Fig. 6

Experimental comparison of soliton red-shifting in a tapered and a uniform multimode fiber. a The output spectrum after a 3-m tapered multimode fiber with a core radius decreasing from 30 to 10 µm. As the input power level increases, the soliton experiences a significant red-shifting that extends up to 2300 nm. b The recorded output spectrum from a 3-m uniform graded-index multimode fiber having a core radius of 25 µm. In this regime, the solitons experience a subdued red-shifting up to 1900 nm. c The transmission efficiency curve as obtained by comparing the fiber output power before and after the tapered segment. As the input power level increases, the efficiency drops. In all cases, 100-fs pulses at 1550 nm are used