Learning Forum

[Fakhriyya Mammadova]

Hello Amrita, thank you for your response.

I am simulating a ring resonator. I will describe shortly what I did below.

I started with some gap btw ring and waveguide and was running 3d fdtd simulations, while gradually increasing the gap. These simulations were not diverging until I reached 300nm gap. Now, no matter what I do I cannot resolve divergence.

Here are the steps I took trying to resolve it (none of them worked):

1)I switched to metal to see if the reason for divergence is pml. It gave the picture I posted initially

2)Because of the picture I thought that it is either not because of pml but because of dt stability factor or the reason is actually pml layers but the simulation with metal boudaries needs more time to catch it.

3)I put the time monitors from which I saw that energy starts increasing exponentially at the through port (I use ports in 3D FDTD).

4)I gradually was running the simulations and decreasing the dt stability factor form 0.99 to 0.5, but none of its values resolved divergence.

5)Next, I decided to increase PML layers and alpha. I first switched from standard to stabilized; it didn't work, so I switched to custom and continued gradually increasing the number of layers and alpha. Nothing I tried could resolve divergence.