Birefringence-Induced Heterogeneous Vector Pulses in Ultrafast Fiber Lasers

Single-mode fiber lasers are capable of supporting trapped vector solitons with two similar orthogonally polarized components, due to the delicate balance between fiber birefringence and chromatic dispersion. Here, we demonstrate that heterogeneous vector pulses (HVPs) universally exist in anomalous-dispersion and near-zero-dispersion regimes, from hybrid-structure fiber lasers composed of low- and high-birefringent fibers. The vector pulses include two distinct orthogonally polarized components, one of which is a robust pulse, while the other is a gradually attenuated wavepacket composed of terahertz- (THz) repetition-rate subpulses. Simulation and analytical results fully reproduce experimental observations and demonstrate that the robust pulse couples a fraction of its energy to the orthogonally polarized component per roundtrip at the high-birefringent fiber, forming the unique HVPs. Apart from the intriguing nonlinear dynamics, the HVP can work as a flexible workhorse for various applications, ranging from optical polarization multiplexing to THz synthesis and optical precision spectroscopy.