Octave-spanning Infrared Supercontinuum Generation in a Graded-Index Multimode tellurite Fiber

High-power mid-IR supercontinuum generation has attracted significant interest in the past decade due to the potential diverse applications in this spectra region ranging from molecular finger printing [1] , absorption spectroscopy, non-invasive imaging [2] and atmospheric LIDAR [3] . Despite many reports of SC generation in the mid-infrared using various fibers made of different materials, there are still important aspects to address for generating sources in the mid-infrared with performance similar to that of supercontinuum in the visible-near infrared, and in particular in terms of power spectral density. The main limitation typically arises from the soft-glasses used and whose damage threshold is much lower than that of silica. Among the different glasses used for supercontinuum generation in the mid-infrared, tellurite glasses exhibit transmission band comparable with that of fluoride while offering lower intrinsic losses than chalcogenide, making them an excellent candidate for supercontinuum generation in the mid-infrared [4] . Recently, the use of multimode graded-index (GRIN) fibers in supercontinuum generation has been demonstrated, allowing to generate ultrabroadband spectra with very high power spectral density while preserving a near single-mode spatial beam profile due to nonlinear self-beam cleaning dynamics [5] . All demonstrations of supercontinuum generation in GRIN fibers have been so far limited to silica fibers.