Esta tesis constituye un estudio detallado y exhaustivo de las propiedades de una variedad específica de ondas ópticas solitarias. Observadas experimentalmente por primera vez en 1995, estas ondas estan formadas por un haz óptico a frecuencia fundamental y su segundo armónico que están ligados entre sí y viajan juntos en el material cuadrático; y son debidas al equilibrio entre la difracción lineal que sufre el haz al propagarse y un término no lineal de segundo orden en la susceptibilidad del medio. Las llamamos por eso solitones ópticos en medios cuadráticos o simplemente 'solitones cuadráticos'. También se les conoce como 'Solitones Multicolor' aludiendo al hecho de que requieren de haces a diferentes frecuencias para formarse.Un medio no-lineal cuadrático tiene por fuerza que ser no-centrosimétrico, lo cual es una variedad de anisotropía. Una gran parte de los materiales no-lineales cuadráticos (los que tienen mayor interés para la industria) son uniaxiales lo que significa que presentan un eje de simetría que suele llamarse eje óptico. De la dirección de un haz relativa a ese eje óptico dependen las características de la propagación del haz en el medio cuadrático no-lineal. Una consecuencia de eso en configuraciones de interés es un desvío ('walk-off') sufrido por el haz respecto a su dirección de propagación inicial al entrar en el material no-lineal.Las propiedades de los solitones cuadráticos 'caminantes' son también estudiadas en la tesis, estableciendo que existe una relación entre la potencia inyectada en el medio y el ángulo de desvío (walking angle).Una parte importante de la tesis está dedicada al estudio a través de exhaustivos experimentos numéricos del potencial de estas ondas solitarias para constituir la base de dispositivos de conmutación y encaminamiento totalmente ópticos que puedan hacer realidad la promesa de la red transparente totalmente óptica. Los experimentos han permitido identificar varias configuraciones de interés con niveles de potencia y dimensiones que permiten plantearse el diseño y construcción de dispositivos comerciales de conmutación y encaminamiento totalmente ópticos basados en solitones ópticos cuadráticos. / This thesis is a comprehensive study of the fundamental properties of a specific kind of optical spatial solitary waves. First observed experimentally in 1995, these solitary waves are formed by an optical beam at a fundamental frequency and its second harmonic which propagate together and are mutually entangled; and are due to a balanced interplay between the beams' linear diffraction and a second-order nonlinear susceptibility of the medium. They are thereby referred as 'Optical Solitons in Quadratic Nonlinear Media' or simply 'Quadratic Solitons', They are also known as 'Multicolor Solitons' recalling that they are formed by beams at different frequencies.A quadratic nonlinear media needs to be non centrosymmetric which is a special kind of anisotropy. A great deal of quadratic nonlinear materials (the most used by industry such as lithim niobate, KTP, etc.) are uniaxial meaning that they feature a symmetry axis known as 'optical axis'. The direction of propagation of an optical beam relative to that axis determines the characteristics of the beam's propagation through the quadratic nonlinear material. A main result of that in some configurations of interest is a walk-off suffered by the beam as it enters the quadratic material.The properties of the families of quadratic solitons in the presence of a linear walk-off (quadratic walking solitons) are studied as well in the thesis stating that there is a relationship between the power injected into the medium and the walking angle, suitable to applications of all-optical switching and routing.An important last part of the thesis is devoted to the study from a practical viewpoint and through extensive numerical experiments of the potential of these solitary waves as the basis of practical all-optical switches and routers which could take the all-optical transparent network to a reality. The experiments have allowed to identify several configurations of interest with power level and dimensions suited to practical applications which could allow the production of commercial all-optical switching and routing devices based on quadratic solitons.

Pour des applications technologiques d’enregistrement magnétique de l’information à haute densité et vitesse d’écriture et de lecture ultra-rapide, les chercheurs se sont penchés vers des méthodes de manipulation de l’aimantation sans application de champ magnétique externe. Il a été découvert qu’il était possible de renverser de manière déterministe l’aimantation de plusieurs matériaux ferri- et ferro-magnétiques à l’aide uniquement d’impulsions laser ultracourtes polarisées circulairement. Ce retournement tout-optique s’est avéré être un processus cumulatif nécessitant plusieurs impulsions ultracourtes dans les matériaux ferromagnétiques. Notamment dans les multicouches (Co/Pt), le retournement tout-optique se fait en deux étapes : une désaimantation indépendamment de l’hélicité suivie d’une ré-aimantation dans une direction ou l’autre selon l’hélicité. Pour autant, le mécanisme à l’origine du rétablissement de l’ordre magnétique n’a pas été étudié jusqu’à présent. Dans cette thèse, nous avons étudié le mécanisme de renversement de l’aimantation dans les couches ferromagnétiques résultant de l’excitation par impulsions laser ultracourtes polarisées circulairement. Pour cela, nous étions intéressé par la réponse d’une paroi de domaine dans les couches minces de Pt/Co/Pt à la suite d’une excitation laser et en fonction de la polarisation de la lumière. Nous avons démontré la possibilité d’induire un déplacement tout-optique et déterministe d’une paroi de domaine. Nous montrons que la propagation de la paroi résulte de la compétition entre trois contributions : le gradient de température dû aux effets de chauffage par le laser, l’effet de l’hélicité de la lumière et les effets de piégeages de la paroi. Par ailleurs, par mesures expérimentales du dichroïsme circulaire, nous excluons un mécanisme purement thermique du déplacement de paroi. Ainsi nous confirmons que le retournement tout-optique des couches ferromagnétiques se fait par une nucléation suivie d’une ré-aimantation par propagation déterministe des parois de domaines selon l’hélicité. De plus, nous avons exploré la possibilité d’utiliser le retournement tout-optique dans des dispositifs spintroniques pour l’enregistrement de l’information à haute densité. Pour se faire, il est nécessaire d’étudier les effets de tailles du retournement lorsque le matériau est structuré en îlots à l’échelle du micro- ou nanomètre. Nous avons montré qu’un plus grand nombre d’impulsions laser est nécessaire afin de renverser l’aimantation de micro-disques comparés à la couche continue ferromagnétique. Il en résulte que le champ dipolaire aide le renversement de l’aimantation dans les couches continues rendant ainsi le retournement tout-optique énergétiquement plus favorable / Over the past decade, the demand for an even higher capacity to store data has been gradually increasing. To achieve ultrafast and ultrahigh density magnetic data storage, low-power methods to manipulate the magnetization without applying an external magnetic field has attracted growing attention. The possibility to deterministically reverse the magnetization with only circularly polarized light was evidenced in multiple ferri- and ferro-magnetic materials. This phenomenon was called helicity-dependent all-optical switching (HD-AOS). In ferromagnets, it was demonstrated that HD-AOS was a cumulative and multishot process with a helicity-independent demagnetization followed by a helicity-dependent magnetization recovery. Yet, the microscopic mechanism of this helicity-dependent remagnetization remained highly debated. In this thesis, we investigated the magnetization reversal mechanism of all-optical switching in ferromagnetic materials. To explore a potential switching process through domain nucleation and domain wall (DW) propagation, we studied the response of a DW upon femto- or pico-second laser irradiation in Co/Pt thin films that exhibit HD-AOS. We reported helicity-dependent all-optical domain wall motion. We demonstrated that it results from the balance of three contributions: the temperature gradient due to the laser heating, the helicity effect and the pinning effects. By measuring the magnetic circular dichroism, a purely thermal mechanism of the laser-induced DW motion appears to be excluded. Furthermore, we examined the size effects in AOS in Co/Pt films patterned into microdots with a diameter between 10 and 3 μm. This allowed us to explore the role of the dipolar field in the switching mechanism. We discovered that a larger number of laser pulses was required to reverse the magnetization of a microdot compared to the continuous film. This indicated that the dipolar field actually eases the magnetization reversal in the full film. Thus, AOS is less energy-efficient in patterned films, hence making Pt/Co/Pt multilayers not an ideal candidate for integrating AOS in spintronic devices

Orientadores: Evandro Conforti, Carlos Allan Caballero Petersen / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-16T07:18:34Z (GMT). No. of bitstreams: 1 Toazza_AdrianoLuis_D.pdf: 4079607 bytes, checksum: bb3aa0dd52628e849f97cb827da20ffb (MD5) Previous issue date: 2010 / Resumo: A técnica de pré-distorção com a adição de um impulso ao degrau que normalmente chaveia o Amplificador Óptico a Semicondutor - (SOA) , permite diminuir os tempos de chaveamento eletro-óptico do SOA para valores inferiores a nanosegundos, obtendo-se contrastes da luz amplificada na saída da chave acima de 25 dB e bandas de passagem da ordem de 60 nm. Entretanto, estes tempos de chaveamento de alta velocidade vêm acompanhados de efeitos deletérios ligados às flutuações do ganho óptico durante o processo de ligar a chave, do estado "off" para o estado "on". Nesta tese é efetuada a análise destes fenômenos, com boa correspondência com resultados experimentais. Mostram-se, também, caminhos a seguir para diminuir as flutuações de ganho. O estudo aqui apresentado baseia-se no comportamento da impedância da montagem com o SOA em alta frequência, até 20 GHz. A obtenção dos valores dos componentes do circuito equivalente incluem o SOA (a partir de sua porta elétrica) e a montagem de microondas do chaveamento eletro-óptico. O modelo para o SOA foi baseado em um circuito desenvolvido para laser a diodo semicondutor. Os parâmetros do circuito equivalente para a montagem do SOA foram obtidos por técnicas de extração de parâmetros, através de aproximações sucessivas entre as respostas experimentais e teóricas, utilizando um programa desenvolvido neste trabalho. Em seguida, a partir da impedância do SOA, foram estimados os tempos de transição, o casamento em banda larga, assim como a influência do encapsulamento do dispositivo, aprimorando o entendimento do seu comportamento e limitações, com boa correspondência com resultados experimentais / Abstract: Reduction of the Semiconductor Optical Ampli.er (SOA) switching times can be achieved with the pre-distortion technique consisting of impulse(s) addition to the current step that generally switches the SOA. With this technique it is possible to reduce the electro-optical switching time to sub-nanoseconds with a contrast approaching 25 dB between the "off" and the "on" state of the optical gain, and with a bandwidth in excess of 60 nm. However those high speed switching times comes jointly with deleterious effects of overshoot and optical gain fluctuations during the switch state variation from the "off" to the "on" state. This thesis analyzes those phenomena with good correspondence to experimental results, and actions to decrease those deleterious effects are revealed. The results make use of SOA electrical gate impedance measurements up to 20 GHz, with the accomplishment of the SOA equivalent circuit extraction including the effects of the microwave lines and SOA encapsulation. The SOA model was based in the literature results for semiconductor lasers. The parameters extraction was based in a software and in measurements prepared here to obtain the circuit parameters values through successive approximations between practice and theory. Finally, the obtained SOA equivalent circuit was used to find the switching time estimation, the broadband matching, the encapsulation influences, in order to achieve a better theoretical understanding of the deleterious effects. The computer simulated results are in good correspondence with the experimental results / Doutorado / Telecomunicações e Telemática / Doutor em Engenharia Elétrica

Orientadores: Evandro Conforti, Napoleão dos Santos Ribeiro / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-16T11:21:52Z (GMT). No. of bitstreams: 1 Figueiredo_RafaelCarvalho_M.pdf: 10424465 bytes, checksum: b93608291545cc7a53e52e2050a3dc39 (MD5) Previous issue date: 2010 / Resumo: Apresenta-se a modelagem de um circuito elétrico equivalente e a extração de parâmetros de amplificadores ópticos a semicondutor (SOA), a partir de um modelo para lasers semicondutores. Foi realizado um estudo do comportamento da impedância de um SOA em chip, sem encapsulamento, em função da corrente de polarização e em ampla faixa de frequência . de 300 kHz a 40 GHz. A modelagem do circuito equivalente da montagem, a qual é cascateada com os modelos da região ativa do SOA, é apresentada para correntes abaixo e acima da operação em transparência. A metodologia utilizada para a extração dos parâmetros dos elementos parasitas que compõe o circuito é descrita; resultados obtidos através de simulações em programa comercial (Agilent ADS) são comparados com medidas experimentais obtidas em mesa óptica. São apresentados ainda resultados teóricos da impedância do SOA quando desconsiderada a presença dos elementos parasitas da montagem. A modelagem e extração dos parâmetros realizada para o chip foi repetida para SOAs encapsulados, também apresentando boa concordância entre teoria e experimento, reforçando a viabilidade da abordagem utilizada / Abstract: The equivalent electric circuits and its parameters.extraction of semiconductor optical amplifiers (SOA) are attained based on a diode-laser model. Additionally, the impedance behavior of a SOA-chip (without package) was measured as function of the bias current in wide frequency range, from 300 kHz to 40 GHz. In these procedures, the microwave setup used for the SOA current injection was also characterized and its equivalent circuit obtained. Next, a theoretical analysis is developed for this setup for currents below and above the transparency condition. A methodology for the parameters extraction of parasitic elements is also described, as well as the results obtained through simulations using the Agilent ADS software, compared with the experimental data. The optical bench used in the experiments is also described, and theoretical results illustrates the SOA impedance without parasitic elements. The equivalent circuits with parameters.extraction were also obtained for packaged SOAs, with good agreement between theory and experiment, conforming the employed methodology / Mestrado / Telecomunicações e Telemática / Mestre em Engenharia Elétrica

Orientador: Peter Jurgen Tatsch / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-14T19:07:29Z (GMT). No. of bitstreams: 1 Monte_LuisRenato_M.pdf: 9957740 bytes, checksum: 0889b0686d62fd3269d4a48322410bf6 (MD5) Previous issue date: 2009 / Resumo: Este trabalho apresenta as especificações arquitetônicas e funcionais de uma rede ótica avançada, fundamentada na comutação óptica de rajadas e que objetiva um melhor aproveitamento dos enlaces ópticos e a redução do gargalo eletrônico decorrente das conversões eletro-ópticas. Uma proposta de concepção do núcleo de processamento de dados baseado em dispositivos lógicos programáveis e o projeto dos circuitos utilizados na etapa experimental, que compreendem uma placa comercial e três placas desenvolvidas serão apresentadas. Este trabalho tem como escopo apresentar uma nova arquitetura de rede de chaveamento de rajadas ópticas, seu princípio de funcionamento e a estrutura do nó de chaveamento óptico. É proposta uma estrutura para o núcleo de processamento de dados e apresentado o protótipo desenvolvido para a prova de conceito. / Abstract: This work presents the architectural and functional specifications of a new optical network, based on optical burst switching that aims at the better use of optical links and the reduction of the bottleneck resulting from electro-optics conversions. A proposed design of the core data-processing based on programmable logic devices and design of circuits used in the experimental stage, which include a business board and three boards developed exclusively for this project, will be presented. This work aims to present a new architecture for an optical burst switching network, its basic operation and the structure of an optical switching node. The data processing core structure is proposed and the circuitry prototypes developed to do the proof of concept are presented. / Mestrado / Eletrônica, Microeletrônica e Optoeletrônica / Mestre em Engenharia Elétrica

A unique all-optical 1x2 self-routed switch is introduced. This switch routes an optical packet from one input to one of two possible outputs. The header and payload are transmitted separately in the system, and the header bits are processed in parallel thus increasing the switching speed as well as reducing the amount of buffering required for the payload. A 1x2 switching operation is analysed and a switching ratio of up to 14dB is obtained. The objective of the research was to investigate a unique all-optical switch. The switch works by processing the optical bits in a header packet which contains the destination address for a payload packet. After the destination address is processed the optical payload packet gets switched to one of two outputs depending on the result of the optical header processing. All-optical packet switching in the optical time domain was accomplished by making use of all-optical parallel processing of an optical packet header. This was demonstrated in experiments in which a three bit parallel processing all-optical switching node was designed, simulated and used to successfully demonstrate the concept. The measure of success that was used in the simulated experiments was the output switching ratio, which is the ratio between the peak optical power of a high bit at the first output and the peak optical power of a high bit at the second output. In all experimental results the worst case scenario was looked at, which means that if there was any discrepancy in the peak value of the output power then the measurement’s minimum/maximum value was used that resulted in a minimum value for the switching ratio. The research resulted in an optical processing technique which took an optical bit sequence and delivered a single output result which was then used to switch an optical payload packet. The packet switch node had two optical fibre inputs and two optical fibre outputs. The one input fibre carried the header packet and the other input fibre carried the payload packet. The aim was to switch the payload packet to one of the two output fibres depending on the bit sequence within the header packet. Also only one unique address (header bit sequence) caused the payload packet to exit via one of the outputs and all the other possible addresses caused the payload packet to exit via the other output. The physical configuration of the all-optical switches in the parallel processing structure of the switching node determined for which unique address the payload packet would exit via a different output than when the address was any of the other possible combinations of sequences. Only three Gaussian shaped bits were used in the header packet at a data rate of 10 Gbps and three Gaussian shaped bits in the payload packet at a data rate of 40 Gbps, but in theory more bits can be used in the payload packet at a decreased bit length to increase throughput. More bits can also be used in the header packet to increase the number of addresses that can be reached. In the simulated experiments it was found that the payload packet would under most circumstances exit both outputs, and at one output it would be much larger than at the other output (where it was normally found to be suppressed when compared to the other output’s optical power). The biggest advantage of this method of packet-switching is that it occurs all-optically, meaning that there is no optical to electronic back to optical conversions taking place in order to do header processing. All of the header processing is done optically. One of the disadvantages is that the current proposed structure of the all-optical switching node uses a Cross-Gain Modulator (XGM) switch which is rather expensive because of the Semiconductor Optical Amplifier (SOA). In this method of packet-switching the length of the payload packet cannot exceed the length of one bit of the header packet. This is because the header processing output is only one header bit length long and this output is used to switch the payload packet. Thus any section of the payload packet that is outside this header processing output window will not be switched correctly / Dissertation (MEng (Electronic Engineering))--University of Pretoria, 2007. / Electrical, Electronic and Computer Engineering / unrestricted

Orientador: Evandro Conforti / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-26T17:49:28Z (GMT). No. of bitstreams: 1 Figueiredo_RafaelCarvalho_D.pdf: 7764328 bytes, checksum: 3a3b008ba1f610e5a7c3ef694ff3f04d (MD5) Previous issue date: 2015 / Resumo: O desempenho de chaves eletro-ópticas baseadas em amplificadores ópticos a semicondutor (SOA), incluindo experimentos e simulações usando diferentes formatos de pulso na injeção de corrente elétrica, é apresentado. Quatro SOAs com características físicas distintas são analisados de acordo com seu comportamento de chaveamento. Em seguida, com o intuito de melhorar a resposta eletro-óptica dos SOAs, uma nova técnica de injeção de multi-impulso (MISIC ¿ Multi-Impulse Step Injected Current) é apresentada, alcançando tempo de subida ultrarrápido (115 ps) com baixo overshoot (< 30 %) e alto contraste óptico (30 dB). Os resultados obtidos podem permitir aplicações usando SOAs, por exemplo, como chaves eletro-ópticas em redes de Data Centers, reduzindo a latência de chaveamento entre os nós e compensando perdas por divisões do sinal. Além disso, os circuitos equivalentes para três diferentes SOAs (dois encapsulados e um sem encapsulamento) são propostos. Os modelos são validados através de comparações dos resultados numéricos e experimentais, com boa concordância. A modelagem é realizada em programas de análise de circuitos, exigindo pouco recurso computacional e possibilitando a inclusão dos elementos parasitas das montagens de micro-ondas e dos chips dos dispositivos / Abstract: The performance of electro-optical space switches based on semiconductor optical amplifiers (SOA), including experiments and simulations using different formats of the electrical current injection pulses, is presented. Four SOAs with distinct physical characteristics are analyzed according to their switching behavior. Then, to improve the SOAs¿ electro-optical response, a new Multi-Impulse Step Injected Current (MISIC) technique is presented, achieving ultrafast switching time (115 ps) with low overshoot (< 30 %) and high optical contrast (30 dB). The results obtained might enable SOA applications, for example, as electro-optical switches in Data Center Networks, reducing switching latency between nodes and compensating signal¿s splitting losses. Furthermore, the equivalent circuits for three different SOAs (one chip-on-carrier and two encapsulated) are proposed. The models are validated by comparisons involving numerical and experimental results, with good correspondence. The modeling is carried out using circuit analysis software, requiring small computational resources and enabling the inclusion of parasitic elements of SOA devices¿ chip and microwave mounts / Doutorado / Telecomunicações e Telemática / Doutor em Engenharia Elétrica

The topic of this thesis is development ofdevices fortelecom applications based on poled optical fibers. The focusis on two different specific functions, wavelength conversionand optical switching. Optical switching is demonstrated in a poled optical fiberat telecom wavelengths (~1.55 mm). The fiber has two holesrunning along the core in which electrodes are inserted. Thefiber device is made electro-optically active with a polingprocess in which a strong electric field is recorded in thefiber at a temperature of 270 o C. The fiber is then put in onearm of a Mach-Zehnder interferometer and by applying a voltageacross the two electrodes in the fiber the refractive index ismodulated and the optical signal switched from one output portto the other. So far the lowest switching voltage achieved is~1600 V which is too high for a commercial device, but byoptimizing the design of the fiber and the poling process aswitching voltage as low as 50 V is aimed for. A method to deposit a thin silver electrode inside the holesof an optical fiber is also demonstrated. A new way of creatingperiodic electrodes by periodically ablating the silver filmelectrode inside the holes of an optical fiber is also shown.The periodic electrodes can be used to create a quasi-phasematched (QPM) nonlinearity in the fiber which is useful forincreasing the efficiency of a nonlinear process such aswavelength conversion. Poling of a fiber with silver electrodesshowed a huge increase in the nonlinearity. This could be dueto a resonant enhancement caused by silver nanoclusters. <b>Keywords:</b>Poling, twinhole fiber, fiber electrodes,silver film electrodes, silver diffusion, quasi-phase matching,optical switching, frequency conversion, optical modulation / NR 20140805

No description available.

<p>The topic of this thesis is the development of devices for telecom applications based on poled optical fibers. The focus is on a specific function, optical switching/modulation.</p><p>Some of the most important results are summarized below. Optical switching at telecom wavelengths (1.55 μm) is demonstrated in an all-fiber switch based on a fiber with internal electrodes. The fiber is made electro-optically active with a thermal poling process in which a strong electric field is recorded in the glass at a temperature of 255 °C. After poling, the fiber is put in one arm of a Mach-Zehnder interferometer and by applying a voltage across the two electrodes the refractive index is modulated and the optical signal switched from one output port to the other. A switching voltage of 190 V at 1550 nm was achieved, which to the best of our knowledge is the lowest value reported. By carefully matching the lengths of the fibers in the two arms of the interferometer the optical bandwidth could be made as large as 20 nm. The extinction ratio, determined by the power ratio in the two arms, was 30 dB and the highest modulation frequency was 30 MHz. Poled fibers were packaged to increase the thermal and mechanical stability and to make handling easier. 40 Gb/s transmission test through the device showed no bit-error-rate performance degradation. Protection switching of a 10 Gb/s signal is also demonstrated.</p><p>The depletion region in a poled fiber was found to be wedge-shaped and very wide, 13 μm and completely overlapped with the core. In a time-resolved poling experiment the recorded electric field was measured. The sign of the field changed after ~20 min, when the depletion region passed through the core, which led to the conclusion that an electric field is present also outside of the depletion region.</p><p>A ring laser was constructed with an erbium doped fiber as the gain medium. A fiber modulator was placed inside the cavity and when a small RF signal, with a frequency matched to the cavity ground frequency, was applied to the modulator the laser was modelocked. The output pulse train contained pulses of sub ns duration and is the first demonstration of mode-locking using poled fibers.</p><p>A sampled grating with 16 channels spaced by 50 GHz was inserted into the cavity. The fiber modulator had optical bandwidth of 7 nm with center wavelength that depends on the applied voltage. By applying of 10 – 210 V to the modulator it was possible to tune the laser to 11 of the 16 channels for a total tuning range of over 4 nm.</p><p>A scheme to deposit 1 μm thin silver electrodes inside the holes of an optical fiber is demonstrated together with a new method of creating periodic electrodes by periodically ablating the silver film electrodes. The periodic electrodes are used to create a quasi-phase matched (QPM) nonlinearity in a fibers which is showed in a proof of principle experiment.</p>