Automatic Bias Point Control Technology For MZM Modulator Based On Correlation Detection

The wave of global informatization is developing rapidly.Applications such as Internet of things,big data,cloud computing,and AR/VR are increasingly demanding broadband Internet,and high-speed,low-latency,reliable mobile communication networks have become the most important requirements.Mach-Zehnder modulator is the most commonly used external modulator in optical communication system.Based on the optical characteristics of lithium niobate crystal,Mach-Zehnder modulator converts the input electrical signal into optical signal.The transmission curve of Mach-Zehnder modulator is a non-linear periodic function.Due to external temperature or mechanical vibration and other factors,the bias point will inevitably drift,which will reduce the quality of the transmitted signal and affect the transmission efficiency of the system.Therefore,it is very important to study the bias point automatic control system.This paper studies the automatic control technology of the bias point of the MachZehnder modulato.First,the principle of the Mach-Zehnder modulator is studied,and through the derivation of the formula,we can find the idea of adjusting the bias voltage to make the bias point of the modulator stably.A new method,named correlation detection,is proposed in our research,which can better solve the positioning and adjustment of bias point drift.Based on this idea,a bias point automatic control module is designed.Through the specific algorithm of correlation detection,a bias point automatic control system independent of input light power is realized.The analysis results show that,the complexity of the proposed scheme is n,which is lower than the traditional FFT based on ABC algorithm with the complexity of n*log2(n).By observing the eye diagram at the initial moment,2 hours after the ABC is switched on,and 2 hours after the ABC is switched off,it can be found that the automatic bias control module can stabilize the OOK signal with bandwidth of 2GHz.This module is also applied to the RoF(radio over fiber)system with 50 km optical fiber,and the OFDM signal with a rate date of 400 Mbps is transmitted in the harsh environment.After 30 minutes,the constellation diagram is basically unchanged,and the EVM remains stable at about 5%,which also indicates the stable performance of the automatic bias control module.