Reply To: simulating transmission within a phC waveguide – Lumerical FDTD

[Guilin Sun]

I first suggest you to move the left PML closer to the cavity, eg, the input waveguide should penertate out the left PML. This will reduce reflection cased by the ending input waveguide, which may cause the uneven result.

If you want to reduce memory, please shorten the distance between left and right PML BCs as only a small portion of the straight waveguides should work in your case.

The loss  can arise from the sides of the photonics crystal waveguide because it has limited number of periods whereas in band structure simulation we assume infinite number of perioids. You can add some side power monitors to check the transmissions scattered out from the limited photonic crystal.  In addition, due to strong lattice resonance inside the photonic crystal, you may need to use smaller autoshutoff min provided the simulation time is long enough. You can use "checkpoint" to resume the simulation with reduced autoshutoff min and compare the results.

https://optics.ansys.com/hc/en-us/articles/360046368573-Running-FDTD-simulations-from-the-design-environment

so you do not need to simulate it from time zero when you reduce the autoshutoff min. Make sure you set the simulation time long enough and let the autoshutoff min to terminate the simulation. You can check the log file and see the percentage estimated from the simulation time. In all the times the percentage should be less than 100% at termination.