Investigation Of Double-Clad Erbium-Ytterbium Co-Doped Fiber Amplifier

Application of optical fiber amplifiers has played a great role in the development of all optic communication, with the emergence of new technologies, fiber amplifier industry has undergone tremendous changes. At present, the development trends of optical fiber amplifier are high power, broader gain bend, lower noise and multiple function OFAs. 1550nm-band low-loss high-power fiber amplifiers have impressive applications in DWDM, FTTH, CATV optical transmission systems and optical space communications, the study on this field has become the hot spot at home and abroad. Er/Yb co-doped double-clad fiber amplifier(EYDCFA) is based on cladding pumping technology, where high-power multimode pump light can be easily coupled into the inner cladding of double-clad fiber, which can greatly increase the pump absorption efficiency; Yb doped solution can resolve the concentration quenching caused by high concentration of Er in traditional EDFAs, it also helps in the enhancement of the effective pump absorption efficiency, so, Er/Yb co-doped double-clad fiber amplifier is able to achieve 1550nm-band high-power output.In this paper, I have done some research and comparison on the clad pump coupling method of double-clad fiber(DCF) in order to decide the pump coupling method of the experiment, both theoretical and experimental studies on the performances of Er/Yb co-doped double-clad fiber amplifier are my major job. The theoretical model of EYDCFA is established, and a forward pump using taper coupling side-pump method EYDCFA is designed and established, the performance of the EYDCFA is tested and analyzed. The works done in this paper are as follows:Firstly, the current development trend of optical fiber amplifier is discussed, the application of high-power fiber amplifiers in DWDM systems, CATV and high-power distribution system of HTTP is analyzed, the current double-clad fiber amplifier development is introduced.Secondly, the structure and working principle of double-clad fiber is briefly introduced, several pump coupling methods of double-clad fiber that has been broadcasted is introduced and compared. According to the results of comparing and the current experimental condition of the laboratory, taper coupling method is chosen for the establishment of the experiment.Thirdly, theoretical analysis and simulation on EYDCFA is made. According to the energy transfer relationship of Er/Yb co-doped system, the rate equation and the equations of level populations during steady-state in EYDCFA is obtained. The power transfer equation, together with the above-mentioned results, is numerically calculated with the use of fourth-order Runge-Kutta method. According to the results of numerical iteration, plotted and analyzed the curves about the relationship between the fiber amplifier gain characteristics and fiber length, pump power, signal power. For the first time, the relationship between optimize fiber length and the pump power, signal power is studied, the results of which can do help to choose the proper optical fiber length in accordance with the circumstances and conditions of the workplace, it can also help with fiber length optimization.The relationship between amplifier gain characteristics and doping concentration ratio of Yb and Er ions is studied, although the ratio of the doping concentration can not be changed, the results have certain reference value on the preparation and production of Er/Yb co-doped fiber.Finally, a forward pump using taper coupling side-pump method EYDCFA is designed and established; the performance of the EYDCFA is tested with the use of tunable laser light source as a signal input, and the system characteristics of the amplified spontaneous emission (ASE) and gain performance is tested. According to the testing results, an analysis on the effects of pump power, the signal optical power, optical wavelength of the signal on the amplification properties of the system is made. The amplifier noise performance-the noise figure is calculated using linear interpolation method. With the use of wide-spectrum light source, the amplifier's small-signal gain curve is measured, calculated and plotted according to the simple methods proposed by Nankai University. Several particular phenomenon (Green light, 1060nm broadband fluorescence, self-excitation at ASE peak wavelength) found in the experiment is described and the causes of the phenomenon is analyzed.