In this project, the spatiotemporal mode-locking (STML) in multimode fibers will be investigated by a theoretical model and preliminary experimental demonstrations. Compared with conventional mode-locking, the STML system can sustain high power, have high nonlinearity, a high degree to control coherent optical fields in 3D+1 dimension. Different effects leading to the mode-locking will be investigated, such as saturable absorber, Kerr effects, polarization control. Intelligent algorithms, such as machine learning, will be designed in multimode fiber lasers to automatically lock on and switch to any possible operation regime in a fixed laser cavity, such as FML, HML, QS, and QML. Moreover, other solutions also will be investigated, such as transverse mode-locking, spiral fields, conical waves. Preliminary experimental demonstrations will be implemented to verify the model. This work will open new directions in the studies of three-dimensional nonlinear wave propagation in multimode fibers.
Over the past decades, enormous research and technological development in ultrafast lasers, including fiber lasers, have been realized with just one transverse mode of the cavity.
The spatiotemporal mode-locking (STML) was recently proposed. Compared with conventional mode-locking, the advantages of this STML can be seen as follows.
1. The STML needs to consider the discovery of 3 spatial dimensions and 1 temporal dimension (3D+1). This provides a potential for control of coherent optical fields in 4-dimensions. Mode-locked states are just a special restricted case of coherent self-organization. Since STML provides a better testbed than a conventional system composed of single-mode fibers, a much richer world of physics is possible.
2. This system allows for larger optical beams in a larger fiber core, hence it naturally sustains much higher power pulses and average power than conventional single transverse mode mode-locking. Therefore with a suitable spatiotemporal cavity design, these systems may generate unprecedented peak power.
3. Higher power in pulses means higher nonlinearity in the system, such as higher values of Kerr effects. To some extent, this higher nonlinearity can compensate for high dispersion values, which can sustain high peak power soliton formations in a large dispersion condition.
The innovation of the research is reflected in the following points.
1. We will develop a theory that is necessary to predict possible interesting solutions for revealing spatiotemporal dynamics in ultrafast lasers with multimode fibers. It will connect conventional mode-locking theory with multimode nonlinear fiber optics. It will give many possible predictions for experiments in the future. This theory will be verified by our preliminary experiments.
2. This model will allow us to test different effects that lead to the mode-locking in multimode fibers, such as saturable absorber, Kerr effects, polarization control. Different dynamics of the lasers will be investigated, such as fundamental mode-locking (FML), harmonic mode-locking (HML), Q-switching (QS), and Q-switched mode-locking (QSML) regimes.
3. Intelligent algorithms, such as machine learning, will be designed in multimode fiber lasers to achieve automatically locking on and switching to any possible operation regime in a fixed laser cavity, such as FML, HML, QS, and QML.
4. Locking transverse modes in multimode fibers leads to the oscillation of the pulses in the fiber transverse surface. This can be used for beam scanning.
Within this project, we will provide theoretical, numerical as well as preliminary experimental demonstration of mode-locking in multimode fibers. The significance of this research is that it will not only extend the scope of the mode-locking by controlling coherent optical fields in 4-dimensions but also will demonstrate an intelligent way to find all kinds of solutions for different configurations as described in the project. Moreover, other solutions also will be investigated, such as transverse mode-locking, spiral fields, conical waves. Finally, a preliminary experimental demonstration will be implemented to verify the model.