【作者】 杨旭；

【导师】 龙桂鲁；

【作者基本信息】 清华大学 ， 物理学， 2016， 博士

【摘要】 回音壁模式光学微腔由于具有高品质因子、低模式体积和良好的可集成性,在高灵敏度传感器、非线性光学、微型激光器、光信息处理、腔光力学和量子信息等领域取得了重要的发展和应用。为提升微腔的品质因子等性能,人们在微腔中掺杂稀土离子等光学增益材料制成主动腔。然而主动腔的制作过程相对复杂,而且其泵浦光源和工作范围受到稀土离子等掺杂物质的泵浦带和发光带的限制。因此我们试图以微腔材料中普遍存在的拉曼过程代替增益物质的掺杂,减除额外的加工成本,避免掺杂引入的微腔损耗,同时放宽对泵浦激光和工作范围波长的限制。本论文围绕回音壁模式光学微腔的拉曼调制,主要开展了以下三方面的研究:一、利用回音壁微腔拉曼激光检测纳米粒子。我们同美国圣路易斯华盛顿大学的杨兰教授的研究组合作,利用二氧化硅回音壁微腔的拉曼增益补偿微腔损耗,提升粒子检测的分辨率,并通过微腔拉曼激光模式劈裂产生的自参照的拍频,实现了对半径低至10 nm的单个纳米粒子的检测和计数。实验达到了创纪录的极化率灵敏度(3.82×106μm3)。二、通过拉曼增益调控回音壁微腔系统的耦合机制。我们从理论和实验上研究了不同耦合条件下,波导耦合的回音壁微腔的透射谱随拉曼增益的变化。实验显示拉曼增益的大小不仅影响着透射谱的线宽,还能改变系统的耦合机制。在此基础上,我们通过施加拉曼增益,在不移动任何单个光学元件的前提下,实现对微腔-波导系统耦合机制的连续调控。这种调控达成了此前类似方法无法实现的从欠耦合向过耦合方向的调节,还在调控过程中提高了谱线的分辨率,对光学微腔系统的双向全光调节具有重要意义。三、利用二氧化硅的受激拉曼损耗调控回音壁微腔系统的耦合机制。我们首次研究了二氧化硅的受激拉曼损耗对回音壁微腔系统的影响,并在此基础上利用逆拉曼散射改变了微腔腔内损耗,实现了对光纤锥耦合的微芯圆环腔系统耦合机制的全光调节。我们在不改变微腔或光纤锥位置的前提下,通过注入低功率的泵浦光,将系统由深度过耦合调控到临界耦合。实验中共振透射率降低了19.58dB,远高于此前硅微环腔达到的9dB的对比度,而且相比硅微环腔,本方案不受双光子吸收和自由载流子吸收等效应的干扰。更多还原

【Abstract】 Whispering Gallery mode(WGM)micro-resonators with high quality factor,small mode volume and good integration performance,have been applied in many various fields of modern science,such as high performance sensors,on-chip micro-lasers,nonlinear optics,optical communication devices,cavity optomechanics,quantum information and so on.To achieve better performace(e.g.higher quality factor),WGM resonators are doped with optical gain providing material such as rare earth ions,and these doped resonators are known as active resonators.However,active resonators require additional fabrication process,and are suitable only for specific pumping and working window since each type of rare earth ions has its own specific pumping and emission spectrum.So we attempt to use Raman effect,which have been realized in most of the common used materials of WGM resonators,instead of rare earth iron doping,to avoid dopant or additional fabrication complexities,eliminate doping induced cavity loss,and loosen the requirement of specific wavelength for pump and emission.This thesis is focused on Raman modulation of whispering gallery mode microresonators and my work is listed as follows:1.Highly sensitive detection of nanoparticles with whispering-gallery Raman microlaser.We cooperate with Prof.Lan Yang’s research group in Washington University in St.Louis,improve paticle detection limit through Raman gain-induced loss compensation in silica WGM resonators,and detect and count single nanoparticles down to 10 nm in radius via self-referenced beatnote from mode splitting in a WGM Raman microlaser.This scheme has enabled achieving record-high polarizability sensitivity(down to 3.82 × 106μm3),and has good biological compatibility compared to rare earth doped cavity sensors.2.Raman gain induced mode evolution and on-demand coupling control in whispering-gallery-mode microcavities.We systematically investigated both theoretically and experimentally the evolution of mode splitting spectra under Raman gain in various initial coupling conditions.It is showed that Raman gain compensates losses leading to not only narrower linewidths but also transitions between various coupling regimes.Based on this we propose and experimentally demonstrate that by utilizing Raman gain one can achieve on-demand control of the coupling regime without any mechanical movement in the resonator system.This scheme has good performance in driving the system from under-coupling to over-coupling regime,which is not possible in previous similar schemes,and provide better resolvability of transmission spectra,thus provides an practical route to realize a bidirectional,on-demand all optical control of cavity resonances.3.All optical coupling control in whispering-gallery-mode microcavities.We for the first time to our knowledge study the stimulated Raman loss of silica WGM micro resonantors.On this basis we experimentally demonstrate an all optical coupling control of fiber taper coupled micro-cavity system through adjusting cavity effective loss by stimulated Raman loss.We turn the system from deep over-coupling to critical-coupling just by injecting a low power pump the pump power without moving any part of the system.On resonance transmission is driven down by 19.58 dB,which is a much higher contrast that the previous record of 9 dB in silicon micro-ring,and our control is not disturbed by two-photon absorption or free-carrier absorption.更多还原