Reply To: Farfield calculation of Lumerical

[Guilin Sun]

You are right that the Fraunhofer approximation should only apply the largest diffraction angle is very small, which could be found in Goodman's Fourier Optics.
No, it is not simply the Fourier Transformation. It uses the equivalent principle which may be found in advanced electromagnetics.

From the farfield to near field, it is doable, provided that you have far field angular distributions (not intensity). Example can be found here https://support.lumerical.com/hc/en-us/articles/360041781874-Photolithographic-projection-to-photoresist
Basically, it propagates the decomposed plane waves to the given near-field plane.

However, if you only have far field intensity, the phase information is lost. You may not get accurate near-fields from intensity quantity, since the initial phase place important role in interference.