Metasurface-Based Wide-Angle Beam Steering for Optical Trapping

Mengxia He, Yuhao Guo, Chunshu Li, Xin Tong, Henan Liu, Guifang Li

Metasurfaces become increasingly important for wavefront shaping and beam steering with high efficiency. We propose a wide-angle beam steering device based on all-dielectric metasurfaces consisting of two symmetrical blazed gratings for optical trapping of particles, which can convert the input Gaussian beam to a special beam with intensity gradient along the propagation direction. Two major types of metasurfaces (Pancharatnam-Berry phase and nanoposts) are compared, and dramatic difference is found between them, especially at oblique incidence. We show that the Pancharatnam-Berry phase-based metasurface is more tolerant to the incident angle and that significant optical gradient force can be generated over a large angle range of −50° to 50°, and the maximum attractive force is up to tens of pN/W, with a trapping range of $14~\mu \text{m}$ for particles of $2.5~\mu \text{m}$ in diameter. The proposed scheme exhibits great potential to trap a large fraction of particles floating in a microfluidic channel when the beam is dynamically steered.

DOI