Highly coherent supercontinuum in the mid-infrared region with cascaded tellurite and chalcogenide fibers

We numerically investigate two-step supercontinuum (SC) generation using cascaded tellurite and chalcogenide fibers with all-normal group velocity dispersion pumped by a femtosecond laser at 2 mu m. The optimized tellurite fiber is a hybrid microstructured optical fiber with a core surrounded by 12 rods. It has flat normal chromatic dispersion from 2 to 5 mu m. The chalcogenide fiber is a double-core fiber with flat normal chromatic dispersion from 4 to 10 mu m. The output SC spectrum from the best candidate fibers spans from 0.78 to 8.3 mu m with coherence of unity all over the spectrum. Such high coherence pulse with broad spectrum will be valuable for many applications in tomography, ultrafast transient absorption spectroscopy, etc. The proposed fiber structures are all-solid and are feasible for fabrication with the common rod-in-tube method. This implies that two-step SC is a potential way to obtain broad, highly coherent SC in the mid-infrared. (C) 2018 Optical Society of America