PML vs metal boundary condition gives different value of the propagation loss

- March 22, 2023 at 11:31 am
  
  dubey
  Subscriber
  
  I am trying to calculate the propagation loss in the Si Nitride waveguide (Please see that attached figure). The propagation loss is different for different boundary condition. Also, what does negative loss means here?
- March 22, 2023 at 10:11 pm
  
  Guilin Sun
  Ansys Employee
  
  For propagation loss, you should use PML as the boundary conditions.
- March 22, 2023 at 10:33 pm
  
  dubey
  Subscriber
  
  Hi, I am using PML boundary condition. Why There is large negative loss value in the fundamental mode? Please explain how to get realistic value of propagation loss for such waveguide. Thank you!
- March 23, 2023 at 6:09 pm
  
  Guilin Sun
  Ansys Employee
  
  This might be a back propagation mode, which can have negative real (neff). You can check this: