Spherical Aberration-Corrected Metalens for Polarization Multiplexed Imaging

Achieving focal invariance in different background refractive indices through a dual-environment metalens

A conventional metalens is designed with a fixed working environment, and its focal length depends on the background refractive index. In this study, we propose a dual-environment metalens that can maintain the same focal length in both media of air and water. The metalens consists of 16 types of meta-atoms with different geometries, which can cover the 0-2π phase range in both air and water. We perform finite-difference time-domain simulations to investigate the metalens and demonstrate that its focal length remains unchanged, regardless of whether the background medium is air or water. Furthermore, we investigated the optical forces within the focal field of the metalens in both air and water, indicating its potential trapping capability in these media. Our method provides a new insight into dual-environment metasurfaces and advances the methodology of electromagnetic structures in extensive applications.

Reconfigurable Metalens with Phase-Change Switching between Beam Acceleration and Rotation for 3D Depth Imaging

Depth imaging is very important for many emerging technologies, such as artificial intelligence, driverless vehicles and facial recognition. However, all these applications demand compact and low-power systems that are beyond the capabilities of most state-of-art depth cameras. Recently, metasurface-based depth imaging that exploits point spread function (PSF) engineering has been demonstrated to be miniaturized and single shot without requiring active illumination or multiple viewpoint exposures. A pair of spatially adjacent metalenses with an extended depth-of-field (EDOF) PSF and a depth-sensitive double-helix PSF (DH-PSF) were used, using the former metalens to reconstruct clear images of each depth and the latter to accurately estimate depth. However, due to these two metalenses being non-coaxial, parallax in capturing scenes is inevitable, which would limit the depth precision and field of view. In this work, a bifunctional reconfigurable metalens for 3D depth imaging was proposed by dynamically switching between EDOF-PSF and DH-PSF. Specifically, a polarization-independent metalens working at 1550 nm with a compact 1 mm2 aperture was realized, which can generate a focused accelerating beam and a focused rotating beam at the phase transition of crystalline and amorphous Ge2Sb2Te5 (GST), respectively. Combined with the deconvolution algorithm, we demonstrated the good capabilities of scene reconstruction and depth imaging using a theoretical simulation and achieved a depth measurement error of only 3.42%.