Xiong Xiaoyan Y Z, Jiang Li Jun, Sha Wei E I, Lo Yat Hei, Chew Weng Cho
Department of Electrical and Electronic Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong.
Department of Electrical and Computer Engineering, The University of Illinois at Urbana-Champaign, Illinois 61801, USA.
Sci Rep. 2016 Jan 7;6:18872. doi: 10.1038/srep18872.
Nanoantennas have demonstrated unprecedented capabilities for manipulating the intensity and direction of light emission over a broad frequency range. The directional beam steering offered by nanoantennas has important applications in areas including microscopy, spectroscopy, quantum computing, and on-chip optical communication. Although both the physical principles and experimental realizations of directional linear nanoantennas has become increasingly mature, angular control of nonlinear radiation using nanoantennas has not been explored yet. Here we propose a novel concept of nonlinear Yagi-Uda nanoantenna to direct second harmonic radiation from a metallic nanosphere. By carefully tuning the spacing and dimensions of two lossless dielectric elements, which function respectively as a compact director and reflector, the second harmonic radiation is deflected 90 degrees with reference to the incident light (pump) direction. This abnormal light-bending phenomenon is due to the constructive and destructive interference between the second harmonic radiation governed by a special selection rule and the induced electric dipolar and magnetic quadrupolar radiation from the two dielectric antenna elements. Simultaneous spectral and spatial isolation of scattered second harmonic waves from incident fundamental waves pave a new way towards nonlinear signal detection and sensing.
纳米天线已展现出在宽频范围内操纵光发射强度和方向的前所未有的能力。纳米天线提供的定向光束控制在显微镜、光谱学、量子计算和片上光通信等领域有着重要应用。尽管定向线性纳米天线的物理原理和实验实现都已日益成熟，但利用纳米天线对非线性辐射进行角度控制尚未得到探索。在此，我们提出一种非线性八木 - 宇田纳米天线的新概念，用于引导来自金属纳米球的二次谐波辐射。通过仔细调整分别用作紧凑导向器和反射器的两个无损介电元件的间距和尺寸，二次谐波辐射相对于入射光（泵浦光）方向偏转90度。这种异常的光弯曲现象是由于由特殊选择规则支配的二次谐波辐射与来自两个介电天线元件的感应电偶极和磁四极辐射之间的相长干涉和相消干涉所致。从入射基波中同时对散射二次谐波进行光谱和空间隔离，为非线性信号检测和传感开辟了一条新途径。
