need help in rsoft

Hi all,

Does anyone know how to minitor the instantaneous effective index of a S-bend
waveguide by rsoft?

According to the manual,choosing the "effective index" as the monitor type must
be used with an iterative mode calculation.
So after layout of the waveguide, I set the monitor and run the mode calculation
and comes a ridiculous result.
I guess this way won't apply to my S-bend waveguide for the mode is always
changing as propagating.

How can I solve this problem and get a beautiful plot of effective index vs
propagation length?

Thanks in advance.