Study On Er/Yb Co-doped Fiber Amplifier

Fiber amplifier is one of the key components to realize all optical fiber communication system. Erbium-doped fiber amplifier is applied widely just now. But Erbium-doped fiber amplifier can not provide adequate pump Absorption via short fiber, the structure is very complex because of the long gain fiber, and the efficiency is very low. Doping Yb³⁺ in Erbium-doped fiber is an effective method. Yb³⁺ has bigger peak value absorption section (800-1100 nm), it can offer higher gain, so in this way the efficiency and gain stability of the amplifier can be improved greatly. Considering that the ytterbium ion works only as a tool to transfer energy, the superior characteristic of Erbium-doped fiber amplifier, such as: higher gain, lower noise, bigger output power, wider working frequency spectrum, less insertion loss and 1550nm working wavelength-the low loss area of fiber, is reserved.At first, this paper introduced the basic structure of optical fiber amplifier, at the same time analyzed the Erbium/ytterbium-codoped fiber amplifier theoretically, and studied the Erbium/ytterbium-codoped fiber's gain characteristic in detail.Secondly, designed a small-scale scheme of Erbium/ytterbium-codoped fiber amplifier with forward pumping, the pumping wavelength is 1064nm. Then analyzed the function and performance of the fiber components in this structure, also adopted optical fiber amplifier design software to optimize the length of optical fiber and select fiber components.In the end, the amplifier designed was tested in all aspects.The experiment adopted Nd: YAG solid laser to pump 4.2m Erbium/ ytterbium-codoped fiber, the Doping Concentration ratio is 45:1, through a 99:1 coupler, then via the 1064/1550nm Wavelength Division Multiplexing, 99 percent of the 1064nm pump light is coupled into the fiber, after absorbing energy, Yb³⁺ transferred it to Er³⁺, as a result the erbium ion is stimulated and populationInversion is formed. The 1% output of the coupler is used to monitor the pump power in real time. The signal light enters in the fiber through the same WDM, inducing stimulated emission and getting amplified.Studied on the gain characteristic of the amplifier, got 30nm flat gain spectral width during 1530-1560nm. As for 1550nm signal light, when the pump power is lOOmW, small signal gain is 27.95dB, saturation output power is 8.36dBm. The output power of ASE (amplified spontaneous emission) approximates to increase linearly with the increasing pump power, the threshold pump light power is 20mW. Within the experimental test range, the maximal ASE output power reaches 13.34mW, output power stability is ±0.02dB, concerning the pump light power, the slope efficiency of output light power is 8.9%, at the same time got low noise intensity. Adopted wavelength tunable erbium-doped fiber laser as signal source, the output wavelength can be tuned within 1530-1560nm continuously, signal power is OdBm, when pump power is 60mW, the output power every 0.8nm in this wavelength area is 8.1dBm, the gain variation is less than 0.5dB, it is obvious that its has better flat characteristic.The main features of this paper are:1. The amplifier introduced in this paper adopts Er 3+/Yb3+-codoped fiber as gain medium, Yb3+ as sensitizer, Yb3+ not only has wider absorption spectrum and emission spectrum, but also can transfer energy to Er3+ quickly, in this way, 1550nm wavelength area gets amplified. With the doped Yb3+ the fiber length can be shortened effectively.2. The structure that used 1064nm Nd: YAG solid laser to pump Er3+/Yb3+-codoped fiber amplifier is put forward. This paper also tested the important coefficients such as: gain coefficient, saturation output and so on. The result is comparatively perfect, and there is no same report.3. The Nd: YAG solid laser used in this paper has higher output power, and its cubage is very small, the fiber amplifier structure is miniaturized, this can achieve the development requirement of future fiber amplifier and fiber laser:miniaturization, integrated.As a conclusion, the amplifier studied in this paper possesses many advantages such as: simple structure, short gain medium, high pumping efficiency, easy to encapsulate, etc. As a new generation relay amplifier in all optical communication network, it has broad application prospects.