Abstract
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.
Highlights
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
We propose a novel concept of nonlinear Yagi-Uda nanoantenna to direct second harmonic radiation from a metallic nanosphere
Summary
To achieve a high directivity for the second harmonic radiation, sizes of the reflector and the director and their distances to the feed (metallic sphere) must be carefully engineered and fully optimized. Integrating the dielectric reflector and director with the metallic feed in this geometry, the composite nonlinear Yagi-Uda nanoantenna gains a high directivity of 6.5 for Figure 5. It should be noted, according to the selection rule and the corresponding far-field pattern in Fig. 1 (b), the second harmonic scattering from the feed can be considered approximately as a z-polarized Hertzian dipole source generated by the nonlinear upconversion process. Equivalent electric and magnetic currents on the metallic feed and dielectric elements are responsible for the far-field radiation pattern of the nonlinear nanoantenna. The work is of great importance to nonlinear signal detection and sensing
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