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采用时域有限差分法研究三平行光子晶体直波导的传输特性及模场分布,结合耦合模理论计算光子晶体波导的耦合系数。计算结果表明,在高频段(0.33~0.42)(ωa/2πc)的范围内两耦合波导与主波导表现出相互的能量交换,实现光耦合,耦合系数随入射波频率增加而减小;而在低频段(0.31~0.33)(ωa/2πc)的范围内,两耦合波导与主波导的传输谱图同步变化,耦合波导的传输光强均约为入射光强的四分之一。最后,提出一种采用固定波导耦合长度同时实现超微结构光均分器及1/4功分器的方案,当耦合长度取Lc=(2n+1)π/2 2K时,两耦合波导可将高频段相应入射波实现均分,同时将低频段中的任意入射波实现1/4功分。
The time-domain finite difference method is used to study the transmission characteristics and mode field distribution of a three-parallel photonic crystal waveguide. The coupling coefficient of the photonic crystal waveguide is calculated based on the coupled-mode theory. The calculated results show that the two coupling waveguides exhibit a mutual energy exchange with the main waveguide in the range of (0.33 ~ 0.42) (ωa / 2πc) and achieve optical coupling. The coupling coefficient decreases with the increase of the incident wave frequency. In the low frequency band (0.31-0.33) (ωa / 2πc), the transmission spectra of the two coupled waveguides and the main waveguide change synchronously. The transmitted light intensity of the coupled waveguides is about one quarter of the incident light intensity. Finally, a scheme of using a fixed waveguide coupling length to achieve both an ultrastructural optical equalizer and a quarter-power splitter is proposed. When the coupling length takes Lc = (2n + 1) π / 2 2K, the two coupling waveguides can be The corresponding incident wave of the high frequency band is equally divided, and at the same time, 1/4 of the power of any incident wave in the low frequency band is realized.