Direct design of a non-paraxial diffractive beam splitters is still challenging. Due to the relatively large splitting angle, the feature size of the element is equivalent to or smaller than the working wavelength. Thus, it is often beyond the paraxial modeling approaches. In this example, the iterative Fourier transform algorithm (IFTA) and thin-element approximation (TEA) are used for the initial design of the diffractive element structures, and Fourier modal method (FMM) is then applied for the rigorous performance evaluation.
