An automatic bias control method applied to all bias points of electro-optic modulator

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 -3.010-4rad~1.710-4rad 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.