Study Of Transmission Characteristics For Ultrashout Pulses In Doped Optical Fiber

In the recent years, the fiber-optical communication has developed rapidly. However, there are many issues should be researched in the amplifier transfer, such as the dispersion effect of the gain medium, the nonlinear effect of gain saturation, as well as the impact of the media gain-bandwidth optical pulse. These factors make the pulse shape and spectrum changes, affect the transmission quality of the pulse, and can’t meet the amplifier design requirements. So it’s very important to study the transmission characteristics of the light pulse in the doped fiber amplifier.When the gain bandwidth of the medium is much larger than the pulse width, the nonlinear Schrodinger equation can accurately describe the optical pulse amplification characteristics in the doped fiber amplifier. By solving the transport equation and approximating the medium gain to parabolic, influence of the nonlinear effect and dielectric dispersion to the light pulse amplification is discussed. The results showed that the optical pulse width is spread in the frequency domain and time domain by nonlinear effects and the group velocity dispersion. With the increase of transmission distance, the pulse width may be close to or greater than the bandwidth of the gain medium, the gain narrowing effect and gain saturation effect become increasingly obvious and the light pulse becomes deformed in the doped fiber amplifier. Thus the previous approximation and transmission equation is no longer applicable, and then it should be properly modified and optimized. The results of numerical simulation show that the gain saturation effect makes the enlarging level of leading and trailing edge of the broadband inconsistency and the pulse becomes deformed. According to the corresponding calculation results, the measures are adapted to avoid the lower pulse transmission quality for the design of the fiber amplifier.The spectral characteristics are also important in the high power ytterbium doped fiber amplifier (YDFA). According to the absorption and emission cross section, amplification characteristic of the signal light with1053nm wavelength pumped by the pulse with wavelength of910nm and975nm is researched. By ways of the transmission model of high-power doped Yb3+fiber amplifier and numerical, we discuss the distribution of ytterbium doped fiber amplifier pump power, the amplifier gain, the length of optimum gain fiber, pump threshold power, the distribution of inverted population density and the signal power. At the same time, ASE distribution and pulse saturation amplification characteristics of the amplification are researched, and the results are consistent with the former.