Harnessing a multi-dimensional fibre laser using genetic wavefront shaping

Intelligent 3D lasers: Bio-inspired algorithms help tame multimode fiber lasers Multimode fibres that contain numerous groups of lightwaves, or modes, can now assist lasers in producing tunable emission characteristics. Lihong Wang from the California Institute of Technology in Pasadena, United States, and colleagues have developed a technique to control the complex interactions inside a multimode fibre laser using machine learning. The team created a feedback loop where portions of laser signals travelling through a multimode fibre are sent to a spatial light modulator that adjusts the phases of propagating waves. By using genetic algorithms to direct the spatial light modulator, this setup can optimize parameters such as output power after a few minutes of evolutionary feedback-changing, for instance, an initial speckle-shaped light pattern into a single focused spot. Other tunable laser features including wavelength scanning and pulse control were demonstrated with this approach. The multi-dimensional laser is a fascinating platform not only for the discovery and understanding of new higher-dimensional coherent lightwaves but also for the frontier study of the complex three-dimensional (3D) nonlinear dynamics and solitary waves widely involved in physics, chemistry, biology and materials science. Systemically controlling coherent lightwave oscillation in multi-dimensional lasers, however, is challenging and has largely been unexplored; yet, it is crucial for both designing 3D coherent light fields and unveiling any underlying nonlinear complexities. Here, for the first time, we genetically harness a multi-dimensional fibre laser using intracavity wavefront shaping technology such that versatile lasing characteristics can be manipulated. We demonstrate that the output power, mode profile, optical spectrum and mode-locking operation can be genetically optimized by appropriately designing the objective function of the genetic algorithm. It is anticipated that this genetic and systematic intracavity control technology for multi-dimensional lasers will be an important step for obtaining high-performance 3D lasing and presents many possibilities for exploring multi-dimensional nonlinear dynamics and solitary waves that may enable new applications.