Reply To: Regarding phase-delay spectrum of metasurfaces

[Amrita Pati]

Hi Nayem,

I apologize for the delay in response. In metalens/metasurfaces there is usually a target phase and the metalens is designed such that the total phase imparted by it is as close to the target phase. The approach that we follow in our metalens example is that we first simulate the unit cell of the metasurface. This can be done using either FDTD or RCWA, but RCWA will be much faster. We calculate what would be the phase change for different radii by using the sweep tool (one simulation per radius). This will help us create a library of phase vs radius (similar to the screenshot you have attached).

Next, we create the full metalens geometry (which consists a certain distribution of elements of different radii) by mapping the target phase back to the radius using the library we created in the first step. For example, if the target phase is 0.5 rad at a certain position, we will map it back to the radius that will produce that phase. Then we create an element of that radius at that position. And in this way we design the full metalens geometry. The full metalens usually consists of elements of different radii (non-periodic), so we can not use RCWA. In that case we can either use FDTD or a field-stictching method to calculate the total phase imparted by the overall metalens geometry. Then this is compared to the target phase profile. 

The screenshot that you have attached tells me that this is most likely the unit cell simulation of elements of different radii. Feel free to correct me if I am wrong. If that is the case you can use either FDTD or RCWA, but as I mentioned RCWA will be faster. You can also look at the (Step-2) of the linked article on exact details. I will recommend you to have a look at the article and let me know if you have any further questions.

Regards,
Amrita