Hi,

 I am designing an edge coupler using 3D FDTD and I need to evaluate the collimation of the beam transmitted in the free space after passing through the coupler.

One solution I found was to evaluate the beam radius of the transmitted E field over distance. So, right after the edge coupler I put DFT monitors at a distance of 1 micron from each other to capture Efield in that position.

For example, in the figure attached there are 15 monitors where the first is 1 micron away from the edge coupler and the last 15 microns away from the edge coupler, and the monitors are sequentially 1um distant from each other.

The E fields in each position that is 15 positions are then processed in Matlab and the beam radius is calculated over 15 um.

My questions are, is there any other method in FDTD that I could use to compare with mine? Is my method wrong? "

To get the Electrical field I am using the follwing commands

E = getresult("monitor_"+num2str(j),"E");

E2 = getelectric("monitor_"+num2str(j));

E2 = pinch(E2,4,468);

E2 = sqrt(pinch(E2));

y = E.y;

FinalMatrix=[y,E2];

the FinalMatrix will a txt file that I am processing in Matlab later to get the figure beam radius over distance.

Lumerical Support said to me to use farfieldexact2d - Script command (https://support.lumerical.com/hc/en-us/articles/360034410234-farfieldexact2d-Script-command?source=search) but the results that I get look weird and the results that I get from the getelectric command (https://support.lumerical.com/hc/en-us/articles/360034409974-getelectric-Script-command) look right for this purpose.

I appreciate any help.

regards,

Taynara

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