Observation of Soliton Molecules in NPR Mode-Locked Er-Fiber Laser via Birefringence Management

We have experimentally demonstrated that soliton molecules can be achieved from an Er-doped fiber laser oscillator via polarization dispersion management in the anomalous dispersion regime. In the laser oscillator, selective high-birefringence (HIBI) fibers were cross-spliced twice to counteract the linear polarization dispersion, which could highlight the role of the accumulated nonlinear phase shift and thus ensure the stable generation of mode-locking pulses by means of nonlinear polarization rotation (NPR). Depending on the length of the HIBI fibers, the angle of waveplates, and the pumping power, different types of soliton, such as single-pulse soliton and soliton molecules in tightly and loosely bound state, are observed.