Research On Propagation Characteristics Of Ultroshourt Pulse In Microstructured Fiber

With their novel optical properties and potential application, microstructuredoptical fibers become one of the most heated research topics in recent years.Abundant nonlinear phenomena can be generated when the microstructure fiber ispumped by femtosecond pulse. Supercontinuum is one of the most uniquephenomena generated in microstructured fiber, and solitons dynamics plays animportant role in the evolution of the supercontinuum. At the same time, dispersivewave can be produced when solitons fission in microstructured fiber. The interplaybetween solitons and dispersive wave can produce hyperfine supercontinuumstructure.But there is no unified conclusion on the theoretical mechanism of the newphenomenon.The main content of this paper is listed below:In chapter2, based on Maxwell’s equation, the Generalized NonlinearSchrodinger Equation of femtosecond pulse transmission in MOF is reviewed, andthe nonlinear effect in optical fiber system is discussed.In chapter3, two numerical algorithms: Split-Step Fourier Method and FiniteDifference Time Domain are introduced. By means of Split-Step Fourier Method,solitons-split process, blue shift enhanced supercontinuum generation and theevolution of femtosecond pulse pumped exactly at the zero-dispersion wavelengthare simulated; Spatial distribution patterns at the output face of microstructuredoptical fiber are presented by using Finite Difference Time Domain method.Conclusions can be obtained from simulation as follows:(1) Because the pump wavelength is located in the anomalous dispersion region,ultrashort pulse is high-order solitons due to the interplay between anomalous groupvelocity dispersion and self phase modulation. High-order solitons are split intofundamental solitons with different frequency and transmission speed, and thesefundamental solitons are walk-off in the time domain.(2) In the process of solitons splitting, dispersive waves located in the normaldispersion region is radiated, which satisfies a specific phase-matching conditionwith solitons. As the pump power increases, the red frequency located in the normaldispersion region increases moderately while the blue frequency componentincreased dramatically. Soliton fission and dispersive wave is the main reason for supercontinuum generation.(3) When input pulse is launched exactly at the zero-dispersion wavelength, thesecond order dispersion coefficient is zero, and the sign of the third-order dispersionparameters have great influence on pulse evolution: In the case of a positive TOD,blue components experience normal GVD, whereas red components undergoanomalous GVD, and optical solitons are generated by the redshifted components ofthe spectrum. The initial pulse split occurres, the speed of subpulse is slower thanthat of the initial pulse, each component has a time delay, pulse shape is bent, andpump power is associated with the degree of bending; In the case of a negative TOD,the higher frequency experiences anomalous dispersion, and soliton are formed intime domain. Initial pulse split occurres, the speed of subpulse is faster than that ofthe initial pulse.(4) When light waves are restricted within the fiber core, multiple mode aresupported.In chapter4, soliton fission and blue-enhanced supercontinuum are studiedexperimentally. Experimental results are in good agreement with numericalsimulations. Theoretical analysis is proved to be reasonable;the spatialcharacteristics of the output pulses is analyzed.In chapter5, the research contents is summarized, and the research progress oflight bullets is briefly introduced.