条形耦合波导对光子晶体耦合缺陷模的影响

Impact of a stripe waveguide to coupled defect modes of photonic crystals

光子晶体的耦合缺陷模可以通过透射谱形状来表征,而透射谱形状则与连接缺陷的条形耦合波导相关.不同于直接耦合时信号相移只依赖于缺陷模的共振频率,当存在耦合波导时信号相移也决定于波导的长度和色散关系.随着波导长度的增加,透射谱形状发生从三峰到两峰,再到平项,最后又回到三峰的周期性变化.时间耦合模的分析表明,在缺陷模频率附近理论结果与时域有限差分法的计算结果完全一致,表明在此复杂情况下理论模型依然有效.

Coupled defect modes of photonic crystals can be characterized by the transmission spectrum shape that is closely linked to the stripe waveguide connecting the defects. Unlike the direct coupling cases where the phase shift of lightwave depends only on the defect mode frequency, we found that for the waveguide coupling cases the waveguide length and the dispersion relation must be also considered. By changing the waveguide length, the spectrum can exhibit periodically three-peak appearance, two-peak appearance, and fiat top appearance. At frequencies close to the defect mode, the results of the coupled mode theory are in good agreement with the simulations using the finite-difference time-domain technique, verifying the validity of the theoretical model even in the complicated cases.