Switchable in-phase and out-phase polarization rotation vector solitons in a birefringence-managed fiber laser

Nonlinear polarization evolution of vector solitons is an interesting subject in nonlinear science and laser dynamics. Here, we demonstrate two types of switchable multiple polarization rotation vector solitons (PRVSs) in a mode-locked fiber laser through birefringence management. It is found that due to the polarization evolution induced gain competition and mode-coupling effect, the intensities of the two orthogonal polarization components of neighboring solitons differ in each round-trip, manifesting as the out-phase PRVSs. By adjusting the polarization orientation of injecting pulses with respect to the principal axis of polarization-maintaining fiber, neighboring solitons can project equal weight of intensity in two orthogonally-polarized directions, thus switching the out-phase PRVSs to the in-phase PRVSs. Real-time spectral measurement results validate the formation of two PRVSs, and reveal the distinct evolution dynamics. This work provides an effective method to control the polarization state of each soliton in multi-pulses mode-locked fiber lasers, and a potential avenue to introduce polarization-coding in optical soliton communications.