Soliton pairs in a fiber laser: from anomalous to normal average dispersion regime

Abstract

We report the observation of self phase-locked pulse pairs in a stretched-pulse fiber laser operating in the normal path-averaged dispersion regime. Numerical simulations agree with our experimental results. More insight is provided with a numerical comparison between intracavity profiles of pulse pairs in anomalous and in normal dispersion regimes.

Generation of Soliton Molecules in a Normal-Dispersion Fiber Laser

“…Our work gives the counterpart in the normal-dispersion regime. The separation between the bounded pulses increases with the pump power, and varies with the settings of polarization controllers, which is consistent with other kinds of bounded pulses such as solitons [13], [14], stretched-pulses [15] and similaritons [16]. Our study implies that though DSs can contain high energy, nonlinearity management is crucial to further increase single-pulse energy.…”

Soliton Molecules and Multisoliton States in Ultrafast Fibre Lasers: Intrinsic Complexes in Dissipative Systems

“…Based on more simulation results from refs. [22,44], we believe that a sole dispersion sign of the cavity is not able to determine or predict the possible phase difference of the solutions. It is rather tricky to select proper parameters for a stable bound state since such an exact balance is reached only when all effects related to gain, loss, nonlinearity and dispersion compromise to a same attractor, which enables soliton molecules an intriguing form in dissipative systems.…”

“…Such nearly zero net-cavity dispersion regime allows existence of Gaussian pulses which are more tolerant with nonlinear phase shift compared to traditional sech-profiled solitons in anomalous dispersion fibre lasers. As some of the pioneers who study soliton molecules, Grelu, Soto-Crespo et al have performed remarkable experiments and simulations in both anomalous and normal path-averaged cavity dispersion fibre lasers where kinds of bound solitons were observed [18,22,44]. As an example, Figure 13a,b illustrates the temporal and spectral details of a bound state in a laser cavity with normal dispersion-managed configuration.…”

“…So far bound states have been studied by simulated and/or experimental methods in types of fibre laser cavities, i.e., in soliton [16,17], stretched-pulse [18], gain-guided [19] and self-similar [20] regimes, as well as dissipative soliton regime associating with large net-normal dispersion and spectral filtering [21]. A lot of experimental observations of bound solitons have been reported in fibre lasers mode-locked by nonlinear polarization evolution (NPE) [22][23][24], nonlinear amplifying loop mirror (NALM) [8,25] and some real saturable absorbers (e.g., semiconductor saturable absorber mirror (SESAM) [26], carbon nanotubes (CNT) [27][28][29], graphene [30,31], topological insulator [32], molybdenum disulphide (MoS 2 ) [33] and black phosphorus [34]). Although a lot of experimental findings have been made in many different cavities, in-phase two-soliton bound states and a systematic observation of soliton molecules with different phase differences were only reported several years ago [28], due to large degree of freedom of manipulation on the experimental configurations in a fibre laser using a real saturable absorber.…”

Bound states of solitons in a fiber laser mode locked with carbon nanotube saturable absorber

“…Depending on the strength of the soliton interaction, two types of bound states of solitons were identified: tightly bound solitons formed under strong soliton-soliton interaction. These states of bound solitons have the characteristics that their soliton separations exhibit fixed discrete values, and the bound solitons have a fixed π or π/2 phase difference [7][8][9][10]; and loosely bound solitons formed under weak soliton-soliton interaction. The loosely bound solitons, in contrast, normally have large soliton pulse separation and unfixed soliton phase difference.…”