Wriggles or little oscillations on the reflection spectrum?

Hi all,

As seen from the above figure, does anyone know why does wriggles or little oscillations appear on my reflection spectrum as i increase my FDTD region (both x,y - span) from 300 nm to 700 nm? I tried increasing my z-span as well, but it does not help. I am doing an infinite array simulation. I placed periodic boundary condition on the x, y- directions and PML on the z-direction.

Please let me know if you need more information. Thank you.

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Did you play with the mesh size for the important features? How far is the reflection monitor located from the PML layer and from the array? If you can upload the file, it might be easier to solve the issue.

Best Wishes,


Try increasing the FDTD simulation time and see it those ripples become smaller.

random.fsp (491.0 KB)

Hi all,

I have uploaded my fsp file.
I tried both increasing the simulation time to 5000 fs and smaller mesh size, but the wriggles still appear.

Thanks for your help.


Would anybody be able to enlighten me?

Hi @wxlim1,

After I made some modifications on your model, I could get rid of the interferometric oscillation in the spectrum.

  • I disabled the override mesh to reduce the simulation time
  • I applied the symmetric/anti-symmetric BCs to the array to save the time
  • I guessed the interference might appear in the spectrum because there was not enough simulation time to stabilize the optical response of the gold nanostructure on a substrate; or the default the level of the auto shutoff was relatively high for an optical stabilization. So I lowered the auto shutoff min from 1e-5 to 1e-6.

Here is the spectrum from the “R” power monitor. You can see the negligible wriggles in the spectrum.

I attacehed revised project file.
random_v2.fsp (491.6 KB)


Dear @isawjsy,

Thank you very much, you are my life saver!

1 Like

Hi @wxlim1,

You’re welcome. It’s my pleasure to help you out. :grinning: