Broadband high-efficiency polymerized liquid crystal metasurfaces with spin-multiplexed functionalities in the visible

Xinjian Lu; Xiaoyin Li; Yinghui Guo; Mingbo Pu; Jiangyu Wang; Yaxin Zhang; Xiong Li; Xiaoliang Ma; Xiangang Luo

doi:10.1364/PRJ.452272

Abstract

Traditional optical components are usually designed for a single functionality and narrow operation band, leading to the limited practical applications. To date, it is still quite challenging to efficiently achieve multifunctional performances within broadband operating bandwidth via a single planar optical element. Here, a broadband high-efficiency polarization-multiplexing method based on a geometric phase polymerized liquid crystal metasurface is proposed to yield the polarization-switchable functionalities in the visible. As proofs of the concept, two broadband high-efficiency polymerized liquid crystal metalenses are designed to obtain the spin-controlled behavior from diffraction-limited focusing to sub-diffraction focusing or focusing vortex beams. The experimental results within a broadband range indicate the stable and excellent optical performance of the planar liquid crystal metalenses. In addition, low-cost polymerized liquid crystal metasurfaces possess unique superiority in large-scale patterning due to the straightforward processing technique rather than the point-by-point nanopatterning method with high cost and low throughput. The high-efficiency liquid crystal metasurfaces also have unrivalled advantages benefiting from the characteristic with low waveguide absorption. The proposed strategy paves the way toward multifunctional and high-integrity optical systems, showing great potential in mobile devices, optical imaging, robotics, chiral materials, and optical interconnections.

Conventional optical elements achieve specific optical functions based on the gradual phase changes accumulated along the propagation path, leading to a large form factor that is not compatible with the miniaturized, lightweight, and compact systems [1,2]. Therefore, planar optics components have received extensive attention in recent years benefiting from the compact and ultrathin design and excellent manipulation capability in multi-dimensional physical parameters [3]. The generalized laws of reflection and refraction offer the theoretical explanation for the principle of unique performance in planar optics components, leading to arbitrary wavefront modulation due to the phase discontinuities in light propagation [4]. In general, the phase discontinuities can be implemented by geometric phase, dynamic phase, and so forth. Compared with the dynamic phase arising from the optical path difference in propagation, the geometric phase, also known as Pancharatnam–Berry (PB) phase, originates from the photonic spin–orbit interaction in asymmetric anisotropic structures [5,6]. In contrast with the dynamic phase that is adjusted by the equivalent refractive index of the material, the PB phase is a broadband non-dispersion phase modulation method that is only related to the rotation angle of the anisotropic structure [7]. Therefore, PB phase has been widely used in multitudinous practical applications due to its precise phase control ability and robustness against fabrication tolerances.