A Study Of Costas Loop Application In Fiber Laser Coherent Combination

High power laser is widely applied to industrial, military and other fields.There is an important solution in which many low-power lasers are synthesized to a high power output laser. In this scheme, phase-locked loop plays an important role in measuring laser phase and getting the output of synthesizing many low-power lasers. Therefore, it has an important practical significance to research laser coherent synthesis.The main worth of this thesis is to build a mathematical model of coherent combining laser with Costas loop, and the system simulation experiment using Simulink is also given. At first, we study the related theories of coherent combining laser output based on the Costas loop, such as the coherence theory, the structure of MOPA. At the same time, the climbing method, heterodyne method, the stochastic parallel gradient descent algorithm and the adaptive phase control algorithm are presented. The advantages and disadvantages of these methods are carefully compared. Then we examine several common structural PLLs such as the Balanced loop, the Costas loop, the Decision-driven loop, the SyncBit loop and the Dither loop. Finally,we decide to adopt the Costas loop which require a minimum line width, and analyze the Costas loop in detail.According to the theoretical analysis of coherent combining laser output, and selected modules, a proper mathematical model is built. Then the simulation of the coherent combination system is made by use of Simulink. Then we can analyze the output properties of different types of phase jitter noise, different types of phase jitter noise offset and different types of phase jitter noise intensity.Finally, the applications of the fiber laser coherent synthesis system are presented. And some shortcomings of this experiment are discussed, and some further improvement are also given.