The wavelength-division multiplexing (WDM) is a well know technique capable of increasing the total capacity of a lightwave communication system; however, the system performance can be significantly limited by the dispersive and nonlinear effects, among others. This dissertation is mainly focused on the nonlinear effects upon the short-haul and long-haul lightwave systems.The short-haul lightwave system is mainly adopted in the access network. A passive optical access network is generally used to connect individual homes to a central office of a local area, and since there is no active component installed outside the central office of the passive optical access network, the system complexity and maintenance frequency can be significantly reduced. This dissertation provides a long-reach passive optical network (LR-PON) which can further reduce the system complexity and system cost. We found that four-wave mixing (FWM) and Rayleigh backscattering induced crosstalk were two main reasons to degrade the transmission performance in our proposed LR-PON. The long-haul lightwave system is mainly adopted in the transoceanic application. Although differential phase-shit keying (DPSK) modulation format has been confirmed to be suitable for long-haul WDM system, we found that a performance dip can be observed near the system zero dispersion avelength. In this dissertation, we designed various experiments to confirm the nonlinear effect to cause the performance dip being observed, and concluded that self-phase modulation (SPM) was the dominant reason to cause the performance dip rather than cross-phase modulation (XPM) or nonlinear phase noise.

O emaranhamento é uma propriedade intrinsecamente quântica, que pode ser empregada em protocolos de comunicação quântica de informação, como criptografia quântica e teletransporte, e um recurso importante no processamento quântico de informação, visando a implementação de algoritmos mais eficientes que os atualmente empregados, de uso limitado em problemas ditos insolúveis, nos quais, as etapas de processamento crescem exponencialmente com o tamanho dos dados de entrada. O Processo de Mistura de Quatro Ondas [4WM: Four Wave Mixing] na configuração duplo- em vapor de Rubídio tem-se mostrado como uma fonte robusta de estados fortemente emaranhados [Boyer et al., 2008b]. No presente trabalho é caracterizado o ganho paramétrico G dos campos Stokes e anti-Stokes no processo de 4WM associado à linha D 1 do Rubídio. Os parâmetros estudados foram a dessintonia do campo de bombeio , sua intensidade I B e a temperatura da célula de Rubídio T Rb . Além da caracterização do ganho, estudaram-se também a absorção eletromagneticamente induzida e as intensidades dos feixes conjugados. Obtiveram-se ganhos de até 450% ajustáveis via sintonização destes parâmetros. Os elevados ganhos em meios atômicos permitem geração de emaranhamento sem uso de cavidade e aceitam operação multimodo. Consequentemente podem ser usados na realização de medidas ultraprecisas e ensejam a possibilidade de explorar regimes até agora inatingíveis pelos Osciladores Paramétricos Óticos [OPO] baseados em cristais (nos quais os ganhos são da ordem de 4%). O OPO tem sido estudado em situações acima ou abaixo do limiar, mas na transição rareiam resultados experimentais. Os resultados obtidos foram comparados com a literatura, e o próximo passo é usá-los em cavidades abertas para construir um OPO que seja facilmente operado acima ou abaixo do limiar, e estudar o limite entre vácuo enmaranhado e feixes intensos. Espera-se observar estados emaranhados não gaussianos gerados neste sistema e estudar suas aplicações em processamento de informação com variáveis contínuas da luz. / Entanglement is an intrinsically quantum property that can be used in quantum communication protocols, such as quantum cryptography and teleportation. It is a basic piece for quantum information processing, aiming at the implementation of more efficient algorithms than those currently used. These new algorithms are important to attack the so called nonsolvable problems, in which, the processing steps grow exponentially with the size of the input data. On the other hand, the Four Wave Mixing Process in the double- level configuration in Rubidium vapor has been shown to be a robust source of strongly entangled fields [Boyer et al., 2008b]. In the present work the parametric gain G of the Stokes and anti-Stokes fields in the 4WM process associated with the D 1 line of Rubidium is characterized. The parameters studied were the detuning and intensity I B of the pumping field and the temperature of the Rubidium cell T Rb. Besides the gain characterization, the electromagnetically induced absorption and the intensities of the conjugated fields were also studied. Adjustable gains up to 450% were achieved via the tuning of those parameters. The high gains in atomic media allow the generation of entanglement without cavity, and permit multi-mode operation. Therefore, they can be used to carry out ultra-precise measurements and allow the possibility of exploring schemes hitherto unattainable by crystal-based Optical Parametric Oscillators (OPO) (with gains of 4 %). The OPO has been studied in situations above or below the threshold, but in the transition experimental results are rare. The results we obtained were compared with literature, and the next step is to use them in open cavities to construct an OPO that can be easily operated above or below the threshold, and to study the boundary between entangled vacuum and intense beams. In this system, it is expected to be observed non-Gaussian entangled states, and to be able to study its applications in information processing with continuous variables states of light.

This dissertation presents experimental and theoretical studies of transient degenerate four wave mixing (DFWM) in organic dyes. Chapter 1 is an introduction to DFWM. Chapter 2 describes DFWM experiments that were performed in the gain medium of a dye laser. Chapter 3 presents the theory of DFWM of short pulses in three level saturable media. Chapter 4 presents DFWM experiments of femtosecond pulses in the saturable absorber of a passively modelocked ring dye laser. Chapter 5 presents the theory of DFWM of ultrashort pulses in resonant media.

Beginning with the discovery of graphene, two-dimensional materials have amassed a strong interest. Like graphene, transition metal dichalcogenides (TMDs) can be coaxed into atomically thin sheets which have some impressive properties. Unlike graphene, TMDs also has a change in their electronic band structure causing an indirect band gap to a direct gap transition in its monolayer form. Additionally, these materials lose their inversion symmetry as a monolayer. These unique properties make TMDs a strong candidate for being used in optoelectronic and valleytronic devices. In order for these devices to be successful, the optical properties of TMDs must be thoroughly understood. Due to this class of material's strong Coulomb interaction, the optical properties are dominated by excitons, a quasiparticle made up of an electron-hole pair. Therefore, the success of these devices relies, in part, on understanding and manipulating excitons. One key parameter of excitons is their dephasing rate which characterizes the lifetime of the coherent superposition of two states (i.e. how the coherence decays which is caused by excitons interacting with their environment). In this work, two optical properties are investigated: (1) How the linear absorption of the TMDs A-exciton peak varies as the material increases in thickness. By looking at how the absorption varies by sample thickness, the interaction between emitters can be understood. Experimental results for the diamagnetic shift are presented which are used to determine the lateral excitonic size. Through theoretical calculations, based on the semiconductor Maxwell-Bloch equations, additional insight into the radiative coupling of the systems are obtained. (2) How the coherence prole of the exciton changes in the presence of an external magnetic eld and specic valley excitation. By varying the polarization scheme in the four wave mixing measurement, specic valley excitation can be selected, allowing for insight into the dephasing mechanisms. By applying an external magnetic eld, the energy levels of the electron and hole can be discretized and the corresponding eects on the system's coherence seen. In conjunction with time-dependent density function theory calculations and the experimental results, a deeper understanding of exciton dynamics and multi-exciton complexes was obtained. Finally, a new system is proposed in which complex spectroscopic techniques can be performed on micron sized samples as well as devices in the presence of an external magnetic eld at cryogen temperatures. This system will allow for the investigation of the optical properties of stacked monolayers (heterostructures) as well as devices.

Monolithic passively mode-locked colliding pulse semiconductor lasers generating pico- to sub-picosecond terahertz optical pulse trains are promising sources for future applications in ultra-high speed data transmission systems and optical measurements. However, in the absence of external synchronization, these passively mode-locked lasers suffer from large amplitude and timing jitter instabilities resulting in broad comb linewidths, which precludes many applications in the field of coherent communications and signal processing where a much narrower frequency line set is needed. In this dissertation, a novel quantum dot based coupled cavity laser is presented, where for the first time, four-wave mixing (FWM) in the monolithically integrated saturable absorber is used to injection lock a monolithic colliding pulse mode-locked (CPM) laser with a mode-locked high-Q ring laser. Starting with a passively mode-locked master ring laser, a stable 30 GHz optical pulse train is generated with more than 10 dB reduction in the RF noise level at 20 MHz offset and close to 3-times reduction in the average optical linewidth of the injection locked CPM slave laser. The FWM process is subsequently verified experimentally and conclusively shown to be the primary mechanism responsible for the observed injection locking. Other linear scattering effects are found to be negligible, as predicted in the orthogonal waveguide configuration. The novel injection locking technique is further exploited by employing optical hybrid mode-locking and increasing the Q of the master ring cavity, to realize an improved stabilization architecture. Dramatic reduction is shown with more than 14-times reduction in the photodetected beat linewidth and almost 5-times reduction in the optical linewidth of the injection locked slave laser with generation of close to transform limited pulses at ~ 30 GHz. These results demonstrate the effectiveness of the novel injection locking technique for an all-on-chip stability transfer and provides a new way of stabilizing monolithic optical pulse sources for applications in future high speed optical networks.

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付記する学位プログラム名: 京都大学卓越大学院プログラム「先端光・電子デバイス創成学」 / 京都大学 / 新制・課程博士 / 博士(工学) / 甲第23904号 / 工博第4991号 / 新制||工||1779(附属図書館) / 京都大学大学院工学研究科電子工学専攻 / (主査)教授 竹内 繁樹, 教授 川上 養一, 准教授 浅野 卓 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

Desenvolvemos um modelo teórico para tratar a mistura de várias ondas em meios absorvedores saturáveis, considerando a auto-difração de duas ondas incidentes numa grade de população, a qual é induzida no meio não-linear. O modelo foi investigado através de resultados experimentais observados em rubi (Al2O3:Cr3+), alexandrita (BeAl2O4:Cr3+) e GdAlO3: Cr3+. Demonstramos, pela primeira vez, transferência de energia por mistura não degenerada de duas ondas (NDTWM) em alexandrita e GdAlO3: Cr3+. Neste ultimo, também observamos a difração de primeira ordem do feixe forte e medimos a variação de sua intensidade com relação a velocidade de deslocamento da grade. No GdAlO3: Cr3+, medimos o espectro de absorção do estado excitado e o espectro da parte real do índice de refração não-linear em quatro linhas do laser de argônio e na região de 560-620 nm de um laser de corante operando com rodamina 6G. Os resultados indicam uma interação entre pares de cromo no estado excitado, seguida da absorção de um fóton, a qual pode explicar a variação da parte imaginaria n2 com a intensidade, conforme observado experimentalmente. Nós tentamos observar bi-estabilidade óptica em GdAlO3: Cr3+ mas não tivemos êxito, provavelmente por causa de efeitos transversais e também pelo aumento da absorção com a intensidade. Por outro lado, observamos um regime multi-estável numa cavidade Fabry-Perot vazia, onde o meio não-linear é o material usado na fabricação dos espelhos, que no caso foi o ZrO2. Também observamos comportamento multi-estável em filtros de inconel, causado pelo acoplamento termo-óptico entre o filtro e a radiação laser. / We have developed a new approach to deal with multi-wave mixing in saturable absorbing media, by considering the self diffraction of two incident waves in a population grating which is created by them in the nonlinear medium. Wehave also made experimental work on ruby (Al2O3:Cr3+), alexandrite (BeAl2O4:Cr3+) and GdAlO3: Cr3+ in order to compare with our theoretical model. We have demonstrated energy transfer by nearly degenerated two wave mixing (NDTWM) in alexandrite and GdAlO3: Cr3+ for the first time. We measured the intensity of the first order diffracted intense beam as a function of the frequency shift between the incident beams in GdAlO3: Cr3+. For this crystal, we have obtained the spectra of the excited state absorption and the real part of the nonlinear index at four wavelengths of an argon laser and in the range 560-620 nm of a rodamine 6G dye laser. These kinds of spectra had never been reported before in that material. The result seems to support our proposal of an excited chromium pair interaction with an additional photon absorption which can explain the observed variation of the imaginary part of the nonlinear Kerr index with the intensity. We tried to observe optical bistability in GdAlO3: Cr3+ but we were unsuccessful, probably due to strong transverse effects and increasing absorption with the intensity. However we observed multistable regime in empty Fabry-Perot cavities in which the mirrors were made of thin films of ZrO2 deposition. A multistable thermo-optical behavior in inconel filters was also observed.

Os estados emaranhados da luz são de grande importância para protocolos de comunicação quântica. Uma das principais fontes que vem sendo estudada no Laboratório de Manipulação Coerente de Átomos e Luz - LMCAL é o oscilador paramétrico ótico (OPO) no qual, através de processos paramétricos não lineares de segunda e terceira ordem (x(2) e x(3)), são produzidos feixes intensos que apresentam correlações quânticas. Recentemente, o LMCAL vem explorando o processo de mistura de quatro ondas (fenômeno derivado da susceptibilidade de terceira ordem x(3)) como fonte geradora de feixes emaranhados. Inicialmente, foi realizado a partir de células de rubídio e agora, em colaboração com o grupo de pesquisa da Profa. Michal Lipson da Universidade de Columbia, em chips de nitreto de silício (Si3N4); permitindo assim possibilidades de modulação ultra-rápida, confinamento de luz em volumes muito reduzidos, além da ótica não-linear do OPO. O presente projeto visa estudar as propriedades quânticas da luz nos OPOs em chips de silício, permitindo que sistemas muito eficientes em informação clássica possam ser usados também para implementação de protocolos de informação quântica. / Entangled States of light beams are of great importance for quantum communication protocols. One of the most relevant source of such states which is being studied at the Laboratory of Coherent Manipulation of Atoms and Light - LMCAL (in portuguese) is the Optical Parametric Oscillator (OPO) which through second and third order nonlinear parametric processes (x(2) and x(3)) produces intense fields that have quantum correlations. Recently, LMCAL is exploring four-wave mixing (FWM), a third-order nonlinear parametric process, as a source of entangled beams. Initially, on rubidium cells and now, in collaboration with Prof. Michal Lipson from the Columbia University, on silicon nitride (Si3N4) chips; opening a new avenue for ultrafast modulation, light confinement in reduced light volumes, as well as the nonlinear optics of the OPO. This project is intended to study quantum properties of light of on-chip OPOs in order to achieve the integration of these highly efficient devices for implementations of quantum information protocols.