Effect of gain media characteristics on the formation of soliton molecules in fiber laser

Erbium doped fiber and Er³⁺/Yb³⁺ codoped phosphate glass fiber are used as the laser media, respectively, to achieve self-started mode-locking based on nonlinear polarization rotation. It is found that the formation of the soliton molecule is the popular phenomenon in fiber laser. The laser media with high gain coefficient and short length is benefit of the formation of the soliton molecule at fundamental repetition rate and will generate evident soliton molecule pulse profile with strong accompanied structures. The achievement of soliton molecule owes to the partial operation of polarization filter effect in laser cavity due to the weak nonlinear polarization rotation in gain media with high gain coefficient and short length.