  Compact chip-scale comb sources are of significant interest for many
practical applications. Here, we experimentally study the generation of
supercontinuum (SC) in an axially varying integrated waveguide. We show that
the local tuning of the dispersion enables the continuous blue shift of
dispersive waves thanks to their trapping by the strongly compressed pump
pulse. This mechanism provides new insight into supercontinuum generation in a
dispersion varying integrated waveguide. Pumped close to 2.2 $\mu$m in the
femtosecond regime and at a pulse energy of $\sim$ 4 pJ, the output spectrum
extends from 1.1 $\mu$m up to 2.76 $\mu$m and shows good coherence properties.
Octave-spanning SC is also observed at input energy as low as $\sim$ 0.9 pJ. We
show that the supercontinuum is more robust against variations of the input
pulse parameters and is also spectrally flatter in our numerically optimized
waveguide than in fixed-width waveguides. This research demonstrates the
potential of dispersion varying waveguides for coherent SC generation and paves
the way for integrated low power applications, such as chip-scale frequency
comb generation, precision spectroscopy, optical frequency metrology, and
wide-band wavelength division multiplexing in the near-infrared.
