Coupling characteristics of electromagnetic waves in ultra-short parallel four photonic crystal waveguides and its application

We consider the coupling between four photonic crystal waveguide as a multimode interference system and showed that the dispersion curves of the eigenmodes intersect or almost intersect. Degenerate modes appear in the system. At the crossing point, the multimode interference is deprived and power is confined to its input direction without observable transfering to other photonic crystal waveguides. On the basis of these, a wavelength de-multiplexer or multiplexer is designed.