Research For Sbs Threshold Enhanced In Single-mode Fiber

Among the nonlinear effects, stimulated Brillouin scattering (SBS) is the most easily generated in optical fiber due to its low threshold power. SBS can change the energy distribution in the fiber and lead to the signal damaged when it happens. At the same time, it will cause crosstalk in bidirectional DWDM systems, resulting in the distorted signal. When there is a strong SBS phenomenon in fiber, the most of the input power will converted to the backward Stokes, producing a giant pulse with high power. And it can cause some damage to the fiber end and light source and hinder the transmission of the signal. So it is important to research the SBS in signal mode fiber. In this thesis, we made a systematic study about the SBS in SMF. The contents are as follows.(1) The physics mechanism and quantum explanation of SBS in fiber is discussed in the dissertation. The basic characteristics are also introduced, especially the threshold power of SBS.(2) The various factors which have influence on the threshold power are analyzed in detail. And the methods of the improving SBS threshold for every factors are given from the point of view of the waveguide and the doping, especially the method about the acousto-optic effective area.(3) The experiment system for measuring SBS threshold is designed and built up. And the thresholds for single mode fiber such as G.652 and G.657 at room temperature are measured under continuous wave. From the spectra of SBS and the experimental data which are processed by using polynomial fitting and spline fitting method, we draw a conclusion that ? ?0.01 is best for SBS threshold power definition in single-mode fiber communication system, which has a good agreement with the popular view. At the same time, the peak Brillouion gain of some test fibers were given, and the order of magnitude is 10-11.(4) We use the MATLAB software to do the SBS numerical simulation in fiber. A novel approach of making large effective area fiber with higher threshold for SBS using Ge/F co-doping in the fiber core was proposed. The increased SBS threshold is achieved by reducing the acoustic-optic overlap integral while keeping the optical refractive index profile with a step structure. And the designed high threshold fiber was made by the PCVD method. We found that the designed fiber yielded about 6.77dBm higher SBS threshold than the conventional single mode fiber G.652 with the same length.