A double-clad AsSe2-based photonic crystal fiber possessing ultra-flat near-zero dispersion has been introduced, here to achieve flat-top and coherent supercontinuum generation at Mid-IR range. Also, the required conditions to obtain flat-top, broadband, and coherent supercontinuum generation have been discussed based on the systematic study carried out here, by GNLSE regarding the input pump pulse characteristics and the dispersion regime. The proposed photonic crystal fiber in this study, presents nearly-zero all-normal dispersion of about D ∼ −3.4 ps(nm.km)−1 corresponding to minimum group velocity dispersion at 6.9 μm. For the pump pulse with λ = 6.9 μm, time duration of T = 50 fs, and low peak power of P = 1 kW, a coherent flat-top supercontinuum generation has been realized with the span of 4.14 μm and 4.97 μm at 8 dB and 20 dB levels, respectively. Moreover, a figure of merit covering the essential characteristics of supercontinuum generation spectra (bandwidth, coherency, and flatness) has been introduced to compare the performance of different structures. It has been shown that β 2 tailoring with near-zero and flat characteristic is essential to achieve higher figure of merit.

Slot waveguides comprised of Ge 23 Sb 7 S 70 and Si with and without graphene are considered for super-continuum generation in the mid-infrared range. The dispersion characteristics are optimized for the proposed waveguides comprised of Si and Ge 23 Sb 7 S 70 chalcogenide as the core and cladding, respectively with and without graphene sheets embedded in the proposed structure. The proposed waveguide without graphene possesses all-normal dispersion and the super-continuum spectra with bandwidth of 1.75 µm is obtained for a pump with wavelength of 2 µm, peak power of 100 W, and time duration of 50 fs, at 20 dB level. Also, the total length of the waveguide is 8 mm. The optimized structure with three graphene sheets presents flat anomalous dispersion and the super-continuum spectra with bandwidth of 3 µm is obtained for a pump with wavelength, peak power, and time duration of 3 µm, 7 mW, and 50 fs, respectively at 10 dB level. It is demonstrated that the proper dispersion region for super-continuum generation depends on the sign of Kerr-index of the nonlinear material. The proposed waveguides are highly compatible with fabrication technologies for mid infrared applications. IntroductionRecently, super-continuum generation (SCG) has attracted a great deal of interest in the design of broadband optical sources. [1] SCG originates from the interaction between diverse nonlinear and linear effects. The nonlinear effects include self-phase modulation (SPM), [2] cross-phase modulation, [3] soliton formation, [4] soliton fission (SF), stimulated Raman scattering, [5] four-wave mixing (FWM), [6,7] and the main linear characteristics are the dispersion and loss. SCG is applicable in optical coherence tomography, spectroscopy, high-precision frequency metrology, and pulse