I met a problem in the simulation of multilayer edge coupler.
The structure is from the example https://kb.lumerical.com/en/pic_passive_edge_couplers_final_eme.html
In the Mode Solutions, the boundary conditions are set as PML. The result is
The Ey distribution of mode 1 is
The loss of mode 1 is 9.1e-4 dB/um=9.1dB/cm which seems too large. In my following calculation, this large loss coefficient would lead to a low conversion efficiency.
However, using the same setting in FDTD , the same input mode was chosen. But here the loss is zero.
Two different loss coefficients were gotton when using the same boundary condition PML. Could anyone help me to find where the problem is. Which one is right ?
The files are listed here
Eme.lms (250.2 KB)
FDTD.fsp (309.7 KB)