A novel algorithm for designing diffractive optical elements for two colour far-field pattern formation

One of the many uses for diffractive optical elements (DOEs) is in pattern formation for display purposes. These images can be made much more arresting to the eye if they are constructed from more than just one colour. To achieve this with DOEs is not simple, as they are inherently wavelength specific. We present a novel approach to designing quantized elements that produce distinct intensity patterns, in the far field, for two wavelengths. The technique uses a modification of the Gerchberg-Saxton algorithm to design the phase profiles, together with phase delays greater than 2p to give the required extra degree of freedom. We will further discuss methods of enhancing the design algorithm. Experimental examples are presented to illustrate the success of these techniques. Efficiencies of 50%-60% are typical for 16 level, 128 × 128 elements with a maximum phase delay of 8p. © 2005 IOP Publishing Ltd.