Learning Forum

[Fateme Salahshuri]

Hello,

I am simulating two waveguides on top of each other with a gap in between, and I'd like to see how the coupling works and also take a close look at the transmission. For some reason, I cannot detect a small percentage of the light despite using multiple monitors. I can see that at the input port, I have 100% injected into the first waveguide, and around 88% comes out of both waveguides at the output port. I used a monitor to observe the entire simulation area, including the cladding on the output, but I only detect 97.5%. I detect 0.5% reflection, and I also have monitors at each PML boundary, which also show less than 0.5%. I'm unable to detect the remaining light, and I can't figure out where this small amount of light is disappearing. Could you please help me understand what I'm doing wrong?

 

[Guilin Sun]

There are a few reasons for not having 100% transmission:

1: the moitors do not enclose a complete box to cover the whole device

2:the source mode might be cut

3: discrete error from simulation. you may reduce this by increasing the mesh accuracy

4: the simulation time is not long enough, or the autoshutoff min is not small enough as now it is a cavity with multiple reflections.

Please also check if there is any material loss. One more: do you add the total powers from the ports, or just use abs(S)^2? when there is abruption of the waveguides, it can excite higher-order of modes. You should use the total power from the ports. I believe that you calcualted the total power from other monitors.