Encoding technique for design of zero-order (on-axis) Fraunhofer computer-generated holograms

Diffractive optical elements able to generate zero-order (on-axis) distributions with phase as well as amplitude distributions are described. The proposed elements are surface relief plates, i.e., phase-only elements, that are based on the concept of computer-generated masks followed by common etching processes. The encoding method assumes fixed spatial partitioning of the cell and a phase-only value allocated to each subelement. The reconstructed amplitude and phase distributions contain imperfections (noise) resulting from the encoding process. Methods of error reduction and improvements are provided.