A circular photonic crystal fiber(C-PCF)based on As2 Se3 is designed,which has three zero dispersion wavelengths and flat dispersion.Using this fiber,a wide mid-infrared supercontinuum(MIR-SC)can be generated by launching a femtosecond pulse in the first anomalous dispersion region.The simulation results show that the MIR-SC is formed by soliton self-frequency shift and direct soliton spectrum tunneling on the long wavelength side and self-phase modulation,soliton fission on the short wavelength side.Further,optical shocking and four-wave mixing(FWM)are not conducive to the long-wavelength extension of MIR-SC,while the number and intensity of fundamental solitons have a greater effect on the short-wavelength extension of MIR-SC.The generation of optical shocking waves,FWM waves and fundamental solitons can be obviously affected by changing the fiber length and input pulse parameters,so that the spectrum range and flatness can be adjusted with great freedom.Finally,under the conditions of 4000 W pulse peak power,30 fs pulse width,47 mm fiber length,and 0 initial chirp,a wide MIR-SC with a coverage range of 2.535μm-16.6μm is obtained.These numerical results are encouraging because they demonstrate that the spread of MIR-SC towards the red and blue ends can be manipulated by choosing the appropriate incident pulse and designing optimized fiber parameters,which contributes to applications in such diverse areas as spectroscopy,metrology and tomography.
We demonstrate manipulating the interactions of a second-order soliton with a weak probe pulse under the condition of group velocity match and group velocity mismatch(GVMM).During these interactions,the second-order soliton acting as an effective periodic refractive-index barrier leads to the polychromatic scattering of the probe pulse,which is represented as unequally spaced narrow-band sources with adjustable spectral width.In the case of GVMM,almost all the spectral components of the narrow-band sources meet the nonlinear frequency conversion relationship by using the wavenumbermatching relationship due to the robustness of the second-order soliton under moderate high-order-dispersion perturbations,so this case is more conducive to the study of the soliton wells.In addition,different transmission states of a soliton well are demonstrated under different probe pulse properties in the fiber-optical analog of the event horizon.When the power of the probe pulse is strong enough,a dispersive wave can be generated from the collision of two fundamental solitons split from the two second-order solitons.These interesting phenomena investigated in this work as a combination of white-and black-hole horizons can be considered as promising candidates for frequency conversion and broadband supercontinuum generation.
