Learning Forum

[Saar Poplinger]

Hi, I have the following question:

How do the "farfield" and "grating" in FDTD differ, in their calculations, from simply applying a FFT on a monitor's field? Are there other calculations happening in these functions?

[Guilin Sun]

farfield and grating analysis are not directly transformed by FFT from the monitor data. 

For farfield projection, it uses more accurate physics whereas the FFT simply is the Fraunhofer diffraction approximation.

Far field projections in FDTD overview – Ansys Optics

Please find a FDTD book such as this ebook chap14.pdf (wsu.edu) for more details.

For grating analysis, it decomposes the fields on monitor into different diffraction orders: Grating projections in FDTD overview – Ansys Optics