天文探测中，要求类地行星探测中视向速度的测量精度达到10 cm/s。圆形光纤扰模引起的谱线漂移成为影响视向速度测量精度的一个主要因素。提出了圆形结合多边形光纤的分段式光纤传输系统,以改善圆形光纤的扰模特性。利用搭建的测试光纤远近场光斑质量的光学系统，评价光纤出射场的光斑质量；分别研究了圆形光纤、圆形结合正方形光纤、圆形结合八边形光纤的分段式光纤传输系统在不同耦合条件下的远近场分布；分析了系统的扰模增益及能量变化。结果表明，圆形结合多边形光纤的分段式光纤传输系统提高了系统的扰模特性和稳定性。当多边形光纤芯径小于圆形光纤时，较大的入射偏移量引起耦合能量损失；当多边形光纤芯径大于圆形光纤芯径时，能量守恒。圆形结合八边形光纤传输系统的近场质心偏移较小，扰模系数较高，可有效减小耦合误差引起的谱线漂移，从而提高视向速度的测量精度。

In astronomical detection, the measurement precision of radial velocity in Earth-like planet detection is required to reach 10 cm/s. The spectrum drift caused by circular fiber scrambling is becoming a major factor that influences the measurement precision of radial velocity. The sectional fiber transmission systems of circular fiber combined with polygonal fiber are proposed to improve the scrambling property of circular fiber. The spot quality of fiber output field is evaluated by an optical system for testing spot quality of far field and near field. The far field and near field distributions of sectional fiber transmission systems, which are consisted of circular fiber, circular fiber combined with square fiber, and circular fiber combined with octagonal fiber, are studied under different coupling conditions. The scrambling gains and energy variations of these fiber transmission systems are analyzed. The results show that the scrambling property and the system stability are improved by the sectional transmission system of circular fiber combined with polygonal fiber. The coupling energy loss is caused by large incidence shift on the condition that the core diameter of polygonal fiber is smaller than the core diameter of circular fiber, and the conservation of the energy holds on when the core diameter of polygonal fiber is larger than or equal to the core diameter of circular fiber. The transmission system of circular fiber combined with octagonal fiber, which is with a small mass center offset in the near field and a large scrambling coefficient, can decrease the spectrum drift induced by coupling error, and increase the measurement precision of radial velocity.