A new optical nonlinear media comes up---optical fibres with embedded two-dimensional materials

Here we used two-step chemical vapor deposition method to fabricate ultrahigh nonlinear optical fibre with tremendous prospects in nonlinear community including optical frequency conversion and all-fibre mode-locked laser.

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Nonlinear optical fibre is becoming the key component in devices of optical communication, optical frequency conversion, ultrafast laser, optical frequency comb and supercontinuum laser1. However, current manufacture-methods-based materials injection and structure well-design are not enough to satisfy the ultimate demand for ultrahigh nonlinearity in commercial due to low nonlinearity or poor material designing flexibility. It is therefore particular imperative to simultaneously realize high nonlinear response, muti-functionalization, batch production of nonlinear optical fibres by unique way.

In recent year, atomically thin transition metal dichalcogenides (TMDs), such as MoS2 and WS2, have exhibited excellent optic-electronic property and ultrahigh nonlinearity, which inspire widespread research interest on interdiscipline of two-dimensional (2D) materials and optical fibre optics. Thus far however, attempts towards fabricating TMDs hybrid optical fibre by transferring or coating nanosheets of TMDs on fibre always bear the distortion of propagation capacity, the short light-materials interaction length and difficulty of batch manufacture. Thanks to the great progress of 2D materials growth, it is possible to directly fabricated the graphene optical fibre with gaseous feedstock2. However, in TMD embedded optical fibre growth, the feedstocks are usually solid precursor and thus very difficult to transfer effectively and homogeneously in fibre.

Fabrication and nonlinear applications of 2D-materials-embedded optical fibre. a Schematic of the designed two-step growth method. b Optical images of a photo crystal fibre (PCF) with a hollow-core honeycomb and corresponding side view. c Ultrafast laser based on MoS2-embedded PCF. d Output pulse train with ~24 ns interval (~41MHz repetition rate). e Spectrum of the output laser with Δλ~19 nm. f Autocorrelation trace with FWHM (Δτ) of ~720 fs fitted by a Gaussian function, corresponding to a pulse duration of ~500 fs.

Here our group, including researchers from Beijing Graphene Institute (BGI), Peking University, Institute of Physics (CAS) and other collaborators, employs a unique technology, two-step chemical vapor deposition, for directly fabricating a 25 cm-long MoS2-embedded optical fibre with homogenous thickness and high quality. The pre-deposition of liquid phase transition metal source plays a key role in this process and guarantee a homogenous feedstock prior to a uniform MoS2 growth along the whole fibre wall. Besides, our fabrication strategy is amenable to other TMDs and alloys, which provides rich choices for all-fibre nonlinear optics and optoelectronics application.

Moreover, we also demonstrated that the nonlinear optical second and third harmonic generation (SHG and THG) of the MoS2-embedded optical fibre was greatly enhanced compared with bare capillary fibre, which possesses hardly SHG and THG. This outstanding nonlinear performance lays a solid foundation for multifunctional frequency conversion devices in future. For another hand, we have demonstrated an all-fibre mode-locked laser (~6 mW output, ~500 fs pulse width and ~41 MHz repetition rate) by integrating the MoS2- embedded optical fibre as a saturable absorber (SA), which has almost equal and more superior performance compared with others SA. Only pity is that phase matching between excitation light and nonlinear signal in 2D-materials-embedded optical fibre was not considered here and effected its maximum nonlinear frequency conversion potential exploited. So, we anticipate the cooperation with other groups with rich experiences of fibre fabrication to achieve various nonlinear applications in future.

If you are interested in our work, please refer to the paper published in Nature Nanotechnology: “Optical fibres with embedded two-dimensional materials for ultrahigh nonlinearity” following the link: https://www.nature.com/articles/s41565-020-0770-x

 

Reference

  1. Markos, C. et al. Hybrid photonic-crystal fiber. Rev. Mod. Phys. 89, 045003 (2017).
  2. Chen, K. et al. Graphene photonic crystal fibre with strong and tunable light–matter interaction. Nat. Photon. 13, 754–759 (2019).

Zhongfan Liu

Prof., Peking University

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