微纳光纤具有大比例倏逝场传输的光学特性，相比于普通光纤，其耦合现象更加明显。利用基于有限元法的COMSOL Multiphysics软件对三根平行微纳光纤进行了详细的数值模拟研究。计算结果表明，纤芯间距改变时，三根平行微纳光纤随传输距离变化的功率耦合分布的规律是相似的，都呈周期性分布。纤芯间距不同时，耦合周期发生变化，且随着纤芯间距的增大，耦合周期也逐渐增大。且入射光的偏振态对耦合周期和耦合效率也有一定的影响。利用三根平行微纳光纤的耦合特性，设计了一种3×1微纳光纤耦合器，当选取恰当的纤芯间距和耦合区长度时，3×1微纳光纤耦合器的耦合效率最高可达93.3%。

Micro/nano optical fibers have the optical property of large evanescent fields, which makes their coupling phenomenon more obvious compared with the normal optical fibers. The simulation of three parallel micro/nano optical fibers is performed by using the software of COMSOL Multiphysics which is on the basis of the finite element method. The results show that the coupling power distributions are approximation as the transmission distance changing when the distance between parallel micro/nano optical fibers is changed. The distributions are periodical and coupling periods increase when the distances increase. The polarization of incident light has an influence on coupling period and coupling efficiency. By utilizing the coupling characteristics among three parallel micro/nano optical fibers, a 3×1 micro/nano optical fiber coupler is designed and its coupling efficiency is approximately 93.3% when the appropriate coupling length and distances between the optical fibers are chosen.