how to set grid size and time step for dispersive media

[gell]

rsoft fdtd

Recently, I'm using Rsoft's FDTD to simulate some dispersive media, that is, n+ki. I find when k is very large, suppose, 2+11i, the FDTD will scater. So I want to make sense of the grid size and time step. So far, I define grid size and time step based on lossless media, that is, grid size<lambda/10, time step<grid size/2. For dispersive media, is there any change for time step or grid size? Is there any rule for this? Could anyone help me? Many thanks.

 

[ridley96]

The wavelength varies nonlinearly in dispersive media. You have to consider the longest lambda which can appear in your simulation, in determing the grid size and time step.

 

[zhu_yan]

I think is not the longest wavelength, but the shortest wavelength in your pulse.

I read that in this case when dispersion occurs, the step size should be very small. But I don't know how small...... Also struggling about the settings similarly.

I have another question though, could you guys get normalized spectrum in the FFT output of the monitor? I always have troubles there……