Spatio-spectral coupling in spatio-temporally mode-locked fiber laser

We experimentally and numerically reveal a spatio-spectral coupling (SSC) mechanism mediated by spatially dependent gain in the spatio-temporally mode-locked fiber laser. In the experiment, the spectral tuning is observed to be accompanied by a change in the spatial mode content. To further elucidate this relation between the spectral and spatial properties of the three-dimensional (3D) pulse, the gain spectrum and its field attractor are theoretically analyzed. The underlying mechanism through which the multimode gain affects the SSC is identified with the simulated results that well reproduce the modal composition exponentially varying with the spectral centroid. Moreover, harnessing the SSC enables the generation of asynchronous dichromatic 3D pulses, offering a potential route for dual-comb generation in a single laser cavity.