Study On Output Characters Of Fiber Amplifiers Operating Near 980 Nm

In recent years, the output power of fiber lasers has been increasing rapidly. However, one of the main factors that limit the further the expansion of fiber laser is the low brightness of the laser diodes(LDs) pump source. The use of tandem pumping technology provides high brightness pump source. The 980 nm fiber laser, which is an effective tandem pump has drawn much attention. Besides, in the application of blue light lasers, 980 nm fiber lasers also have great value. In this paper, we focus on the 980 nm fiber amplifier and study its characters thoroughly, aiming to find the efficient way to suppress the parasitic ASE and thus improve the output property. The main contents are as follows:Considering the energy level and spectrum character of Yb3+ icon, the basic theory of Yb-doped fiber laser is discussed. The rate equation which describes the dynamic process for both oscillator and amplifier is given. Detailed study is carried out about the 980 nm fiber amplifiers through numerical simulation and experiment. The following conclusions are obtained:(1) The proper choice of both the length of the active fiber and the dopant concentration is beneficial to the fully-absorption of pump power and can prevent the re-absorption of 980 nm signal power. To some extent, if the product of length of the active fiber and the dopant concentration is constant, the output signal power is certain.(2) In the region of 980 nm, light with longer wavelength has better emission property. The power of the seed light should be large enough to fully extract the gain of the amplifier. If the seed light contains the ASE near 1030 nm, the absolute value of ASE power has a greater influence on the output of 980 nm fiber amplifiers. For it can cause strong ASE emission. When the ASE suppression is constant, the increase of seed power may cause the output efficiency decrease.(3) The output signal power increases with the ratio of core to cladding diameter. With the same core to cladding ratio, the smaller the inner cladding diameter, the higher output signal power.(4) The 980 nm fiber amplifier systems need sufficient pump light to ensure the population inversion of about 50%. The pump threshold increases with the length of active fiber exponentially approximately. The point when the slope ratio increases rapidly is the optimum active fiber length. The pump threshold is not sensitive to the core diameter. However it increases rapidly with the cladding diameter monotonicly.(5) In the experiment, the transverse distribution of seed light and the pump light in the active fiber has a great influence on the output properties of 980 nm fiber amplifiers with large core to cladding ratio. In order to increase the output properties, it is suggested that the seed light and the pump light be fully combined.