Thank you fro your suggestion. Sorry for the confusion about the mesh size. Please look at the below results for a mesh size of 98 nm.

I see a difference in the results in cylindrical co-ordinate system but they are not proper modes as like as cartesian co-or. But What I understand is the eigen mode solver solves Maxwells equations in the respective co-ordinate system based on the symmetry of the structure that whatever the structure we create. If it is cylindrical symmetry, the solver solves in cylindrical co-or sys. Am I correct ? The x,y and z axes are just for the representation of geometrical co-ordinates. Please clarify.

I tried searching for 500 modes and looking for the higher order mode corresponding to lower effective index.

I see some closure results as similar as Comsol results but the extra garbage fields are coming in the straight waveguide region. How to reduce these fields ? What should be the cause of this ?