为了提高卡塞格林望远镜像斑耦合多模光纤的效率，采用一种在光纤前端放置锥形导管的方法，利用光线在锥形导管中经过多次内全反射耦合进多模光纤中，通过几何光学理论及数值方法分析卡塞格林零视场光束像点的最大耦合角，确定锥形导管初始结构参数。将此参数作为Zemax仿真的初始条件，进行优化仿真计算和误差分析。结果表明：加工误差控制在0.03 mm之内，采用锥形导管后可以使像斑整体耦合效率较直接耦合提高4倍以上。

In order to improve the efficiency of coupling Cassegrain telescope image disk into multimode fiber, we put forward a new method of putting an axicon duct close to the import of multimode fiber. By using total internal reflection several times in axicon duct, the rays could rip into multimode fiber. To determine the initial structural parameters of axicon duct, we analyzed the maximum coupling angle of image spot of Cassegrain at 0° field of view(FOV) by employing geometrical optical theory and numerical method. These parameters were used as the initial conditions of simulation in Zemax. After simulation optimization and tolerance analysis, the conclusions show that when the fabrication tolerance is controlled in 0.03mm, the coupling efficiency of image spot at full FOV is at least 4 times as the direct coupling.