Dual-wavelength pulse superposition states in a fiber laser

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.