Photonics Research, 2020, 8 (9): 09001435, Published Online: Aug. 12, 2020
All-dielectric silicon metalens for two-dimensional particle manipulation in optical tweezers 
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Fig. 1. Schematic concept and optical characterization of the all-dielectric metalens. (a) The conceptual image illustrates the trapping of a polystyrene microbead with the help of an all-dielectric metalens, which converts an RCP incident Gaussian beam to a focused LCP beam. (b) SEM image of the fabricated metalens that consists of amorphous silicon nanofin array. The red inset shows a region at the edge of the metalens. (c) and (d) Cross sections of the intensity distribution of the focused beam along the optical axis for incident beams with different circular polarizations, drawn on a logarithmic scale. For LCP (RCP) illumination, the metalens acts as a concave (convex) lens, which results in a virtual (real) focal point at z = − 530 μm z = + 530 μm z = 0
Fig. 2. Measurement of the metasurface diffraction efficiency and the optical characterization of the vortex metalens. (a) Schematic image of the diffraction efficiency measurement: the metasurface diffraction grating with LCP incident light deflects the RCP beam to the − 1 − 1 z = − 545 μm z = + 545 μm
Fig. 3. Schematic illustration of the measurement setup. A nonpolarizing beam splitter (BS) is used to insert white light (WL) for sample illumination at the front side of the metasurface (MS, either metalens, vortex metalens, or metasurface diffraction grating) and to measure the incident laser power with a power meter (PM). Three different configurations can be used (blue dashed boxes). (a) Metalens-based optical tweezers system. Laser light with the desired polarization state is focused by the metalens onto the microbeads sample (S) while the focal plane of the metalens is imaged on the camera (CAM) through a microscope objective (MO) and a tube lens (TL). (b) Optical propagation measurement setup. The polarization states were separated by a polarization analyzer consisting of a quarter-wave plate (Q) and a linear polarizer (P). (c) Setup for efficiency measurement with the metasurface diffraction grating. (d) Arrangement of the MS and S in the metalens-based optical tweezers system. H, half-wave plate; CL, collimating lens; F, filter; f1, f2, and f3, lenses.
Fig. 4. Metalens for 2D polarization-sensitive drag and drop manipulation of particles. Polystyrene particles with diameters of (a) 4.5 μm, (b) 3.0 μm, (c) 2.0 μm, and (d) 4.5 μm are dispersed in water and arranged by polarization-sensitive drag and drop using the metalens. (e) Radial stiffness k r P
Fig. 5. Vortex metalens for OAM transfer. (a) A vortex metalens with a numerical aperture of NA = 0.35 t = 0 s k r P
Teanchai Chantakit, Christian Schlickriede, Basudeb Sain, Fabian Meyer, Thomas Weiss, Nattaporn Chattham, Thomas Zentgraf. All-dielectric silicon metalens for two-dimensional particle manipulation in optical tweezers[J]. Photonics Research, 2020, 8(9): 09001435.
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