The complex nonlinear dynamics of mode-locked fibre lasers, including a broad variety of dissipative structures and self-organization effects, have drawn significant research interest. Around the 2 μm band, conventional saturable absorbers (SAs) possess small modulation depth and slow relaxation time and, therefore, are incapable of ensuring complex inter-pulse dynamics and bound-state soliton generation. We present observation of multi-soliton complex generation in mode-locked thulium (Tm)-doped fibre laser, using double-wall carbon nanotubes (DWNT-SA) and nonlinear polarisation evolution (NPE). The rigid structure of DWNTs ensures high modulation depth (64%), fast relaxation (1.25 ps) and high thermal damage threshold. This enables formation of 560-fs soliton pulses; two-soliton bound-state with 560 fs pulse duration and 1.37 ps separation; and singlet+doublet soliton structures with 1.8 ps duration and 6 ps separation. Numerical simulations based on the vectorial nonlinear Schr¨odinger equation demonstrate a transition from single-pulse to two-soliton bound-states generation. The results imply that DWNTs are an excellent SA for the formation of steady single- and multi-soliton structures around 2 μm region, which could not be supported by single-wall carbon nanotubes (SWNTs). The combination of the potential bandwidth resource around 2 μm with the soliton molecule concept for encoding two bits of data per clock period opens exciting opportunities for data-carrying capacity enhancement.
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Funding: EU Horizon2020 Marie S.-Curie IF MINDFLY project; Russian Science Foundation (grant 14-21-00110); Ministry of Higher Education Sultanate of Oman; Royal Academy of Engineering Fellowship (Graphlex); the Marie-Curie International Research Staff Exchange Scheme “TelaSens” project (Research Executive Agency Grant No. 269271, Programme: FP7-PEOPLE-2010-IRSES and
European Research Council through the FP7-IDEAS-ERC grant ULTRALASER).
Chernysheva, M., Bednyakova, A., Al Araimi, M., Howe, R. C. T., Hu, G., Hasan, T., Gambetta, A., Galzerano, G., Ruemmeli, M., & Rozhin, A. (2017). Double-wall carbon nanotube hybrid mode-locker in Tm-doped fibre laser: a novel mechanism for robust bound-state solitons generation. Scientific Reports, 7, . https://doi.org/10.1038/srep44314