为了提高光纤和光器件之间的耦合效率，设计了由热扩芯光纤和自聚焦透镜构成的新型热扩芯光纤准直器。理论上分析了热扩芯光纤准直器的基本结构参数与光学特性的关系以及由3种失配导致的耦合插入损耗。研究发现，热扩芯光纤准直器的耦合特性与自聚焦透镜的参数有关，热扩芯光纤准直器在轴向间距和角度偏差上的耦合失配容限明显优于普通光纤准直器，横向位移损耗则高于普通光纤准直器。采用模场半径为15.4 μm的热扩芯光纤与自聚焦常数为0.295 mm-1的自聚焦透镜制备了热扩芯光纤准直器，并对热扩芯光纤准直器因3种失配导致的耦合插入损耗进行了理论和实验比较，结果表明实验数据与理论吻合较好，说明所设计的热扩芯光纤准直器可用于长距离光耦合和旋转连接器件。

In order to improve the coupling efficiency between fibers and optical devices, a new thermally expanded core fiber collimator is designed. It consists of thermally expanded core (TEC) fiber and gradient index (GRIN) lens. The relation between TEC fiber collimator and its optical characteristics is analyzed. The coupling insertion losses caused by three kinds of misalignments are calculated. The results show that the coupling characteristics of TEC fiber collimator is related to the GRIN lens parameters, the lateral and angular coupling tolerances have been greatly improved compared with single-mode fiber collimators and the loss of axial offset is higher than that of single-mode fiber collimators. We fabricate the TEC fiber collimator by using the TEC fiber with 15.4 μm mode-field radius and the GRIN lens with 0.295 mm-1 gradient constant. The coupling insertion losses measured are consistent well with the theoretical results. The TEC fiber collimator can be used for long working-distance optical coupling and rotary connection devices.