Study On Automatic Gain Control Circuit Of Erbium-Doped Fiber Amplifiers

Optical networks based on wavelength-division-multiplexing (WDM) and Erbium-Doped Fiber Amplifiers(EDFAs) have become the mainstream of the development of optical fiber communication technology. But when EDFAs are cascaded in a long-haul WDM system, there still exists one major question which is the dynamic characteristics of the network. This dynamic characteristics arise from the network management such as the add/drop of WDM channels, traffic rerouting, equipment upgrade, and protection switching. Since WDM channels share optically active devices such as EDFAs, network management of one channel may affect the power and noise features of the other channels. In order to minimize this influence, it is very important to study the automatic gain control (AGC) of EDFA.The thesis studies and designs the automatic gain control circuit of EDFAs. Firstly, the history and actuality of the EDFA and its prospect in practical applications is introduced. Then a brief introduction of spectral characteristics of Er3+ and the principle of EDFA is given, and also the concerned parameters are interpreted and analyzed. Finally, the importance of the AGC in WDM system is discussed. Due to its relatively low cost and high long term reliability, electrical AGC EDFA is popular in practical systems. The main work completed is summarized as follows:1. Firstly, the control circuit for EDFA has been designed. Hardware design includes automatic temperature control circuit (ATC), automatic power control circuit (APC), protecting circuits, sampling circuits for both operating parameters i.e. the pump power and the input/output power, and the man-machine interface design. Software is used to monitor the operating parameters of the EDFA, alarm in condition of danger, and communicate with the upper processor.2.Secondly, the thesis provides a brief summary of the AGC technologies used for the EDFA. After analyzing the dynamic gain characteristics of EDFA in a WDM system, it can be seen that the transient response of EDF is the function of the wavelength and the power of the survival channels and the pump power. So the control algorithm must adopt the self-adaptive algorithm to control the gain. In addition, in order to minimize the gain excursion caused by network management, the combination of electrical feedforward and feedback control method is proposed. 3.Finally, the self-adaptive algorithm based on DSP is adopted to control the gain of the EDFA and the corresponding software and hardware are designed, including the circuit design, the PCB design, software development. The experimental results show that the AGC of EDFA based on DSP is feasible.In conclusion, the thesis intends to design and study the control circuits of EDFAs in terms of engineering and then discuss some interrelated theories and technologies. It is hoped that the thesis is useful to the practical R&D and fabrication of EDFAs.