I am trying simulate a simple slot WG. The WG is composed of 70 nm SiO2 topped with 300 nm of Si, the width of the WG is 400 nm. The WG is formed over a 300 nm Si layer deposited all over the substrate. My simulations are at 1550 nm wavelength, where materials are well defined.
The cross-sectional view of the WG:
The excited mode:
The design is simple, but there is a problem in this simulation. The electric field exceeds 1.
I tried to change the PML types. I followed the steps on knowledge base for diverging simulations. I tried to replace the PML with metal boundary conditions in all directions. The results got worse. I tried to use different PML: stretched coordinate PML and uniaxial anisotropic PML. I tried choosing custom PML and changing the parameters manually; also, I set the PML to stabilized. I tried to reduce the FDTD mesh and adding override mesh to reduce the reflections. None of these trials helped reducing the divergence problem.
The results I get:
Really I don’t know where is the problem. If any one could help I would be very grateful. This is the first step in my project and I am stuck in it for more than two weeks.
str8 WG.fsp (1.4 MB)