The Characteristics And Applications Of Asymmetrically Confined Photonic Crystal Defects

We investigate the transmission characteristics of the asymmetrically confined photoniccrystal (PC) defects based on the results of theoretical analysis and numerical simulation. Thetransmission differences from the linear case when Kerr nonlinearity is introduced are alsoinvestigated, which shows promising application on the design of the all-optical diodes.The transmission characteristics of the asymmetrically confined PC defects have beendetailedly investigated using the coupled-mode theory (CMT). It shows that in the framework ofCMT, an asymmetrically confined PC defect can be considered as the combination of twodifferent symmetrically confined PC defects, and its transmission characteristics are decided bythe decay-rates of the two involved symmetrically confined defects. By using the parameters ofthese symmetrically confined PC defects, we can readily get the parameters of resonantfrequency, quality factor, and resonant transmission of the asymmetrically confined one, whichfully describe the transmission characteristics of the structure. As the parameters of thesymmetrically confined PC defects are easy to obtain, such an approach saves much computertime that had to be spent in the study of the asymmetrically confined PC defects.Optical nonlinearity and structure asymmetry are two key factors for realizingunidirectional transmission. By considering the nonlinear Kerr effect using the perturbationviewpoint, we can get the nonlinear transmission formula of a single asymmetrically confinedPC defect. Based on the resulting formula, we further investigate the unidirectional transmissionof the asymmetrically confined PC defects. It is revealed that the launch direction-dependence ofthe characteristic power of the structure leads to the unidirectional transmission. Furthermore,the transmission contrast is found to have an upper limit that approaches 9 for a single PC defectstructure. All the analyses are supported by the finite-difference time-domain simulations. Ourresults can act as useful guidance in developing the all-optical diodes that base on the nonlinearPC defects.