Influence Of Dispersion Slope On Soliton Spectral Tunneling In Photonic Crystal Fiber

The generation of supercontinuum spectrum is a physical phenomenon of pulse spectrum broadening,which is due to the ultrafast pulse transmitted in nonlinear medium is influenced by the medium dispersion effect and abundant nonlinear phenomena.In recent years,the advent of photonic crystal fibers has opened up new opportunities for the study of supercontinuum.Because of the controllable structural characteristics of photonic crystal fibers,we can obtain multiple zero-dispersion wavelengths,which facilitates the study of soliton spectrum tunneling(SST)effects in the generation of supercontinuum.The physical phenomenon of tunneling occurs when femtosecond solitons in the spectral domain pass through a locally non-uniform group velocity dispersion(GVD).The SST effect can be understood as: when there is a dispersion barrier,i.e.,a normal GVD regime is sandwiched between two abnormal GVD regimes in the fiber,and the soliton phase matching condition is met,the optical soliton in the short-wavelength abnormal GVD regime passes through the middle normal GVD regime(that is,the barrier region)in the form of dispersive wave,and then forms a new soliton state in the long-wavelength abnormal GVD regime.In this paper,the influence of the dispersion slope on the generation and evolution of the SST effect in three zero-dispersion wavelengths photonic crystal fibers is numerically studied based on the generalized nonlinear Schrodinger equation.The main results include:(1)The generation conditions and specific process of the SST effect in the photonic crystal fiber are analyzed.First,the Maxwell equations are derived to obtain the basic transmission equation of the optical pulse signal in the optical fiber,i.e.,the generalized nonlinear Schrodinger equation.Then the equation is solved using the fractional Fourier algorithm.And a cross-correlation frequency resolution optical switch technology for the time-frequency analysis of the optical pulse is also introduced.The transmission characteristics of solitons and dispersive waves,and their complex interactions are analyzed through the establishment of a numerical model.At the same time,the conditions and specific processes of the SST effect are also analyzed in detail.(2)The characteristics and laws of the dispersion slope affecting the SST effect are studied.By separately pumping femtosecond pulses in a set of three zero-dispersion wavelengths photonic crystal fibers with different dispersion slopes,the changes of the SST effect are compared from the perspective of time and frequency domains.Meanwhile the energy changes of each spectral component during the process of soliton tunneling are also analyzed.It is found that a large dispersion slope is not conducive to soliton tunneling,and leakage dispersive wave will occur.Its short-term energy storage property may be applied to the field of communication security.However appropriately reducing the dispersion slope can promote soliton tunneling,which is beneficial to obtain a wider supercontinuum.