Working principle for active beam switching metasurface. (a) The fundamental building block consists of two rows of differently sized nano-antenna elements A and B. Antennas A are longer and resonant at 3.2 μm for an amorphous GST substrate. The antennas are arranged such that each consecutive antenna, going from the left to the right, is clockwise rotated by 12° with respect to the previous antenna. Antennas B are shorter and resonant at 3.2 μm for a crystalline GST substrate. They are arranged in counter-clockwise rotation. (b) Phase plots of the cross-converted scattered field (LCP) from full-field simulations with RCP light impinging. Depending on the state of the GST substrate, the beam is deviated into different directions. (c) Simulated transmittance of beam switching metasurface for a-GST and c-GST.