Ultrashort 2-D photonic crystal directional couplers

A novel approach to reduce the coupling length and to increase the coupling coefficient in waveguide directional couplers implemented on two-dimensional (2-D) photonic crystals (PhC) is proposed. To increase the coupling coefficient of a 2-D PhC directional coupler, which is composed of two parallel PhC waveguides separated by one or several rows of rods, the radius of the rods between both waveguides is reduced. The application of this feature to ultrasmall channel interleavers and wavelength demultiplexers is addressed.