frequency modulated signal (NLFM) etc. Additionally a proof of concept Radio-Over-Fiber (RoF) link is established to prove the superior transmission of microwave signal through an optical link. The analysis is supported with measurements on amplitude, delay, frequency and phase variations. The NLFM waveforms transmissions are further analysed using a matched _ltering process to confirm the side lobe requirement. Further a prototype WDM link is built to study the performance when digitally modulated channels are also multiplexed into the link. The link is again validated for signal levels, delay, frequency and phase parameters. Since amplitude and delay are deterministic, it is proposed that these parameter variations can be compensated by using suitable components either in the electrical or the optical domain. Radar systems use low frequency digital signals of different duty-cycles for synchronization and control across various transmit-receive modules. In the proposed link, these digital signals also modulate a WDM channel and hence the link is called a hybrid system. As the proposed link has EDFA to compensate for the splitting losses, there are chances of transient effects at the EDFA output for these low bitrate channels. Owing to the long carrier lifetime, low bitrate digital channels are prone to EDFA transient effects under specific signal and pump power conditions. Additionally, the synchronization signals used in radar application vary the duty-cycle over time, which is found to introduce variations in transient output. This practical challenge is further studied and the thesis for the first time, includes an analysis of EDFA transient e_ects for variable duty-cycle pulsed signals. The analysis is carried out for various parameters like bitrate, input power, pump power and duty-cycle. Investigations on EDFA transients on variable duty-cycle signals help in proposing a viable method to predict the lower duty-cycle transients from higher duty-cycle transients. The predicted transients were again validated against simulated transients and experimental results. As these transient effects are not desirable for radar signals, we propose a novel transient suppression techniques in optical and electrical domain which are validated with simulation and experimental measures. One suppression technique tries to avoid transient effect by keeping the optical input to EDFA always constant by feeding an inverted version of the original pulse into the EDFA along with the actual pulse. It is observed that as the wavelength of the inverted pulse is closer to the original input pulse, the transient effect settles faster. These EDFA transients are evaluated with WDM link configurations, where both high and low bitrate signals are co-propagated. Another challenging aspect of the link operation is the non-at gain spectrum of EDFA. i.e., EDFA provides unequal power level for various signals at WDM link output. This is especially true in the case of local oscillator signals, where it is preferable to have the same amplitude signals before feeding it to the mixer stages. But in the radar applications, this will require additional hardware circuits to equalize the signal level within a phased array antenna. This work also proposes some of the power equalization methods that can be used along with the WDM links. This part of the work is also supported with simulation model and experimental results. The analytical and experimental study of this thesis aids the evaluation process of a suitable optical Wavelength Division Multiplexed(WDM) distribution network that can be used for the distribution of both RF and digital signals. The optical WDM links being superior with its light weight, less loss and EMI/ EMC immunity provides a better solution to future class of radars.