M.Ing. / In recent years, many research and development projects have focused on the study of fibre Bragg gratings. Fibre Bragg gratings have been used in the field of sensors, lasers and communications systems. Commercial products that use fibre Bragg gratings are available. On the other hand, in the field of software development, object-oriented programming techniques are also becoming very popular and powerful. The focus of this work is on solving fibre Bragg grating problems by a simulation program with object-oriented programming techniques. For fibre Bragg grating problems, widely used theories and numerical methods such as the coupled-mode theory and the transfer matrix method will be applied in the analysis, modelling and simulation. The coupled-mode theory is a suitable tool for analysis and for obtaining quantitative information about the spectrum of a fibre Bragg grating. The transfer matrix can be used to solve non-uniform fibre Bragg gratings. Two coupled-mode equations can be obtained and simplified by using the weak waveguide approximation. The spectrum characteristics can be obtained by solving these coupled-mode equations. The optical numerical libraries of fibre Bragg gratings have been built by using object-oriented techniques. The code was realized by C++ and Object Pascal language in the Delphi4, C++ Builder4 and Visual C++6 environment. The compiled binary files and the code of the simulation program are available for both the end user and program developer. This simulation program can be used to analyze the performance of sensors and communication systems that use fibre Bragg gratings. Uniform, chirped, apodized, discrete phase shifted and sampled Bragg gratings have already been simulated by using the direct numerical integration method and the transfer matrix method. The reflected and transmitted spectra, time delay and dispersion of fibre Bragg gratings can be obtained by using this simulation program. At the same time, the maximum reflectivity, 3dB-bandwidth and centre wavelength can also be obtained. This thesis consists of three parts. The first part introduces a suitable theory and modelling that have been used to analyze the characteristics of fibre Bragg gratings. Secondly, the codes of the modelling are realized by the suitable programming languages in different development environments. Finally, this simulation program is utilized to analyse real physical problems with fibre Bragg grating applications.

D.Ing. (Electrical and Electronic Engineering) / The subject of this research work was the reflective fibre optic ring interferometer utilizing allow coherence length source. The interferometer consists of an interrogating fibre connected to a fibre ring via an input/output splitting coupler, and a reflector. The fibre ring is formed between one input and one output leg of a fibre coupler. The reflector can be of any type, including a fibre loop mirror, Faraday rotator mirror, a silvered fibre end-face or multilayer dielectric mirror deposited on the fibre end face. A theoretical treatment was developed for the interferometer. It was shown that the interferometer had a reflectance vs nonreciprocal phase shift characteristic, similar to that of a Fabry-Perot interferometer. Upon phase modulation of the interferometer quadrature terms were obtained at harmonics of the modulation frequency. It was shown that by decreasing the finesse of the sensor a quadrature phase tracker could be employed. The dependence of the sensor's reflectance, finesse and sensitivity on various system parameters were simulated with the aid of the abovementioned theory. A high finesse interferometer was proposed. It utilizes a fibre doped amplifier which would increase the sensitivity above that of a Sagnac interferometer. Intermediate and low finesse versions of the reflective ring interferometer were applied as gyroscopes...

A proof of the Moore theorem which in the case of a principal fibration gives a spectral sequence converging to the homology of the base space is given. Also computed is the algebra structure of the homology of the Grassmannians, using Hopf algebra techniques and the cohomology of Grassmanians. Finally, it is shown that a spectral sequence for regular covering which was constructed earlier is a special case of the Moore Theorem. / Science, Faculty of / Mathematics, Department of / Graduate

L’utilisation de capteurs à fibres optiques pour le génie civil n’est pas une idée nouvelle. Leur intérêt repose principalement sur les propriétés intrinsèques des fibres optiques: neutralité électromagnétique, capacité de multiplexage importante et accès à de longues distances de mesure. Ces capteurs sont susceptibles de couvrir de nombreuses fonctions des capteurs traditionnels : détection, localisation et surveillance. Grâce à des interactions entre la lumière et la fibre optique, telle que la diffusion Brillouin, la fibre optique peut constituer, sur toute sa longueur, un capteur continûment distribué. Le phénomène de diffusion Brillouin est très étudié de part sa grande efficacité de diffusion, sa dépendance vis-à-vis de la température et de la déformation et sa portée pluri-kilométrique. Cependant, la sensibilité de la fréquence de décalage Brillouin à la fois à la température et à la déformation rend problématique la mesure simultanée de ces deux paramètres. Nous présenterons une possibilité de discrimination de la température et de la déformation correspondant aux précisions souhaitées en terme de surveillance d'ouvrage de génie civil. / Optical fibers sensors for civil engineering are not a new idea. Their interest is based mainly on the intrinsic properties of optical fibers: electromagnetic neutrality, important capacity of multiplexing and access to long distances of measure. These sensors may cover numerous functions of the traditional sensors: detection, localization and surveillance. Thanks to interactions between the light and the optical fiber, such Brillouin scattering, the optical fiber can be on all its length, a continuously distributed sensor.The phenomenon of Brillouin scattering is well studied due to its big efficiency of scattering, its dependence towards temperature and strain and its pluri-kilometric reach. However, the double sensibility of the Brillouin frequency in temperature and strain is problematic for the simultaneous measurement of these two parameters. We shall present a possibility of discrimination of temperature and strain corresponding to the precisions wished for surveillance health monitoring.

Terahertz spectroscopy shows promise in applications including quality control, security and medical imaging, but remains limited by slow data acquisition. This also poses an impediment to the study of samples undergoing irreversible transitions, as typical schemes rely on the assumption that results are consistent from pulse to pulse. In this work, we propose a high-speed terahertz detection technique based on chirped-pulse encoding that can enable single-shot measurements up to laser repetition rates in the MHz. An all-normal dispersion optical fiber is used to create a broadband probe spectrum, onto which the terahertz pulse waveform is encoded as a phase modulation. The sampling process makes use of the dispersive Fourier transform, a technique which maps the spectral features of a pulse into the time domain, in this case via the dispersion of a long commercial optical fiber. The elongated pulse can subsequently be detected with a high-speed photodetector and oscilloscope. We show steps toward implementing the technique by characterizing the components required to shape the probe pulse and providing some proof-of-concept measurements. In addition, fiber optic simulation procedures are detailed including complete coupled generalized nonlinear Schrödinger equations to provide insight into polarization effects that occur during highly nonlinear processes such as supercontinuum generation.

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Despite the fact that frequency modulation (FM) was firstly applied to radio signaling 80 years ago (1936, by Edwin Howard Armstrong), it has never been deployed in fiber-optic communication systems. In this thesis, a novel frequency modulated fiber-optic communication system with optical discriminator is proposed. The noise configuration and anti-dispersion property of the FM system are investigated through an analytical model that has been derived and validated with numerical simulations. The performance of the proposed FM system is compared with an amplitude modulated (AM) fiber-optic communication system, owing to the fact that the widely used modulation formats, intensity modulation and quadrature amplitude modulation (QAM), can be extracted as a model of the basic AM format. Depending on the property of the filter, two types of frequency discriminators are discussed: the leading edge filter (LEF) and the tail edge filter (TEF). Since the amplified spontaneous emission (ASE) noise is averagely distributed without any frequency dependence, the noise characteristics are not affected by the choice of the frequency discriminator. However, when it comes to the dispersion impairment, the difference between two frequency discriminators is dramatic because the distortion induced by dispersion strongly hinges on the operated frequency. The results show that, with the presence of noise, the proposed FM scheme can lead to one or two orders of magnitude enhancement in the system’s output signal-to-noise ratio (SNR) as compared to that of the conventional AM scheme. Also, with the presence of dispersion, it is proved that the span of the FM system can reliably reach 110km with bit rate up to 10Gbit/s, surpassing the AM system with a maximum signal reach of 70km. A real application, with the presence of both noise and dispersion, demonstrates the overall superiority of the FM system’s performance over that of the AM system. The obtained results suggest a promising future for the FM technique in fiber-optic communication. / Thesis / Master of Applied Science (MASc)

Humidity measurement in industries is a critical factor, since it may affect the business cost of the product, end product quality, optimal functioning of equipment, and the health and safety of the personnel. Hence, humidity sensing is becoming very important, especially in the control systems for industrial processes. Since humidity is expressed in different ways, it is very difficult to come up with a reliable, consistent, and repeatable humidity measurement approach. In contrast to other sensors employed for measuring other parameters like temperature and pressure, a humidity sensor has to be in contact with the process environment and hence is difficult to implement. This research was initiated at the Diagnostic Instrumentation and Analysis Laboratory (DIAL) for the requirement from the DOE to monitor the moisture in the soil at the nuclear waste storage facility. The idea was to monitor the leakage, if any, in the storage cylinders to avoid any hazard that may come up. The humidity sensor in this case had to be able to transmit the measurement over a distance far away from the actual measurement site. Keeping all these factors in mind, a chemically deposited optical fiber humidity sensor was developed. It was based on the evanescent tail absorption of light passing through an optical fiber due to hygroscopic material deposited on it. The hygroscopic material used was an aqueous solution of Poly-vinyl-acetate (PVA) and Cobalt Chloride (COCl2). The sensor yielded a consistent humidity measurement from 75% to 95%. Based on the above research, research is currently in progress to bring up a commercial prototype of the sensor.

Laser Raman Spectroscopy (LRS) has received worldwide acknowledgement as a powerful molecular ‘finger print’ technique. The Raman spectrum of sample contains useful information such as molecular identity, composition, constituent’s concentration ratio etc. These information are manifested in the Raman spectrum in band heights, peak wavelength, band areas etc. The basis of quantitative analysis in Raman spectroscopy lies in the measurement of Raman band intensity, which is linearly dependent upon the sample concentration. On the other hand, Raman spectroscopy can also yield the qualitative information of samples by exhibiting bands corresponding to various chemical constituents in the sample mixture. The potentiality of Raman spectroscopy to perform quantitative as well as qualitative analysis of samples has been exploited in the development of Raman sensors in conjugation with the techniques of fiber optics. The main focus of the presented doctoral work is to realize a fiber optic Raman sensor to monitor the quality of liquid oxygen (LO2) in a rocket engine feed line. In this research investigation, I have shown how a bulk experimental configuration can be transformed to miniaturized prototype sensor, which is equally capable to determine the ratio of liquid oxygen and liquid nitrogen in their cryogenic mixture. This research was extended to monitor the concentration of oxygen and nitrogen in their gaseous mixture. Further, I have demonstrated that the Raman spectroscopy has the potentiality to measure the temperature of hydrogen in a laboratory environment by monitoring the variation in Raman rotation-vibrational line of hydrogen gas with temperature. Finally, I have experimentally studied the surface enhanced Raman spectroscopy (SERS) of silver colloidal solution, which is another interesting branch of Raman spectroscopy that has transcended the limitation of very low Raman cross-section to offer more insight to the chemical properties of samples.