Pulse-onset dynamics via instabilitiesin a bidirectionalmode-locked fibre laser

Here we present experimentally obtained switch-on dynamics of counter-propagating ultrashort pulses in a bidirectional mode-locked fibre laser with delayed pulse formation via Q-switched and modulation instabilities with multiple-pulse formation. We define a localisation parameter using round-trip resolved pulse autocorrelation function to quantify the extent of the pulse formation, which indicates a complex energy interchange between coherent features and background radiation. The round-trip time-resolved intensity and spectral measurements also reveal a pronounced drift of the central wavelength during the build-up process. Furthermore, we report the formation of synchronised and unsynchronised dispersion waves which has been numerically predicted recently. Our results reveal the complexities of the establishment of coherent features and their interaction with background radiation, contributing further towards the understanding of nonlinear systems in general.<br>