Chalcogenide Ge20Sb5Se75 photonic crystal fiber with seven air-hole rings for ultraflat mid-infrared supercontinuum generation

Supercontinuum (SC) generation in solid-core circular photonic crystal fibers (PCFs) made of Ge₂₀Sb₅Se₇₅ is numerically analyzed. A large core is projected to increase light coupling efficiency into selected PCFs as well as raise coupling to standard silica fibers. High nonlinear coefficient and near-zero flat dispersion allow ultraflat SC spanning 1.5–4.6 μm in an all-normal dispersion regime. This requires 3 kW of peak power with 180 fs of pulse duration. The fiber with one zero-dispersion wavelength (ZDW) generates SC bandwidth in the range of 1.54–7.39 μm at 3.5 μm using peak power of 10 kW. For the same input power, the SC spectral covers from 1.39 to 7.36 μm in 10 cm of fiber with two ZDWs. These are wider SC bandwidths than those of previous chalcogenide fibers reached with lower peak powers. Therefore, the proposed Ge₂₀Sb₅Se₇₅ PCFs are excellent candidates for the broadband ultraflat mid-infrared SC spectra used in high-speed nonlinear imaging and frequency measurement.