How to do a parameter sweep of a 2D axisymmetric resonator with EWFD and guarantee I store the effective index of the fundamental 00 mode??

Hello,

I have a 2d axisymmetric model that is just a rectangular ring resonator waveguide.

I would like to do a paremeter sweep over waveguide geometry and get the effective index of the TE00 or TM00 modes.

The problem is that if I choose to search for my effective index via the "closest in absolute value" or "highest real value" approach as I do my parameter sweet over waveguide geometry, the effective index of the, for instance, TE01 mode becomes the one that the parameter sweet stores and the effective index of the TE00 mode as I would like.

Is there a way to guarantee during a sweep that the effective index of the fundamental mode is stored?

Thank you.