对光纤熔锥耦合器拉制过程中的偏振调制效应作了定性的理论分析，耦合区内的几何双折射和应力双折射导致的对称模和反对称模在x偏振方向和y偏振方向上的传播常数差不一致，从而引起两个方向的偏振光耦合的空间周期不同，存在相位差别，当相差正好达到π时实现偏振分离。在此基础上制作了熔锥型偏振分束器，消光比达到了16．5dB。

Polarization modulating effect was analyzed theoretically for pulling process of fused biconical taper fiber coupler. Geometrical and stressed birefringence caused different propagation constant for symmetric and antisymetric modes on x polarization and y polarization in coupling region. Therefore,it resulted in different coupling spatial period of two polarization orientation,with phase difference. The polarization beam splitting function was realized when the phase difference reached π. Also polarization beamsplitters were built in practice,with 16.5 dB extinction ration.