Multi-soliton pulse generation in a fiber laser by using a long-period fiber grating

In this paper, multi-soliton pulse generation is realized by incorporating a long period fiber grating into an Er-doped mode-locked fiber ring laser cavity. By using nonlinear polarization rotation mode-locking technique and a long period fiber grating that plays the role of spectral filter in the laser cavity, discretely tunable multi-soliton pulses can be produced at low lasing threshold of 80 mW. The number of solitons can be controlled by simply adjusting the polarization controller in the laser cavity. It is found that Kelly sideband of the traditional mode-locked solitons become weak as a result of introducing the long period fiber grating in the laser cavity, due to the fact that the nonlinearity and dispersion in the cavity are balanced, and hence stabilizing the soliton pulses. The use of long-period fiber grating has the advantages of effectively reducing the pumping threshold for the multi-soliton pulse generation, and supporting stable laser operation.