Guilin Sun
Ansys Employee

EME: it depends on which model you used. Luke's and Phillio's models have virtually zero absorption.

VarFDTD: the mode source must be inside the waveguide that supports a mode. in addition, the simulation time must be long enough to let the signal pass through the waveguide in order to get correct frequency-domain result.


Suggestion: since mode has effective refractive index n=n_real+j*n_imag, you do not need to simulate to get the propgation loss. FDTD gives the loss in dB/cm from the n_imag:

You will get the propagation loss by multiplying the length to dB/cm with correct length unit, from FDE mode result.