Using the simple inverse Flourier transformation, we can design the index modulation structure of the sampled period of the sampled fiber Bragg gratins (FBGs). In this method the enable channels are identical wavelength operation while the unable channels are almost suppressed completely. The enable and unable channels can be established at will based on the applications. This technique is very useful for flexible design optics devices such as optical add and drop multiplexers (OADMs), and interleavers with dispersion and dispersion slope compensation.