Η εφεύρεση του laser έδωσε την δυνατότητα μελέτης της αλληλεπίδρασης ύλης-φωτός σε υψηλές εντάσεις ακτινοβολίας με αποτέλεσμα να οδηγηθούμε σε φαινόμενα κατά τα οποία οι συνήθεις οπτικές παράμετροι δε μπορούν να θεωρηθούν σταθερές, αλλά εξαρτώνται από την ένταση. Σε αυτή την περίπτωση, η συχνότητα δύναται να μεταβληθεί κατά την διάδοση της ακτινοβολίας σε ένα μέσο, ενώ η αρχή της επαλληλίας κυμάτων παραβιάζεται. Ο κλάδος της μη γραμμικής οπτικής μελετά φαινόμενα αλληλεπίδρασης της ύλης με ακτινοβολίες υψηλής έντασης. Αυτά τα φαινόμενα προέρχονται από την μεταβολή των οπτικών ιδιοτήτων της ύλης λόγω ισχυρών ηλεκτρικών πεδίων και η μη γραμμικότητα αυτών των φαινόμενων έγκειται στο ότι η απόκριση του υλικού είναι μη γραμμική συνάρτηση της έντασης της ακτινοβολίας. Οι θεμελιώδεις φυσικές αρχές που διέπουν τα μη γραμμικά φαινόμενα έχουν πλέον πλήρως αποσαφηνιστεί και το ενδιαφέρον έχει πια στραφεί στην μελέτη των μη γραμμικών οπτικών ιδιοτήτων διαφόρων υλικών. Σκοπός των ερευνών αυτών αποτελεί η εύρεση υλικών με μεγάλη μη γραμμική απόκριση, που θα μπορούσαν να χρησιμοποιηθούν σε διάφορες εφαρμογές στις οπτικές τηλεπικοινωνίες και στην οπτική επεξεργασία της πληροφορίας (π.χ. ως οπτικοί διακόπτες). Σε αυτήν την εργασία λοιπόν μέσω των τεχνικών ΟΚΕ και Z-Scan, ασχοληθήκαμε με την μελέτη της μη γραμμικής απόκρισης μιας σειράς παραγώγων φουλλερενίων, οι οπτικές ιδιότητες των οποίων είναι άμεσα συνδεδεμένες με την δομή τους και τον τρόπο σύνδεσης των επιμέρους ενώσεων από τις οποίες αποτελούνται.Στο πρώτο μέρος αυτής της εργασίας παρατίθενται οι βασικότερες έννοιες της μη γραμμικής οπτικής και περιγράφονται ορισμένα πολύ σημαντικά μη γραμμικά φαινόμενα. Στο δεύτερο μέρος παρουσιάζονται οι τεχνικές ΟΚΕ και Z-Scan οι οποίες χρησιμοποιήθηκαν για την μελέτη των μη γραμμικών οπτικών παραμέτρων των δειγμάτων των παραγώγων των φουλλερενίων στο πειραματικό μέρος της εργασίας αυτής και στη συνέχεια αναλύεται ο τρόπος επεξεργασίας των πειραματικών δεδομένων. Τέλος στο τρίτο μέρος περιγράφονται τα πειράματα που διεξήχθησαν, τα αποτελέσματα καθώς και τα συμπεράσματα που προέκυψαν. / The development of lasers has been a turning point in the history of science. It gave birth to the new field of nonlinear optics (NLO), which is the study of the interaction between intense light radiation and matter. In this regime, the response of matter cannot be considered linearly dependent on the intensity of the applied field, giving rise to significant new types of behavior and a wide spectrum of novel phenomena. Nonlinear optics has now become a rapidly growing field. It is at the forefront of progress in the area of photonics and optoelectronics. This vast development necessitates new materials with large nonlinearities, suitable for NLO applications in the laser and the optical communication technologies (e.g. optical switches). In that context, fullerenes have justifiably attracted considerable interest due to their intriguing physical and chemical properties; the extensive delocalization of their charge, as well as, their small reorganization energy can give rise to fast and high nonlinear optical response. Inevitably, the interest of the scientific community has now turned to the study of sophisticatedly altered fullerene derivatives. Depending on their ability to act as excellent electron acceptors, fullerenes are one of the most prominent chromophores that have been incorporated into multi-component molecular structures. Novel synthetic methods that enable the chemical modification of pristine molecules with electron donating moieties have been developed. This chemical functionalization of fullerenes can result in strong donor-acceptor interactions and photo-induced electron transfer, invigorating their nonlinear optical response. Their potential usage, which can range from photonics and photovoltaics implementations to applications in the biomedical area, is the main driving force of all this research. In the present study, the measurements were performed via the Z-Scan and the Optical Kerr Effect (OKE) techniques. The third order nonlinear susceptibility χ(3) and the second order hyperpolarizability γ of the derivatives were determined employing 4 ns and 35 ps laser pulses respectively, at excitation wavelength of 532 nm. In that respect, the main aim of the current study is threefold. Firstly, to provide a complete overview of the third order nonlinear parameters determined. Secondly, to briefly discuss the linkage between the observed nonlinearities with the molecular structures of the examinant hybrids, as well as, the possible effect of photo-induced charge transfer. Lastly, to shed light upon the role of the different pulse duration in the measurements and the dominant contributing physical processes related. Consequently, the first part of this work provides some basic concepts of nonlinear optics and the physical processes related with it. Then reference will be made to the experimental techniques used, including the fundamental background of the data analysis procedure. Finally, the nonlinearities observed in the picosecond and nanosecond regime are presented.

Short optical pulses and engineered nonlinear media is a powerful combination. Mode locked pulses exhibit high peak powers and short pulse duration and the engineered ferro-electric KTiOPO4 facilitates several different nonlinear processes. In this work we investigate the use of structured, second-order materials for generation, characterization and frequency conversion of short optical pulses. By cascading second harmonic generation and difference frequency generation the optical Kerr effect was emulated and two different Nd-based laser cavities were mode locked by the cascaded Kerr lensing effect. In one of the cavities 2.8 ps short pulses were generated and a strong pulse shortening took place through the interplay of the cavity design and the group velocity mismatch in the nonlinear crystal. The other laser had a hybrid mode locking scheme with active electro-optic modulation and passive cascaded Kerr lensing incorporated in a single partially poled KTP crystal. The long pulses from the active modulation were shortened when the passive mode locking started and 6.9 ps short pulses were generated. High-efficiency frequency conversion is not a trivial task in periodically poled materials for short pulses due to the large group velocity mismatch. Optimization of parameters such as the focussing condition and the crystal temperature allowed us to demonstrate 64% conversion efficiency by frequency doubling the fs pulses from a Yb:KYW laser in a single pass configuration. Quasi phase matching also offers new possibilities for nonlinear interactions. We demonstrated that it is possible to simultaneously utilize several phase matched second harmonic interactions, resulting in a dual-polarization second harmonic beam. Short pulse duration of the fundamental wave is a key parameter in the novel method that we demonstrated for characterization of the nonlinearity of periodically poled crystals. The method utilizes the group velocity mismatch between the two polarizations in a type II second harmonic generation configuration. The domain walls of PPKTP exhibit second order nonlinearities that are forbidden in the bulk material. This we used in a single shot frequency resolved optical gating arrangement. The spectral resolution came from Čerenkov phase matching, a non-collinear phase matching scheme that exhibits a substantial angular dispersion. The second harmonic light was imaged upon a CCD camera and with the spectral distribution on one axis and the temporal autocorrelation on the other. From this image we retrieved the full temporal profile of the fundamental pulse, as well as the phase. The spectral dispersion provided by the Čerenkov phase matching was large enough to characterize optical pulses as long as ~200 fs in a compact setup. The Čerenkov frequency resolved optical gating method samples a thin stripe of the beam, i.e. the area close to the domain wall. This provides the means for high spatial resolution measurements of the spectral-temporal characteristics of ultrafast optical fields. / QC 20100831

This thesis is concerned with the photophysical and nonlinear optical responses, and applications of a set of conjugated polymers and small molecules in the visible and near-IR spectral regions. Poly(phenylene ethynylene) PPE polymers were substituted with conjugated side-arms in a cruciform fashion to determine the impacts of electronic coupling on the one-photon (1PA), two-photon (2PA), and excited state absorption (ESA) properties of the co-polymer system. The cruciform-like PPEs showed significant changes in their nonlinear and phophysical behavior relative to their linear models, including shifts and splittings of the 1PA bands due to moderate mixing of the lowest singlet excited states, an increase in the 2PA cross section (δ) values, and an increase in the yield of triplet excited-state species. The cruciform-like PPE polymers exhibited effective optical pulse suppression of femtosecond and nanosecond laser pulses over a broad spectral range of ~200 nm in the visible and near-IR. The suppression capability of the cruciform-like PPEs exceeded the best reported value for alkyl-substituted PPE polymers. The spectroscopic effects due to conjugation length, structural configuration, and intramolecular charge transfer (ICT) are discussed for a family of bent donor-acceptor-donor (D-A-D) -type conjugated oligomers, which incorporate electron-rich triarylamine donors and electron-deficient triarylborane acceptor units into its conjugated structure. These organoborane oligomers are highly fluorescent and exhibit strong 2PA in the visible region with δ values as large as 1410 GM, as well as overlapping ESA bands attributed to singlet-singlet and triplet-triplet absorption. Saturation of the molar absorptivity, ε, and δ was observed at less than two repeat monomer units due to conformational disorder in the oligomer with increasing length. Positive solvatochromism of fluorescence with solvent shifts as large as ~70 nm was observed as a result of ICT from the arylamine donors to boryl-centered acceptor sites. The excited-state dynamics also show sensitivity to the solvent environment. Experimental findings suggest that these organoborane oligomers may have potential use as nonlinear material for optical power limiting (OPL) and two-photon sensing applications. The spectral properties of two bis-donor chromophores, (bis(diarylamino)biphenyl (TPD) and distyrylthiophene (DST), were investigated with and without the presence of AgNPs in order to better understand the local-field enhancement and subsequent effects on the photophysics and nonlinear behavior of 2PA dyes. While little changes were observed in the excited-state dynamics, measurements of nanoparticle aggregate-dye composite solutions with TPD revealed a 1.6-enhancement in the two-photon excited fluorescence signal. OPL measurements of nanosecond laser pulses at 532 nm revealed a reduction in threshold energy by a factor of 2 in solutions containing TPD and AgNP aggregates, relative to solutions of TPD alone. DST shows exceptional solubility (>1 M) in several organic solvents and exhibits a 2PA spectrum that overlaps well with its singlet-singlet and triplet-triplet ESA bands. Consequently, DST exhibits effective optical limiting of nanosecond laser pulses through two-photon induced excited-state absorption over a broad spectral range of approximately 200 nm in the red and near-IR.

The objective of the present dissertation is to advance the science and engineering of metal-dielectric thin-film structures for ultrafast all-optical applications. The research presented consists of three parts: first, the linear and nonlinear optical (NLO) properties of Au and Ag/Au bilayer metallic thin films are comprehensively studied; then the design and properties of a novel nonlinear device structure are presented and finally an ultrafast all-optical shutter is developed and applications are discussed. In the first part, this study describes the linear and NLO properties of bilayer metallic films and shows that they can be tuned by controlling the mass-thickness ratio between Au and Ag. The combined properties of these bilayers are attractive for active plasmonic applications and nonlinear optical filters. Detailed physical models describing the linear and NLO response of Au and Ag/Au bilayers are presented and compared with experiments. In the second part, these models are used to optimize the NLO response of a novel Au-based NLO device. With only four layers, this novel device strongly amplifies the NLO response of the component Au thin film. NLO devices with broad spectral and angular bandwidths in the visible spectral region are demonstrated. The narrow band dependent NLO response of the NLO device is shown to lead to all-optical controls of high peak-power optical signal pulses. Finally, the NLO device technology is integrated into a novel ultrafast all-optical shutter, which allows temporal opening windows (the time shutter remains open) as short as a few ps. Ultrafast all-optical shutter potentially can temporally shape high peak-power nanosecond optical pulses, which could benefit biomedical and micromachining applications. Other possible optical applications such as short electron, X-ray pulse generations, ultrafast photography, and biomedical imaging will also be discussed.

Nos últimos anos, materiais orgânicos tem ganhado grande interesse em áreas que envolvem espectroscopia óptica não linear. Isso se dá devido aos materiais possuirem consideráveis efeitos ópticos não lineares, apresentarem facilidade de síntese e possuirem propriedades fotofísicas e fotoquímicas que os tornam capazes de serem empregados em um vasto número de possíveis aplicações. Entre os materiais orgânicos, é possível destacar as Porfirinas e Ftalocianinas. A síntese desses materiais possibilita um grande número de classes ou grupos distintos, os quais podem ser distinguidos por suas estruturas periféricas e/ou íons metálicos que podem ser inseridos no interior dos macrociclos. Isso resulta em alterações das suas propriedades ópticas, ou seja, através de alterações das estruturas químicas das Porfirinas e Ftalocianinas é possível modelar suas propriedades ópticas, e assim, de acordo com essas propriedades, discriminar em quais aplicações podem ser empregados. Tais materiais, tendo em vista suas propriedades fotofísicas, podem ser empregados como fotossensitizadores na terapia fotodinâmica, células solares, limitadores ópticos ou fotobactericidas entre outras mais. Sendo assim, nesta Dissertação de Mestrado é realizado uma caracterização espectroscópica linear e não linear desses materiais, para assim deterinar propriedades ópticas específicas que podem ser empregadas nas aplicações citadas. Para tal caracterização espectroscópica, foram empregadas técnicas de espectroscopia linear e não linear, dentre elas a técnica de Varredura-Z foi empregada em três configurações distintas (Varredura-Z por Pulso Único, por Trem de Pulsos e por Luz Branca Supercontínua) para determinação de absorções de estados excitados. Tempos de vida de fluorescência, tempos de decaimento radiativo e de conversão interna, seções de choque de absorção de estado singleto e tripleto (fundamental e excitado) e eficiências quânticas (fluorescência, conversão interna e converção para tripleto) foram os parâmetros determinados e, assim, através desses parâmetros, foi possível entender como alterações nas estruturas químicas (periféricas e íons metálicos) influenciam consideravelmente as propriedades de Porfirinas e Ftalocianinas. / In last years, organic materials have won great interest in areas involving non-linear optical spectroscopy. This is due to the fact that the materials have considerable non-linear optical effects, are easy to synthesize, and have photophysical and photochemical properties that make them capable of being used in a wide range of possible applications. Among the organic materials, it is possible to highlight Porphyrins and Phthalocyanines. The synthesis of these materials enables a large number of distinct classes or groups, which can be distinguished by their peripheral structures and / or metal ions that can be inserted into the macrocycles. It results in changes of its optical properties, that is, replacing the chemical structures of such Porphyrins and Phthalocyanines, it is possible to tune its optical properties, and thus, according to these properties, to discriminate in which applications they can be used. Such materials, in view of their photophysical properties, can be used as photosensitizers in photodynamic therapy, solar cells, optical limiters or photobactericides among others. Thus, in this Master\'s Dissertation, a linear and nonlinear spectroscopic characterization of these materials is carried out in order to determine specific optical properties that can be employed in the cited applications. For this spectroscopic characterization, linear and nonlinear spectroscopy techniques were employed, among them the Z-Scan technique was employed in three distinct configurations (Z-Scan by Single Pulse, by Pulse Train and by Supercontinuum White Light) for determination of absorptions of excited states. Fluorescence lifetimes, radiative decay and internal conversion times, single and triple triplet (fundamental and excited) and quantum efficiencies (fluorescence, internal conversion, and triplet formation) were the parameters determined, and with these parameters, it was possible to understand how changes in the chemical structures (peripheral and metallic ions) modify considerable the optical properties of Porphyrins and Phthalocyanines.

Femtosecond laser has been an essential tool for nonlinear optics and materials processing at micrometer scale, in which chalcogenide and heavy metal oxide glasses have received special attention not only for their high third-order optical nonlinearities but also due to their transparency up to the infrared regions. Although metallic nanoparticles are expected to improve the optical properties of glasses, there are no enough experimental researches about their influence on the nonlinear refractive index (n2) and nonlinear absorption coefficient (&#946), moreover at femtosecond regime. Based on the scientific and technological interests on highly nonlinear glasses, the goal of this thesis was to apply femtosecond laser pulses in two main domains: (i) at the basis of fundamental science, to study the effect of metallic nanoparticles in the third-order nonlinear optical properties of glasses; and (ii) at the field of applied science, aiming the development of photonic devices, performed by the fabrication of 3D optical waveguides containing metallic nanoparticles. This aim was achieved through the techniques of z-scan and femtosecond laser micromachining, which provided the nonlinear optical characterization and waveguides development, respectively. First, we analyzed the third-order nonlinear optical properties of the GeO2-Bi2O3 glass containing gold nanoparticles, which promoted saturation of the absorption in the region of the surface plasmon resonance band. On the other hand, these gold nanoparticles did not affect the n2 that kept constant in the wavelength range of 480 - 1500 nm. The same features were investigated for a Pb2P2O7-WO3 matrix doped with copper nanoparticles. In contrast to the gold doped ones, these samples showed a slight enhancement of the nonlinear refractive index when the energy of the excitation approaches the surface plasmon band. We also found out that the Pb2P2O7-WO3 matrix is a good host to grow silver nanoparticles by fs-laser micromachining. Similarly, copper nanoparticles were produced in a borosilicate glass using single-step laser processing. The explanation for metallic nanoparticle formation is addressed in this thesis, as well as, its application in waveguides. Thus, we demonstrated the functionality of optical waveguides containing Cu0 or Ag0 nanoparticles. Still based on the technological interests on glasses doped with nanoparticles, we showed a single-step synthesis of silver sulfide nanoparticles in chalcogenide glass, which was carried in partnership with researches at Princeton University. The materials investigated in this PhD work are of great importance for photonics, in which the synthesis of nanoparticles, fabrication of waveguides and nonlinear optical characterization have been performed. / O laser de femtossegundos tem sido uma ferramenta essencial tanto para a óptica não-linear quanto para o processamento de materiais na escala micrométrica, na qual os vidros calcogenetos e óxidos de metais pesados têm recebido atenção especial, não apenas pelas suas elevadas não-linearidades ópticas de terceira ordem, mas também devido à sua transparência até o infravermelho. Embora seja esperado que nanopartículas metálicas melhorem as propriedades ópticas dos vidros, não existe investigações experimentais suficientes sobre a sua influência no índice de refração não linear (n2) e no coeficiente de absorção linear (&#946), sobretudo no regime de femtossegundos. Com base nos interesses científicos e tecnológicos de vidros altamente não-lineares, o objetivo deste trabalho foi aplicar pulsos laser de femtossegundos em dois domínios principais: (i) na campo da ciência fundamental, para estudar o efeito de nanopartículas metálicas nas propriedades ópticas não lineares de terceira ordem destes materiais; e (ii) no domínio da ciência aplicada, visando o desenvolvimento de dispositivos fotônicos, realizado pelo fabricação de guias de onda tridimensionais contendo nanopartículas metálicas. Este objetivo foi alcançado através das técnicas de varredura-z e microfabricação com laser de femtossegundos, que proporcionaram a caracterização óptica não-linear e o desenvolvimento de guias de onda, respectivamente. Primeiramente, foram investigadas as propriedades ópticas não-lineares de terceira ordem do vidro GeO2-Bi2O3 contendo nanopartículas de ouro, as quais promoveram saturação da absorção na região da banda de ressonância de plásmon. Por outro lado, essas nanopartículas não afetaram o n2, que se manteve constante no intervalo de comprimento de onda 480 - 1500 nm. As mesmas características foram investigadas para uma matriz Pb2P2O7-WO3 dopada com nanopartículas de cobre. Em contraste com os vidros dopados com ouro, estas amostras apresentaram um ligeiro aumento do índice de refração não linear quando a energia de excitação está próxima da banda de ressonância de plásmon. Observou-se ainda que a matriz Pb2P2O7-WO3 é ideal para a obtenção de nanopartículas de prata através da microfabricação com laser de femtossegundos. Similarmente, nanopartículas de cobre foram produzidas em vidro de borosilicato usando somente uma varredura a laser. A explicação para a formação de nanopartículas metálicas é abordada nesta tese, bem como sua aplicação em guias de onda. Deste modo, demonstrou-se a funcionalidade de guias de onda ópticos compostos por nanopartículas de Cu0 e Ag0. Ainda com base nos interesses tecnológicos em vidros dopados com nanopartículas, demonstrou-se uma síntese de nanopartículas de sulfeto de prata em vidro calcogeneto usando o processamento de única etapa, realizada em parceria com pesquisadores da Universidade de Princeton. Os materiais investigados neste trabalho de doutorado são de grande importância para aplicações em fotônica, em que a síntese de nanopartículas, a fabricação de guias de onda e a caracterização óptica não-linear foram realizadas.

Orientador: Newton Cesário Frateschi / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-17T01:57:53Z (GMT). No. of bitstreams: 1 Barea_LuisAlbertoMijam_M.pdf: 3934128 bytes, checksum: 9cd5c7861ac2af0dc42057f7f99ef89b (MD5) Previous issue date: 2010 / Resumo: As micro-cavidades ópticas são componentes essenciais em sistemas ópticos integrados, pois elas permitem capturar seletivamente, liberar e armazenar fótons, além de promoverem suas interações. Como exemplo, os micro-discos e micro-anéis são elementos que proporcionam tempos de vidas fotônicos extremamente longos, que podem ser utilizados tanto para filtros espectrais quanto para interações de fótons com alta eficiência não linear. Seu pequeno volume e seu alto tempo de vida fotônico são importantes para promoção eficiente de efeitos ópticos não lineares e, especialmente, o processo de mistura de quatro ondas com uma única freqüência de bombeio. No entanto, acoplar luz em um ressonador ainda é realizado com integrações híbridas utilizando fibras estranguladas. Nesta dissertação, nós apresentamos uma nova técnica para a fabricação de estruturas com ressonadores integrados monoliticamente a guias de ondas planares estrangulados, baseados em camadas de Si3N4/SiO2 depositadas sobre silício. Para isto, foi utilizada uma técnica que combina a nano fabricação, baseada em corrosões com um feixe de íons focalizados (FIB), com a técnica convencional de micro fabricação. Utilizando esta combinação, foi possível fabricar ressonadores acoplados a guias de ondas estrangulados e caracterizá-los. Para finalizar, nós observamos a geração de fótons em uma ressonância de um micro-anel devido ao efeito não linear de mistura de quatro ondas gerada pelo bombeio em uma ressonância subseqüente do anel / Abstract: Optical microcavities are essential components in optical integrated systems for they provide selective capture, release, and storage of photons as well as interaction with matter and other photons. As an example, micro-disks and micro-rings are elements that provide extremely long photon lifetime that can be used for spectral filtering as well for highly efficient non-linear photon interaction. For instance, its small volume and the high photonic lifetime are very important for the efficient promotion of nonlinear effects and, specially, the four wave-mixing (FWM) process with a single pumping frequency. However, coupling light to and from the resonator is still achieved with hybrid integration using tapered silica fibers. But, in this dissertation, we present a new technique for the fabrication of structures with monolithically integrated resonators and planar tapered waveguides, all based in Si3N4/SiO2 layers deposited on silicon. We use an approach that combines nano fabrication techniques based on focused ion beam (FIB) milling and conventional micro fabrication techniques. Using this approach, we could fabricate resonators coupled to tapered waveguides and characterize them. Finally, we observed the photon generation at a micro-ring resonance due to four-wave mixing generated by pumping at a subsequent micro-ring resonance / Mestrado / Física da Matéria Condensada / Mestre em Física

Este trabalho propõe uma extensão do método de propagação de feixe (BPM - Beam Propagation Method) para a análise de guias de ondas ópticos e acopladores baseados em materiais não-lineares do tipo Kerr. Este método se destina à investigação de estruturas onde a utilização da equação escalar de Helmholtz (EEH) em seu limite paraxial não mais se aplica. Os métodos desenvolvidos para este fim são denominados na literatura como métodos de propagação de feixe de ângulo largo. O formalismo aqui desenvolvido é baseado na técnica das diferenças finitas e nos esquemas de Crank-Nicholson (CN) e Douglas generalizado (GD). Estes esquemas apresentam como característica o fato de apresentarem um erro de truncamento em relação ao passo de discretização transversal, &#916x, proporcional a O(&#916x2) para o primeiro e O(&#916x4). A convergência do método em ambos esquemas é otimizada pela utilização de um algoritmo interativo para a correção do campo no meio não-linear. O formalismo de ângulo largo é obtido pela expansão da EEH para os esquemas CN e GD em termos de polinômios aproximantes de Padé de ordem (1,0) e (1,1) para CN e GD, e (2,2) e (3,3) para CN. Os aproximantes de ordem superior a (1,1) apresentam sérios problemas de estabilidade. Este problema é eliminado pela rotação dos aproximantes no plano complexo. Duas condições de contorno nos extremos da janela computacional são também investigadas: 1) (TBC - Transparent Boundary Condition) e 2) condição de contorno absorvente (TAB - Transparent Absorbing Boundary). Estas condições de contorno possuem a facilidade de evitar que reflexões indesejáveis sejam transmitidas para dentro da janela computacional. Um estudo comparativo da influência destas condições de contorno na solução de guias de ondas ópticos não-lineares é também abordada neste trabalho. / This work introduces an extension of the beam propagation method (BPM) for the analysis of optical waveguides and couplers based on Kerr-type nonlinear materials. This method is intended for the investigation of structures where the paraxial scalar Helmholtz equation (EEH) no longer holds. The numerical methods developed for this situation are known in the literature as wide-angle beam propagation methods. The formulation developed in this work is based on finite differences and on the Crank-Nicholson (CN) and Generalized Douglas (GD) schemes. These schemes are characterized by a truncation error with respect to the transverse discretization step, &#916x, proporcional to O(&#916x2) for the CN and to O(&#916x4) for the GD scheme. The convergence of the method for both schemes is optimized by the application of an iterative algorithm for the correction of the field in the nonlinear medium. The wide-angle formalism is obtained by the expansion of the EEH for the CN and GD schemes in terms of Padé approximant polynomials. The expansions addressed in this work utilize Padé approximants of order (1,0) and (1,1) for the CN and GD scheme, and (2,2) and (3,3) for the CN scheme. Approximants orders higher than (1,1) show serious stability problems. This problem is circumvented by rotating the approximants in the complex plane. Two boundary conditions on the edge of the computational window are also investigated: 1) transparent boundary condition (TBC) and 2) transparent absorbing boundary (TAB). These boundary conditions are necessary in order to avoid unwanted reflections back to computational domain. A comparative study of the influence of these boundary conditions on the solution of nonlinear optical waveguides is also addressed in this work.

Orientadores: Hugo Enrique Hernandez Figueroa, Jorge Diego Marconi / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-20T04:06:46Z (GMT). No. of bitstreams: 1 RumaldoBustamante_YesicaRaquel_M.pdf: 23599528 bytes, checksum: 6361d5bb8b67de6d0a1d0e691d1040e0 (MD5) Previous issue date: 2011 / Resumo: Nos últimos anos, dispositivos paramétricos baseados em fibras ópticas têm sido foco de interesse em diversas aplicações, sendo uma delas o trocador de comprimento de onda. No presente trabalho estudamos esse dispositivo, que, como todo dispositivo paramétrico, está baseado no efeito não-linear de mistura de quatro ondas. O trocador de comprimento de onda foi estudado através de simulações e experimentos. As simulações foram feitas utilizando o software comercial VPI Photonics. Esse software resolve a equação não-linear de Schrödinger utilizando o método Split Step Fourier para simular a propagação da luz ao longo da fibra óptica. Devido à importância das características da fibra no funcionamento do trocador de comprimento de onda, primeiramente utilizamos uma técnica baseada no fenômeno de instabilidade modulacional (amplificação de ruído) para obter parâmetros intrínsecos da fibra, tais como o coeficiente não-linear e o comprimento de onda de dispersão nula. Devido ao fato do trocador de comprimento de onda funcionar com bombeios de alta potência, o limiar de espalhamento Brillouin estimulado foi incrementado alargando a linha do laser de bombeio por modulação de fase. Essa modulação de fase foi otimizada para o dispositivo paramétrico estudado, conseguindo um aumento do limiar de 10 dB. Finalmente, foi construído um trocador de comprimento de onda com um segmento de 1 km de comprimento da fibra altamente não-linear previamente caracterizada...Observação: O resumo, na íntegra, poderá ser visualizado no texto completo da tese digital / Abstract: In recent years, parametric devices based on optical bers have been the focus of interest in many applications, being one of these applications the wavelength exchanger. In this work we study the wavelength exchanger in optical fibers which, as all parametric devices is based on the non-linear effect of four-wave mixing. The wavelength exchanger was studied through simulations and experiments. The simulations were performed by using a commercial software called VPI Photonics. This software solves the nonlinear Schrödinger equation by using the Split Step Fourier method to simulate the light propagation along the optical fiber. Since the fiber characteristics are very important for the performance of the exchanger, firstly a technique based on modulation instability was used to measure intrinsic parameters of the fibers, such as the nonlinear coefficient and the zero dispersion wavelength. Due to the fact that the exchanger works with high power pumps, the stimulated Brillouin scattering threshold was increased by broadening the pump laser linewidth by phase modulation. Such a phase modulation was optimized for the studied parametric device, obtaining a threshold increase of 10dB. Finally, a wavelength exchanger was mounted with a 1km segment of the previously characterized fiber ...Note: The complete abstract is available with the full electronic document / Mestrado / Telecomunicações e Telemática / Mestre em Engenharia Elétrica

Orientador: Luís Eduardo Evangelista de Araujo / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-21T04:46:52Z (GMT). No. of bitstreams: 1 BecerraCastro_EmilioManuel_D.pdf: 3066640 bytes, checksum: 3e7ff0e58dae7364f9f6d0b5f37924eb (MD5) Previous issue date: 2012 / Resumo: Neste tese apresentamos um estudo teórico dos efeitos de coerência atómica em vapor atómico com o propósito de estudar teoricamente efeitos óticos não-lineares transversais a baixas intensidades de luz. Sob a condição da transparência induzida eletromagneticamente, um meio atómico pode desenvolver não-linearidades óticas gigantes, possibilitando a observação de efeitos óticos não-lineares a baixas intensidades. Investigamos três efeitos transversais: emissão cónica, focalização induzida e feixes de vórtices induzidos eletromagneticamente. Todos estes três efeitos têm origem na modulação de fase cruzada entre um laser de prova e um laser sinal, ambos fracos, com intensidades abaixo da intensidade de saturação das transições às quais estão acopladas. Em emissão cónica, descrevemos a formação de anéis ao redor de um feixe de prova fraco. No estudo de focalização induzida, descrevemos como que a aplicação de uma máscara de intensidade ao feixe sinal pode levar à formação de lentes GRIN no vapor atómico, induzindo à focalização do laser de prova. Por último, estudamos a conversão do feixe de prova em um feixe de vórtice ótico pela aplicação de uma máscara de intensidade espiral ao feixe sinal / Abstract: In this thesis we present theoretical study of the effects of atomic coherence in atomic vapor for the purpose of studying theoretically transverse nonlinear optical effects at low light levels. Under the conditions of electromagnetically induced transparency, an atomic medium can develop giant optical nonlinearities, allowing the observation of nonlinear optical effects to low intensities. We investigate three transverse effects: conical emission, induced focusing and electromagnetically induced vortices. All three of these effects stem from cross-phase modulation between probe and a signal laser, both weak with intensities below the saturation intensity the transitions to they coupled. In conical emission, we describe the formation of rings around a weak probe beam. In the study of induced focusing, we describe how applying an intensity mask to the signal beam can lead to the formation of GRIN lenses the atomic vapor, leading to focusing of the probe laser. Finally, we studied the conversion of the probe beam into an optical vortex beam by applying a spiral intensity mask to the signal beam / Doutorado / Física / Doutor em Ciências