Dear all,

i was wondering if someone could explain to me following issues:

- The bandstructure analysis group (https://kb.lumerical.com/en/pic_passive_bragg_initial_design_with_fdtd.html) returns only two peaks. But the grating structure should have spectrum in between those two peaks also. i looked at the script written in bandstructure analysis group but i don’t understand how it suppresses the intermediate spectrums. And is it necessary that the 2 peaks always lie at band edge (to get the correct value of BW)?

2.Band structure of Bragg grating for the wide range of Bloch wavevector:a

Is the line mentioned in the figure light line? it does not look like higher order band. - is it correct to calculate the effective index at a particular frequency by the expression neff=c
*k/(f*period) from this band diagram? or do i need to plot band diagram for a normal waveguide to calculate effective index?

i would appreciate the reply.

thank you.