Band-extended angular spectrum method for accurate diffraction calculation in a wide propagation range

The band-extended angular spectrum method (ASM) is proposed in this Letter for both near- and far-field diffraction calculation with high accuracy. Due to the aliasing problem of the transfer function (TF), the ASM is not suitable for far-field diffraction calculation. For band-limited ASM, the non-aliased bandwidth of the TF would shrink rapidly with the increase of the propagation distance, which would reduce the calculation accuracy in the far field. For the proposed band-extended ASM, the non-aliased bandwidth is significantly extended by rearranging the sampling points in the spatial frequency domain. Therefore, more frequency components of the TF contribute to the wave-field calculation, leading to a much wider propagation range and a higher computational accuracy.