In this paper, a 4-channel demultiplexer for WDM systems is designed by using 2-dimensional photonic crystals with square structure. Various wavelengths can be conducted in the certain paths of crystals using defects that look like ring resonator. The characteristic of this demultiplexer can be analyzed by obtaining the pass band spectrum. The property of this designation relative to previous works can be stated as size reduction, minimum crosstalk in output channels, minimum distance (about nm) for distinct wavelengths in output bands and bandwidth increasing in consequence. These improvements have been verified by simulation results.
