Application of photonic crystal defects in constructing all-optical switches, optical delay lines and low cross-talk waveguide intersections for ultrashort optical pulses

We present a systematic study of coupled defects in photonic crystals (PCs) and explore their applications in constructing optical components and devices for ultrafast all-optical signal processing. First, we find that very deep band gaps can be generated in the impurity bands of coupled cavity waveguides (CCWs) by a small periodic modulation of defect modes. This phenomenon implies a high-efficiency all-optical switching mechanism. The switching mechanism can be easily extended from one-dimensional (1D) to two-dimensional and three-dimensional PC structures by utilizing the coupling of defect pairs which are generally present in PCs. Second, we suggest that CCWs with quasiflat and narrow impurity bands can be employed as efficient delay lines for ultrashort pulses. Criteria for designing such kind of CCWs have been derived from the analysis of defect coupling and the investigation of pulse transmission through various CCWs. It is found that the availability of quasiflat impurity bands depends not only on the intrinsic properties of the constituting defects but also on the detailed configuration of CCWs. In experiments, optical delay lines based on 1D monorail CCWs have been successfully fabricated and characterized. Finally, we have proposed a new mechanism for constructing waveguide intersections with broad bandwidth and low cross-talk.