The analogy of optical system to other physical systems has been attracting much attention over the past decades. In coupled optical lattices, phenomena originated from electronic systems, such as Bloch oscillations, Dynamic localization and Zener tunneling, have been extensively investigated and led to novel research directions and applications. Following this idea, harmonic oscillations are spatially mimicked by the propagation of supermodes in quadratically-coupled waveguide arrays. By analyzing the field envelope with the propagation constants and the superposition of the supermodes, we achieve conjugate-imaging at the half-period plane and self-imaging at the full-period plane, which give rise to the linear switching. Combining the linear switching and the nonlinear light propagation triggered at high power level, we demonstrate the superior performances of nonlinear power switching compared with traditional nonlinear directional couplers. Through the linear and nonlinear observation on AlGaAs waveguide array, we present the first experimental proof of the harmonic oscillations in optical waveguide arrays.

The analogy of optical system to other physical systems has been attracting much attention over the past decades. In coupled optical lattices, phenomena originated from electronic systems, such as Bloch oscillations, Dynamic localization and Zener tunneling, have been extensively investigated and led to novel research directions and applications. Following this idea, harmonic oscillations are spatially mimicked by the propagation of supermodes in quadratically-coupled waveguide arrays. By analyzing the field envelope with the propagation constants and the superposition of the supermodes, we achieve conjugate-imaging at the half-period plane and self-imaging at the full-period plane, which give rise to the linear switching. Combining the linear switching and the nonlinear light propagation triggered at high power level, we demonstrate the superior performances of nonlinear power switching compared with traditional nonlinear directional couplers. Through the linear and nonlinear observation on AlGaAs waveguide array, we present the first experimental proof of the harmonic oscillations in optical waveguide arrays.

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / Grades de Bragg nÃo-lineares tÃm sido consideradas desde o final do sÃculo passado para aplicaÃÃes em sistemas de comunicaÃÃes Ãpticas e sensoriamento. O estudo de pulsos ultra-curtos em grades de Bragg lineares, entretanto, sà tem sido considerado nos Ãltimos anos, devido ao desenvolvimento de tÃcnicas numÃricas especÃficas para se resolver o problema. Neste trabalho, foi realizado um estudo analÃtico-numÃrico das caracterÃsticas de transmissÃo e reflexÃo das grades de Bragg nÃo-lineares. Pela primeira vez, foram consideradas variaÃÃes periÃdicas da nÃo-linearidade no dispositivo operando no regime de onda continua, levando a uma nova classe de grades nÃo-uniformes. CaracterÃsticas dos estados bi- e multi-estÃveis foram extensamente investigados nas grades de Bragg nÃo-lineares. TambÃm, pela primeira vez, foi realizado o estudo numÃrico de pulsos ultracurtos ($sim$1 ps) incidindo em grades nÃo-lineares. O enfoque foi dado para a dependÃncia da intensidade de um pulso ultracurto ao passar por tal grade. Foram estudadas, ainda, as dependÃncias na forma temporal da profundidade de modulaÃÃo da grade e do Ãndice nÃo-linear. Grades apodizadas foram consideradas, jà que estas sÃo de importÃncia fundamental nos sitemas de comunicaÃÃes modernos. / Nonlinear fiber Bragg gratings has been considered since the end of last century for applications in optical communications and sensor techniques. The investigation of ultrashort pulses in linear Bragg gratings, however has been considered in the last few years due the development of specifical numerical techniques to solve this problem. In the present work an analytical and numerical study of the reflection and transmission characteristics of nonlinear Bragg gratings was done. For the first time, it has been considered periodic variations of the nonlinearity in that devices operating in the continuous wave regime, leading to a new class of nonuniform gratings. It was extensively investigated the bi- and multistable characteristics in these nonlinear fiber Bragg gratings. Also, for the first time, the numerical study of ultrahsort pulses ($sim$1 ps) incident in nonlinear gratings was done. The focus was the input pulse intensity dependence on that gratings. Also, the depedences in the time shapes of grating index modulation depth and nonlinear index were studied. Apodized gratings were considered since they are of fundamental importance in modern communications systems.