  Self-referenced dissipative Kerr solitons (DKSs) based on optical
microresonators offer prominent characteristics including miniaturization, low
power consumption, broad spectral range and inherent coherence for various
applications such as precision measurement, communications, microwave
photonics, and astronomical spectrometer calibration. To date, octave-spanning
DKSs with a free spectral range (FSR) of ~1 THz have been achieved only in
ultrahigh-Q silicon nitride microresonators, with elaborate wavelength control
required. Here we demonstrate an octave-spanning DKS in an aluminium nitride
(AlN) microresonator with moderate loaded Q (500,000) and FSR of 374 GHz. In
the design, a TE00 mode and a TE10 mode are nearly degenerate and act as pump
and auxiliary modes. The presence of the auxiliary resonance balances the
thermal dragging effect in dissipative soliton comb formation, crucially
simplifying the DKS generation with a single pump and leading to a wide single
soliton access window. We experimentally demonstrate stable DKS operation with
a record single soliton step (~80 pm) and octave-spanning bandwidth (1100-2300
nm) through adiabatic pump tuning and on-chip power of 340 mW. Our scheme also
allows for direct creation of the DKS state with high probability and without
elaborate wavelength or power schemes being required to stabilize the soliton
behavior.
