{"id":361207,"date":"2024-04-08T23:39:31","date_gmt":"2024-04-08T23:39:31","guid":{"rendered":"\/forum\/forums\/topic\/fdtd-simulation-of-directional-coupler\/"},"modified":"2024-04-08T23:39:31","modified_gmt":"2024-04-08T23:39:31","slug":"fdtd-simulation-of-directional-coupler","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/fdtd-simulation-of-directional-coupler\/","title":{"rendered":"FDTD:: simulation of directional coupler"},"content":{"rendered":"

Hi,<\/p>\n

I am simulating a directional coupler combined with a specific symmetric coupling region and designed S bends. I first simulate it in VarFDTD and figure out the rough length of the coupling region for 3dB splitting, and then transfer it to FDTD for 3D re-confirmation and accurate simulation. Probably due to the large configuration (attached image, FDTD X length=260um and Y length=30um, this is because my platform does not have confinement of mode as strong as that in SOI) with waveguide thickness=2um, height=300um, waveguide gap=1um, mesh size near waveguide = (dx,dy,dz)=(0.2,0.2,0.2)um, it’s time-consuming  and the divergence is not good no matter how I tune my PML boundary setting:<\/p>\n

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A. with the PML isotropic setting (I have tried PML layer = 8~24) <\/p>\n

It’s diverged after auto-shutoff reaches 0.0025; results shown below<\/p>\n

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Diverge may be due to the PML boundary settings, so I tried method B to set anisotropic boundary of PML:<\/p>\n

B. with PML anisotropic setting (X min\/max: stabilize PML, Other boundaries: Standard PML layer=16)<\/p>\n

I set running time=5000fs and it’s not reaching to preset 10^-5 at the end but only 0.06 (slower divergence than method A). It should be noted that the propagation is strange, seems like a standing wave inside the directional coupler this time. Also, another input port without setting any source now has light output as well, which is pretty abnormal.<\/p>\n

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Any suggestions to further optimize the divergence?<\/p>\n

 <\/p>\n

Zhongdi<\/p>\n

 <\/p>\n

 <\/p>\n","protected":false},"template":"","class_list":["post-361207","topic","type-topic","status-closed","hentry"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t