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Abstract. We present a comparison of some of the most used iterative Fourier transform algorithms (IFTA) for the design of continuous and multilevel diffractive optical elements (DOE). Our aim is to provide optical engineers with advice for choosing the most suited algorithm with respect to the task. We tackle mainly the beam-shaping and the beamsplitting problems, where the desired light distributions are almost binary. We compare four recent algorithms, together with the historical errorreduction and input-output methods. We conclude that three of these algorithms are interesting for continuous-phase kinoforms, and two, namely the three-step method proposed by Wyrowski and the overcompensation of Prongué , still perform well with multilevel-and binaryphase DOE.

Improved diffraction efficiencies can be obtained in the paraxial domain of diffractive optics by considering light explicitly as an electromagnetic rather than a scalar field because of the extra freedoms provided by the state of polarization. For example, diffractive beam splitters with 100% efficiency are made possible by means of space-variant subwavelength-carrier surface-relief elements. Some aspects of the general design theory of polarization-modulating elements for vector fields, including design freedoms and constraints, are presented. Upper bounds of diffraction efficiency are derived and compared with those for the scalar case. Iterative design algorithms are developed. Several design examples with different constraints are presented, and the effects of replacing continuous-fringe structures by pixel structures containing locally linear gratings are evaluated.

Replication of surface relief microstructures into COC (cyclic ole®n copolymers) plastics using a hot embossing technique is considered. The replication accuracy has been investigated by optical characterization and scanning electron microscopy (SEM) of the replicated surface pro®le, which is a diffractive anti-re¯ection layer. Good agreement between theoretical and experimental results is shown.

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