No description available.

In this thesis, a fully millimetre-wave (mm-wave) generation and transmission system is proposed for futuristic communications. Significant challenges have been dealt with regarding the proposed system, including designing the mm-wave generation and transmission technique, and its application in cellular networks. These challenges are presented through five main contributions and validated via Optiwave Design Software and MATLAB simulation tools. Firstly, three novel photonic generation methods are proposed and designed based on the characteristics of Brillouin fibre laser and the Stimulated Brillouin Scattering (SBS) effects with phase modulation. The mm-wave carriers are successfully generated with a tuning capability from 5 to 90 GHz. Also, these carriers are with good Signal to Noise Ratio (SNR) up to 51 dB, and low noise signal power of about -40 dBm. The impact of these methods is obtaining stable mm-waves appropriate for Radio over Fibre (RoF) transmission systems in 5G optical networks. Secondly, a full-duplex RoF system with the generation of a 64 GHz mm-wave is proposed. Successful transmission of the mm-wave over a fibre link is achieved for up to 100 km of fibre with a data rate of 5 Gbits/s. The main impact of this system is cost reduction and performance improvement by simplifying mm-wave generation and transmission over fibre. Also, it ensures a useful communication link for small cell networks. Thirdly, a hybrid Fibre/Free-space optical (FSO) system for the generation and transmission of 64 GHz mm-wave is proposed. This optical system provides a low latency communication link and overcomes mm-wave high path losses. A successful mm-wave transmission is achieved over a 10 km fibre length, and 2 km FSO link length with a good Bit Error Rate (BER) of about 1.5×10-13 and a data rate of 10 Gbits/s. This system increases the network coverage area by transmitting the mm-wave over the FSO link to the areas with natural obstacles the laying of fibre cables impossible. Also, it can be used as an effective solution under emergency disaster conditions. Fourthly, a comprehensive study of the wireless propagation performance for different mm-wave bands (28, 60, and 73 GHz) as cellular networks is investigated and compared with the 2.4 GHz Ultra-High Frequency band (UHF). A map-based scenario is proposed for the deployment of Base Stations (BSs) within the Brunel University London Campus map to consider real blockage effects. This investigation involved specifying which mm-wave spectrum can enhance the futuristic cellular networks, by evaluating the coverage and rate trends. Comparative results show that the 73 GHz bands can achieve the higher rate with good coverage and the lowest interference effects than the other mm-wave bands. Finally, a simplified path loss model is proposed to estimate precisely the 28 GHz mm-wave performance, which is considered a key component in 5G networks in outdoor applications. The proposed path loss model captures the diffraction and specular reflection impacts on mm-wave wireless propagation.

The primary objective of this work was to develop a laser source for fundamental investigations in the field of laser – materials interactions. In particular it is supposed to facilitate the study of the influence of the temporal energy distribution such as the interaction between adjacent pulses on ablation processes. Therefore, the aim was to design a laser with a highly flexible and easily controllable temporal energy distribution. The laser to meet these demands is an SBS-laser with optional active mode-locking. The nonlinear reflectivity of the SBS-mirror leads to a passive Q-switching and issues ns-pulse bursts with µs spacing. The pulse train parameters such as pulse duration, pulse spacing, pulse energy and number of pulses within a burst can be individually adjusted by tuning the pump parameters and the starting conditions for the laser. Another feature of the SBS-reflection is phase conjugation, which leads to an excellent beam quality thanks to the compensation of phase distortions. Transverse fundamental mode operation and a beam quality better than 1.4 times diffraction limited can be maintained for average output powers of up to 10 W. In addition to the dynamics on a ns-timescale described above, a defined splitting up of each ns-pulse into a train of ps-pulses can be achieved by additional active mode-locking. This twofold temporal focussing of the intensity leads to single pulse energies of up to 2 mJ at pulse durations of approximately 400 ps which corresponds to a pulse peak power of 5 MW. While the pulse duration is of the same order of magnitude as those of other passively Q-switched lasers with simultaneous mode-locking, the pulse energy and pulse peak power exceeds the values of these systems found in the literature by an order of magnitude. To the best of my knowledge the laser presented here is the first implementation of a self-starting mode-locked SBS-laser oscillator. In order to gain a better understanding and control of the transient output of the laser two complementary numerical models were developed. The first is based on laser rate equations which are solved for each laser mode individually while the mode-locking dynamics are calculated from the resultant transient spectrum. The rate equations consider the mean photon densities in the resonator, therefore the propagation of the light inside the resonator is not properly displayed. The second model, in contrast, introduces a spatial resolution of the resonator and hence the propagation inside the resonator can more accurately be considered. Consequently, a mismatch between the loss modulation frequency and the resonator round trip time can be conceived. The model calculates all dynamics in the time domain and therefore the spectral influences such as the Stokes-shift have to be neglected. Both models achieve an excellent reproduction of the ns-dynamics that are generated by the SBS-Q-switch. Separately, each model fails to reproduce all aspects of the ps-dynamics of the SBS-laser in detail. This can be attributed to the complexity of the numerous physical processes involved in this system. But thanks to their complementary nature they provide a very useful tool for investigating the various influences on the dynamics of the mode-locked SBS-laser individually. These aspects can eventually be recomposed to give a complete picture of the mechanisms which govern the output dynamics. Among the aspects under scrutiny were in particular the start resonator quality which determines the starting condition for the SBS-Q-switch, the modulation depth of the AOM and the phonon lifetime as well as the Brillouin-frequency of the SBS-medium. The numerical simulations and the experiments have opened several doors inviting further investigations and promising a potential for further improvement of the experimental results: The results of the simulations in combination with the experimental results which determined the starting conditions for the simulations leave no doubt that the bandwidth generation can primarily be attributed to the SBS-Stokes-shift during the buildup of the Q-switch pulse. For each resonator round trip, bandwidth is generated by shifting a part of the revolving light in frequency. The magnitude of the frequency shift corresponds to the Brillouin-frequency which is a constant of the SBS material and amounts in the case of SF6 to 240 MHz. The modulation of the AOM merely provides an exchange of population between spectrally adjacent modes and therefore diminishes a modulation in the spectrum. By use of a material with a Brillouin-frequency in the GHz range the bandwidth generation can be considerably accelerated thereby shortening the pulse duration. Also, it was demonstrated that yet another nonlinear effect of the SBS can be exploited: If the phonon lifetime is short compared to the resonator round trip time we obtain a modulation in the SBS-reflectivity that supports the modulation of the AOM. The application of an external optical feedback by a conventional mirror turns out to be an alternative to the AOM in synchronizing the longitudinal resonator modes. The interesting feature about this system is that it is ― although highly complex in the physical processes and the temporal output dynamics ― very simple and inexpensive from a technical point of view. No expensive modulators and no control electronics are necessary. Finally, the numerical models constitute a powerful tool for the investigation of emission dynamics of complex laser systems on arbitrary timescales and can also display the spectral evolution of the laser output. In particular it could be demonstrated that differences in the results of the complementary models vanish for systems of lesser complexity. / Ziel der Arbeit ist die Entwicklung einer Laserstrahlquelle, die zur Untersuchung von Laser-Material-Wechselwirkungen eingesetzt werden soll. Im Mittelpunkt des Interesses steht hierbei der Einfluss der zeitlichen Pulsstruktur des Lasers auf Materialabtragsprozesse. Daraus ergibt sich die Anforderung einer möglichst hohen Flexibilität in der Pulsstruktur des Lasers sowie einer möglichst guten Strahlqualität. Eine gute Strahlqualität zeichnet sich durch eine homogene räumliche Intensitätsverteilung aus und ist Voraussetzung für eine gezielte Energiedeponierung auf dem Material. Diese Anforderungen wurden mit einem SBS-Laser erfüllt. Dabei handelt es sich um einen Laser, der einen SBS-Spiegel verwendet, dessen Reflektivität auf der Streuung des Lichts an Schallwellen beruht, die von dem einfallenden Licht selbst erzeugt werden. Als Resultat hat dieser Spiegel eine Reflektivität, die abhängig von der Energie des eingestrahlten Lichts ist. In einem Laser verwendet führt diese energieabhängige Reflektivität zu einer sogenannten Güteschaltung, die sich in der Ausbildung von kurzen Lichtpulsen mit Dauern von etwa 100 Nanosekunden äußert. Die Abstände zwischen den Pulsen, die Pulsdauern und die Pulsenergien können sehr leicht durch die Randbedingungen, wie etwa die Reflektivität der konventionellen Spiegel des Lasers, gesteuert werden. Durch eine zusätzliche, aktiv herbeigeführte Verlustmodulation im Laserresonator wird eine Aufspaltung der Nanosekundenpulse in eine Reihe von Pulsen mit Dauern von nur noch einigen 100 Pikosekunden erreicht. Diese Technik ist unter dem Begriff Modenkopplung bekannt. Es liegt jetzt also eine doppelte Pulsstruktur vor: Nanosekundenpulse, die sich jeweils aus vielen Pikosekundenpulsen zusammensetzen. Durch diese doppelte zeitliche Bündelung der Ausgangsleistung werden während der Pulse Spitzenleistungen von bis zu 5 MW erreicht. Die Pulsenergien der ps-Pulse erreichen bis zu 2 mJ. Diese Werte liegen um den Faktor 10 über denen vergleichbarer Systeme. Meines Wissens ist dies die erste Umsetzung eines selbsttätigen SBS-Lasers mit zusätzlicher Modenkopplung. Um die verschiedenen Einflüsse auf diese Emissionsdynamik besser verstehen und kontrollieren zu können, wurden zwei Modelle mit komplementären Ansätzen entwickelt, auf deren Basis diese Dynamik durch numerische Simulationen wiedergegeben werden kann. Insbesondere können auf diese Weise auch die Einflüsse von einzelnen Materialparametern isoliert betrachtet werden, was im Experiment im allgemeinen nicht möglich ist. Der SBS-Laser wurde bereits erfolgreich in Laser-Materialbearbeitungsexperimenten eingesetzt. So konnte beispielsweise gezeigt werden, dass sich die Bearbeitungsdauer beim Wendelbohren durch die Verwendung von Pulszügen, also einer Reihe kurz aufeinander folgender Pulse, gegenüber dem Einsatz von Pulsen mit gleichmäßigen Abständen erheblich verbessern lässt.

Techniques to control dispersion in a medium have attracted much attention due to potential applications to devices such as ring laser gyroscopes, interferometric gravitational wave detectors, data buffers, phased array radars and quantum information processors. Of particular interest is an optical resonator containing a medium with an anomalous dispersion corresponding to fast-light, which behaves as a White Light Cavity (WLC). A WLC can be tailored to improve the sensitivity of sensing devices as well as to realize an optical data buffering system that overcomes the delay-bandwidth product of a conventional cavity. This dissertation describes techniques to tailor the dispersion for fast-light in intracavity media. We present first a demonstration of fast-light in a photorefractive crystal. When placed inside a cavity, such a medium could be used to enhance the bandwidth of a gravitational wave detector. We then describe how a superluminal laser can be realized by adding anomalously dispersive medium inside a ring laser. We identify theoretical conditions under which the sensitivity of the resonance frequency to a change in the cavity length is enhanced by as much as seven orders of magnitude. This paves the way for realizing a fast-light enhanced ring laser gyroscope, for example. This is followed by the development of a novel data buffering system which employs two WLC systems in series. In this system, a data pulse can be delayed an arbitrary amount of time, without significant distortion. The delay time is independent of the data bandwidth, and is limited only by the attenuation experienced by the data pulse as it bounces between two high-reflectivity mirrors. Such a device would represent a significant breakthrough in overcoming the delay-time bandwidth product limitation inherent in conventional data buffers. We then describe our experimental effort to create a fiber-based WLC by using stimulated Brillouin scattering (SBS). Experimental results, in agreement with our theoretical model presented here, show that the WLC effect is small under the conditions supported by current fiber optic technology. We conclude that future efforts to induce a large WLC effect would require fibers with high Brillouin coefficient and low transmission loss, as well as optical elements with very low insertion loss and high power damage thresholds.

High-speed optical networks will require all-optical signalprocessing to avoid bottleneck due to optical-to-electrical (O/E)and electrical-to-optical (E/O) conversion. Enabling of opticalprocessing tasks such as optical buffering and data synchronizationwill require large tunable delay. Recently, slow-light physics gotwide attention to generate tunable delay. However, for a slow-lightsystem large delay comes at the expense of increased distortion.This dissertation presents a study of the slow-light systems andquantifies the limitations imposed on delay due to distortion andsystem resource constraints. Optimal designs for two- and three-lineBrillouin slow-light systems showed fractional pulse delay of up to1.7 compared to a single-line gain system. Optimal designs forbroadband Brillouin gain system showed upto 100\% delay improvementcompared to the Gaussian pump. Wavelength conversion and dispersionbased tunable delay systems showed bit delay of 15 bits. An opticalbuffer based on photorefractive medium for real-time data storagewas demonstrated by storing and retrieving a 7-bit data sequence.

No description available.

In this dissertation, high-power ytterbium-doped fiber amplifiers designed with advanced waveguide concepts are characterized and power scaled. Fiber waveguides utilizing cladding microstructures to achieve wave guidance via the photonic bandgap (PBG) effect and a combination of PBG and modified total internal reflection (MTIR) have been proposed as viable single-mode waveguides. Such novel structures allow larger core diameters (>35 μm diameters) than conventional step-index fibers while still maintaining near-diffraction limited beam quality. These microstructured fibers are demonstrated as robust single-mode waveguides at low powers and are power scaled to realize the thermal power limits of the structure. Here above a certain power threshold, these coiled few-mode fibers have been shown to be limited by modal instability (MI); where energy is dynamically transferred between the fundamental mode and higher-order modes. Nonlinear effects such as stimulated Brillouin scattering (SBS) are also studied in these fiber waveguides as part of this dissertation. Suppressing SBS is critical towards achieving narrow optical bandwidths (linewidths) necessary for efficient fiber amplifier beam combining. Towards that end, new effects that favorably reduce acoustic wave dispersion to increase the SBS threshold are discovered and reported. The first advanced waveguide examined is a Yb-doped 50/400 µm diameter core/clad PBGF. The PBGF is power scaled with a single-frequency 1064 nm seed to an MI-limited 410 W with 79% optical-to-optical efficiency and near-diffraction limited beam quality (M-Squared < 1.25) before MI onset. To this author's knowledge, this represents 2.4x improvement in power output from a PBGF amplifier without consideration for linewidth and a 16x improvement in single-frequency power output from a PBGF amplifier. During power scaling of the PBGF, a remarkably low Brillouin response was elicited from the fiber even when the ultra large diameter 50 µm core is accounted for in the SBS threshold equation. Subsequent interrogation of the Brillouin response in a pump probe Brillouin gain spectrum diagnostic estimated a Brillouin gain coefficient, gB, of 0.62E-11 m/W; which is 4x reduced from standard silica-based fiber. A finite element numerical model that solves the inhomogenous Helmholtz equation that governs the acoustic and optical coupling in SBS is utilized to verify experimental results with an estimated gB = 0.68E-11 m/W. Consequently, a novel SBS-suppression mechanism based on inclusion of sub-optical wavelength acoustic features in the core is proposed. The second advanced waveguide analyzed is a 35/350 µm diameter core/clad fiber that achieved wave guidance via both PBG and MTIR, and is referred to as a hybrid fiber. The waveguide benefits mutually from the amenable properties of PBG and MTIR wave guidance because robust single-mode propagation with minimal confinement loss is assured due to MTIR effects, and the waveguide spectrally filters unwanted wavelengths via the PBG effect. The waveguide employs annular Yb-doped gain tailoring to reduce thermal effects and mitigate MI. Moreover, it is designed to suppress Raman processes for a 1064 nm signal by attenuating wavelengths > 1110 nm via the PBG effect. When seeded with a 1064 nm signal deterministically broadened to ~1 GHz, the hybrid fiber was power scaled to a MI-limited 820 W with 78% optical-to-optical efficiency and near diffraction limited beam quality of M_Squared ~1.2 before MI onset. This represents a 14x improvement in power output from a hybrid fiber, and demonstrates that this type of fiber amplifier is a quality candidate for further power scaling for beam combining.

Hybrid microstructured fibers, utilizing both air holes and high index cladding structures, provide important advantages over conventional fiber including robust fundamental mode operation with large core diameters (>30 mu m) and spectral filtering (i.e. amplified spontaneous emission and Raman suppression). This work investigates the capabilities of a hybrid fiber designed to suppress stimulated Brillouin scattering (SBS) and modal instability (MI) by characterizing these effects in a counter-pumped amplifier configuration as well as interrogating SBS using a pump-probe Brillouin gain spectrum (BGS) diagnostic suite. The fiber has a 35 mu m annularly gain tailored core, the center doped with Yb and the second annulus comprised of un-doped fused silica, designed to optimize gain in the fundamental mode while limiting gain to higher order modes. A narrow-linewidth seed was amplified to an MI-limited 820 W, with near-diffraction-limited beam quality, an effective linewidth similar to 1 GHz, and a pump conversion efficiency of 78%. Via a BGS pump-probe measurement system a high resolution spectra and corresponding gain coefficient were obtained. The primary gain peak, corresponding to the Yb doped region of the core, occurred at 15.9 GHz and had a gain coefficient of 1.92x10(-11) m/W. A much weaker BGS response, due to the pure silica annulus, occurred at 16.3 GHz. This result demonstrates the feasibility of power scaling hybrid microstructured fiber amplifiers

In 1920, Leon Brillouin discovered a new kind of light scattering – Brillouin scattering – which occurs as a result of the interaction of light with a transparent material’s temporal periodic variations in density and refractive index. Many advances have since been made in the study of Brillouin scattering, in particular in the field of fiber optics. An in-depth investigation of Brillouin scattering in optical fibers has been carried out in this thesis, and the theory of stimulated Brillouin scattering (SBS) and combined Brillouin gain and loss has been extended. Additionally, several important applications of SBS have been found and applied to current technologies. Several mathematical models of the pump-probe interaction undergoing SBS in the steady-state regime have emerged in recent years. Attempts have been made to find analytical solutions of this system of equations, however, previously obtained solutions are numerical with analytical portions and, therefore, qualify as hybrid solutions. Though the analytical portions provide useful information about intensity distributions along the fiber, they fall short of describing the spectral characteristics of the Brillouin amplification and the lack of analytical expressions for Brillouin spectra substantially limits the utility of the hybrid solutions for applications in spectral measurement techniques. In this thesis, a highly accurate, fully analytic solution for the pump wave and the Stokes wave in Brillouin amplification in optical fibers is given. It is experimentally confirmed that the reported analytic solution can account for spectral distortion and pump depletion in the parameter space that is relevant to Brillouin fiber sensor applications. The analytic solution provides a valid characterization of Brillouin amplification in both the low and high nonlinearity regime, for short fiber lengths. Additionally, a 3D parametric model of Brillouin amplification is proposed, which reflects the effects of input pump and Stokes powers on the level of pump wave depletion in the fiber, and acts as a classification tool to describe the level of similarity between various Brillouin amplification processes in optical fibers. At present, there exists a multitude of electro-optic modulators (EOM), which are used to modulate the amplitude, frequency, phase and polarization of a beam of light. Among these modulators, phase modulation provides the highest quality of transmitted signal. As such, an improved method of phase-modulation, based on the principles of stimulated Brillouin scattering, as well as an optical phase-modulator and optical phase network employing the same, has been developed. Due to its robustness, low threshold power, narrow spectrum and simplicity of operation, stimulated Brillouin scattering (SBS) has become a favourable underlying mechanism in fiber-based devices used for both sensing and telecommunication applications. Since birefringence is a detrimental effect for both, it is important to devise a comprehensive characterization of the SBS process in the presence of birefringence in an optical fiber. In this thesis, the most general model of elliptical birefringence in an optical fiber has been developed for a steady-state and transient stimulated Brillouin scattering (SBS) interaction, as well as the combined Brillouin gain and loss regime. The impact of the elliptical birefringence is to induce a Brillouin frequency shift and distort the Brillouin spectrum – which varies with different light polarizations and pulse widths. The model investigates the effects of birefringence and the corresponding evolution of spectral distortion effects along the fiber, and proposes regimes that are more favourable for sensing applications related to SBS – providing a valuable prediction tool for distributed sensing applications. In recent years, photonic computing has received considerable attention due to its numerous applications, such as high-speed optical signal processing, which would yield much faster computing times and higher bandwidths. For this reason, optical logic has been the focus of many research efforts and several schemes to improve conventional logic gates have been proposed. In view of this, a combined Brillouin gain and loss process has been proposed in a polarization maintaining optical fiber to realize all-Optical NAND/NOT/AND/OR logic gates in the frequency domain. A model describing the interaction of a Stokes, anti-Stokes and a pump wave, and two acoustic waves inside a fiber, ranging in length from 350m-2300m, was used to theoretically model the gates. Through the optimization of the pump depletion and gain saturation in the combined gain and loss process, switching contrasts of 20-83% have been simulated for different configurations.

[ES] Los efectos no lineales son herramientas valiosas en el procesamiento óptico. El obje-tivo de esta Tesis es contribuir con las nuevas arquitecturas y métodos a este campo, en particular al control de la polarización de la luz con luz y filtrado óptico de señales de microondas. La manipulación de las propiedades de la polarización de la luz en medios guiados es crucial en muchos sistemas ópticos clásicos y cuánticos. Sin embargo, la capacidad de la tecnología actual para definir con precisión el estado de polarización de determina-das longitudes de onda está lejos del nivel de madurez conseguido en el control de la amplitud. En el capítulo 3, se presenta un nuevo enfoque para el control totalmente óptico del estado de polarización con selectividad en longitud de onda, basado en el cambio del retardo fase por medio del stimulated Brillouin scattering. Los experimen-tos muestran que se puede llegar a cualquier punto de la esfera de Poincaré desde un estado de polarización de entrada arbitrario con tan solo una ligera variación en la amplitud de la señal (<2.5 dB). A diferencia de otros esquemas de procesamiento Bri-llouin, la degradación de la figura de ruido es pequeña (1.5 dB para una rotación completa en la esfera, 2pi). Este controlador de polarización completamente óptico puede forjar el desarrollo de nuevas técnicas basadas en la polarización en comunica-ciones ópticas, ingeniería laser, detección, sistemas cuánticos y sondeo basado en luz de sistemas químicos y biológicos. La segunda área de interés de la tesis se centra en el filtrado fotónico de microondas. La fotónica proporciona una implementación alternativa a los filtros de microondas. Las características proporcionadas por el scattering de Brillouin son muy atractivas para el diseño de filtro con especificaciones competitivas. El capítulo 4 está dedicado a los nuevos esquemas para el filtrado fotónico de microondas basado en SBS. En parti-cular, se presenta un método para mejorar la pendiente de los filtros fotónicos de mi-croondas basados en Brilouin. Esta mejora se logra mediante la combinación de las respuestas en ganancia y atenuación del Brillouin sobre la señal modulada en fase. Los resultados experimentales muestran una respuesta paso banda que exhibe una pendiente de 16.7 dB por octava, lo que corresponde con una mejora de 3 veces en comparación con la respuesta Lorentziana natural de la ganancia Brillouin. Sin embargo, la necesi-dad de 3 ondas de bombeo, es decir tres osciladores de microondas, incrementan la complejidad del sistema y dificulta la capacidad de ajuste. Para superar estas limita-ciones, se propone una segunda técnica para mejorar la pendiente de un filtro fotónico de microondas basado en scattering de Brillouin estimulado, el cual mantiene una fácil sintonización. Esta propuesta se basa en la dependencia de la polarización de la ganan-cia del Brillouin en fibras birrefringentes. La presencia de dos respuestas ortogonales de ganancia/atenuación Brillouin en fibras birrefringentes da como resultado dos res-puestas del filtro, que pueden ser sustraídas en un fotodetector balanceado para elimi-nar el lento decaimiento de la respuesta de ganancia natural Lorentziana del Brillouin. Los resultados experimentales muestran que se puede obtener una pendiente del filtro de 8.3 dB/oct. Finalmente, el documento de tesis proporciona conclusiones y actividades futuras abiertas por este trabajo de doctorado. / [CAT] Els efectes no lineals son ferramentes valuoses en el processament òptic. L'objectiu d'aquesta tesi es contribuir amb les noves arquitectures i mètodes a aquest camp, en particular al control de la polarització de la llum amb llum i filtrar òptic de senyals de microones. La manipulació de les propietats de la polarització de la llum en mitjans guiats es cru-cial en molts sistemes òptics clàssics i quàntics. No obstant això, la capacitat de la tecnologia actual per definir amb precisió l'estat de polarització de determinades lon-gituds d'ona està lluny del nivell de maduresa aconseguit en el control de l'amplitud. En el capítol 3, es presenta un nou enfocament per al control totalment òptic de l'estat de polarització amb selectivitat en longitud d'ona, basat en el canvi del retard de fase mitjançant el stimulated Brillouin scattering. Els experiments mostren que es pot arri-bar a qualsevol punt de l'esfera de Poincaré des d'un estat de polarització d'entrada arbitrari amb tant sols una lleugera variació de l'amplitud de la senyal (<2.5 dB). A diferencia d'altres esquemes de processament Brillouin, la degradació de la figura de soroll es petita (1.5 dB per a una rotació completa en l'esfera, 2pi). Aquest controlador de polarització completament òptic pot forjar el desenvolupament de noves tècniques basades en la polarització en comunicacions òptiques, enginyeria làser, detecció, sis-temes quàntics y sondeig basat en llum de sistemes químics i biològics. La segona àrea d'interès de la tesi es centra en el filtrar fotònic de microones. La fo-tònica proporciona una implementació alternativa als filtres de microones. Les caracte-rístiques proporcionades per el scattering de Brillouin son molt atractives per al dis-seny de filtres amb especificacions competitives. El capítol 4 està dedicat als nous esquemes per al filtrat fotònic de microones basat en SBS. En particular, es presenta un mètode per a millorar la pendent dels filtres fotònics de microones basats en Bri-llouin. Aquesta millora s'aconsegueix mitjançant la combinació de les respostes en guany i atenuació del Brillouin sobre la senyal modulada en fase. Els resultats experi-mentals mostren una resposta pas banda que exhibeix una pendent de 16.7 dB per octava, el que correspon amb una millora de 3 vegades en comparació amb la resposta Lorentziana natural del guany Brillouin. Tot i això, la necessitat de 3 ones de bom-beig, es a dir tres oscil·ladors de microones, incrementen la complexitat del sistema i dificulta la capacitat d'ajust. Per superar aquestes limitacions, es proposa una segona tècnica per millorar la pendent d'un filtre fotònic de microones basat en scattering de Brillouin estimulat, el qual manté una fàcil sintonització. Aquesta proposta es basa en la dependència de la polarització del guany del Brillouin en fibres birefringents. La presència de dos respostes ortogonals de guany/atenuació Brillouin en fibres birefrin-gents dona com a resultat dos respostes del filtre, que poden ser sostretes en un fotode-tector balancejat per eliminar el lent decaïment de la resposta de guany natural Lo-rentziana del Brillouin. Els resultats experimentals mostren que es pot obtenir una pendent del filtre de 8.3 dB/oct. Finalment, el document de tesi proporciona conclusions i activitat futures obertes per aquest treball de doctorat. / [EN] Nonlinear effects are valuable tools in the field of optical processing. This Thesis is aimed at contributing with new architectures and methods to this field, in particular to the light-by-light control of polarization and optical filtering of microwave signals. The manipulation of the polarization properties of light in guided media is crucial in many classical and quantum optical systems. However, the capability of current technology to finely define the state of polarization of particular wavelengths is far from the level of maturity in amplitude control. In Chapter 3, a new approach for all-optical control of the state of polarization with wavelength selectivity based on the change of the phase retardance by means of stimulated Brillouin scattering is present-ed. Experiments show that any point on the Poincaré sphere can be reached from an arbitrary input state of polarization with little variation of the signal amplitude (< 2.5 dB). Unlike other Brillouin processing schemes, the degradation of the noise figure is small (1.5 dB for a full 2pi rotation). This all-optical polarization controller can forge the development of new polarization-based techniques in optical communication, laser engineering, sensing, quantum systems and light-based probing of chemical and biological systems. The second area of interest of the Thesis is photonic microwave filtering. Photonics provides an alternative implementation of microwave filters. The features provided by Brillouin scattering are very attractive to design filters with competitive specifications. Chapter 4 is devoted to new schemes for photonic microwave filtering based on SBS. In particular, a method to enhance the filter slope of Brillouin-based photonic microwave filters is presented. This improvement is achieved by the combination of Brillouin gain and loss responses over phase modulated signals. The experimental results show passband responses exhibiting a slope of 16.7 dB per octave, which corresponds with a 3-fold improvement in comparison to the natural Lorentzian response for the same gain. However, the need of three pump waves, i.e. three microwave oscillators, increases the system complexity and make tunability more difficult. To overcome these limitations, a second technique to enhance the slope of a photonic microwave filter based on stimulated Brillouin scattering is proposed, that maintains easy tunability. It relies on exploiting the polarization dependence of Brillouin gain in birefringent fibers. The presence of two orthogonal Brillouin gains/loss in birefringent fibers results in two filter responses that can be subtracted in a balanced photodetector to remove the slow Lorentzian decay of the natural Brillouin gain response. Experimental results show that a filter slope of 8.3 dB/oct can be obtained. Finally, the Thesis document provides conclusions and future activities opened by this PhD work. / Samaniego Riera, DP. (2019). OPTICAL PROCESSING BASED ON BRILLOUIN SCATTERING [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/124820 / TESIS