Method of designing a spatial phase modulation element and a spatial phase modulation element

摘要

A method of designing a spatial phase modulation element which has a plurality of hologram surfaces with mutually different phase patterns, and a spatial phase modulation element produced in the method. The spatial phase modulation element is designed to have a variable-phase medium located on one side of each of the hologram surfaces and modulating means for modulating the phase patterns of the hologram surfaces independently of each other. Further, if the number of output patterns to be obtained with the spatial phase modulation element is n and if the number of hologram surfaces is N, the spatial phase modulation element is so designed as to meet the condition n≧N+2, N≧2. In other words, the method of designing such a spatial phase modulation element has the following steps of: determining the number of hologram surfaces according to the number of desired output patterns; determining the number of phase values according to the shapes of the desired output patterns and forming phase patterns; coding each of the phase patterns into a binary digit string; optimizing each of the coded phase patterns independently of each other; and forming a combination pattern by combining the independently optimized phase patterns and optimizing the combination pattern.