Highly Compact Circulators in Square-Lattice Photonic Crystal Waveguides

We propose, demonstrate and investigate highly compact circulators with ultra-low insertion loss in square-lattice- square-rod-photonic-crystal waveguides. Only a single magneto- optical square rod is required to be inserted into the cross center of waveguides, making the structure very compact and ultra efficient. The square rods around the center defect rod are replaced by several right-angled-triangle rods, reducing the insertion loss further and promoting the isolations as well. By choosing a linear-dispersion region and considering the mode patterns in the square magneto-optical rod, the operating mechanism of the circulator is analyzed. By applying the finite-element method together with the Nelder-Mead optimization method, an extremely low insertion loss of 0.02 dB for the transmitted wave and ultra high isolation of 46 dB∼48 dB for the isolated port are obtained. The idea presented can be applied to build circulators in different wavebands, e.g., microwave or Tera-Hertz.我们提出、实验验证并研究了一种应用于方格子方杆光子晶体波导（square-lattice-square-rod-photonic-crystal waveguides）的超紧凑、超低插入损耗环行器（circulators）。仅需在波导的交叉中心处插入单个磁光方杆（magneto-optical square rod），即可使该结构兼具极高紧凑性与超优效率。将中心缺陷杆周围的方杆替换为若干直角三角杆（right-angled-triangle rods），可进一步降低插入损耗并提升隔离度。通过选取线性色散区域（linear-dispersion region）并结合方形磁光杆内的模式场分布，我们对该环行器的工作机理展开了分析。通过结合有限元法（finite-element method）与内尔德-米德优化算法（Nelder-Mead optimization method），我们实现了传输波0.02 dB的超低插入损耗，以及隔离端口46 dB~48 dB的超高隔离度。本文提出的设计思路可用于构建不同波段的环行器，例如微波波段或太赫兹（Tera-Hertz）波段。