The Design And Implementation Of Bias Point Stabilization System For Mach-Zehnder Modulator Based On DSP

Mach-Zehnder(MZ) modulator is a kind of optical external modulator which was widely used in the high-speed optical communication system. Its transfer function is similar to the cosine function, when it's put into use, we should first set the bias point.Whereas the bias point would deviate the first set as the modulator continue its working, because of its component material and the outer temperature etc. The deviation of bias point seriously influences the optical communication links, causing it couldn't continue stable and durable.As no special material replaces the widely used lithium niobate(LiNbO3), the researchers usually control the deviation by a feedback circuit. With the development of digital communication, microwave photonics, the demand of bias stability is more and more strict. The demand of some common bias points' stability gradually becomes the need of all bias points' stability.This thesis is concerned about the problem of MZ modulator bias deviation. The control methods of bias point stabilization for MZ modulator were researched. A bias point stabilization system for MZ modulator based on DSP was designed and implemented which could realize arbitrary bias point stabilization for MZ modulator. The main work and achievements are as follows:1. The basic principle and the transmission curve characteristic of the MZ modulator were researched. The necessity of the bias point stabilization for MZ modulator was analyzed.2. Several methods of bias point stabilization were researched,including the method based on the ratio of the input and output optical power, the method based on the dither could stabilize the common bias points, the method that based on the dither could stabilize any bias points and the method that based on the output optical power could stabilize common bias points etc.3. A method based on the output optical power which could realize arbitrary bias point stabilization for MZ modulator is proposed.The basic principle of this method was analyzed. The implementation scheme of the system was designed. The control algorithm of the system was researched. The scanning of the transfer curve and the stabilization controlling of arbitrary bias point were implemented.4. The design and implementation of circuits were completed and the bias point stabilization control system based on DSP was realized.The experiments of common bias point stabilization and arbitrary bias point stabilization for MZ modulator were carried out. The experiment result shows that the system is efficient to stabilize any bias points of MZ modulators.