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Study On The Propagation Properties Of Optical Solitons In The Nonlinear Schroedinger Models With Variable Coefficients

Posted on:2006-06-08Degree:MasterType:Thesis
Country:ChinaCandidate:Y GuoFull Text:PDF
GTID:2168360152989060Subject:Communication and Information System
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The phenomena of soliton has been seen in many fields. Since soliton wave was found in the 19 century, the theories of soliton always have been an important research aspect in many fields, such as math, physics and communication. The generating of the optical soliton is a very graceful kind of physical process, which is a balance of fiber dispersion and self phase modulation (SPM). Optical soliton is not only an important research aspect, but also it has very important application foreground, which will be the new mold of optical communication and high speed full-optical switch. In the paper, the basic theory of fiber soliton, the fundament of optical fiber soliton communications and its development are introduced in detail. On the theoretic basis that soltion pulse propagation meets the nonlinear Schrodinger equation in fiber, the propagation characteristics of soliton pulse are studied. The main contents of the paper are as follws:First, the modulation instability of the optical soliton pulse is studied in the condition of decreasing dispersion fiber with 3 kinds of group dispersion profiles. The properties of MI gain spectrum are found to vary as the change of the group dispersion profile and self-steepening parameter. The range of gain spectrum is narrowed and the growth rate of amplitude is slowed down by self-steepening. The ilt is also found that the gain spectrum width will be widest when the pump power, the propagation distance and the fiber loss are at the certain value. Moreover the Gaussian profile is the optimum profile for achieving better modulation instability.Second, modulation instability of electromagnetic waves in a birefringent fiber with the four different kinds of group dispersion profiles is investigated by the coherently coupled nonlinear Schrodinger equation. The properties of MI gain are studied. The results show that the gain spectral width varies as the type of the group dispersion profile changes. When there is a certain relation between fiber dispersion parameter and fiber loss, the spectral width is discovered simply relevant to transmitted distance for the type of exponential, and the curve of spectral widthversus transmitted distance has a vale for the type of linear and Gaussian, but a firstly broadening and then a gradual decrease are gotten for the type of hyperbolic.Finally, the nonlinear Schrodinger equation with variable coefficients is analyzed by means of the projection matrix method. An exact analytical solution is obtained, which clearly shows how the variable fiber dispersion, nonlinear, and loss coefficients affect the propagation of ultrashort pulses. The obtained solution is used to analyze the propagation properties of ultrashort pulses in dispersion- decreasing fibers. It is found that the ultrashort pulse can realize stable soliton transmission if the fiber dispersion has some certain profiles related to the fiber loss and nonlinear properties. A small variation in the dispersion has a similar perturbative effect to an amplification or loss. The exponentially decreasing dispersion fiber is studied exemplificatively to demonstrate the obtained results. Numerical simulations confirm the analytical solution.
Keywords/Search Tags:optical soliton, NLS of with variable coefficients, decreasing dispersion fiber, modulation instability, the exact solution of soliton
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