I’m designing integrated optical components which should have extremely low (<50 dB) reflections. I would like to simulate these structures with FDTD but I am having some trouble with the mode expansion monitors.
In the attached script I inject an optical mode into a Si waveguide and monitor the optical power in 2 micron intervals in front of the source. A mode expansion is then done on each of the monitors and the data is plotted in MATLAB. The simulation takes less than a minute to run on my PC.
Can someone explain why the mode expansion monitors show light travelling backwards in the waveguides, when light should only be propagating forward? Furthermore, why do the results (both transmission and reflection) change when the position of the monitor is changed? I’ve tried adjusting the PMLs and the simulation mesh size but neither eliminates the problem.
Any help is greatly appreciated.
Mode Injection_LumericalHelp.lsf (3.5 KB)