Spatial Kerr Beam Self-Cleaning in Yb-Doped Multimode Fiber Taper

Spatial Kerr beam self-cleaning (KBSC), which transforms an output speckled beam in a quasi-single mode beam in graded index (GRIN) multimode optical fibers (MMFs), has been reported recently [1,2]. GRIN MMFs are also interesting waveguides for supercontinuum (SC) generation in the visible and near infrared regions, as successfully demonstrated by launching femtosecond or subnanosecond pulses in the anomalous (1550 nm) or normal (1064 nm) dispersion regime, respectively [1,3]. The spectral broadening features were explained through the interplay between spatiotemporal multimode soliton oscillations and dispersive wave generation in fibers with parabolic index profile. On the other hand, tapered optical fibers are well known to provide a number of useful features, including strong mode confinement capability, small scale diameter and broad SC generation [4,5]. Herein, we report visible-short infrared SC generation in combination with KBSC in long (∼10 m) tapered Yb-doped MMFs, with parabolic index profile and parabolic doping concentration.