Bandwidth measurement

How to measure the bandwidth of a given photonic crystal using FDTD

For something like a periodic photonic crystal waveguide, the method to determine the bandwidth would be similar to the Bragg waveguide bandwidth example here:
https://kb.lumerical.com/en/index.html?pic_passive_bragg_initial_design_with_fdtd.html

If you are referring to the band gap of a photonic crystal lattice, the method described here can be used to extract the bandstructure:
https://kb.lumerical.com/en/index.html?diffractive_optics_pc_bandstructure.html