Wei Shibiao, Cao Guiyuan, Lin Han, Yuan Xiaocong, Somekh Michael, Jia Baohua
Nanophotonics Research Center, Shenzhen Key Laboratory of Micro-Scale Optical Information Technology & Institute of Microscale Optoelectronics, Shenzhen University, Shenzhen 518060, China.
Centre for Translational Atomaterials, Faculty of Engineering, Science and Technology, Swinburne University of Technology, John Street, Hawthorn, VIC 3122, Australia.
ACS Nano. 2021 Mar 23;15(3):4769-4776. doi: 10.1021/acsnano.0c09395. Epub 2021 Feb 16.
The ever-increasing demand for miniaturized optical systems has placed stringent requirements on the core element: lenses. Developing ultrathin flat lenses with a varifocal capability and broadband spectral response is critical for diverse applications, but remains challenging and has been the focus of intensive research. The recent demonstration of tunable focal length for a single wavelength with metalenses marked an important milestone for transforming the complex and bulky tunable lens kit into a single flat lens. However, achieving color imaging with desired tunability over the entire visible spectrum essential for practical applications still remains elusive. Here we propose and demonstrate experimentally a broadband varifocal graphene metalens (250 nm in thickness) covering the entire visible spectrum. It is able to simultaneously tune the focal lengths for different wavelengths continuously. By laterally stretching the lens, an over 20% focal length tuning range can be achieved for red (650 nm), green (550 nm), and blue (450 nm) light as three example wavelengths. Zoom imaging of different objects located along the axial direction has been demonstrated at these wavelengths by simply controlling the stretch ratio of the graphene metalens. This broadband graphene zoom lens enables enormous applications in miniaturized imaging devices such as cell phones, wearable displays, and compact optical or communication systems with multi-color-channel functionalities.
对小型化光学系统不断增长的需求对核心元件——透镜提出了严格要求。开发具有可变焦距能力和宽带光谱响应的超薄平面透镜对于多种应用至关重要，但仍然具有挑战性，一直是深入研究的焦点。最近利用超构透镜实现单波长焦距可调证明了一个重要的里程碑，即将复杂且笨重的可调透镜套件转变为单个平面透镜。然而，在整个可见光谱范围内实现具有所需可调性的彩色成像对于实际应用而言仍然难以实现。在此，我们提出并通过实验证明了一种覆盖整个可见光谱的宽带可变焦距石墨烯超构透镜（厚度为250纳米）。它能够同时连续地调节不同波长的焦距。通过横向拉伸该透镜，对于作为三个示例波长的红色（650纳米）、绿色（550纳米）和蓝色（450纳米）光，可实现超过20%的焦距调谐范围。通过简单地控制石墨烯超构透镜的拉伸比，已在这些波长下展示了沿轴向定位的不同物体的变焦成像。这种宽带石墨烯变焦透镜在诸如手机、可穿戴显示器以及具有多色通道功能的紧凑型光学或通信系统等小型化成像设备中具有大量应用。
