Fig. 2: The design principle of arbitrary spatial caustic engineering, the fabrication of complex-amplitude 3D-printed metasurfaces, and the characterization of optical caustics.
From: Arbitrary engineering of spatial caustics with 3D-printed metasurfaces
a Initial complex-amplitude distributions of the spatial focal curve in Fourier space. The dots are the circle centers corresponding to different propagation distances. b Rays emitted from the circles intersect on a specified focal curve. c Visualization of the caustic curve and transverse projections of rays (blue) aligning with the caustics (red) at z = 0, z = zmax/2, and z = zmax, respectively. d Schematic of one meta-atom. The parameters W, L, H and θ denote the width, length, height and in-plane rotation angle of the polymer nanofin, respectively. LCP and RCP refer to left- and right-handed circular polarized light. The height (H) and in-plane rotation (θ) enable independent control of both the amplitude and phase characteristics of the transmitted light. e, f SEM images of the metasurfaces for cases in Fig. 1c, d, together with their magnified images in the top- and oblique views, as well as an image of a single element. g Schematic of the experimental setup for optical caustic characterization. LP linear polarizer, QWP quarter-wave plate, MO microscope objective; CMOS complementary metal oxide semiconductor.
