need help for my fdtd for phc

i wrote my fdtd for pbg of Phc,but i can't get the correct fft from ez field evolution ,
if i set the time step too little ,the frequency which i get by fft always be a line (w=0); i can't understand why , are there anybody to help me?

I think that from the theory of standard fourier transform
the time should be large . please try (2^14) for example which makes the
Fast Fourier Transform very efficient.

but for the FDTD running it is still time consuming,

Ok, my problem is,
I could not get all the frequcies compared with the diagram obtained by pwe. if two frequencies is close to each other, sometime, one of time is missing.

any body know why?

Can u send me your Matlab code for photonic crystal? I shall be highly obliged to you.