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.

<p>All-optical devices have attracted many research interests due to their ultimately low heat dissipation compared to conventional devices based on electric-optical conversion. With recent advances in nonlinear optics, it is now possible to design the optical properties of a medium via all-optical nonlinear effects in a table-top device or even on a chip.</p><p>In this thesis, I realize all-optical control of the optical group velocity using the nonlinear process of stimulated Brillouin scattering (SBS) in optical fibers. The SBS-based techniques generally require very low pump power and offer a wide transparent window and a large tunable range. Moreover, my invention of the arbitrary SBS resonance tailoring technique enables engineering of the optical properties to optimize desired function performance,</p><p>which has made the SBS techniques particularly widely adapted for</p><p>various applications.</p><p>I demonstrate theoretically and experimentally how the all-optical</p><p>control of group velocity is achieved using SBS in optical fibers.</p><p>Particularly, I demonstrate that the frequency dependence of the</p><p>wavevector experienced by the signal beam can be tailored using</p><p>multi-line and broadband pump beams in the SBS process. Based on the theoretical framework, I engineer the spectral profile</p><p> to achieve two different application goals: a uniform low group velocity (slow light) within a broadband spectrum, and a group velocity with a linear dependence on the frequency detuning (group velocity dispersion or GVD).</p><p>In the broadband SBS slow light experiment, I develop a novel noise current modulation method that arbitrarily tailors the spectrum of a diode laser. Applying this method, I obtain a 5-GHz broadband SBS gain with optimized flat-topped profile, in comparison to the ~40 MHz natural linewidth of the SBS resonance. Based on the broadband SBS resonance, I build a 5-GHz optical buffer and use this optical buffer to delay a return-to-zero data sequence of rate 2.5 GHz (pulse width 200 ps). The fast noise modulation method significantly stabilizes the SBS gain and improves the signal fidelity. I obtain a tunable delay up to one pulse-width with a peak signal-to-noise ratio of 7. I also find that SBS slow light performance can be improved by avoiding competing nonlinear effects. A gain-bandwidth product of 344 dB.GHz is obtained in our system with a highly-nonlinear optical fiber.</p><p>Besides the slow light applications, I realize that group velocity dispersion is also optically controlled via the SBS process. In the very recent GVD experiment, I use a dual-line SBS resonance and obtain a tunable GVD parameter of 7.5 ns$^2$/m, which is 10$^9$ times larger than the value found in a single-mode fiber. The large GVD system is used to disperse an optical pulse with a pulse width of 28 ns, which is beyond the capability for current dispersion techniques working in the picosecond and sub picosecond region. The SBS-based all-optical control of GVD is also widely tunable and can</p><p>be applied to any wavelength within the transparent window of the</p><p>optical fiber. I expect many future extensions following this work</p><p>on the SBS-based all-optical GVD control using the readily developed SBS tailoring techniques.</p><p>Finally, I extend the basic theory of backwards SBS to describe the forward SBS observed in a highly nonlinear fiber, where asymmetric forward SBS resonances are observed at the gigahertz range. An especially large gain coefficient of 34.7 W$^{-1}$ is observed at the resonance frequency of 933.8 MHz. This is due to good overlap between the optical wave and the high order guided radial acoustic wave. The interplay from the competing process known as the Kerr effect is also accounted for in the theory.</p> / Dissertation

No description available.

Orientador: Hugo Luis Fragnito / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin. / Made available in DSpace on 2018-08-12T16:20:28Z (GMT). No. of bitstreams: 1 Wiederhecker_GustavoSilva_D.pdf: 26845631 bytes, checksum: f23a4b48df09da35f76ca70361b0231d (MD5) Previous issue date: 2008 / Resumo: Neste trabalho são investigadas técnicas para controlar o confinamento de fótons e fônons em fibras ópticas de cristal fotônico (PCF). Utilizando métodos numéricos robustos para resolver as equações de Maxwell, um novo tipo de PCF com núcleo tubular é proposto. Simulações e experimentos demonstram que esta estrutura confina a luz em um buraco de ar com diâmetro de apenas 110 nm. A figura de mérito para efeitos não-lineares nesta pequena região é 10 bilhões de vezes maior do que no caso de um feixe gaussiano altamente focalizado e 100 vezes maior que o atual estado-da-arte em fibras de band-gap fotônico. Também é analisada teoricamente uma fibra PCF do tipo kagomé. Modelos que explicam suas complexas características de guiamento são investigados de forma analítica e numérica. No que diz respeito à fônons em PCFs, é investigado o espalhamento Brillouin copropagante e contra-propagante. Em particular, são demonstradas maneiras de reduzir a interação acusto-óptica nos casos de co- e retro-espalhamento. Também é demonstrada a presença de band-gaps fonônicos nestas estruturas. Finalmente, é investigado o controle óptico coerente de modos acústicos nestas fibras, mostra-se que é possível amplificar ou frear modos acústicos com freqüência de oscilação na faixa de GHz. / Abstract: Techniques that may allow control and tight confinement of photons and phonons in photonic crystal fibers (PCFs) are investigated in this thesis. By means of robust numerical methods to solve Maxwell equations, a new kind of PCF with a tubular core is proposed. Simulations and experimental results show that such structure is able to confine light tighly inside the 100 nm bore, the nonlinear figure of merir for such tiny bore is found to be 10 billion fold larger the focused Gaussian beam counterpart, it is also 100 times larger than the state-of-the-art hollow core photonic band-gap fibers. The guidance mechanism of kagomé structure hollow-core PCF is also investigated, simple models are proposed to explain most of the experimentally observed features and compared to full numerical simulations. In what concerns phonons, both forward and backward Brillouin scattering is investi-gated in PCFs. It is demonstrated how one may suppress both using such fibers. It is also shown the existence of complete band-gaps for in-plane propagation in the PCF cladding. Another set of experiments show that one can perform coherent optical control of the acoustic modes of such fibers, 100-fold amplification or almost complete suppression of GHz oscillations is achieved. / Doutorado / Física / Doutor em Ciências

Orientador: Hugo L. Fragnito / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-09T05:15:29Z (GMT). No. of bitstreams: 1 DaineseJunior_PauloClovis_D.pdf: 4977952 bytes, checksum: 68cd4c3ce792cf4994babe5cce9b77a9 (MD5) Previous issue date: 2006 / Resumo: Esta tese apresenta estudos experimentais e teóricos sobre o processo de espalhamento Brillouin em Fibras de Cristal Fotônico. Formadas por um núcleo sílica pura e uma casca micro-estruturada (sílica e ar), estas fibras permitem o confinamento óptico e acústico em regiões da ordem do comprimento de onda. Como resultado, a interação acústo-óptica apresenta características radicalmente diferentes daquelas observadas em meio bulk ou em fibras convencionais. Investigamos experimentalmente ambos co- e retro-espalhamento Brillouin. Observamos que quando o diâmetro do núcleo é ~70 % do comprimento de onda óptico no vácuo, o espectro de retro-espalhamento espontâneo apresenta múltiplos picos, os quais atribuímos a famílias de modos acústicos guiados no núcleo da fibra. Além disso, o limiar de retro-esplhamento Brillouin estimulado aumenta por um fator ~5 quando o diâmetro do núcleo é diminuído de 8 .m para 1.22 .m , resultado da natureza complexa dos modos acústicos no núcleo, contendo fortes componentes de deslocamento longitudinal e transversal. No caso de co-espalhamento, realizamos medidas de espalhamento espontâneo e de excitação impulsiva de ondas acústicas utilizando pulsos ópticos de alta intensidade, através do efeito de eletrostrição. Estes experimentos nos possibilitaram observar o confinamento transversal de ondas acústicas no núcleo da fibra fotônica. Desenvolvemos um modelo analítico para a interação acústo-óptica, aproximando o núcleo da fibra como um cilindro de silica suspenso no vácuo, sem a presença da casca. Este modelo nos permitiu entender a física envolvida no processo e também explicar qualitativamente as observações experimentais. Modelos numéricos mais sofisticados foram utilizados para o cálculo dos modos acústicos e óptico suportados pela estrutura completa da fibra fotônica, os quais nos permitiram explicar mais precisamente as observações experimentais. Finalmente, realizamos cálculos numéricos da estrutura de bandas da região micro-estruturada, demonstrando a presença de bandas proibidas (ou gaps fonônicos) para as ondas acústicas / Abstract: This thesis presents experimental and theorethical studies on Brillouin scattering in Photonic Crystal Fibers. With a pure silica core surrounded by a microstructed cladding (silica and air), these fibers allow the confinement of both acoustic and optical waves in sub-wavelength regions. The result is a radically different acousto-optic interaction from what has been observed in bulk media or conventional fibers. We investigate experimentally both forward and backward Brillouin scattering. We observed that for core diameters of around 70% of the vacuum wavelength of the launched laser light, the spontaneous Brillouin signal develops an unusual multi-peaked spectrum, these peaks we attribute to several families of guided acoustic modes. At the same time the threshold power for stimulated Brillouin scattering increases five-fold when the core diameter is reduced from from 8 .m to 1.22 .m , as a consequence of the complex nature of the acoustic modes, each with different proportions of longitudinal and shear strain, strongly localised to the core. In the case of forward scattering, we performed measurements of the spontaneous scattering and also of impulsive excitation of acoustic waves using high intensity optical pulses, through the effect of electrostriction. These experiments allowed us to observe the transverse confinment of acoustic waves in the core of the photonic crystal fiber. An analitic model for the acousto-optic interaction was developed by approximating the core of the photonic fiber by a circular strand of glass in vaccum, initially neglecting the presence of the micro-structured cladding. This simple model allowed us to understand the physics involved in the scattering process and also to qualitatevely explain our experimental observations. Numerical models were then implemented to calculate the acoustic and optical modes of the actual photonic fiber structure, and we were able to explain more precisely our observations. Finnally, we performed numerical calculation of the band structure of the micro-structured region, demonstrating the presence of prohibited gaps for the acoustic wave (phononics band gaps) / Doutorado / Física / Doutor em Ciências

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

Brillouin scattering has been verified to be an effective mechanism in temperature and strain sensing. This kind of sensors can be applied to civil structural monitoring of pipelines, railroads, and other industries for disaster prevention. This thesis first presents a novel fiber sensing scheme for long-span fully-distributed pressure measurement based on Brillouin scattering in a side-hole fiber. After that, it demonstrates that Brillouin frequency keeps linear relation with temperature up to 1000°C; Brillouin scattering is a promising mechanism in high temperature distributed sensing. A side-hole fiber has two longitudinal air holes in the fiber cladding. When a pressure is applied on the fiber, the two principal axes of the fiber birefringence yield different Brillouin frequency shifts in the Brillouin scattering. The differential Brillouin scattering continuously along the fiber thus permits distributed pressure measurement. Our sensor system was designed to analyze the Brillouin scattering in the two principal axes of a side-hole fiber in time domain. The developed system was tested under pressure from 0 to 10,000 psi for 100m and 600m side-hole fibers, respectively. Experimental results show fibers with side holes of different sizes possess different pressure sensitivities. The highest sensitivity of the measured pressure induced differential Brillouin frequency shift is 0.0012MHz/psi. The demonstrated spatial resolution is 2m, which maybe further improved by using shorter light pulses. / Master of Science