The objective of this research paper is to study the band gap of different materials, so they can be used for designing of an efficient photonic crystal based add drop filter for an optical communication system. Today most of the transmission takes place in 1550 nm window, which is the most modern mode of communication. So a suitable material can help to enhance the overall system performance. The composition of gallium, indium, and phosphorus introduce the semiconductor material called GaInP. It is used in high-power and high-frequency electronics because of its superior electron velocity with respect to the more common semiconductors silicon and gallium arsenide, but in this case the Si is considered to be more promising than the GaInP due to the band gap structure which is analyzed by various simulations. A crystal is periodic arrangement of atoms and molecules and the pattern which the atoms and molecules are repeated in space is the crystal lattice. In the PhC the atoms or molecule are replaced by macroscopic media with differing dielectric constants and the periodic potential is replaced by a periodic dielectric function. The Wavelength Division Multiplexing (WDM) is considered to be a propitious scheme for high capacity optical interconnects and it is essential for designing of an optical filter. The FDTD and PWE methods are ideal for the structural analysis of an PhC structures, here in this paper the Rsoft and Lumerical softwares are used for carrying out required simulations.