混合纤芯光子晶体光纤超平坦色散的研究

利用平面波展开法，系统地研究了一种具有混合纤芯结构的光子晶体光纤的色散特性. 数值计算结果表明，通过优化结构参量，这种新型结构的光子晶体光纤在通信窗口1.55 μm 附近可以获得带宽超过800 nm的超平坦色散区域（色散曲线的变化范围不超过 ±0.6 ps·km－1·nm－1）.     

Investigation and Modification of Coupling of Photonic Crystal Defects

We investigate the coupling of photonic crystal (PC) defects by using coupled-mode theory. The PC molecules formed by the coupling of two identical PC atoms are the focus of our study. It is revealed that the flatness of the transmission spectra of the PC molecules is determined uniquely by the phase shift of the travelling wave between the two coupled PC atoms. By properly adjusting the distance between the two constitutional PC atoms, we are able to modify the transmission spectrum of the resulting PC molecule. Theoretical analyses based on the coupled-mode theory are in good agreement with the simulation results obtained by the transfer matrix method and the finite-difference time-domain technique.     

Subpicosecond pulse compression in nonlinear photonic crystal waveguides based on the formation of high-order optical solitons

We investigate by numerical simulation the compression of subpicosecond pulses in two-dimensional nonlinear photonic crystal (PC) waveguides. The compression originates from the generation of high-order optical solitons through the interplay of the huge group-velocity dispersion and the enhanced self-phase modulation in nonlinear PC waveguides.Both the formation of Bragg grating solitons and gap solitons can lead to efficient pulse compression. The compression factors under different excitation power densities and the optimum length for subpicosecond pulse compression have been determined. As a compressor, the total length of the nonlinear PC waveguide is only ten micrometres and therefore can be easily incorporated into PC integrated circuits.     

Formation of Optical Solitons in Nonlinear Photonic Crystal Waveguides

Relying on the huge group velocity dispersion available in photonic crystal (PC) waveguides, we observe the formation of both Bragg grating solitons and gap solitons in nonlinear PC waveguides in numericalexperiments. Also, we indicate the potential applications of optical solitons in optical limiting, optical delay, and pulse compression and the feasibility of observing optical solitons in practical experiments.     

Analysis and engineering of coupled cavity waveguides based on coupled-mode theory

The analytical expression for the transmission spectra of coupled cavity waveguides （CCWs） in photonic crystals （PCs） is derived based on the coupled-mode theory （CMT）. Parameters in the analytical expression can be extracted by simple numerical simulations. We reveal that it is the phase shift between the two adjacent PC defects that uniquely determines the flatness of the impurity bands of CCWs. In addition, it is found that the phase shift also greatly affects the bandwidth of CCWs. Thus, the engineering of the impurity bands of CCWs can be realized through the adjustment of the phase shift. Based on the theoretical results, an interesting phenomenon in which a CCW acts as a single PC defect and its impurity band possesses a Lorentz lineshape is predicted. Very good agreement between the analytical results and the numerical simulations based on transfer matrix method has been achieved.