Fig. 5: Focal points along a 3D conical spiral trajectory.
From: Multifaceted control of focal points along an arbitrary 3D curved trajectory

a The schematic diagram of the super metalens M4 for generating 200 focal points on a continuous 3D conical spiral trajectory with a decreasing radius. The maximum and minimum radii are 30 µm and 0, respectively. The wavelength is modulated with an operating range spanning from 501 to 700 nm with a step size of 1 nm. b The 3D view of the conical spiral shape with a decreasing radius. c The simulated and measured intensity distributions of the designed super metalens for the selected focal points on a 3D conical spiral trajectory under the illumination of an RCP incident light beam. The results for the selected focal points (26th, 100th, and 200th) are acquired at the operating wavelengths (526, 600, and 700 nm) and longitudinal distances (326, 399, and 499 µm). The dashed yellow circles represent the maximum and initial value of the radius. The solid red portion and dotted white portion of spiral curves are used to illustrate the evolution of the generated focal points along the curved trajectory of a conical spiral with a decreasing radius in 3D space