Learning Forum

[Carlos O]

How can I get the phase shift as a function of the rotation of a nanofin when circularly polarized light is applied?
Can I use the s_parameters or need to use another analysis?
This is related to the geometric phase (Berry phase) in meta-atoms.

To simulate a circularly polarized source, I added a plane wave source with a 90-degree polarization and a 90-degree phase shift. I did this within the S-parameters analysis. I'm unsure if this is the correct approach for performing a parameter sweep, or if the additional source should be placed outside the S-parameters analysis.

How can I obtain the phase as a function of optimization parameters, such as the angle of rotation of a nanofin?
Note: In the figure, I have a circular pillar but I replace it with a rectangular one.

Thank you for your help.

 

 

[Carlos O]

I have been trying to replicate the phase results as a function of the rotation angle of the nanofin shown in the figure:

These results correspond to those reported in (https://doi.org/10.1364/OE.25.021419).

The configuration I have been using is shown in the following figure:

and the script I am using to try to obtain the phase versus rotation angle plot of the nanofin is as follows:

With what I have done so far, I am not obtaining a linear behavior as reported in the article.

Could you please help me with this?

[Amrita Pati]

Hi Carloso,

I believe the s-params analysis group would only work for s and p-polarized inputs and outputs (Metamaterial S parameter extraction). As you can see in this older post: How can I calculate s-parameter of circular polarization source? It seems that you either have to modify the code in the analysis group to incoporate both components of the fields or calculate the S parameter from the first principles. Let me see if there is a simpler approach for obtaining the phase, I will come back to you soon.

Regards,
Amrita

[Carlos O]

Hi Amrita,

I appreciate your help, I'll be waiting for your reply, thanks a lot!

[Amrita Pati]

Hi Carloso,

I spoke to my colleague, and he also agreed that modifying the analysis group would be the simplest approach. I am planning to do it as a side project. However, it may take me a while as I am also involved in many other tasks. I will recommend you to go through the analysis group script to understand what it is doing. If you starting work on the modifications, I am certainly willing to work with you on the code.

Regards,
Amrita

[Carlos O]

Hi Amrita,

Thank you very much for the suggestion. I will study the analysis group script and try to modify it to obtain the phase as a function of the rotation angle of the nanofin.

I hope to make progress soon and will share updates in this post for feedback.

Thank you very much!

Regards!

Carlos

[Amrita Pati]

Hi Carloso,

Sure, let me know. 

Regards,
Amrita

[Carlos O]

Hi Amrita,

I've been reviewing some other posts related to my query, and I found one that I think could help me: Questions about the calculation of the cross-polarization conversion efficiency of metasurface.

In one of the questions, they precisely calculate the phase as a function of frequency.

My question is: Can I do something similar to obtain the phase as a function of the rotation angle of the nanofins?

I think this approach might be simpler without modifying the analysis group (s-parameters). Is this correct, or would it be more complicated?"

[Amrita Pati]

Hi Carloso,

It looks like the approach would work.

I haven't gone through it in detail. You might have to rely on a purely scripted solution (as opposed to using the in-built sweep utility) to find the phase as a function of nanofin rotation (as you need some post-processing in between the sweeps). Or maybe you could do a sweep for different rotation angles, save the 'S_polarization" result and then perform the post-processing for all the parameter values at once. The exact methodology depends upon your preference. But let me know if you come across any issues.

Regards,
Amrita

[Carlos O]

Hi Amrita,

Reading more about S-parameters, I found the following:

The analysis group generates two S-parameter results: “S” and “S_polarization”. The first one is the S parameter for dominant input polarization and the same output polarization (e.g., if the source is s-polarized, it will calculate the result only for the s-polarized transmitted and reflected light). The second one is the S parameter for dominant input polarization and both output polarizations, which is only useful when we expect the polarization to be rotated by the metamaterial. In the simple case considered here, there is no polarization rotation, so we can simply use the “S” result and its attributes: “S11_Gn” and “S21_Gn” (source in medium 1) and “S22_Gn” and “S12_Gn” (source in medium 2). Therefore, I modified the script to have a source with circular polarization and adjusted the sweeps to obtain the results of S_polarization. However, when I want to plot the phase, I encounter the error marked in the image at line 30.

Can you help me with this?
what I’m doing is correct?