This work presents a 4-channel demultiplexer totally based on a two-dimensional photonic crystal (2 DPHC) with silicon rods and defects with the advent of a graphene sheet, in multiplexing systems that use DWDM (Dense Wavelength Division Multiplexing) [1]. In these projects, methods that incorporate plane wave expansion (PWE) and finite difference time domain (FDTD) are used, as they have significant efficiency to generate the photonic hollow modes of the demultiplexer and analyze the global distribution and transmission, respectively. Parameters of transmission overall performance, Q factor, spectral width and channel spacing of the demultiplexer are very important statistics to confirm the general overall performance of the device, whose values are about 100%, 1722.22, 0.9 nm and 10 nm, respectively [2], whose consequences are problem to the validation of the requirements of the DWDM device (ITU.G.694.1) [3]. The proposed demultiplexer includes a bus or linear waveguide with graphene to guide the slight wave and 4 resonant cavities wherein graphene is placed withinside the center to select out the wavelength in a hexagonal lattice form (RCH) of dielectric rods in air. The bus waveguide transmits slight into the resonant hole area and exits thru the respective falling waveguide. The proposed device is nanometer and can be used for the implementation of photonic protected circuits [4].