Learning Forum

[Giovanni Piscopo]

Dear all, 

I hope you are doing well. 

I am currently working on high Q-factor metasurfaces to exploit the near field enhancing capability associated with narrow resonances.

I have a doubt about the field normalization in lumerical FDTD/RCWA and consequenly about the definition of field enhancement E/E0.

Starting from the latter, in literature many define the "field enhancement" as E/E0 where E0 is either the input electric field amplitude or the electric field amplitude in absence of the metasurface.

Regardless of the definition, the doubt I have is associated with the field normalization that Lumerical FDTD/RCWA does on the fields.

Basically, the normalization that I have set now is the CWNorm (first source) which, as written on the website, gives as results the field distribution as if the structure is injected with a CW source at a given frequency with amplitude set to 1.

Additionally, all the simulations I did, consider a plane wave with amplitude set to 1.

So, considering also the field plot reported below, my question is:

Can I say that the maximum value reported of 124 is actually the field enhancement E/E0? (About that, the criticality arises from the fact that if I reduce the amplitude of the input plane wave to 0.5, the field distribution I get has a maximum value of 62 which is the exact half of 124 so that if I calculate 62/0.5 I get exacty 124).

 

While, in case the value read from the monitor is not the field enhancement E/E0? How could I calculate it having the field distribution?

I wish you all a good day.

 

Regards

 

Giovanni

 

[Amrita Pati]

Hi Giovanni,

Can I say that the maximum value reported of 124 is actually the field enhancement E/E0? 

Yes, I would say that 124 is the field enhancement.

In linear simulation, we do not actually need to change the amplitude of the source. The field enhancement will not depend on the value of the amplitude. As you mentioned, it is going to remain 124 even when you reduce the amplitude by 0.5. The absolute power will depend upon the amplitude of the source. But, if you know the power for any given amplitude, you can easily determine the power for other amplitudes by simple multiplication. So, in any case (linear simulation), I would recommend you to keep the source amplitude 1, and then you can use the field distribution to calculate the field enhancement.

Regards,
Amrita

[Giovanni Piscopo]

Dear Amrita,

 

thank you very much for your detailed answer! At the moment I'm investigating all dielectric metasurfaces exploiting the Bound States in the Continuum so in general at the moment I'm not looking into any non-linear effect that might be power dependent.

So just to confirm, If I understand well, you suggest keeping the source amplitude to 1 and then by means of a frequency domain field and power monitor reading the field distribution which should already give me the field enhancement E/E0 without doing any other post process calculations.

I wish you a good day.

Best Regards

 

Giovanni

[Amrita Pati]

Hi Giovanni,

You are welcome! That is correct.

Regards,
Amrita