In this paper, simulation-based (software-based) teaching of a 4-channel optical demultiplexer based on photonic crystal is presented by using the R-Soft software. The teaching of the demultiplexer structure is based on the use of a photonic crystal filter. In this analysis, with the variation of the radius of the cylindrical nano-ring resonator and the radius of the scattering rods, the critical length parameter of 1573. 6 nm is improved in the design of the filter. The advantages of the 4-channel demultiplexer include the mean quality factor of 4525, mean channel power transfer factor of 95%, and maximum and minimum channel cross-talk of-19. 6 and-40. 4, respectively. Also, mean channel width is obtained as 0. 375 nm. Moreover, the proposed 4-channel demultiplexer can be used in WDM systems. The simulation-based teaching of these structures is very important to develop and improve the multiplexers performance. Therefore, the related syllabus is suggested for master of science (MSc) students in Electronic Engineering major. This syllabus can be considered as a part of Photonic Crystal or Photonics courses.