The Design And Development Of DSP-Based Electro-optic Modulator Bias Control System

After the rapid development in recent years, optical fiber communication has become an important part of communication field. The advantages of optical fiber communication include: strong ability of anti-interference, large capacity of communication, good confidentiality, etc. Whether these advantages can fully exert in the process in communication depends on the development of many key technologies one of them is the bias control of the electro-optic modulator.MZ electro-optic modulator has become widely used for its advantages in transmission bandwidth and stability. Meanwhile, the technology of DC bias voltage control for MZ modulator has become a hot issue both in study and practical application.Most of previous researches in bias voltage control system are based on analog signal. This paper however developed and built a MZ modulator bias control system with the center of the digital signal processor (DSP) which is used widely in recent years. Compared to the analog systems, it provides a higher process speed and overcome the shortcoming of environment sensitive, at the same time, it can combine several modes of bias control system such as QPSK (Quadrature Phase Shift Keying) and QAM (Quadrature Amplitude Modulation) in one which have be built separated based on analog system, so that it can meet variety needs in communication, which means the optimization in performance and reduction in the cost of production.The design and development of MZ modulator bias control system based on DSP in this thesis includes the following major components:1. The fundamental theory of MZ modulator and the DSP, demonstrated the rationality and superiority of digitalizing the bias control system into a DSP system.2. Introduction of TMS320F28027 which is a DSP chip built by the Taxes Instruments. And based on which determined the periphery chips and built the circuits for the bias control system.3. design of the program of digital filter, signal synchronization and digital PID control based on C language.The experiment results showed that compared to the analog system, the bias voltage control system based on DSP in this thesis has improvement in speed, accuracy and flexibility and at the same time reduces the jitter. More over it's user-friendly which means the operation parameters can be modified by users according to the different characteristics from different kinds of modulators. And this system bhas been used in the QAM and QPSK applications and is recognized by the market.