Study On Nonlinear Management In Optical Fiber And Nonlinear Optical Coupler

With the development of demand, many characteristics such as fast transmissionspeed, large capacity and long distance are required in optical fiber communicationsystem. However, that many nonlinear optical effects exist in optical fiber constraintsthe increase of the transmission distance and meanwhile significantly affects fibertransmission rate. These nonlinear effects directly influence on transmissionperformance of optical fiber communication system. Many researchers, based on theidea about dispersion management, began to focus on non-linear managementtechniques, namely, how to make rational and effective use of the nonlinear opticalproperties to improve the transmission performance of optical communication systems,and how to use non-linear management techniques, on the other hand, to suppress thenon-linear effects which adversely affect communication systems.This dissertation studies the applications of nonlinear management techniques inoptical fiber communication system. With light pulses in the optical fiber transmissionas the research object, it focuses on how to use management techniques to achievenon-linear optical pulses in optical fiber transmission control, and furthermore delvesswitching characteristics and coupling characteristics of nonlinear optical fiber couplers.The main results are shown as follows:(1) By variational method, we have studied the performance of light pulses inoptical fiber transmission. And with nonlinear management research and analysis oftransmission characteristics of optical pulses, we have derived the relationship betweenthe dispersion coefficient, the initial pulse width and non-linear coefficient in the case ofthe same pulse width. Moreover, we have firstly studied the transmission characteristicswith fifth-order nonlinear management, which indicates that the fluctuations of thepulse width are greatly reduced, even almost constant.(2) By the method of moments, the evolution equation of the width, frequency,phase and center of ultra short pulses in the cases of varying transmission distances isderived in optical fiber transmission. After analysis of the influence of the Raman effectand self-steep effect on pulse width and frequency, it is firstly found that non-linear effects such as Raman effect and self-steep effect are to be greatly suppressed bynon-linear management.(3) By the method of moments, the evolution equation of the separation distance,width, and frequency in the cases of varying transmission distances is firstly derived ininteraction of two pulses. In addition, the effect of the pulse spacing and non-linearcoefficient on the interaction of the two pulses has been studied.(4) With light pulses in optical fiber transmission and optical pulse interactionscontrolled by the combination of dispersion management and nonlinear of managementfirstly, it turns out that the system transmission performance can hardly decline andalmost no change in pulse width is observed even if the transmission distance increases.Furthermore, the interaction of light pulses is greatly reduced, even to zero. And evenwith less pulse spacing and more transmission distance, the light pulse has almost nointeraction.(5) By the variational method and the split-step Fourier transform method, we havestudied how to use the core's nonlinear coefficient, gain and phase difference of theinput pulses to control the switching and coupling characteristics of nonlinear opticalfiber couplers. It is found that high switching efficiency and lower threshold power canbe achieved between Asymmetric nonlinear coupling and the symmetric nonlinearcoupler. Not only can the switching characteristics of a coupler be improved by gainand phase control, but also different output coupling ratio is available, which can helpproduce variable couplers. Finally, we studied the influence of the nonlinear coefficientand gain of the core on multi-core nonlinear fiber coupler output characteristics.This work was supported by the National Science Foundation for DistinguishedYoung Scholars of China (Grant No.60588502) and the National Natural ScienceFoundation of China (Grant No.60877033,60607005).