We present a new method for the analysis of diffractive optical elements, which we refer to as field stitching. It is suitable for use with grating structures of arbitrarily large period, even when the local feature size is of the order of a wavelength. Furthermore, the concept is straightforwardly extendable to aperiodic structures. To assess its applicability, we have calculated the diffracted orders from a 1 × 81 fan-out grating with periods of 100λ and 10, 000λ. The field-stitched calculations agree very well with independent rigorous predictions for the small-period element and scalar-regime predictions for the large-period element. We believe that a variety of areas within the diffractive-optics field will benefit from this new analytical tool. It promises accurate analysis and, by facilitating component optimization, high-performance designs.
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