Fast and flexible optical propagation using the scalable angular spectrum method

Efficient wave optical propagation has been a long addressed problem in optics. One standard tool is the angular spectrum method of plane waves which solves free space propagation without approximations. Another popular method is the single step Fresnel propagation which allows scaling of the final output plane however confined to the paraxial regime. Here we present the Scalable Angular Spectrum propagation (SAS) which combines the strength of both methods while having a computational complexity proportional to three Fast Fourier Transforms (FFTs). We discuss the working limits for the SAS and how to use it for off-axis geometries.