I have designed a 2-D planner photonic crystal, with Si rods in air background, offering photonic bandgap around 200THz. Using line defects, I have designed a coupled-resonator optical waveguide (CROW).

Now, I want to find the effective refractive index of the entire system for each variation of defects' radii.

I have used CST FDTD and CST frequency domain solver. Both of them are calculating the same effective refractive index, equal to one for all frequencies. 

Can anyone suggest me what the wrong thing I am doing?