Cascaded generation of Raman solitons at 1800 nm and 2000 nm in an Erbium-doped fiber laser

We report the cascaded generation of mid-infrared Raman solitons in an Erbium-doped fiber laser (EDFL) with a tunable Fabry-Perót filter. The first- and second-order Raman solitons were experimentally achieved at 1856 nm and 2029.6 nm, respectively, under pumping by a 1530-nm continuous wave (CW) laser with a 3-dB bandwidth of 0.1 nm generated from the EDFL. Their 3-dB bandwidths were 13.4 nm and 2.4 nm, respectively. It was found that the balance of Raman gain induced by nonlinear effects broadening the laser spectrum and Fabry-Perót filtering narrowing the laser spectrum in the EDFL resulted in the cascaded generation of Raman solitons within the wavelength band from 1800 to 2100 nm. It is the first time for a mode-locked EDFL operating at the wavelength band of 2.0 μm. Our work has great potential application as a novel optical source from near- to mid-infrared regimes.