【作者】 席铮；

【导师】 明海； 鲁拥华；

【作者基本信息】 中国科学技术大学 ， 光学， 2014， 博士

【摘要】 光学天线能够实现局域光频电磁能量与远场传播光场能量之间的高效、定向性转换。由于金属局域表面等离激元共振的影响,光学天线在近场能量馈入,工作波长以及耦合方式等方面与微波天线有很大不同。基于这些特点,光学天线在增强分子荧光辐射,纳米尺度光束方向调制,突破衍射极限的光学成像等方面表现出优异的性质,被认为是现代光学发展的重要方向之一。本论文针对光学天线体系中共振耦合特性进行研究分析,重点开展了天线结构对于荧光分子发光增强,荧光分子辐射方向控制,类量子效应等方面的研究。本论文主要研究成果如下：1.研究了荧光分子与不同光学天线结构相互耦合的荧光增强,以及辐射方向的调控,设计了超小型耦合金属棒纳米光学天线,在荧光分子激发和辐射波长具有局域等离子体双共振特性,并进一步探讨了其对荧光分子激发和辐射方向性的影响,以及组阵天线结构对天线方向性的增强特性。2.基于并矢格林函数理论方法,系统研究了不同偏振的偶极子点源与不同材料的半无限大介面相互作用的机理过程,分析了水平和垂直方向偶极子场对称性不同对于辐射效应的影响,并基于此设计了一种可主动调控辐射方向的光学天线结构。3.通过对圆偏振偶极子角谱特性研究,发现该偏振的偶极子能够很好地单向激发导波模式,基于此设计了一种产生涡旋场的简单光学天线,其作用与圆偏振偶极子类似,可有效地用以激发高定向性的导波模式。4.利用金属光学天线结构中的明、暗模式相互叠加,数值分析研究了T型纳米颗粒中的Fano共振效应,并通过谐振子模型给出了对应解释。研究了不同耦合点对应的模式耦合强度的区别,发现了T型耦合结构具有更大的耦合强度,同时这种构型对光谱和位置信息都可以提供更高的折射率传感灵敏度。5.使用数值算法研究了表面等离子体法珀腔模和局域纳米线磁模式的强耦合过程,并与经典原子-腔强耦合体系中的极子模型(Polariton Model)获得的结果一致。利用这种结构得到了845倍的局域磁场增强和280meV的Rabi分裂。本论文的创新点和特色：1.提出了基于调制偶极子偏振特性的纳米尺度光束操控结构。通过改变圆偏振偶极子和金属衬底之间的相互距离,可以获得单向性较好并且辐射方向可调的远场出射光；通过构造合适的纳米天线结构,模拟圆偏振偶极子的作用,实现定向激发导波模式。2.设计了一种可用于荧光分子探测的双共振光学天线结构。该天线的两个共振峰可通过改变天线结构尺寸独立调节,以适应不同荧光分子的激发和辐射能级。同时,该结构也可对荧光分子激发光和辐射光的远场方向进行独立调节,空间上将激发光散射噪声和荧光分子辐射的信号有效分离,可用于高性噪比的荧光探测。3.基于光学天线模式特点与原子能级结构的相似性,数值上通过设计相应光学天线结构实现了Fano共振和强耦合这两种量子效应。提出了一种对光谱和位置信息都敏感的局域折射率传感方法。获得了280meV的Rabi分裂。为传统的量子效应提供了光学天线这一新的研究平台。更多还原

【Abstract】 Optical antennas can serve as an effective tool for efficient and directive conversion between localized energy and far-field radiation at optical frequency. Influenced by the Localized Surface Plasmon Resonance(LSPR), optical antennas exhibit great differences with microwave antennas in the case of feeding, working wavelength and coupling characteristics. Based on these, optical antennas have important applications ranging from antenna assisted fluorescence enhancement, nano scale light beaming and direction control, optical imaging beyond diffraction limit and is believed to be a promising direction in future developments in the field of optics. This thesis mainly focuses on the resonant and coupling phenomena inside optical antenna system, with a special emphasize on the antenna-assisted fluorescent enhancement, the control over the emission direction using optical antennas and quasi-quantum effect inside the optical antenna system.The main research achievements of this thesis can be summarized as follows:1. The radiation enhancement as well as radiation directional control are studied using different optical antenna systems. In specific, an ultra-compact optical antenna aims at spatial isolation of emission and excitation is developed. The enhancement of the directivity using antenna arrays is also studied.2. Based dyadic Green’s function method, the interaction between dipoles of different polarizations as well as different materials is studied in detail. The asymmetry of induced field pattern by vertically and horizontally oriented dipoles is considered to design an optical antenna structure with dynamically controlled emission direction.3. Through analysis of the angular spectrum of circularly polarized dipole, a mechanism of unidirectional excitation of guided mode is developed. An optical antenna is designed to have a similar function.4. Fano-like resonance in plasmonic system is explained in terms of the interaction of bight mode and dark mode. The effect of coupling strength on the lineshape, sensitivity is studied to develop a plasmonic sensor to monitor local changes in refractive index change both spatially and spectrally.5. Strong coupling between magnetic plasmons and Farbry-Perot cavity plasmons is studied in detail. A polariton theory is applied to describe the coupling behavior. A field enhancement of845times and280meV Rabi splitting is observed in numerical simulation.The highlights of the thesis are as following:1. A new way of controlling the far-field emission pattern is presented in this thesis. By utilizing the interference between different dipole components, the emission of the circularly polarized dipole can be actively controlled. Also, an optical antenna is designed to mimic the role of circularly polarized dipole as a tool to unidirectional launching of guided modes.2. A two-resonance optical antenna is proposed. This antenna utilizes the two plasmonic resonances covering both the excitation and the emission of the fluorescent molecule to control the direction of the excitation laser beam as well as the emission of the fluorescent molecule independently.3. Plasmonic analog of two quantum effects are discussed using optical antennas based on similarity between modes in optical antennas and energy levels in atom structure. A plasmonic sensor to monitor refractive index changes both spectrally and spatially is proposed. A large Rabi splitting of280meV is achieved. This offers a new platform to study traditional quantum effects.更多还原