Mode-locked fibre lasers, featuring ultrafast temporal information, ultrahigh peak energy, and exceptional stability, have become essential tools in modern optics and industries, including telecommunications, micromachining and ultrafast probing. The heart of mode-locked fibre lasers lies in saturable absorber, which can convert continuous-wave light into pulsed laser output. However, traditional saturable absorbers still rely on free-space configurations. Attempts to develop compact fibre-based saturable absorbers for all-fibre lasers are severely hindered by imbalanced saturable absorption properties.
In a new paper published in Light: Science & Applications , a team of scientists, led by Professor Kaihui Liu and associated professor Hao Hong from School of Physics, Peking University, China, Professor Fengqiu Wang, School of Electronic Science and Engineering, Nanjing University, China and co-workers have developed a novel robust saturable absorber by integrating a nanocavity heterostructure composed of MoS 2 -BN-graphene-BN-MoS 2 onto the fibre end facet. With significantly enhanced saturable absorption properties, the heterostructure-saturable absorber reduces the possibility of pulse splitting under different polarization states in the fibre ring cavity, achieving single-pulse generation in approximately 85% of configurations, compared to only 20% for bare graphene-saturable absorber. Its excellent environmental tolerance eliminates the need for a polarization controller in ultrafast fibre lasers and offers outstanding robustness and compactness, making it valuable for communication systems, high-precision sensing and bio-photonics.
The heterostructure-saturable absorber is stacked by 2D materials to precisely modulate the optical field within the nanocavity, achieving a significant reduction in the saturation intensity (~65%), which is beneficial for the mode-locked self-starting. The researchers compared the soliton buildup and evolution of the bare graphene-saturable absorber and the heterostructure-saturable absorber via the time-stretch dispersive Fourier transform technique. They identified that heterostructure-saturable absorber effectively suppressed nonsoliton components near the central wavelength and mitigated competing background pulses prior to soliton formation, which are responsible for the observed unstable output states in bare graphene-saturable absorber system.
“The 2D heterostructure nanocavity exhibits excellent compatibility with fibre end facet integration, offering promising potential for improving the performance and miniaturizing of all-fibre components. By optimizing the heterojunction structure and fibre cavity dispersion this platform can achieve mode-locking and optical frequency comb generation across multiple bands, making it valuable for communication systems, high-precision sensing, and bio-photonics.” the scientists forecast.
Light Science & Applications
Robust mode-locking in all-fiber ultrafast laser by nanocavity of two-dimensional heterostructure