Fig. 2: Design, fabrication, and characterization of a super metalens with 12 focal points.
From: Multifaceted control of focal points along an arbitrary 3D curved trajectory
a The schematic of a super metalens M1 with 12 focal points on a 3D cylindrical helix trajectory. The right inset shows the values of the polarization rotation angles. The color gradient represents the operating wavelengths ranging from 480 to 700 nm with a step size of 20 nm. The total longitudinal length TL of the cylindrical helix is 220 µm, which spans from 300 to 520 µm. The longitudinal separation Δz between the focal points is a constant and equal to 20 µm. b The total phase profile of the proposed super metalens. c An SEM image of the fabricated metasurface consisting of gold nanorods. d The schematic of an optical setup for characterizing the super metalens. LPa and LPb: linear polarizers, QWPa and QWPb: quarter-wave plates, OL: ×50 objective lens, CCD: charge-coupled device. For results with LP incident light beam, both quarter-wave plates are removed from the optical setup. e Intensity distributions of the selected focal points (1st, 4th, 7th, 10th, and 12th focal spots) along the 3D cylindrical helix path at various operating wavelengths (480, 580, 600, 660, and 700 nm) and longitudinal distances (300, 360, 420, 480, and 520 µm). Under the illumination of the RCP incident light beam, the first and second rows show the simulation and experimental results, respectively. The third row shows the modulated intensity distributions with an analyzer, which are used to indirectly confirm the designed polarization rotation angles under the illumination of incident LP light. The regions of corresponding focal points are highlighted with dotted white circles. The constant radius of the cylindrical helix is shown with solid white circles as references. The dashed white arrows and solid yellow arrows represent the direction of incident polarization and the transmission axis of the analyzer, respectively. The solid white arrows with the white-dotted circles show the initial polarization rotation angles (at β = 0°) for each focal point
