Abstract
Physics phenomena of multi-soliton complexes have enriched the life of dissipative solitons in fiber lasers. By developing a birefringence-enhanced fiber laser, we report the first experimental observation of group-velocity-locked vector soliton (GVLVS) molecules. The birefringence-enhanced fiber laser facilitates the generation of GVLVSs, where the two orthogonally polarized components are coupled together to form a multi-soliton complex. Moreover, the interaction of repulsive and attractive forces between multiple pulses binds the particle-like GVLVSs together in time domain to further form compound multi-soliton complexes, namely GVLVS molecules. By adopting the polarization-resolved measurement, we show that the two orthogonally polarized components of the GVLVS molecules are both soliton molecules supported by the strongly modulated spectral fringes and the double-humped intensity profiles. Additionally, GVLVS molecules with various soliton separations are also observed by adjusting the pump power and the polarization controller.
Highlights
Mode-locked fiber lasers have attracted intensive research for the applications of ultrashort pulsed light source with unprecedented pulse energy or repetition rate, as well as the exploration of dynamics of optical dissipative solitons (DSs)[1,2,3]
If no polarization discrimination component is used in fiber lasers, the two orthogonally polarized components could be coupled together to form another type of multi-soliton complexes, namely vector solitons in fiber lasers, which possess much more plentiful behaviors and richer dynamics than their scalar counterparts, and pave a promising way for numerous applications from nano-optics to high-capacity fiber optic communications[25,26,27]
The mergence of soliton molecules and vectorial nature of light spreads a new concept of vector soliton molecules that inspires us to reveal more interesting behaviors and underlying dynamics of these compound multi-soliton complexes formed at both time domain and polarization directions in a unique testbed[35,36,37]
Summary
GVLVS molecules shown in Fig. 6(a) and (b) possess a spectral modulation period of 1.8 nm and a corresponding soliton separation of 4.4 ps, which is around 4.2 times of the pulse width of 1.05 ps if a sech[2] pulse shape is assumed. It should be noted that birefringence induced polarization dispersion enforces the pulse splitting during propagation in the PMF segment; while solitons along the fast axis and the slow axis shift their central frequencies in opposite directions to slow down and speed up, respectively In effect, these two orthogonally polarized components create an attractive potential well, trapping each other through cross-phase modulation and propagating as a non-dispersive soliton complex at the same group velocity. With careful polarization-state manipulation, these separate particle-like GVLVSs can be bound together at time domain to form the compound multi-soliton complexes, namely GVLVS molecules. The investigation on the interesting behaviors and underlying dynamics of these compound multi-soliton complexes provides the opportunities for both enriching the life of DSs and extending their potential applications
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