a, b, simulated optical intensity distribution of metalens before and after optimization; c, d, real part of y-component electric field before and after optimization; e, f variation in electric field intensity along x-axis before and after optimization (y = 0 μm, z = 125 nm)

a, antenna array embedded in the device, inset: cell of the array; b, optical field intensity versus uy for far-field projection (yellow line is the collimated light, purple line is the uncollimated light, with ux = 0.185); c, far-field projection of guided wave without collimation; d, far-field projection of guided wave after collimation by our metalens, with the spot focused at 10°; e, f, uncollimated and collimated guided wave in far-field projection, wavelength versus offset angle (uy = 0)