Plasmonic nanoantennae



I was trying to observe with FDTD solver a red shift in the resonance while decreasing the gap size of two antennae.
However, the proper behavior is not observed and I can not find which is the mistake in the design.
dimer 20nm gap.fsp (279.7 KB)

I would really appreciate some advise.



Do you have a plot or some sketch that shows approximately how you expect the resonance to behave when the gap is decreased?



I checked your simulation file and made some changes:

  • PML: adjusted distance from the structure to the PML so that it is at least half the maximum wavelength; also used “steep angle” settings
  • Improved material fit as you can see in the Material Explorer.
  • Mesh override region: extended it to cover the entire TFSF source since it is convenient to use a uniform mesh in the directions normal to the propagation direction as explained here.
  • Global monitor settings: added more frequency points to resolve the resonance better.
  • Added a sweep over position of the gold rectangles.

A similar case is discussed here.

After these changes (see dimer 20nm gap_modified.fsp (325.2 KB)) I got these results for the absorption cross section:

You can see the peak shifting to longer wavelength (red shift) for decreasing gap.

Hope this helps!