Design And Performance Analysis On Wide Band Distributed Fiber Raman Amplifier

Distributed Fiber Raman Amplifier (DFRA) magnify light signal directly by using transmitted fiber as gain medium. The wider gain bandwidth and better flatness can be obtained by choosing pumping wavelength and power of pumping laser suitably. DRFA can perform an important function in DWDM, because of its lower noise factor and higher optical signal noise ratio. The optical fiber transmission length can be extended and transmission cost can be reduced. The DFRA researched in this paper is supported gravely by science and technology item "Research and manufacture on Distributed Fiber Raman Amplifier" of zhejiang province. It includes the measurement of Raman gain spectra in DCF and G652, new design and set up of S+C band DFRA, measurement and analyze of performance and noise. The ideas of lowing down noise and improving performance are put forward.In chapter one, the basic principle of FRA is introduced. The history and actuality of development on FRA are reviewed. The research direction and keystone are decided.The measurement of gain spectra in FRA is researched in chapter two. A new method of measuring optical fiber gain coefficient is put forward. Gain coefficient is a key factor of designing and manufacturing DFRA . It is obtained by division on spontaneous Raman scatter light signals under higher and lower pumping laser power. This result is almost consistent with that measured by stolen. Comparing to small signal gain method, this way is more fast and stable. The relation of gain and pump power can be measured expediently.In order to obtain wider bandwidth and better flatness, a program of optimizing and designing FRA is accomplished according to the reciprocity of light and fiber medium in chapter three. The gain, bandwidth and flatness are optimized by Effective shooting algorithm on the basis of Runge-Kutta arithmetic in S+C band. The test scheme is decided about pumping direction, wavelength and laser power.In chapter four, a DFRA working in S+C band is set up in according to the simulatiing design result. Its transmission span is lOOkm.The gain, bandwidth and flatness are consistent with the optimized result in a less pumping laser power of some hundreds mW, but they are different in a bigger pumping laser power, such as 1500 mW.This is because the bandwidth of pumping laser affects on the performance of FRA. So the variance of gain flatness is adjusted by geometry compensated balance idea. The gain, bandwidth and flatness meet the needs of item supported gravely by science and technology item of zhejiang province finally. The transmission performance of DFRA are measured and analyzed in detail, simultaneity. The reciprocity of pump and pump, pump and signal, signal and signal is analyzed. This disturbs the singal in multi-channel signal transmission.A kind of new method designing DFRA(dynamic extraction designing way) are firstly put forward for three wavelength pumping framework in chapter five. The pump powers of three wavelengths can be found quickly and conveniently for DFRA with certain gain and flatness, and the way is not reported by domestic and foreign. This way can extend to design multi-wavelength pumped RFA, and design results can be obtained.In chapter six, noise factor (NF) is measured, analyzed and discussed. ASE noise and influence on RFA system are researched especially. The NF and OSNR are measured. The influence on OSNR by signal and pumping mode is analyzed. The bi-direction pumping mode is the preferred pump scheme on the basis of improving OSNR. The effect on OSNR of RFA by coupling and isolator is studied. Some mending ideas are pointed out. Pump source relative intensity noise and double Rayleign back-scattering are analyzed, This can provide guidance idea improving the characteristics of RFA finally.A brief sum-up for this dissertation is presented in chapter seven. The keystone and innovation are put forward. Furthermore, the study trend for FRA is also discussed.