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The effects of structure parameters and structural deviations on the characteristics of photonic crystal directional couplers (PCDCs) were analyzed through a systematic simulation study. The relationship between coupling characteristics and structure parameters was discussed. The results reveal that the remained power in the coupling region is detrimental to reducing the insertion loss of PCDCs, especially for the PCDCs with shorter coupling length. An improved structure, which increases the radii of air holes in the post coupling region, was proposed to suppress the remained power and reduce the insertion loss effectively. The influence of structural deviations, which is caused by fabrication imperfections and results in the mismatch between experimental results and theoretical predictions, was also investigated using statistical methods. The simulation results show that the air hole position misalignment perpendicular to the waveguide direction has the largest effect on the insertion loss of PCDCs, and reducing r/a is helpful to improving the robustness of PCDCs.
Date of Publication: Sept.15, 2009