Department of Physics, University of Paderborn, Warburger Straße 100, D-33098, Paderborn, Germany.
School of Physics and Astronomy, University of Birmingham, Birmingham, B15 2TT, UK.
Adv Mater. 2018 Feb;30(8). doi: 10.1002/adma.201703843. Epub 2018 Jan 8.
The abrupt phase change of light at metasurfaces provides high flexibility in wave manipulation without the need for accumulation of propagating phase through dispersive materials. In the linear optical regime, one important application field of metasurfaces is imaging by planar metalenses, which enables device miniaturization and aberration correction compared to conventional optical microlens systems. With the incorporation of nonlinear responses into passive metasurfaces, optical functionalities of metalenses are anticipated to be further enriched, leading to completely new application areas. Here, imaging with nonlinear metalenses that combine the function of an ultrathin planar lens with simultaneous frequency conversion is demonstrated. With such nonlinear metalenses, imaging of objects with near infrared light while the image appears in the second harmonic signal of visible frequency range is experimentally demonstrated. Furthermore, the functionality of these nonlinear metalenses can be modified by switching the handedness of the circularly polarized fundamental wave, leading to either real or virtual nonlinear image formation. Nonlinear metalenses not only enable infrared light imaging through a visible detector but also have the ability to modulate nonlinear optical responses through an ultrathin metasurface device while the fundamental wave remains unaffected, which offers the capability of nonlinear information processing with novel optoelectronic devices.
超表面的光的突然相变在无需通过色散材料累积传播相位的情况下提供了对波的操控的高灵活性。在线性光学范围内，超表面的一个重要应用领域是平面金属透镜成像，与传统的光学微透镜系统相比，这实现了器件小型化和像差校正。通过将非线性响应纳入无源超表面，预计金属透镜的光学功能将进一步丰富，从而开辟全新的应用领域。在这里，演示了结合超薄平面透镜功能和同时频率转换的非线性金属透镜的成像。利用这种非线性金属透镜，实验演示了用近红外光对物体成像，而图像出现在可见光频率的二次谐波信号中。此外，通过切换圆偏振基波的手性，可以修改这些非线性金属透镜的功能，从而实现真实或虚拟的非线性成象。非线性金属透镜不仅能够通过可见探测器进行红外光成像，还能够通过超薄的金属透镜器件调制非线性光学响应，而基本波不受影响，从而为新型光电设备提供了进行非线性信息处理的能力。
