Farfield Angular Projection [FDE]

Dear Community,

I have a question regarding farfield angular projection in MODE Solutions.

I’m simulation a simple waveguide (SiN 1um x 1um, buried in SiO2), and would like to extract the angular projection from it to air. I use FDE solver, chose the mode of interest (fundamental TE) and plot the farfield. It looks good in the plot, but when I try to export the data in .mat format, I cannot reproduce it afterwards: even when I just plot farfield1_angular_E2, there are two peaks instead of one.

My general goal is to extract the projection to define angles for 1/e^2 power or at FWHM.

Could you please suggest on how to do it properly?

Kind regards

Hello @jab
I have the same question. Did you figure out how to do it?

Hello @prova and @jab,

Sorry for missing this, @jab. The easiest way to do this would probably be to use Lumerical’s built-in script commands for farfield integration, like farfield3dintegrate (see the “Far field projections” tab on this page: Lumerical script commands).

For example, here is a script used to calculate the power within a cone with a given angle in the farfield:

farfield = getresult("FDE::data::mode1", "farfield");
E2 = pinch(farfield.E2);
ux = farfield.ux;
uy = farfield.uy;
halfangle = 0:90;
theta0 = 0;
phi0 = 0;
power_integral = farfield3dintegrate(E2, ux, uy, halfangle, theta0, phi0); # integrate over cones
total = farfield3dintegrate(E2, ux, uy); # integrate over entire hemisphere
results = power_integral/total; # fraction of far field power
plot(halfangle, results);

Here are the results of this script for the fundamental TE mode of your waveguide at a wavelength of 1550 nm @jab:

image

I hope this helps. Let me know if you have any questions.

Hi @kjohnson,

Thanks for your response. The mode I am simulating is elliptical. In this case, how can I get the vertical and horizontal farfield data (E intensity) as a function of angle and get their corresponding FWHM or Half angle?

image

This page demonstrates how to get data along different line traces of the far field projection (parameterized by phi):

The example from this page uses FDTD, but the techniques used will work for data from MODE as well. The data along the horizontal (uy = 0) line corresponds to phi = 0, and the vertical (ux = 0) line corresponds to phi = 90 degrees. You might find this page, which discusses how the ux/uy variables correspond to spherical coordinates, useful:

Let me know if you have any questions about this.