Radiation build-up and dissipation in Raman random fiber laser

Raman random fiber lasers (RRFL) have attractive features such as simple structure, excellent wavelength-tunability, high optical-optical conversion efficiency, etc., showing great potential for long-distance fiber sensing, speckle-free imaging, high-energy physics, and other applications. The unique feedback in the RRFL comes from distributed fiber Rayleigh scattering with intrinsic randomness. Investigating the dynamics properties in its steady state has become a bridge to probe complex physical systems with the optical platform, including turbulence, spin glasses behaviors, etc. Meanwhile, the transient state, such as the laser build-up and dissipation processes, is of great value to reveal light-wave interactions and explore the formation process of some complex physical systems, but there have been no relevant reports in the RRFL domain.

The transient state of RRFL is investigated for the first time by Zinan Wang and co-authors from UESTC and SCU. Based on the generalized nonlinear Schrödinger equations, the temporal and spectral evolution of RRFL at transient state is analyzed theoretically, and the corresponding experimental verification is carried out, then a series of interesting conclusions are drawn. The specific significance and novelty are summarized as follows:

1) For the RRFL build-up transient state, the output power of the RRFL shows a continuous growth curve, which is fundamentally different from the step-like growth curve of conventional Raman fiber lasers, providing intuitional evidence to differentiate the lasing mechanisms of the two cavities. Particularly, the RRFL growth curve satisfies the Verhulst logistic model, which is widely observed in biological growth dynamics. Based on the cross-disciplinary approach, this work could open up new important avenues for understanding complex biological phenomena through the RRFL system.

2) Above the threshold, the RRFL build-up time is inversely related to the pump power, and only several optical round-trip times is required at a relatively high pump power. This finding is crucial for any applications which require a precise understanding of the RRFL build-up time. For example, in long-distance RRFL point-sensing, the build-up time decides the upper bound of the sensing bandwidth, and the results in this work provide a lucid guideline for achieving wideband dynamic sensing.

This work provides valuable insights into the underlying complex physics of the RRFL dynamics, and the results would be also beneficial for research on other complex systems, such as biological dynamics, rogue wave build-up, etc. For the full paper, see http://engine.scichina.com/doi/10.1007/s11432-022-3677-7.