problems with a e.m. computation

Dear all,

I would like to find the resonances of a ring resonator.
I used a axisymmetric model (2D) with eigenfrequency analysis.
The materials are air and a polymer for the ring.
I put the PMLs but the solutions don't correspond to the confined modes that we expected.
Is it correct what I did?

Can you give me some advices?
The geometry is below.

Thank you in advance