Design and focus correction of 3D-printed multi-focus metasurfaces based on particle swarm optimization

A multi-focus metasurface is designed based on the phase multiplexing principle and geometric phase structures, and its foci are optimized. Traditional multi-focus metasurfaces relying on phase multiplexing often suffer from focal shift and non-uniform energy distribution in both simulations and experiments. To address this, the particle swarm optimization (PSO) algorithm is introduced. By taking the deviation between the preset focal positions and the actual focal-spot center coordinates, together with the focal energy distribution, as the cost function, the phase distribution of the metasurface elements is optimized in a closed loop. Samples are fabricated using 3D printing technology, and experiments are conducted. For the optimized four-focus metasurface, the positioning accuracy at the target focal plane is greatly improved, and the focal-spot symmetry and energy uniformity are significantly enhanced.