Research On EDFA Characteristics In WDM System

It has been over two decades since the first experiment of fiber communication was operated in 1978. Fiber-optic communication technologies have been put into commerce step by step. The speed of fiber-optic communication has been growing from 45Mbits/s to 40Gbit/s. How to use the existing communication system to widen the communication capability to meet increasingly demands has become the research hotspot of the optical communication realm, when all kinds of data services require more and more transmission bandwidth.Adopting wavelength-division-multiplexing (WDM) technique can improve transmission capability largely, so 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 and high-speed WDM system, there still exists some problems: (1) bandwidth problem: Conventional C-band (1530nm~1565nm) can't meet the demands of WDM system transmission capability, which need to be widen further. (2) gain-flatten problem: For the energy level structure of Er3+, property of EDFA gain has its inherent disadvantage: EDFA gain is different vs wavelength, in other words, its gain spectrum is not ideally flat, so the output signals will be different if the input signals have the same power. This effect will accumulate as several EDFAs are used in the long-distance WDM system, in the end, the signal will have low Signal-to-Noise. (3) gain-clamped problem: This problem 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. In this paper, theoretical research on above problem was presented, in order to give a theoretic instruction of utilizing EDFA in WDM system.In this paper, firstly, kinds of optical amplifiers which were used in optical communication realm were introduced; emphasis was laid on the development history and research progress of EDFAs recently. Secondly, the existing EDFA models were theoretically studied; especially the Saleh and Giles models were deduced. And the shooting arithmetic about Giles model was discussed. Thirdly, the characteristics of C-EDFA and L-EDFA were simulated and discussed by using the Giles model. Moreover, the intrinsic flat gain property was investigated. Gain spectrum is flat on optimum population inversion level (~40%). And the problem of L-EDFA low pump conversion efficiency (PCE) was solved by using a fiber loop mirror (FLM) at the foreside of the L-EDFA to reflect the backward ASE. The PCE increase of 8.76% compared with the conventional structure. Fourth, gain-clamped C-EDFA and L-EDFA were theoretically investigated. Finally, the thesis was concluded and the further direction was brought.