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.
In this paper, we report two types of dual-wavelength pulse superposition states, i.e., heterogeneous and homogeneous pulse patterns, in a ring fiber laser mode-locked by nonlinear polarization rotation (NPR) with a Fabry–Perót (F–P) minicavity. The heterogeneous pulse pattern is characterized by the coexistence of the triangular spectrum and soliton-like spectrum with central wavelengths of 1558.3nm and 1565.4 nm, respectively. Meanwhile, the homogeneous pulse is formed by the superposition of two solitons whose central wavelengths are 1558.7 nm and 1565.6 nm, respectively. The switching between heterogeneous and homogeneous pulse patterns is realized through adjusting polarization controllers and the pump power. Theoretical analysis shows that the two-type pulse superposition state generation is due to two independent filtering effects in the fiber laser, which originate from NPR and F–P filtering effects, respectively. Our results will provide a new method to produce abundant dual-wavelength pulse patterns.
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