Design And Fabrication Of Automatic Bias Controller For Electro-optic MZ Modulator

In the modern optical communication system, the process of converting the source information from the electrical signal form to the optical signal form is the modulation process. The device used in this process is the modulator, and the most widely used modulator is the electro-optical MZ modulator. The electro-optic MZ modulator can't work well without the bias point control. Because when using the electro-optic MZ modulator, the bias point is easily influenced by the external environment such as temperature, mechanical vibration and so on and the drift of the bias point will have a bad impact on the entire communication system.We studied the bias point control of the electro-optic MZ modulator and designed a device to automatically control the bias point.Details are as follows: The automatic bias controller is designed by controlling the output optical power of electro-optic MZ modulator. Our device uses analog circuits for control which makes it extremely easy to adjust the bias point. Our device can stabilize the electro-optic MZ modulator at multiple bias points. To read the optical power value directly,we have added an auxiliary module for displaying optical power which can provide convenience for the experiment.In this paper, we complete the production of the device. After measuring, the control accuracy of the device is less than 0.5 degrees during 12 hours, and the control range is from 21 degrees to 155 degrees.Then, we design and build a system experiment to verify the performance of the device. After one hour, when not using the automatic bias controller,the maximum offset of the output RF amplitude is 26.9%. If we use the home-made automatic bias controller, the offset can be reduced to 11.78%,which is similar to the results of using commercial devices. And the home-made device does not generate spurious, which is better than the commercial device used in the experiment.