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光诱导光子学微结构中的光传输与光调控研究

Study on Light Propagation and Steering in Optically Induced Photonic Microstructures

【作者】 叶卓艺

【导师】 陈志刚;

【作者基本信息】 南开大学 , 光学, 2012, 博士

【摘要】 在过去的十年中,光波与光子学微结构相互作用吸引了人们越来越多的关注。最近人们在微加工领域取得的进展比如半导体中的制备工艺、熔石英玻璃中的飞秒激光直写技术、光折变晶体中的实时光诱导技术等大大拓宽了传统光学领域。当前的大量研究成果使人们开始掌握未来由光子学微结构带来的一系列潜在应用,比如集成光学、全光网络等。本论文基于光诱导技术,在光折变非线性晶体中建立了几种可实时调控的光子学微结构。得益于这些新型的光子学微结构的构建,成功地观测到了基于带隙导光的涡旋光线性局域、基于入射角度非线性光波的偏折、光波分束和能量单方向转移、艾里光的加速度操控以及新型光束的非线性调控。本文主要取得了以下几个方面的成果:首先,利用光诱导技术在光折变非线性晶体中首次构建了缺陷深度可调的单缺陷光子晶格,提出了在两种光诱导缺陷光子晶格中操控光波的方法。其一,利用线性带隙导光机制在二维缺陷中观测到了涡旋光模式。实验研究结果表明,只有在光强为非零的缺陷光子晶格中能够支持这类线性涡旋导光。其二,从理论和实验上分别观测到了非线性光波在低于某个阈值角度的情况下能被负缺陷反射。而在大于阈值角度入射时,它能够顺利地通过缺陷透射。该现象在一维和二维的光子晶格中都能发生,它提供了在阵列网络中基于角度控制光传播的技术。其次,研究拓展到了更复杂的缺陷光子晶格。从理论上系统地研究三缺陷光子晶格材料及其缺陷本征模,深入地讨论了材料物理参数对缺陷本征模的影响。基于该材料提出了对称三缺陷光子晶格和反对称三缺陷光子晶格。前者的应用是光波的分束和汇聚;对于后者,通过绝热地改变缺陷深度建立了能量单一转移方向的通道。此外,又讨论了在对称的三缺陷光子晶格中非线性的影响和多色光的传输特性。再次,利用光诱导技术在光折变非线性晶体中构建了折射率梯度分布的光子学微结构,首次从理论和实验上成功地调控了一维和二维艾里光的加速度。利用线性梯度折射率可以实现艾里光加速度的增强和减弱。艾里光在线性梯度折射率中传输时它的光学波包分布能保持不变。这种基于梯度折射率材料的艾里光加速度调控的一系列结论将为研究艾里光在多种环境中传输奠定基础。最后是新型光束的构建和光折变自诱导波导的研究。从已有的艾里光研究基础出发,在实验上巧妙地通过三个无限能量的艾里函数乘积构造出了局域的二维新型光波场。从实验上研究了这类新型光束的线性和非线性的传输特性。特别的,在自聚焦非线性下,这类新型光束的能量产生局域并自诱导形成波导通道,而自散焦非线性对该波包的形貌基本不产生影响。在傅里叶空间上观测发现:在自散焦作用下其空间频谱破碎成三个点,而在自聚焦作用下频谱则向中心收缩。

【Abstract】 Light interactions with the photonic microstructures have attracted a great dealof interest in the past decade. Recent advances in microfabrication technology such assemiconductor fabrication, fs-laser-written in fused silica and lattices induced inphotorefractive crystals have broadened the field of optics. The flourish of activitywill lead to potential applications of these photonic microstructures in tomorrow’sintegrated optics and all-optical network. In this dissertation, several reconfigurablephotonic microstructures in photorefractive crystals have been created through theoptical induction technique. Based on these novel photonic microstructures, we havesuccessfully demonstrated a number of novel phenomena including vortexlocalization by bandgap guidance, angle-dependent nonlinear beam deflection, beamsplitting, one-way energy transfer passage, controlled acceleration of Airy beams andthe nonlinear evolution of the product of three Airy beams. The main achievementsare summarized as follows:Firstly, the optically induced photonic lattices with tunable negative defects arefirst created in photorefractive crystals. Two methods are proposed to manipulate theflow of light through the defect in the induced photonic lattice. One is that weexperimentally demonstrate linear bandgap guidance of optical vortices intwo-dimensional photonic lattices and the defect strength is set at an appropriate level.The other is that we demonstrate both theoretically and experimentally that anonlinear beam can be reflected by a negative defect in a photonic lattice if theincident angle is below a threshold value. Above this threshold angle, the beamsimply passes through the defect. This phenomenon occurs in both one-andtwo-dimensional photonic lattices, and it provides a way to use the incident angle tocontrol beam propagation in a lattice network.Next,the investigations are extended to more complex defect photonic lattices.We theoretically study the light propagation dynamics in tri-core photonic latticeswhich support three defect modes. The effects of physical parameters on the defectmodes are deeply discussed. Two types of tri-core photonic lattices are designed. One is called symmetric tri-core photonic lattices which can support beam splitting. Theother is called asymmetric tri-core photonic lattices which might lead to one-wayenergy delivering in an adiabatic passage. Furthermore, we also discuss the effects ofnonlinearity on the beam propagation and polymatic light propagation.Subsequently, we demonstrate both experimentally and theoretically controlledacceleration of one-and two-dimensional Airy beams in optically inducedrefractive-index potentials in photorefractive crystals. Enhancements as well asreduction of beam acceleration are realized by changing the index gradient, while thebeam shape is maintained during propagation through the linear optical potential. Ourresults of active acceleration manipulation in graded media are pertinent to Airy-typebeam propagation in various environments.Finally, we focus on the observation of a new type of beam and its self-inducedwaveguides. Beyond the Airy beams, a new localized two-dimensional field which isa product of three Airy functions with finite energy is observed. We experimentallydemonstrate linear and nonlinear propagation of the product of three Airy functions.Under self-focusing nonlinearity, the energy of the beam can be self-localized in theformation of self-induced waveguides. However,the shape of such beam structure isnearly unchanged under self-defocusing nonlinearity. Interestingly, the powerspectrum breaks up into three spots under the self-defocusing nonlinearity but it ismore localized in the central region in Fourier space in the self-focusing case.

  • 【网络出版投稿人】 南开大学
  • 【网络出版年期】2014年 06期
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