The present disclosure provides systems and methods associated with mode conversion for electromagnetic field modification. A mode converting structure (holographic metamaterial) is formed with a distribution of dielectric constants chosen to convert an input electromagnetic field pattern from a first mode to a second mode to attain a target electromagnetic field pattern (near or far) that is different from the input electromagnetic field pattern. A solution to a holographic equation provides a sufficiently accurate approximation of a distribution of dielectric constants that can be used in conjunction with an electromagnetic radiation device with a known output field pattern to attain a target field pattern. A voxel-based discretization of the distribution of dielectric constants can be used to generate the mode converting structure and/or to facilitate the optimization algorithms. One or more optimization algorithms can be used to improve the efficiency of the mode conversion.