  Coherent dispersive wave emission, as an important phenomenon of soliton
dynamics, manifests itself in multiple platforms of nonlinear optics from fibre
waveguides to integrated photonics. Limited by its resonance nature, efficient
generation of coherent dispersive wave with ultra-broad bandwidth has, however,
proved difficult to realize. Here, we unveil a new regime of soliton dynamics
in which the dispersive wave emission process strongly couples with the
splitting dynamics of the driving pulse. High-order dispersion and
self-steepening effects, accumulated over soliton self-compression, break the
system symmetry, giving rise to high-efficiency generation of coherent
dispersive wave in the ultraviolet region. Simultaneously, asymmetric soliton
splitting results in the appearance of a temporally-delayed ultrashort pulse
with high intensity, overlapping and copropagating with the dispersive wave
pulse. Intense cross-phase modulations lead to octave-wide broadening of the
dispersive wave spectrum, covering 200 to 400 nm wavelengths. The
highly-coherent, octave-wide ultraviolet spectrum, generated from the simple
capillary fibre set-up, is in great demand for time-resolved spectroscopy,
ultrafast electron microscopy and frequency metrology applications, and the
critical role of the secondary pulse in this process reveals some new
opportunities for all-optical control of versatile soliton dynamics.
