Please do not use Conformal Variant 1. Instead use Variant 0. This is because Variant 1 may need much finer mesh and we do not know how fine the mesh should be. https://optics.ansys.com/hc/en-us/articles/360034382614-Selecting-the-best-mesh-refinement-option-in-the-FDTD-simulation-object
in addition, please fix the wavelengh range for simulation:
When the wavelength changes, the mesh and the material fitting will change. So you need to fix it for the simulation.