Big problem--- Microring Resonator

Hi,everyone,

I built a 2D micro-ring resonator model which stated in one publicated paper.

I check all the parameters I set are same as the paper mentioned. But the problem is , even in the ring, no field distributed. But when I further decrease the gap from 540nm-100nm, it occurs. however the extracted S21 is unphysical, I can not get series resonance spectrum.

I attached my mph file. Do someone can help me to find the reason.

Anyhelp is highly appreciated.