As seen from the above figure, does anyone know why does wriggles or little oscillations appear on my reflection spectrum as i increase my FDTD region (both x,y - span) from 300 nm to 700 nm? I tried increasing my z-span as well, but it does not help. I am doing an infinite array simulation. I placed periodic boundary condition on the x, y- directions and PML on the z-direction.
Please let me know if you need more information. Thank you.