Learning Forum

[Luca Sacchi]

Hi,

I am simulating a library of pillars with RCWA following the example of Lumerical (https://optics.ansys.com/hc/en-us/articles/360042097313-Small-Scale-Metalens-Field-Propagation). Here is the picture of my simulation

The unitcell is subwavelength, so only the (0,0) order is dominant. 

Since I am interested in the phase of the plane wave after the pillar I can either use the RCWAFieldMonitor positioned at a specific heigth from the pillar and take the phase of the field in the middle of the monitor. Otherwise I can use the values of the scattering matrix as in the example of lumerical: 

grating_characterization = getresult("RCWA","grating_characterization");

n = find(grating_characterization.n, 0); # n index of 0th order
m = find(grating_characterization.m, 0); # m index of 0th order

STpp(:) = pinch(grating_characterization.Tpp(:,1,n,m));

phase_Ep = angle(STpp);

My problem with this method is that I do not know at with distance from the pillar the phase is taken. While with RCWAfieldmonitor I know at which z I put the monitor, the scattering matrix method just gives me a value of the phase. I have three possible interpretation for phase_Ep: phase_Ep is the phase at the last RCWA interference defined (therefore the end of the pillar), phase_Ep is the phase of the field at the top boundary of the RCWA simulation region or phase_Ep is the phase of the field at "infinity". I tried to look for documentation but I was not able to find an answer. 

To summurize: at which heigth in the simulation region is the phase extracted via the scattering matrix S defined? 

[Guilin Sun]

Hi Luca,
Somehow my previous reply was not successfully shown. Here again is my reply:
RCWA is a semi-analytical method with Fourier plane waves to decompose the physical fields in the device. Thus the phase reference of the amplitude coefficients is at the last/last material interface. The rest, eg the substrate and the superstrate will be considered as uniform, semi-infinite space.