Reply To: FDTD:: simulation of directional coupler

[Zhongdi Peng]

Here is a summary of the two rounds of running:

1. boundary X/Y standard = 64/32 layer, Z is Metal:

2. boundary X standard=64, Y steep angle = 64, Z standard =16:

Neither of them converge. They both diverge after reaching shutoff = 2~4e-3

Using Standard 64 and 16 layers of PML at X/Z boundary is enough, the light in PML will decrease to lower than or near e-4:

But in Y min boundary where it faces the scatter light from input S bend WG, the absorption is not good, especially the steep angle one:

Steep Angle = 64 layer:

Standard layer=32:

Right now the only side where PML can not effectively absorb is Y min boundary. Do you think it's the reason causing the divergence? Let me know why 64 layer steep angle gives a worse result in absorption than standard 32 layers and how I can further optimize. Thanks.