Compact rainbow trapping and demultiplexing by photonic crystal waveguides

Graded Index Photonic Crystals (GRIN PhCs) are artificial periodic materials that possess gradually varying effective refractive indices. GRIN profiles can be formed by adjusting the radii or the locations of PhC unit cells. GRIN PhCs exhibit several intriguing characteristics which can be listed as demultiplexing [1], mode-order conversion [2], asymmetric light propagation [3], compact lensing [4], and coupling between waveguides of different widths [5]. In addition to pure GRIN effects, the effects arising from the combinations of PhC properties (photonic bandgaps) can even enrich the possibilities of light manipulations. As a result, broad band transmission spectrum is combined with the directional band gaps [5]. Angular selectivity also can be utilized to separate different wavelengths [1]. Lastly, point and line defects can be introduced to have cavity and waveguides with GRIN PhC.