为了实现对双电极马赫-曾德尔电光调制器任意直流偏置点的自动偏置控制，采用在闭环控制基础上，引入一个可调移相器使不同直流偏置点处误差信号相同的方法，理论分析了可调移相器相移量与直流偏置相位的关系，仿真得到对于不同偏置点，当调制器直流偏置相位漂移达-0.15rad ~0.08rad，移相器引入附加相位漂移-0.55rad~0.55rad时，经偏置控制后相位漂移被限制在-3.0×10-4rad~1.7×10-4rad范围内。结果表明，该方法有效实现了对电光调制器任意直流偏置点的自动偏置控制。

To control the bias of dual-electrode Mach-Zehnder electro-optic modulators automatically,an adjustable phase shifter was introduced based on closed-loop control method so that the error signal remained the same at different direct-current(DC)bias points. The relationship between phase shift of the adjustable shifter and DC bias phase was derived by theoretical analysis. Simulation showed that,the drift of DC bias phase in the range of -0.15rad~0.08rad with the added phase drift caused by the phase shifter in the range of -0.55rad~0.55rad could be suppressed to -3.0×10-4rad~1.7×10-4rad at different DC bias points. The results show that the automatic bias control of an electro-optic modulator at any DC bias points is effectively achieved.