在正常色散的双折射光纤中传输的暗孤子对之间由于耦合周期性交换能量，一个暗孤子可把能量完全转给另一暗孤子，因此双折射光纤可作光开关。本文讨论了椭圆角为３５°的双折射光纤的开关条件，发现脉冲只有以特定的极化角入射才有开关现象产生，而且建立了光纤长度与孤子对相差、初始能量差的解释关系 The birefringent fiber can be optically switched since a dark soliton can transfer energy completely to another dark soliton due to the periodic exchange of energy between the dark soliton pairs transmitted in a normally-dispersed birefringent fiber. In this paper, we discuss the switching condition of the birefringent fiber with the elliptic angle of 35 °. It is found that the pulse can only be switched on and off with a certain polarization angle, and the relationship between the fiber length and the soliton pair and the initial energy difference is established