Research On The Characteristics Of The Second-order Distributed Raman Amplifier

Continuous progress of the fiber transmission technology makes the information society has rapid development,the usage of dense wavelength division multiplexing(DWDM)which has the larger capacity,longer distance,higher rate makes the fiber transmission technology a new height.At the same time,the rapid growth of communication services and the high quality requirements of optical transmission systems are improving the performance of optical amplifier.Due to the limited bandwidth and bad noise performance,traditional erbium doped fiber amplifier(EDFA)cannot fully meet the requirements of optical transmission system,but fiber Raman amplifier(FRA)has the advantages of wide bandwidth,high gain and low noise,and is playing an important role of the optical amplifier.Distributed Raman amplifier(DRA)is not only more able to fully demonstrate the advantages of broadband,but also can effectively reduce the nonlinear effects.However,first order optical fiber Raman amplifier is still limited.In order to meet the requirements of higher communication quality,second order DRA or higher order DRA is becoming a hot research topic.Second order DRA has higher gain,can obviously optimize the optical signal to noise ratio.Using the second order pumping scheme can effectively improve the performance of RFA,so it is more suitable to the unrepeated long-distance transmission system.In this thesis,second order distributed Raman amplifier is studied.It analyzes the gain flatness optimization method of second order DRA and the relationship of second order DRA's noise characteristic and the ratio of second order pump.The main contents can be summarized as follows:(1)Firstly,the background knowledge of the Raman amplifier is introduced,and the significance of the research of the two order Raman amplifier is introduced,too.Then it summarizes the domestic and foreign research situation on this subject.(2)After the concept of Raman scattering is put forward,we use the method ofquantum theory to explain it,followed by the classic theory to explain it.We have a brief description of the second order Raman pump technology and structural solutions.From the above theoretical knowledge,the second order Raman transmission equation and its solving method on different conditions are given gradually.These lay a theoretical foundation to the analysis of second order Raman amplifier gain flatness and noise characteristics.(3)Several factors are introduced which can affect the Raman gain.Through the analysis on the Raman gain spectrum,it is necessary that Raman gain flatness is optimized of necessity.Then,genetic algorithm and the second step optimization algorithm of second order DRA are introduced.(4)It describes the noise source of second order DRA.the concept of effective noise figure is put forward to measure the noise of distributed Raman amplifier.After that,the relationship of second order DRA noise characteristic and the ratio of second order pump are observed both experimentally and theoretically.(5)The summary and prospect of the whole paper are briefly outlined,and the development of the subject research is predicted.