A multiplexer-demultiplexer (MUX-DEMUX) based on PC waveguide couplers is proposed, and its wavelength demultiplexing properties are theoretically investigated. First, a two-channel MUX-DEMUX is designed and characterized, and then, by cascading, two stages of photonic crystal (PC) waveguide couplers with different coupling coefficients are constructed. The device sizes are expected to be drastically reduced from a scale of a few tens of micrometers to a scale of a few hundreds of micrometers in a MUX-DEMUX with a channel spacing of about 20nm required for wide-passband wavelength division multiplexing (WWDM) systems. The simulation results are obtained using a time-domain beam propagation method (BPM) based on a finite element scheme and a simpler coupled-mode theory.
Masanori Koshiba, "Wavelength Division Multiplexing and Demultiplexing With Photonic Crystal Waveguide Couplers," J. Lightwave Technol. 19, 1970- (2001)