Polarization Satability Analysis Of Nonlinear Coherent Coupling By Using Poincare Sphere In A Weakly Birefringent Fiber

Cross-phase Modulation leads to the nonlinear birefringence, which arises the polarization instablity. As a result of the instablity, very small variations in either the input power or the input polarization to the fiber result in large changes in the output polarization. The phase diagram method and numerical simulation are introduced to analyse the polarization instability of a nonlinear coherent coupling in a weakly birefringent fiber.The whole text can be devided into tree part:preface, main body, conclusion. It introduced the meanning of topic selection and previous research in preface. Main text have three chapters:in firt chapter, we derived the nonlinear coherent coupling equation from the basic optical equation under the Quasi-monochromatic and the slowly-varying-envelop approximationm. In second chapter, Poincare sphere is introduced and the Polarization evolution in poincare sphere is demonstrated. In the third chapter, Nonlinear polarization evolution for different birefringence regions in a weakly birefringent fiber is analysed by using Poincare sphere. This is derived by quoting the Stake’s parameters formalism in the nonlineaer coupled differential equations for the nonlinear coupled-mode; critical power for polarization instability is obtained by using geometrical methods. Meanwihle when two Constant of motion satisfy R=г, the evolution of polarization move towords instability. In conclusion part, we summarized the polarization instability analysis of the weakly birefringent fiber.