© 2016 IEEE.Photonic crystal waveguides supporting band gap guided modes hold great potential to tailor the group velocity of propagating light. We propose and explore different wavelength demultiplexer design approaches that utilize slow light concept. By altering the dielectric filling factors of each waveguide segment, one can show that different frequencies can be separated and extracted at different locations along the cascaded waveguide. Furthermore, to eliminate the inherent reflection loss of such a design, a composite structure involving a tapered waveguide with a side-coupled resonator is also presented. Such a structure features not only a forward propagating wave but also a backward propagating wave acting as a feedback mechanism for the drop channels. We show that by careful design of the waveguide and the resonator, the destructive and instructive interference of these waves can effectively eliminate the reflection loss and increase the coupling efficiency, respectively. Numerical and experimental verification of the proposed structures show that the targeted frequencies can be coupled out with low cross-talks and moderate quality factors, while maintaining a compact size.