Take a look at the Help for this component. I’ll try to summarize it here for you too. The parabolic index measured fiber uses the input field’s spatial information to calculate the coupling coefficients to each of the modes that the fiber supports. It can also include different modal delays and attenuation in the final output time domain calculation.
Since this component is a waveguide I wouldn’t expect the mode field diameter to change. Of course you can have higher order modes excited by scattering (by imperfections in the fiber) or by mode coupling (which could be caused by bends), which unfortunately this model does not incorporate. However, I would not expect the field’s final spatial information to change that drastically.
Is there an article you are trying to replicate?