The Properties And Applications Of Photonic Crystals Defects

We have investigated the character and applications of photonic crystals (PCs) defects by theoretical analysis and numerical simulation.First, we examine the defect mode of linear PC atoms by numerical simulations. We find that by changing the size of a defect, the resonant frequency of the defect can be tuned within the band gap, then we analysis defect mode by use of the coupled mode theory.Second, we investigate the dynamics of nonlinear photonic crystal (PC) atoms by use of numerical simulations in a pump-probe scheme based on a finite-difference time-domain technique. We find that under the excitation of a continuous wave (CW), the defect mode will be shifted and driven to oscillate harmonically between its initial position and a final position that is dependent on the pump intensity. Therefore, the transmission observed at a certain frequency is actually the time average of the transient values within an oscillation period. Then we established the physical model for the dynamics of nonlinear PC atoms, the transmission spectra for nonlinear PC atoms that resulted from the dynamic shift are calculated and they are in good agreement with the simulation results. Final we investigate the unidirectional transmission behaviors of an asymmetrically confined photonic crystal (PC) defect with Kerr nonlinearity, base on this we construct all-optical diodes.Finally, we investigate the unidirectional transmission behavior of PC molecules consisting of nonlinear defect pairs by the finite-difference time-domain technique. We focus on how to enhance the transmission contrast and maximum transmission of the resulting optical diodes. It is found that by intentionally and properly misaligning the resonant frequencies of the constitutional PC atoms, the transmission contrast as well as the maximum transmission of the nonlinear PC molecules can be significantly improved. The figure of merit that characterizes the performance of optical diodes can be enhanced by a factor of 5 as compared with the optical diodes constructed by single asymmetrically confined PC atoms. In addition, the optimum performance of the optical diodes can be achieved only when the operating frequency is properly chosen.