How to get 1-R curve


I need to calculate extinction spectra that is defined by 1-R,similar to the picture below.I have a periodic plasmonic trapezoid arrays as in the figure.I set boundary conditions PML along z and periodic along x and y axes.Plane waves were launched incident to the unit cell along +z direction.The problems that I’m facing are:
1)Reflection profile is greater than 1
2)I don’t know how to get 1-R profile. trapezoid.fsp (274.4 KB)

structure ref-trap extin|361x235extin


Hi @sepideh.avizheh1

I did a few modifications into your simulation file:

  1. Increased the FDTD span to have at least half wavelength between PML and edge of the objects.
    Setting about FDTD Region and mesh

  2. Extended Bottom-Ag into PML

  3. Modified the material fit

  4. Used finer mesh with conformal variant mesh 1 as you have metal in your simulations

Here is the result of reflection:

and simulation file for your review:
trapezoid.fsp (280.0 KB)

You need to perform convergence testing to make sure that results converge and are reliable:

To obtain 1-R, you can use script command similar to the one in the page below:

Please also consider enrolling in our online FDTD and scripting course:
Lumerical University


Thanks for supporting and share the links.I read them,but I confused about first link.Is it possible to give more explain?
Thanks alot


Hi @sepideh.avizheh1

When the boundaries are PML, you need to leave a minimum of half maximum wavelength between boundaries and edge of the last object. For example, if source span is 0.8-1.2 um, you need to leave at least 0.6um between the edge of the last object and PML boundaries. This is to avoid interacting evanescent fields with PML and avoid nonphysical loss.

Hope this was helpful.


Thank you for your complete answer.Can I ask you when my
structure should terminate at the inside boundary of the PML?


Hi @sepideh.avizheh1

The structure can be terminated before reaching PML if your substrate has a finite thickness or if you expect to have Fabry-Perot effect (where a reflection from bottom of the substrate is expected). Otherwise you need to extend your geometry all the way through PML boundaries. Please visit the link that I provided on earlier post.



Thank you very much.


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