Polarized random fibre lasers based on the tilted fibre Bragg grating

In the traditional random fibre lasers (RFLs), it is complicated to generate polarized random fibre lasing. In this thesis, I present a new method to obtain polarized random fibre lasers (RFLs). In my research, 45° tilted fibre Bragg grating (45° TFG) fabricated in single mode fibre (SMF) or in Erbium doped fibre (EDF) has been integrated with the fibre laser and the polarized random lasing was achieved using 45° TFG with high polarization extinction ratio (PER) characteristics. In this thesis, first of all, I present the review of random lasers (RLs), random fibre lasers (RFLs), and corresponding polarization characteristics. And then I present a detailed research work on the method, characteristics and applications of fibre gratings, including fibre Bragg gratings (FBGs), long period gratings (LPGs), and TFG with small and 45° titled structures. One of the major contributions of my work in this thesis is the investigation on phase-match conditions, transmission spectra, PER for different types of fibre gratings including the TFG, FBG, and LPG. The results show that 45o TFG has high PER with 14 dB and the 7o TFG has comb-like resonance transmission. And then I present the experimental research of the thermal sensing of different types of fibre grating. LPG with grating period of 480 m has the highest thermal sensitivity with 297.1 pm/°C, superior to the FBG, small angle TFG and LPG. Meanwhile, I also researched the strain sensing application of FBG. The strain sensitivity of the FBG is 0.71±0.01 pm/°C. The other important contribution from the work is that I researched the polarization random fibre lasing feature with 45° TFG in the two fibre laser systems, which are Raman distributed SMF system and EDF with Raman distributed SMF hybrid system. In the Raman distributed SMF with length of 20.1 km system, there are three kinds of emission spectra with the increase of pump power from 1.70 W to 3.00 W: Raman emission, non-stationary random lasing emission, and stationary random lasing emission. The random lasing threshold is measured as 2.10 W. When the 45°TFG is added in the system, the polarized random lasing with PER of 12.02 dB has been obtained. In the EDF (2 m length) and Raman distributed SMF (11 km length) hybrid system without 45° TFG, there are two kinds of emission with the increase of pump power from 2.60 W to 4.40 W: Raman emission, and non-stationary random lasing. The stationary random lasing has not been observed due to the pump power limit. When the 45° TFG has been integrated in the hybrid system, we observed two kinds of emission in a range of pump power of 1.00 W to 2.20 W: Raman and Er3+ emission, and stationary random lasing. Under the effect of weak cavity formed by 45° TFG reflection and SMF distributed feedback, there occurs stabilized random fibre lasing emission. The threshold has been determined as 1.44 W. In addition, under the effect of 45° TFG, the polarized random fibre lasing with PER of 15.3 dB has been obtained

Contribution to the development of new photonic systems for fiber optic sensing applications

En este trabajo de doctorado se presentan nuevos sistemas y subsistemas de sensores de fibra óptica. Así, se proponen y desarrollan nuevas técnicas, componentes y tecnologías basadas en láseres de fibra con espejos distribuidos (random), fibras de cristal fotónico, estructuras de luz lenta, multiplexores de inserción y extracción (add and drop), conmutadores tele-alimentados por luz, reflectometría óptica tanto en el dominio del tiempo como de la frecuencia o filtros ópticos reconfigurables. También se han demostrado nuevas aplicaciones para estructuras de sensores tradicionales y técnicas de medida ya conocidas. Todas ellas dirigidas a la mejora del funcionamiento de los actuales transductores, redes de sensores y aplicaciones de monitorización de salud estructural. De este modo, y en primer lugar, se han desarrollado nuevos transductores puntuales. En concreto, dos sensores interferométricos basados en fibras de cristal fotónico y otro basado en una estructura resonante en anillo. También se han realizado diferentes redes de sensores utilizando OTDRs comerciales. Por un lado, se han multiplexado diferentes sensores utilizando una red en forma de bus y, por el otro, se ha interrogado de manera remota un sensor FLM/LPG a una distancia de 253 km sin necesidad de amplificación. Se han estudiado láseres basados en efecto de realimentación distribuida random (RDFB) para su uso en interrogación de sensores. Para ello, se han demostrado dos nuevos láseres multi-longitud de onda y también, por primera vez, se ha modulado un laser random. Después, se han demostrado experimentalmente varias redes de sensores de fibra óptica teniendo en cuenta los principales desafíos que estas presentan: multiplexar varios sensores en una misma red y permitir su monitorización de manera remota. En primer lugar, se han multiplexado sensores basados en la modulación de la intensidad óptica utilizando técnicas de multiplexación en dominio del tiempo. En segundo lugar, se han multiplexado sensores basados en fibras de cristal fotónico. En tercer lugar, se presentan tres nuevos métodos para la medida remota de sensores. Por último, se incluye la demostración de un conmutador de fibra óptica tele-alimentado a través de luz. Éste se utiliza en tres redes diferentes para añadir robustez e incrementar la versatilidad en la multiplexación. Finalmente, se han realizado tres pruebas de campo para aplicaciones de monitorización de salud estructural.In this PhD work, different new photonic systems and subsystems for fiber optic sensing are presented. The aim of this thesis has been to contribute to the fiber optic sensors field using modern techniques, components and technologies such as random fiber lasers, photonic crystal fibers, slow light structures, add and drop multiplexers, powered by light switches, optical frequency and time domain reflectometry or reconfigurable optical filters, among others. New applications of traditional sensing structures or techniques have been also demonstrated. All of them focused on improving the performance of current sensors transducers, multiplexing networks and structural health monitoring applications. Thus, new point transducers have been developed: two of them are interferometric sensors based on photonic crystal fibers; and another one is based on a fiber ring resonator structure. Fiber optic sensor networks using commercial OTDRs have been also explored. On the one hand, different sensors have been successfully multiplexed in the same bus network. And, on the other hand, a FLM/LPG sensor was remotely interrogated at a distance of 253 km without using amplification. Random distributed feedback (RDFB) lasers have been explored for sensors interrogation. Two multi-wavelength Raman fiber lasers suitable for sensors interrogation have been demonstrated. Also, a random fiber laser has been internally modulated for the first time. Then, some experimental demonstrations of fiber optic sensors networks have been carried out taking into account the principal challenges they pose: multiplexing a number of optical sensors in a single networks, and enabling the possibility of remote sensing. Firstly, intensity sensors using TDM technology have been multiplexed. Secondly, PCF sensors have been successfully multiplexed. Thirdly, three new approaches to enable remote sensing are presented. Finally, a remote powered by light fiber optic switch have been included in three networks in order to add robustness and multiplexing versatility.Este trabajo se ha llevado a cabo gracias a las aportaciones económicas recibidas de los siguientes organismos, entre otros: - Secretaría de Estado de Investigación, Desarrollo e Innovación, Ministerio de Economía y Competitividad de España a través del programa de Formación del Personal Investigador y asociado al proyecto de investigación TEC2010-20224-C02-01. - Universidad Pública de Navarra mediante las ayudas a tesis doctorares. - Acción Europea COST- TD1001: Novel and Reliable Optical Fibre Sensor Systems for Future Security and Safety Applications (OFSeSa) - También se ha recibido financiación del Proyecto de Investigación de la Secretaría de Estado de Investigación, Desarrollo e Innovación, Ministerio de Economía y Competitividad de España TEC2013-47264-C2-2-R, de Innocampus, del Proyecto Europeo SUDOE-ECOAL-Intereg Project ECOAL-MGT y de los Fondos FEDER.Programa Oficial de Doctorado en Tecnologías de las Comunicaciones (RD 1393/2007)Komunikazioen Teknologietako Doktoretza Programa Ofiziala (ED 1393/2007

Discovery and Correction of Spatial Non-Uniformity in Optical Fibers: Towards the Fabrication of Perfect Ultra-Long Fiber Bragg Gratings for Applications in Non-Linear Optics

Les réseaux de Bragg (FBGs) sont des dispositifs tout-fibre communs en photonique et très utilisés en télécommunications comme filtres, réflecteurs sélectifs, compensateurs de dispersions et bien plus. Le sujet de cette thèse concerne les réseaux de Bragg ultra-longs, soit plus longs que la longueur typique des masques de phase (>20 cm). Les FBG ultra-longs ont la particularité d’avoir une très petite bande passante, un long temps de vie pour les modes de cavités distribués (DFB, cavité dont le champ des modes est distribué sur toute la longueur du réseau) et un grand chirp pour des FBG chirpé. Cette thèse étudie les cavités DFB ultra-longues à saut de phase, idéalement de π. Celles-ci comportent un seul mode de cavité à très haut facteur de qualité qui peut être utilisé comme laser lorsqu’un gain est présent. De tels lasers ont la propriété d’être monomode avec une largeur d’émission très fine en fréquence. Lorsqu’un gain non linéaire est présent, tel que du Brillouin ou Raman stimulé, ce qui est possible avec des FBGs ultra-longs, de tels lasers n’ont pas de restriction bande de longueurs d’onde, ce qui n’est pas le cas du gain des terres rares. En d’autres mots, ils peuvent être opérés à n’importe quelle longueur d’onde. Ces dispositifs ultra-longs spécialisés ont toujours été très difficiles à produire. Même avec les meilleurs systèmes, la reproductibilité de fabrication de FBGs ultra-longs de haute qualité était absente. À cause de cela, de tels dispositifs n’ont jamais été développés pour des applications commerciales. Cette thèse étudie les difficultés d’écriture de FBGs ultra-longs et démontre des solutions permettant une reproductibilité de haute qualité. La méthode d’écriture utilisée et étudiée au long de cette thèse est l’écriture en continu par modulateur électro-optique avec interféromètre de Talbot. La principale difficulté trouvée dans l’écriture de FBGs ultra-longs est la haute non-uniformité dans toutes les fibres optiques, une caractéristique difficile à mesuré et hautement néfaste pour les FBG ultra-longs. La solution proposée : faire une correction de phase pendant l’écriture afin de permettre un réseau parfait dans toute fibre. La thèse présente 4 articles montrant les limitations et solutions de la fabrication de FBGs ultra-longs ainsi que l’opération de laser DFB à fibre par gain Brillouin et Raman dans de tels FBGs. La thèse montre, dans la première publication, l’avantage de FBGs ultra-longs en démontrant un laser DFB avec un gain Brillouin dans de la fibre standard (SMF-28), au lieu de fibre hautement non linéaire typiquement utilisé pour de tels lasers.----------Abstract Fiber Bragg gratings (FBGs) are common all-fiber devices in photonics and have been widely used in telecommunications as filter, selective reflectors, dispersion compensators and more. The subject of this thesis is specialised Ultra-long FBGs, which are defined as longer then the typical length of a phase mask ( >20 cm). Ultra-long FBGs have the particularity of having very narrow bandwidth, long lifetime for distributed feedback (DFB) cavity modes and high chirp for chirped FBGs. A DFB cavity is a single-longitudinal-mode long cavity, as the photon is trapped along the entire length of the FBG. This thesis studies ultra-long DFB cavities known as “phase-shifted” or “π-shifted” and have a single phase defect inside the FBG to create the high Q cavity mode, which can then be used as a laser if an active gain medium is present. Such lasers would have the property of narrow linewidth single-frequency operation. When used with non-linear gain, such as Stimulated Raman or Brillouin gain, which can be done with ultra-long FBGs, those lasers have no specific band of operation restriction, contrary to rare-earth gain. In other words, they can be operated at any wavelength. Those specialised ultra-long FBG devices have long been difficult to produce. Even with the best systems, reproducibility of high quality ultra-long FBGs has always been absent. Because of this, such device was never fully developed for commercial applications. This thesis studies the difficulties of ultra-long FBG writing and demonstrates solution for reproducible high-quality fabrication. Stimulated Brillouin and Raman scattering gain phase-shifted DBF ultra-long FBGs are then modeled, optimized and tested. The writing method is continuous writing using an electro-optic modulator driven Talbot interferometer. The main difficulty found in ultra-long FBG writing, is high non-uniformity found in all optical fibers, a characteristic difficult to measure and very detrimental for ultra-long FBGs. A solution was proposed for this: make a phase correction during writing to allow perfect FBGs in any fibers. The thesis presents 4 articles relating ultra-long FBG fabrication limitations and solutions as well as Brillouin and Raman DFB fiber laser operation in ultra-long FBGs. The thesis shows, in the first publication, the advantage of ultra-long FBG by DFB lasers using non-linear gain (Stimulated Brillouin Scattering) in standard fiber (SMF-28), instead of typical highly non-linear fibers

Untersuchung der Gewinn-Vergrößerung der Stimulierten Brillouin Streuung (SBS) in Silizium-Nano-Wellenleitern und dessen Anwendungen

Stimulated Brillouin scattering is a third order non-linear effect with the lowest power threshold in standard single mode optical fiber, by which an interaction between optical and acoustic modes takes place. During the Brillouin scattering process, part of the pump wave power will be transferred to a counter propagating wave (Stokes), with a frequency shift of about 11 GHz for a telecommunication wavelength of 1550 nm in a standard single mode fiber. The frequency shift effective parameters had been studied as well as the governed equations for the pump and Stokes waves had been given. The Brillouin scattering gain linewidth for a standard single mode fiber was about 35 MHz. Therefore, and due to the increasing demands for ultra-high resolution spectroscopy, integrated photonics and other interesting applications, the effect and utilization of the stimulated Brillouin scattering were studied. It’s effect in silicon-on-insulator waveguides was investigated as well. The effect of stimulated Brillouin scattering in silicon-on-insulator was studied in Strip and rip-waveguides, each with two cases: air and silica cladding. The gain coefficient was simulated for each kind and case. It is found that the rib air cladding waveguide has the highest non-linearity with a gain coefficient of 1.32×104 (m∗W)−1 which is in the order of magnitudes higher than in optical fibers (2e−11 m/W). Therefore, an SOI-waveguide with a length of 100 μm corresponds to a 1 km optical fiber. Furthermore, the stimulated Brillouin scattering was utilized as a narrow band optical filter and amplifier in standard single mode fibers for various applications. First, stimulated Brillouin scattering assisted with polarization pulling was utilized to extract one high quality, narrow linewidth and tunable spectral line out of a frequency comb generated by a mode locked fiber laser. This spectral line had a linewidth of 1 kHz and acted as tunable laser source. The laser was stabilized by measuring the temperature dependent repetition rate drift of the mode locked fiber laser and a subsequent modulation. A residual drift for the extracted spectral line of ± 160 mHz was achieved. Second, two spectral lines were extracted out of the frequency comb by the same manner and mixed in a photo diode to generate a high quality milli-meter wave. It was stabilized via two methods: software and analog circuit. The RF signal showed a linewidth < 1 Hz and a phase noise of -134 dBc/Hz at 10 kHz frequency offset and a stability of 50 Hz in about 40 minutes duration time for the software approach. For the analog circuit approach a phase noise of -58 dBc/Hz at 10 kHz and a stability of 1 Hz over 40 minutes could be achieved.Die stimulierte Brillouin-Streuung, ein nichtlinearer Effekt der dritten Ordnung, besitzt den niedrigsten Schwellwert in optischen Fasern und beruht auf der Wechselwirkung zwischen optischen und akustischen Wellen. Während des Streuprozesses wird ein Teil der Energie der Pumpwelle auf eine sich gegenläufig ausbreitende Stokeswelle übertragen, wobei der Frequenzversatz in Standard-Einmodenfasern bei einer Pumpwellenlänge von 1550 nm ungefähr 11 GHz beträgt. Die Parameter hinsichtlich der Frequenzverschiebung als auch die Gleichungssysteme für die Pump- und Stokeswelle wurden betrachtet. Die Linienbreite der stimulierten Brillouin Streuung in einer Standard-Einmodenfaser beträgt etwa 35 MHz. Deshalb und aufgrund der zunehmenden Anforderungen für ultrahochauflösende Spektroskopie, integrierte Photonik und andere interessante Anwendungen, wurde der Effekt und die Verwendung der stimulierten Brillouin Streuung untersucht. Zusätzlich wurde der Effekt der stimulierten Brillouin Streuung auch in siliconon-insulator Wellenleitern untersucht. Dabei wurden speziell Streifenwellenleiter und rip-waveguides untersucht und dabei das Mantelmaterial variiert. Der Verstärkungskoeffizient wurde für jede Art und jeden Fall simuliert. Dabei ergaben sich die höchsten Nichtlinearitäten für den rip-waveguide mit einem Verstärkungskoeffizienten von 1.32×104 (m∗W)−1, welcher im Vergleich zu Standard-Einmodenfasern (2e−11 m/W) um Größenordnungen höher ist. Daher entspricht die Nicht-Linearität in einem 100 μm SOI-waveguide der von 1 km Faser. Weiterhin wurde die stimulierte Brillouin Streuung als schmalbandiger optischer Filter und Verstärker in Standard-Einmodenfasern für verschiedene Anwendungen eingesetzt. Zuerst wurde die polarisationsabhängige Verstärkung der Brillouin Streuung für die Extraktion einer einzelnen, schmalen und durchstimmbaren Mode aus einem Frequenzkamm, erzeugt von einem modengekoppelten Faserlaser, verwendet. Die Linienbreite dieser Mode ergab sich zu 1 kHz und wurde als durchstimmbarer Laser genutzt. Der Laser wurde durch eine Messung der temperaturabhängigen Drift der Wiederholrate und anschließender Modulation der extrahierten Mode stabilisiert. Dabei wurde ein Restdrift des Lasers von ± 160 mHz erreicht. Zweitens wurden auf die gleiche Weise zwei Spektrallinien aus dem Frequenzkamm extrahiert und in einer Fotodiode gemischt. Dies ermöglichte die Erzeugung von qualitativ hochwertigen Millimeterwellen, welche anhand von zwei unterschiedlichen Methoden stabilisiert wurden. Die erste Methode erfolgte durch eine Software wodurch das Hochfrequenzsignal eine Linienbreite <1 Hz, ein Phasenrauschen von -134 dBc/Hz bei einem Frequenzoffset von 10 kHz und einer Stabilität von 50 Hz für eine Dauer von 40 Minuten hatte. Für die zweite Methode zur Stabilisierung wurde eine analoge Schaltung verwendet, womit ein Phasenrauschen von -58 dBc/Hz bei 10 kHz Offset und eine Stabilität von 1 Hz über 40 Minuten erreicht werden konnten

Vector optical rogue waves in mode-locked fibre lasers

The project consists of an experimental characterisation of optical vector rogue wave (RW) events by using three different testbed fibre laser setups. The first testbed is a long cavity fibre laser (615 m). Here, we have demonstrated for the first time, a new type of vector resonance multimode instability that inherits some features of modulation and multimode instability. This instability leads to emerging different pulse laser regimes from longitudinal modes synchronization to different types of optical RW events. Using the same testbed fibre laser, we have also shown experimentally for the first time fibre twist-based chiral symmetry breaking. This leads to versatile laser dynamics tuneable from a periodic pulse similar mode-locked regime to chaotic oscillations which are revealed as a mechanism for the emergence of RW events. The observed optical RW events have been classified as fast optical RWs or slow optical RWs depending on the autocorrelation function of the experimental data. The classified optical RWs have been studied by collecting experimental data of a 19x19 grid of polarization positions through tuning both intra-cavity and pump polarization controllers. The second testbed is a passively mode-locked fibre laser. Using this system, the control, appearance and disappearance of the soliton rain flow were demonstrated for the first time using a low range of pump power. Harmonics soliton rain, soliton fission and soliton-soliton interactions leading to the emergence of optical RWs have also been demonstrated in this experiment at a different pump power and intra-cavity birefringence. High harmonic (902 MHz) mode-locked fibre laser based on acoustic-optic effect has been realized in the same laser experiment. In the third laser testbed experiment with, a stretched mode-locked fibre laser, vector bright-dark optical RWs were observed experimentally for the first time. These bright-dark RWs have formed in the laser cavity due to modulation instability at close pump power threshold or due to the polarization instability (incoherent coupling) at higher pump power

Generalized Lorenz-Mie theory : application to scattering and resonances of photonic complexes

Les structures photoniques complexes permettent de façonner la propagation lumineuse à l’échelle de la longueur d’onde au moyen de processus de diffusion et d’interférence. Cette fonctionnalité à l’échelle nanoscopique ouvre la voie à de multiples applications, allant des communications optiques aux biosenseurs. Cette thèse porte principalement sur la modélisation numérique de structures photoniques complexes constituées d’arrangements bidimensionnels de cylindres diélectriques. Deux applications sont privilégiées, soit la conception de dispositifs basés sur des cristaux photoniques pour la manipulation de faisceaux, de même que la réalisation de sources lasers compactes basées sur des molécules photoniques. Ces structures optiques peuvent être analysées au moyen de la théorie de Lorenz-Mie généralisée, une méthode numérique permettant d’exploiter la symétrie cylindrique des diffuseurs sous-jacents. Cette dissertation débute par une description de la théorie de Lorenz-Mie généralisée, obtenue des équations de Maxwell de l’électromagnétisme. D’autres outils théoriques utiles sont également présentés, soit une nouvelle formulation des équations de Maxwell-Bloch pour la modélisation de milieux actifs appelée SALT (steady state ab initio laser theory). Une description sommaire des algorithmes d’optimisation dits métaheuristiques conclut le matériel introductif de la thèse. Nous présentons ensuite la conception et l’optimisation de dispositifs intégrés permettant la génération de faisceaux d’amplitude, de phase et de degré de polarisation contrôlés. Le problème d’optimisation combinatoire associé est solutionné numériquement au moyen de deux métaheuristiques, l’algorithme génétique et la recherche tabou. Une étude théorique des propriétés de micro-lasers basés sur des molécules photoniques – constituées d’un arrangement simple de cylindres actifs – est finalement présentée. En combinant la théorie de Lorenz-Mie et SALT, nous démontrons que les propriétés physiques de ces lasers, plus spécifiquement leur seuil, leur spectre et leur profil d’émission, peuvent être affectés de façon nontriviale par les paramètres du milieu actif sous-jacent. Cette conclusion est hors d’atteinte de l’approche établie qui consiste à calculer les étatsméta-stables de l’équation de Helmholtz et leur facteur de qualité. Une perspective sur la modélisation de milieux photoniques désordonnés conclut cette dissertation.Complex photonic media mold the flow of light at the wavelength scale using multiple scattering and interference effects. This functionality at the nano-scale level paves the way for various applications, ranging from optical communications to biosensing. This thesis is mainly concerned with the numerical modeling of photonic complexes based on twodimensional arrays of cylindrical scatterers. Two applications are considered, namely the use of photonic-crystal-like devices for the design of integrated beam shaping elements, as well as active photonic molecules for the realization of compact laser sources. These photonic structures can be readily analyzed using the 2D Generalized Lorenz-Mie theory (2D-GLMT), a numerical scheme which exploits the symmetry of the underlying cylindrical structures. We begin this thesis by presenting the electromagnetic theory behind 2D-GLMT.Other useful frameworks are also presented, including a recently formulated stationary version of theMaxwell-Bloch equations called steady-state ab initio laser theory (SALT).Metaheuristics, optimization algorithms based on empirical rules for exploring large solution spaces, are also discussed. After laying down the theoretical content, we proceed to the design and optimization of beam shaping devices based on engineered photonic-crystal-like structures. The combinatorial optimization problem associated to beam shaping is tackled using the genetic algorithm (GA) as well as tabu search (TS). Our results show the possibility to design integrated beam shapers tailored for the control of the amplitude, phase and polarization profile of the output beam. A theoretical and numerical study of the lasing characteristics of photonic molecules – composed of a few coupled optically active cylinders – is also presented. Using a combination of 2D-GLMT and SALT, it is shown that the physical properties of photonic molecule lasers, specifically their threshold, spectrum and emission profile, can be significantly affected by the underlying gain medium parameters. These findings are out of reach of the established approach of computing the meta-stable states of the Helmholtz equation and their quality factor. This dissertation is concluded with a research outlook concerning themodeling of disordered photonicmedia

Novel Specialty Optical Fibers and Applications

Novel Specialty Optical Fibers and Applications focuses on the latest developments in specialty fiber technology and its applications. The aim of this reprint is to provide an overview of specialty optical fibers in terms of their technological developments and applications. Contributions include:1. Specialty fibers composed of special materials for new functionalities and applications in new spectral windows.2. Hollow-core fiber-based applications.3. Functionalized fibers.4. Structurally engineered fibers.5. Specialty fibers for distributed fiber sensors.6. Specialty fibers for communications

Optical Microwave Signal Generation for Data Transmission in Optical Networks

The massive growth of telecommunication services and the increasing global data traffic boost the development, implementation, and integration of different networks for data transmission. An example of this development is the optical fiber networks, responsible today for the inter-continental connection through long-distance links and high transfer rates. The optical networks, as well as the networks supported by other transmission media, use electrical signals at specific frequencies for the synchronization of the network elements. The quality of these signals is usually determined in terms of phase noise. Due to the major impact of the phase noise over the system performance, its value should be minimized. The research work presented in this document describes the design and implementation of an optoelectronic system for the microwave signal generation using a vertical-cavity surface-emitting laser (VCSEL) and its integration into an optical data transmission system. Considering that the proposed system incorporates a directly modulated VCSEL, a theoretical and experimental characterization was developed based on the laser rate equations, dynamic and static measurements, and an equivalent electrical model of the active region. This procedure made possible the extraction of some VCSEL intrinsic parameters, as well as the validation and simulation of the VCSEL performance under specific modulation conditions. The VCSEL emits in C-band, this wavelength was selected because it is used in long-haul links. The proposed system is a self-initiated oscillation system caused by internal noise sources, which includes a VCSEL modulated in large signal to generate optical pulses (gain switching). The optical pulses, and the optical frequency comb associated, generate in electrical domain simultaneously a fundamental frequency (determined by a band-pass filter) and several harmonics. The phase noise measured at 10 kHz from the carrier at 1.25 GHz was -127.8 dBc/Hz, and it is the lowest value reported in the literature for this frequency and architecture. Both the jitter and optical pulse width were determined when different resonant cavities and polarization currents were employed. The lowest pulse duration was 85 ps and was achieved when the fundamental frequency was 2.5 GHz. As for the optical frequency comb, it was demonstrated that its flatness depends on the electrical modulation conditions. The flattest profiles are obtained when the fundamental frequency is higher than the VCSEL relaxation frequency. Both the electrical and the optical output of the system were integrated into an optical transmitter. The electrical signal provides the synchronization of the data generating equipment, whereas the optical pulses are employed as an optical carrier. Data transmissions at 155.52 Mb/s, 622.08 Mb/s and 1.25 Gb/s were experimentally validated. It was demonstrated that the fundamental frequency and harmonics could be extracted from the optical data signal transmitted by a band-pass filter. It was also experimentally proved that the pulsed return-to-zero (RZ) transmitter at 1.25 Gb/s, achieves bit error rates (BER) lower than $10^{-9}$ when the optical power at the receiver is higher than -33 dBm.La masificación de los servicios de telecomunicaciones y el creciente tráfico global de datos han impulsado el desarrollo, despliegue e integración de diferentes redes para la transmisión de datos. Un ejemplo de este despliegue son las redes de fibra óptica, responsables en la actualidad de la interconexión de los continentes a través de enlaces de grandes longitudes y altas tasas de transferencia. Las redes ópticas, al igual que las redes soportadas por otros medios de transmisión, utilizan señales eléctricas a frecuencias específicas para la sincronización de los elementos de red. La calidad de estas señales es determinante en el desempeño general del sistema, razón por la que su ruido de fase debe ser lo más pequeño posible. El trabajo de investigación presentado en este documento describe el diseño e implementación de un sistema optoelectrónico para la generación de señales microondas utilizando diodos láser de cavidad vertical (VCSEL) y su integración en un sistema de transmisión de datos óptico. Teniendo en cuenta que el sistema propuesto incorpora un láser VCSEL modulado directamente, se desarrolló una caracterización teórico-experimental basada en las ecuaciones de evolución del láser, mediciones dinámicas y estáticas, y un modelo eléctrico equivalente de la región activa. Este procedimiento posibilitó la extracción de algunos parámetros intrínsecos del VCSEL, al igual que la validación y simulación de su desempeño bajo diferentes condiciones de modulación. El VCSEL utilizado emite en banda C y fue seleccionado considerando que esta banda es comúnmente utilizada en enlaces de largo alcance. El sistema propuesto consiste en un lazo cerrado que inicia la oscilación gracias a las fuentes de ruido de los componentes y modula el VCSEL en gran señal para generar pulsos ópticos (conmutación de ganancia). Estos pulsos ópticos, que en el dominio de la frecuencia corresponden a un peine de frecuencia óptico, son detectados para generar simultáneamente una frecuencia fundamental (determinada por un filtro pasa banda) y varios armónicos. El ruido de fase medido a 10 kHz de la portadora a 1.25 GHz fue -127.8 dBc/Hz, y es el valor más bajo reportado en la literatura para esta frecuencia y arquitectura. Tanto la fluctuación de fase (jitter) y el ancho de los pulsos ópticos fueron determinados cuando diferentes cavidades resonantes y corrientes de polarización fueron empleadas. La duración de pulso más baja fue 85 ps y se obtuvo cuando la frecuencia fundamental del sistema era 2.5 GHz. En cuanto al peine de frecuencia óptico, se demostró que su planitud (flatness) depende de las condiciones eléctricas de modulación y que los perfiles más planos se obtienen cuando la frecuencia fundamental es superior a la frecuencia de relajación del VCSEL. Tanto la salida eléctrica como la salida óptica del sistema fueron integradas en un transmisor óptico. La señal eléctrica permite la sincronización de los equipos encargados de generar los datos, mientras que los pulsos ópticos son utilizados como portadora óptica. La transmisión de datos a 155.52 Mb/s, 622.08 Mb/s y 1.25 Gb/s fue validada experimentalmente. Se demostró que la frecuencia fundamental y los armónicos pueden ser extraídos de la señal óptica de datos transmitida mediante un filtro pasa banda. También se comprobó experimentalmente que el transmisor de datos pulsados con retorno a cero (RZ) a 1.25 Gb/s, logra tasas de error de bit (BER) menores a 10-9 cuando la potencia óptica en el receptor es mayor a -33 dBm.Gobernación de NariñoBPIN 2013000100092Doctorad

Sub-nanosecond UV filaments and their applications for remote spectroscopy and high-voltage discharges

Intensive investigations during the past two decades have focused on potential applications of near-infrared (NIR) femtosecond filament for remote spectroscopy. The short length (less than 1 m) and low energy (only several millijoule) of a single NIR filament limit these applications. Long-pulse UV filaments have therefore been proposed at UNM to overcome such limitations. This dissertation describes our investigation and optimization of the high-power UV source, focusing on details of the generation and characterization of the generated pulses, as well as the applications of UV filaments for remote sensing and high-voltage discharge. On the topic of pulse generation, a 266 nm UV system delivering laser pulses below 200 ps with up to 0.4 J per pulse at 1.25 Hz repetition rate is developed. Two aspects of the laser source are closely investigated. On the one hand, the spatio-temporal profile of the laser pulses that has been overlooked for decades is systematically studied. It is shown that a curved energy front, i.e., pulses away from the beam center delayed from the center pulse, originates from the Q-switched unstable cavity Nd:YAG oscillator and evolves during the processes of laser amplification and pulse compression. To eliminate the energy front curvature, a possible solution is proposed based on the numerical simulation. On the other hand, a long existing debate on the minimum pulse duration that can be achieved through stimulated Brillouin scattering (SBS) pulse compression is resolved by this work. It is demonstrated that the lower limit of the compressed pulse duration is not set by the phonon lifetime of the SBS medium. The energy exchange between the pump and compressed Stokes pulses is responsible for the pulse compression below phonon lifetime. Next, using the newly developed powerful and stable UV source, the generation of UV filaments in air is studied. It is shown that, when focused by a 3 m lens, a single filament is generated inside the laboratory, while multiple filaments are observed in an open environment with a 9 m focusing lens. Detailed characterization of the filament spatial profile and the conductivity of the plasma channel created by the filament are performed. Two applications of the UV filaments are investigated. The single UV filament is applied to spectroscopy studies, including both Raman and Laser Induced Breakdown Spectroscopy (LIBS). A UV filament is shown to be very efficient in exciting forward stimulated Raman scattering (SRS) in gases. Backward emission of SRS signal, which could be utilized for remote sensing, has not been observed. However, a side experiment carried out in water discloses a new mechanism of driving efficient backward SRS generation, which can possibly be employed in the case of gas medium. A second study with the single filament is carried out for LIBS. The dynamics of self-absorption dip in LIBS spectrum is investigated, which can be further applied for the high resolution spectroscopy. The last application is filament-induced high-voltage discharge. A fully guided 40 cm long discharge is demonstrated with the UV filament alone, at 1/2 the self-breakdown voltage in air. Two additional lasers are tested to improve the discharge triggering by photo-detaching oxygen negative ions and heating the plasma. The anticipated improvement in reducing the discharge delay or enhancing the discharge probability has not been observed