Thank you @Nanda for the clarification. You are right that this mode does not propagate and it is due to the varFDTD solver settings. Specifically, you need to change the “Polarization” settings on the “Effective index” tab where you select H mode™ or E mode(TE), which is indeed related to the “TE polarization fraction” as you suggested in your original post. For modes with 100% TE polarization fraction use E mode(TE) choice and for modes with 0% TE polarization fraction use H mode™ in the varFDTD settings. This settings is aligned with the TE/TM polarization definition as you mentioned it in your original post, so in this case disregard my previous comment about TE/TM fraction(explained below).

When you select the modes in the source settings, modes with various polarization will be displayed in the list regardless of the varFDTD settings, but you need to select the modes with correct polarization otherwise the results will not be reliable.

Since the TE/TM polarization definition can vary in different application areas, here is a mathematical definition of the “TE polarization fraction” and “TE/TM fraction” from Knowledge Base in order to avoid any confusion:

The “TE polarization fraction Ex” for propagation along the z direction is defined by the following equation:

where |Ex|^2+|Ey|^2 corresponds to |E_parallel|^2 (since we are considering the polarization of the modes, we only consider the fields parallel to the mode cross section). For propagation along the x/y direction (ie. “TE polarization fraction Ey/Ex”), this is similarly defined:

and

“TE/TM fraction” is defined by the following equations:

and

where and refers to the field component in the direction of propagation (ie. perpendicular to the mode cross section).