Numerical and experimental demonstration of a wavelength demultiplexer design by point-defect cavity coupled to a tapered photonic crystal waveguide.

We propose and experimentally demonstrate a demultiplexer with point-defect resonators and a reflection feedback mechanism in a photonic crystal waveguide (PCW). A tapered PCW has been chosen as the necessary reflector, which enhances the drop efficiency. Due to the variation of the single-mode waveguide width of the tapered PCW, spatial alteration of the effective refractive index can be achieved. This phenomenon is used to reflect back the forward propagating wave which is then coupled again to the drop channels via the resonators. High transmission efficiency to the dropout channels is numerically predicted by calculations, either in two- and three-dimensional models, and analytically described by a coupled-mode theory. Moreover, an experimental realization in the microwave regime provides confirmation that the targeted wavelengths can be properly transmitted at the drop channels with low crosstalk and relatively high efficiencies.