 ## Optical

#### Conversion of FDTD far field simulation data into spherical coordinates issues

• P Nair
Subscriber

I have a question related to the conversion of E(ux,uy) data set to spherical coordinates. I have FDTD far-field simulation results E(ux,uy), which is 200x200 matrix data and I need to know how to convert into spherical coordinates r, theta, & phi So that we can extract the data and plot as polar plots in origin. I tried the far-field spherical command line here:https://optics.ansys.com/hc/en-us/articles/360034410194-farfieldspherical-Script-command , but it is not useful for the 200X200 matrix data. As this command line will plot for only one angle, phi=0 for example , at a time. So, it is not possible to generate data for phi= 0 to 360 at a time and convert it into spherical coordinates. Could you please suggest further regarding this?

• Guilin Sun
Ansys Employee

If you pourpose is to visualize the farfield, no need to convert to theta, phi;

If you want to know the peak location of theta and phi, you can specify phi to get theta plot.

• P Nair
Subscriber

We are working with FDTD simulations to plot the far-field from a dipole source inside a thin film structure. However, we are having difficulties with plotting/interpreting the extracted far-field data. Accordingly, we have a few questions regarding this:

Primarily, we want to recreate the polar plot of the 3D far-field using that can be seen using the visualizer inside the FDTD software using OriginLab software. For example, this image is taken from the visualizer:

We have converted the ux and uy data to values of theta and phi using the script at the bottom of this webpage from the Ansys website: https://optics.ansys.com/hc/en-us/articles/360034410194-farfieldspherical-Script-command

However, we have some confusion about the interpretation of these values.

1. From the output of this script, the values of theta range of from -90 to 90. As described here: Understanding direction unit vector coordinates in far field projections – Ansys Optics the fields are calculated on a hemispherical surface located 1 meter away from the simulation region, and the range of theta is from 0 to 180 degrees (0 to pi radians). Why then does script give values from -90 to 90 for theta and what is the physical location of the values from -90 to 0 on the hemisphere/polar plot?
2. In general, what is the proper way to extract this data and plot in a polar plot in an external software like OriginLab?

Thank you!”

• Guilin Sun
Ansys Employee

A1: The theta is from -90 to 90 or 0 to 180  in theory. However, for the semi-sphere it is 0-90.  -90 to 0 is the other half.

A2: I do not know OriginLab. But you have ux,uy, and uz, as well as theeta and phi that you can import to any 3rd party script.

• P Nair
Subscriber

Thnk you for the reply. Could you please explain what is that other half represent? For sphere in theory it from 0 to 180. Then,  for hemisphere it should be from 0 to 90. What does it represent for -90 to 0? 