The properties of two novel random fibre lasers, in which stimulated Brillouin scattering supplies the effective gain mechanism and Rayleigh scattering along the standard telecommunication optical fibre provides random distributed feedback, are characterised. Firstly, ultra-narrow microwave signals with a Dirac delta function profile are successfully created by beating two random-lasing near-Gaussian beams, arising from the synchronization of optical modes from two Stokes signals with random phase accumulated over the ultra-long optical fibre. This finding provides a completely new approach to synthesise high spectral purity microwave signals from Brillouin fibre lasers with randomised feedback. In addition, we also develop a theoretical model of the random fibre Fabry-Pérot resonator based on the fact that the pump depletion effect naturally selects out the effective Rayleigh feedback regions localised in both ends of this long fibre. A narrow random-laser output with the linewidth of ~860 Hz is experimentally demonstrated and is employed to characterise the linewidth of the pump light. Furthermore, the random laser dynamics is studied and one application towards the physical entropy source is eventually achieved.

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.

No / Autodesk Moldflow Simulation Insights has been used to predict the fibre orientation within notched specimen injection mouldings. Currently available fibre orientation models including the classis Folgar-Tucker (FT), the modified version of Folgar-Tucker (MFT) and the Reduced Strain Closure (RSC) [1] have been assessed, alongside the relative effects of their associated parameters, for their suitability for fibre orientation prediction. Compared to experimentally determined values the Reduced Strain Closure model was shown to most closely represent the fibre orientation within the moulded components.

Il y a maintenant des dizaines d'années que les lasers visibles ont fait leur entrée sur le marché et que leur utilité est aussi bien reconnue en sciences fondamentales qu'en sciences appliquées. Ces derniers sont en effet notamment utilisés pour effectuer des traitements médicaux, pour faire avancer la recherche dans le secteur biomédical, pour procéder à l'usinage de matériaux et pour communiquer sous l'eau. Bien que l'utilisation des lasers visibles soit largement répandue, les sources actuellement disponibles comportent toujours des failles majeures en matière de performances, de simplicité et de robustesse. Alors que les fibres optiques dopées aux ions de lanthanides ont la capacité de générer des signaux laser d'une qualité impeccable à travers des montages simples, compacts et robustes, ces dernières ont le potentiel de révolutionner l'industrie des lasers visibles. Cette thèse porte sur le développement de lasers à fibre optique opérant dans la région visible du spectre électromagnétique. L'opération de tels lasers est étudiée en régime continu ainsi qu'en régime pulsé, de manière à générer des impulsions ultrabrèves. Le premier chapitre de cette thèse porte sur le développement d'un laser basé sur une fibre de verre fluoré dopée au praséodyme triplement ionisé opérant en régime continu à 635 nm. Ce laser, qui génère la plus haute puissance rapportée à ce jour pour un laser à fibre visible monomode, possède une architecture entièrement monolithique, ce qui ouvre la voie au développement de lasers visibles fiables, compacts et à hautes puissances. Le chapitre suivant présente un laser basé sur une fibre de silice dopée au dysprosium triplement ionisé opérant en régime continu à 585 nm. Le système laser proposé repose sur ce que l'on peut sans doute décrire comme l'installation la plus robuste, la plus solide et la plus simple rapportée à ce jour pour un laser à fibre visible, en plus de battre le record de puissance pour les lasers à fibre de silice visibles. Alors que l'irradiation de la pompe provoque du photo-noircissement, une réduction significative des pertes photo-induites est démontrée grâce à un processus de photo-blanchiment. Le dernier chapitre de cette thèse est consacré au développement du premier laser à fibre visible générant des impulsions femtosecondes, ce qui constitue une avancée majeure dans le domaine des lasers à fibre visibles. La démonstration est basée sur la rotation non linéaire de la polarisation dans une fibre monomode de verre fluoré dopée au praséodyme triplement ionisé opérant à 635 nm. / Visible lasers have now been on the market for decades, and their usefulness in both fundamental and applied sciences is well recognized. They are for instance used for medical treatments, biomedical research, material processing and underwater communications. Although the use of visible lasers is widely spread, currently available sources still have major shortcomings in terms of performance, simplicity and robustness. While lanthanide-doped optical fibers have the ability to generate laser signals of impeccable quality through simple, compact and robust assemblies, they have the potential to revolutionize the visible laser industry. This thesis focuses on the development of fiber lasers operating in the visible region of the electromagnetic spectrum. The operation of such lasers is studied in both continuous and pulsed modes, so as to generate ultra-short pulses. The first chapter of this thesis deals with the development of a laser based on a praseodymium-doped fluoride fiber operating in the continuous wave regime at 635 nm. This laser, which generates the highest power reported to date for a single-mode visible fiber laser, features a fully monolithic architecture, paving the way for the development of reliable, compact, and high-power visible lasers. The following chapter presents a laser based on a dysprosium-doped silica fiber operating in the continuous wave regime at 585 nm. The proposed laser system is based on what can arguably be described as the most rugged, robust and simple setup reported to date for a visible fiber laser, and breaks the power record for visible silica fiber lasers. While irradiation of the pump causes photodarkening, a significant reduction in photo-induced losses is demonstrated via a photobleaching process. The final chapter of this thesis is devoted to the development of the first visible fiber laser to generate femtosecond pulses, representing a major breakthrough in the field of visible fiber lasers. The demonstration is based on non-linear polarization rotation in a single-mode praseodymium-doped fluoride fiber operating at 635 nm.

Drawing of standard telecommunication-type optical fibres has been optimised in terms of optical and physical properties. Specialty fibres, however, typically have more complex dopant profiles. Designs with high dopant concentrations and multidoping are common, making control of the fabrication process particularly important. In photonic crystal fibres (PCF) the inclusion of air-structures imposes a new challenge for the drawing process. The aim of this study is to gain profound insight into the behaviour of complex optical fibre structures during the final fabrication step, fibre drawing. Two types of optical fibre, namely conventional silica fibres and PCFs, were studied. Germanium and fluorine diffusion during drawing was studied experimentally and a numerical analysis was performed of the effects of drawing parameters on diffusion. An experimental study of geometry control of PCFs during drawing was conducted with emphasis given to the control of hole size. The effects of the various drawing parameters and their suitability for controlling the air-structure was studied. The effect of air-structures on heat transfer in PCFs was studied using computational fluid dynamics techniques. Both germanium and fluorine were found to diffuse at high temperature and low draw speed. A diffusion coefficent for germanium was determined and simulations showed that most diffusion occurred in the neck-down region. Draw temperature and preform feed rate had a comparable effect on diffusion. The hole size in PCFs was shown to depend on the draw temperature, preform feed rate and the preform internal pressure. Pressure was shown to be the most promising parameter for on-line control of the hole size. Heat transfer simulations showed that the air-structure had a significant effect on the temperature profile of the structure. It was also shown that the preform heating time was either increased or reduced compared to a solid structure and depended on the air-fraction.

Drawing of standard telecommunication-type optical fibres has been optimised in terms of optical and physical properties. Specialty fibres, however, typically have more complex dopant profiles. Designs with high dopant concentrations and multidoping are common, making control of the fabrication process particularly important. In photonic crystal fibres (PCF) the inclusion of air-structures imposes a new challenge for the drawing process. The aim of this study is to gain profound insight into the behaviour of complex optical fibre structures during the final fabrication step, fibre drawing. Two types of optical fibre, namely conventional silica fibres and PCFs, were studied. Germanium and fluorine diffusion during drawing was studied experimentally and a numerical analysis was performed of the effects of drawing parameters on diffusion. An experimental study of geometry control of PCFs during drawing was conducted with emphasis given to the control of hole size. The effects of the various drawing parameters and their suitability for controlling the air-structure was studied. The effect of air-structures on heat transfer in PCFs was studied using computational fluid dynamics techniques. Both germanium and fluorine were found to diffuse at high temperature and low draw speed. A diffusion coefficent for germanium was determined and simulations showed that most diffusion occurred in the neck-down region. Draw temperature and preform feed rate had a comparable effect on diffusion. The hole size in PCFs was shown to depend on the draw temperature, preform feed rate and the preform internal pressure. Pressure was shown to be the most promising parameter for on-line control of the hole size. Heat transfer simulations showed that the air-structure had a significant effect on the temperature profile of the structure. It was also shown that the preform heating time was either increased or reduced compared to a solid structure and depended on the air-fraction.

In this thesis a Fully-Photonic DRoF (FP-DRoF) system is proposed for deploying of future super-broadband access networks. Digital Radio over Fibre (DRoF) is more independent of the fibre network impairments and the length of fibre than the ARoF link. In order for fully optical deployment of the signal conversion techniques in the FP-DRoF architecture, two key components an Analogue-to-Digital Converter (ADC) and a Digital-to-Analogue Converter (DAC)) for data conversion are designed and their performance are investigated whereas the physical functionality is evaluated. The system simulation results of the proposed pipelined Photonic ADC (PADC) show that the PADC has 10 GHz bandwidth around 60 GHz of sampling rate. Furthermore, by changing the bandwidth of the optical bandpass filter, switching to another band of sampling frequency provides optimised performance condition of the PADC. The PADC has low changes on the Effective Number of Bit (ENOB) response versus analogue RF input from 1 GHz up to 22 GHz for 60 GHz sampling frequency. The proposed 8-Bit pipelined PADC performance in terms of ENOB is evaluated at 60 Gigasample/s which is about 4.1. Recently, different methods have been reported by researchers to implement Photonic DACs (PDACs), but their aim was to convert digital electrical signals to the corresponding analogue signal by assisting the optical techniques. In this thesis, a Binary Weighted PDAC (BW-PDAC) is proposed. In this BW-PDAC, optical digital signals are fully optically converted to an analogue signal. The spurious free dynamic range at the output of the PDAC in a back-to-back deployment of the PADC and the PDAC was 26.6 dBc. For further improvement in the system performance, a 3R (Retiming, Reshaping and Reamplifying) regeneration system is proposed in this thesis. Simulation results show that for an ultrashort RZ pulse with a 5% duty cycle at 65 Gbit/s using the proposed 3R regeneration system on a link reduces rms timing jitter by 90% while the regenerated pulse eye opening height is improved by 65%. Finally, in this thesis the proposed FP-DRoF functionality is evaluated whereas its performance is investigated through a dedicated and shared fibre links. The simulation results show (in the case of low level signal to noise ratio, in comparison with ARoF through a dedicated fibre link) that the FP-DRoF has better BER performance than the ARoF in the order of 10-20. Furthermore, in order to realize a BER about 10-25 for the ARoF, the power penalty is about 4 dBm higher than the FP-DRoF link. The simulation results demonstrate that by considering 0.2 dB/km attenuation of a standard single mode fibre, the dedicated fibre length for the FP-DRoF link can be increased to about 20 km more than the ARoF link. Moreover, for performance assessment of the proposed FP-DRoF in a shared fibre link, the BER of the FP-DRoF link is about 10-10 magnitude less than the ARoF link for -19 dBm launched power into the fibre and the power penalty of the ARoF system is 10 dBm more than the FP-DRoF link. It is significant to increase the fibre link’s length of the FP-DRoF access network using common infrastructure. In addition, the simulation results are demonstrated that the FP-DRoF with non-uniform Wavelength Division Multiplexing (WDM) is more robust against four wave mixing impairment than the conventional WDM technique with uniform wavelength allocation and has better performance in terms of BER. It is clearly verified that the lunched power penalty at CS for DRoF link with uniform WDM techniques is about 2 dB higher than non-uniform WDM technique. Furthermore, uniform WDM method requires more bandwidth than non-uniform scheme which depends on the total number of channels and channels spacing.

Composite materials have become viable alternatives to traditional engineering materials for many different product categories. Liquid transfer moulding (LTM) processes, specifically resin transfer moulding (RTM), is a cost-effective manufacturing technique for creating high performance composite parts. These parts can be tailor-made to their specific application by optimizing the properties of the textile preform. Preforms which require little or no further assembly work and are close to the shape of the final part are critical to obtaining high quality parts while simultaneously reducing labour and costs associated with other composite manufacturing techniques. One type of fabric which is well suited for near-net- shape preforms is stitched non-crimp fabrics. These fabrics offer very high in-plane strength and stiffness while also having increased resistance to delamination. Manufacturing parts from these dry preforms typically involves long-scale fluid flow through both open channels and porous fibre bundles. This thesis documents and analyzes the flow of fluid through preforms manufactured from non-crimp fabrics featuring through-thickness stitches. The objective of this research is to determine the effect of this type of stitch on the RTM injection process. All of the tests used preforms with fibre volume fractions representative of primary and secondary structural parts. A series of trials was conducted using different fibre materials, flow rates, fibre volumes fractions, and degrees of fibre consolidation. All of the trials were conducted for cases similar to RTM. Consolidation of the fibres showed improvements to both the thoroughness of the filling and to the fibre volume fraction. Experimentally determined permeability data was shown to trend well with simple models and precision of the permeability data was comparable to values presented by other authors who studied fabrics which did not feature the through-thickness stitches.

Limited observing time at large telescopes equipped with the most powerful spectrographs makes it almost impossible to gain long and well-sampled time-series observations. Ditto, high-time-resolution observations of bright targets with high signal-to-noise are rare. By pulling an optical fibre of 450m length from the Vatican Advanced Technology Telescope (VATT) to the Large Binocular Telescope (LBT) to connect the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) to the VATT, allows for ultra-high resolution time-series measurements of bright targets. This article presents the fibre-link in detail from the technical point-of-view, demonstrates its performance from first observations, and sketches current applications.

This thesis presents the development of photonic tools towards the realisation of an optical intensity waveform synthesiser and of an attosecond pulse synthesiser based on the generation and Fourier synthesis of a continuous-wave coherent spectral comb spanning more than 3 octaves (UV to mid-IR) by use of a gas-filled hollow core photonic crystal fibre (HC-PCF).