Design Of DPMZ Automatic Bias Control Algorithm Based On FPGA

In recent years,100 G optical modules have been put into use in large quantities.At the same time,major companies and research institutes have turned their attention to 400 G or even 1T optical transmission research.Among them,high-order code modulation technology is an important means to improve the capacity of transmission systems.Higher order code modulation has higher accuracy requirements for optical modulators.Among the optical modulators,the most widely used is the double parallel Mach-Zehnder modulator(DPMZ),which consists of two Mach-Zehnder modulators(I and Q)and a phase modulator(P-channel).In actual use,due to environmental temperature and humidity,input device optical power,device aging and other factors,the bias point of the modulator will drift.In order to achieve the best modulation,the bias voltage needs to respond in real time to changes in the modulator operating point.In this thesis,the DPMZ bias voltage point stability is studied.The research work is as follows:(1)The dual parallel Mach-Zehnder transmission characteristics are studied.An FPGA-based automatic bias control algorithm is designed.The algorithm is divided into two parts,the initialization part and the tracking lock part based on power detection.The purpose of the initialization part is to find a working point close to the bias voltage to reduce the time it takes for the tracking lock part algorithm to lock the working point;The tracking lock section uses jitter signal detection to find precise working bias points and can track the bias points that vary with the environment in real time.(2)The algorithm is implemented using the verilog program and runs on the FPGA.(3)The influence of important parameters on the accuracy of the automatic bias control algorithm is determined experimentally,and each parameter is determined to make the modulation system more stable.The measured data show that the FPGA-based automatic bias control algorithm designed and implemented in this paper can find the optimal working bias point of the DPMZ modulator in a fast time,and can perform tracking adjustment in real time,so that the modulator can Stable work for a long time.