Optical fibres with embedded two-dimensional materials for ultrahigh nonlinearity

Nonlinear optical fibres have been employed for a vast number of applications, including optical frequency conversion, ultrafast laser and optical communication1–4. In current manufacturing technologies, nonlinearity is realized by the injection of nonlinear materials into fibres5–7 or the fabrication of microstructured fibres8–10. Both strategies, however, suffer from either low optical nonlinearity or poor design flexibility. Here, we report the direct growth of MoS2, a highly nonlinear two-dimensional material11, onto the internal walls of a SiO2 optical fibre. This growth is realized via a two-step chemical vapour deposition method, where a solid precursor is pre-deposited to guarantee a homogeneous feedstock before achieving uniform two-dimensional material growth along the entire fibre walls. By using the as-fabricated 25-cm-long fibre, both second- and third-harmonic generation could be enhanced by ~300 times compared with monolayer MoS2/silica. Propagation losses remain at ~0.1 dB cm–1 for a wide frequency range. In addition, we demonstrate an all-fibre mode-locked laser (~6 mW output, ~500 fs pulse width and ~41 MHz repetition rate) by integrating the two-dimensional-material-embedded optical fibre as a saturable absorber. Initial tests show that our fabrication strategy is amenable to other transition metal dichalcogenides, making these embedded fibres versatile for several all-fibre nonlinear optics and optoelectronics applications. The internal surface of an optical fibre can be covered by uniform two-dimensional-material layers for highly nonlinear and low-loss light propagation.