The recent introduction of a fast Fourier transform– (FFT–) based method for calculating the Rayleigh–Sommerfeld full diffraction integral for tilted and offset planes permits high-speed evaluation of integrated optical systems. An important part of introducing a new calculational tool is its validation and an assessment of its limitations. The validity of the new FFT-based method was determined by comparison of that method with direct integration (DI) of the Rayleigh–Sommerfeld integral, a well-established method. Points of comparison were accuracy, computational speed, memory requirements of the host computer, and applicability to various optical modeling situations. The new FFT-based method is 228 times faster, yet requires 14 times more memory, than the DI method for a 500 µm by 500 µm real computational window.
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