Wang Chang, Sun Yan, Yu Zeqing, Liu Xinyu, Chen Bingliang, Zhang Yang, Zheng Zhenrong
College of Optical Science and Engineering, Zhejiang University, Hangzhou 310027, China.
Intelligent Optics & Photonics Research Center, Jiaxing Research Institute, Zhejiang University, Jiaxing 314000, China.
Nanomaterials (Basel). 2023 Sep 10;13(18):2530. doi: 10.3390/nano13182530.
Optical metasurfaces have been widely investigated for their versatile ability to manipulate wavefront and miniaturize traditional optical components into ultrathin planar devices. The integration of metasurfaces with multifunctionality and tunability has fundamentally transformed optics with unprecedented control over light propagation and manipulation. This study introduces a pioneering framework for the development of tunable metasurfaces with multifunctionality, and an example of a tunable metasurface of dual functionalities is proposed and numerically verified as one of the tunable meta-axicon for generating Bessel beams with a variable depth of focus (DOF) and a continuous-zoom metalens. Specifically, this design achieves dual-functional phase modulation by helicity-multiplexing from the combination of the geometric phase as well as the propagation phase and realizes tunability for both functionalities through rotational actuation between double metasurface layers. As a result, dual functionalities with continuous tunability of the proposed TiO metasurface are enabled independently for the left and right circularly polarized (LCP and RCP) incidences at 532 nm. Specifically, LCP light triggers the metasurface to function as a tunable axicon, generating non-diffracting Bessel beams with variable numerical apertures (NA) and DOFs. Conversely, the RCP incidence induces it to operate as a continuous-zoom metalens and generates variable spherical wavefront focusing on diverse focal lengths. This study not only initially implements the design of tunable meta-axicon, but also achieves the integration of such a tunable meta-axicon and continuous-zoom metalens within a single metasurface configuration. The proposed device could find potential applications in biological imaging, microscopic measurement, laser fabrication, optical manipulation, multi-plane imaging, depth estimation, optical data storage, etc.
光学超表面因其能够灵活操控波前并将传统光学元件微型化为超薄平面器件的能力而受到广泛研究。具有多功能性和可调谐性的超表面集成，从根本上改变了光学领域，实现了对光传播和操控前所未有的控制。本研究引入了一个用于开发具有多功能性的可调谐超表面的开创性框架，并提出了一种双功能可调谐超表面的示例，并通过数值验证其为可调谐元轴锥之一，可用于生成具有可变焦深（DOF）的贝塞尔光束和连续变焦金属透镜。具体而言，该设计通过几何相位与传播相位相结合的螺旋度复用实现双功能相位调制，并通过双层超表面之间的旋转驱动实现两种功能的可调谐性。结果，所提出的TiO超表面在532nm处对于左旋和右旋圆偏振（LCP和RCP）入射能够独立实现具有连续可调谐性的双功能。具体来说，LCP光触发超表面充当可调谐轴锥，生成具有可变数值孔径（NA）和焦深的无衍射贝塞尔光束。相反，RCP入射使其作为连续变焦金属透镜工作，并生成聚焦于不同焦距的可变球面波前。本研究不仅首次实现了可调谐元轴锥的设计，还在单个超表面配置中实现了这种可调谐元轴锥与连续变焦金属透镜的集成。所提出的器件可在生物成像、微观测量、激光制造、光学操控、多平面成像、深度估计、光学数据存储等方面找到潜在应用。
