Reply To: Question regarding the auto shut off in FDTD simulation.

[Amrita Pati]

Hi Miller,

This looks to me like it's converged. Ideally, for grating farfield it is advisable to more number of points rather than less. Otherwise in some cases, the intensity data can be smeared returning incorrect results. This so far looks good to me.

There is one additional thing you could do to make sure that the results are accurate.Sometimes, certain source wavelengths can be resonant wavelengths for the simulated geometry. In those cases, you might need to reduce the auto shutoff level further from the default (1e-05) to let's say 1e-07 and so on. It is easy to tell if there is a resonance from a broadband simulation since you will see a sharp transmission peak in the spectrum, often accompanied by some oscillations. Since this is just a single wavelength simulation, it is hard to tell. 

What you can do is run a broadband simulation and collect the monitor results. For example, if you had a simulation at 0.55 um, you can try running a broadband simulation for 0.4 to 0.7 um. If you don't see a resonant peak at 0.55 um (in the broad-band simulation) or oscillations then you are good to go. But in case you do see them, you would have to reduce the auto shutoff level and rerun the simulation to see if the results change or converge similar to what you did for the mesh density.

Regards,
Amrita