Supercontinuum Generation In Photonic Crystal Fibers With Two Zero-dispersion Wavelengths

Photonic crystal fibers(PCFs) have some unique characteristics compared with the conventional fibers, such as endlessly single mode, rich optical nonlinearity and unusual dispersion, which make PCFs have exhibited wider application potentials in the field of optical communication. Supercontinuum generation(SC) is the most exciting nonlinear optical phenomena of the numerous applications in PCFs since it has wider applications both in scientific research and in practical engineering. Therefor, SC has become a research hotspot in recent years. In this thesis, the SC generation in PCFs with two zero-dispersion wavelengths(ZDWs) is studied. The main research results are listed below:Firstly, the propagation of the optical pulse and the SC generation in PCFs are very complicated, so many high-order linear and nonlinear effects can't be neglected. Since numerical simulation is a crucial research method, the computer program is developed which can simulate the process of nonlinear propagation of optical pulses and SC generation in PCFs with two ZDWs based on the generalized nonlinear Schr?dinger equation.Secondly, the law of SC generation is revealed in two types of PCFs which have different structures by using the numerical simulation method. For the PCFs with two widely lying ZDWs(570nm), it is shown that soliton self-frequency shift(SSFS) has little influence and the spectral broadening is mainly determined by the self-phase modulation and the amplification of the dispersive waves(DWs) in the initial propagation, but stimulated Raman scattering restrains the generation of dispersive waves. During the further propagation, high-order effects play a major role. SSFS makes an amount of energy transfer from anomalous dispersion region to normal dispersion region, and the spectrum width begins to saturate. For the PCFs with two closely lying ZDWs(170nm), spectral broadening mainly depends on self-phase modulation and four-wave mixing. Since anomalous dispersion region is narrower than that of the PCFs with two widely lying ZDWs, most energy has been transferred to the normal dispersion region in a shorter distance and also their saturated lengths of the spectral broadening are shorter.Thirdly, by using the numerical simulation method, the impact of initial noise and initial frequency chirp on SC generation is investigated. For the case of initial noise, the physics model of initial noise is obtained by using the standard linear stability analysis. The results show that initial noise increases the speed of the breakup of pulse. Comparing with the case of no noise, DWs appear in a shorter propagation distance. During the further propagation, higher-order soliton splits into many fundamental solitons and the noise not only weakens the walk-off effect of soliton, but also suppresses the SSFS, which make the quality deterioration of SC in the region of long wavelength. When considering the case of initial frequency chirp, nearly all the energy between the two ZDWs can be transferred to the normal dispersion region from the region within the two ZDWs provided that the initial positive chirp is large enough. In contrast with the complicated and irregular SC generated by negative-chirped pulse, the SC generated by positive-chirped pulses are flatter and much more regular.