Hi Amrita, in that case let me give you some more details on the geometry and materials so that you may be able to replicate:
The purple waveguide is contained in the yellow material, so in your xy view I would expect to see green and yellow, as opposed to green and purple. The yellow material has a refractive index of 1.5 (n=1.5), the purple n=2, the green has n=3.35. The width of the purple wg is 1600nm and 300nm in height. The green has a tip width of 100nm and a height of 350nm. The spacing in the z direction between the purple and green (filled with yellow material) is 100nm.
As for the simulation region, I believe that would be enough to replicate the results. Though my attempt involved two group cells. The first ended 10nm before the green tip and the second had a length of 20nm.
I was using metal boundary conditions throughout.