The Research Of Bias Point Control For Electro-optic Modulator

Electro-optic modulators are the most important part of external modulation system in optical communication.MZMs(Mach-Zehnder Modulators)usually have large modulation bandwidth,low driving voltage and low chirp.Therefore,they are generally the best choice to use in optical communication system.However,thermal or damp effect,changing of electric field and aging will cause the drift of bias point and waveform distortion.In order to stablize bias point of MZMs,a control algorithm which based on the first-order and cotangent value of Average Optical Power proposed.Firstly,we study the modulation theories and the reason for drift of bias point.Next,a bias point control model has been built and modulated with Matlab.After that,we design the hardware circuit and control algorithm according to the compound control methord.Finally,an arbitrary working point control system is founded.During the experiment,the result indicate that the fluctuation of output average optical power is less than ±5%(within one hour)under the condition of 5 dBm laser output power(1550nm),4.2 V half-wave voltage,3 dB insertion loss and 1Gbps/1Mbps speed.The system has the ability to maintain the bias at any point in the optical power curve and it improved the reliability of MZM in optical communication.