The generation of a broadband, spectrally flat supercontinuum extended to the mid-infrared with the use of conventional passive single-mode fibers and thulium-doped single-mode fibers pumped by 1.55 μm pulses

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Flatly broadened supercontinuum (SC) generation spread toward the mid-infrared region is achieved in telecom-grade passive fibers (SMF-28) as well as in single-mode thulium-doped fibers pumped by 1 ns pulses at a wavelength of 1550 nm. Using only a piece of single-mode fiber (SMF) as a nonlinear medium the SC spread from ∼1300 to 2500 nm with an output power of up to 2 W. A spectrum flatness variation below 5 dB in a span of 640 nm (from 1.6 to 2.24 μm) and a corresponding spectral density of ∼1.1 mW nm −1 were obtained. Using a single-mode silica Tm-doped fiber, the SC cut-off wavelength was extended to 2.65 μm. For this case, broadband mid-IR radiation with a <5 dB spectral flatness in the wavelength interval ranging from 1.95 to 2.51 μm (spectral span of 560 nm) was demonstrated. The output average power was over 1 W out of which ∼85% was in a band of >1.9 μm, which is, to the best of our knowledge, the highest average power of an SC generated directly from a single-mode Tm-doped fiber.