  Powerful and efficient optical frequency combs in the mid-infrared (MIR)
spectral region are highly desirable for a broad range of applications. Despite
extensive efforts utilizing various techniques, MIR frequency comb sources are
still lacking power, efficiency, or bandwidth for many applications. Here, we
report the generation of an intrinsically locked frequency comb source centered
at 4.18 {\mu}m from an optical parametric oscillator (OPO) operating in the
simulton regime, in which formation of purely quadratic solitons lead to
enhanced performance. We show advantages of operation in the simulton regime in
direct experimental comparisons to the conventional regime, which are also
supported by simulation and theory. We achieve 565 mW of average power, 900 nm
of instantaneous 3-dB bandwidth, 350% of slope efficiency, and 44% of
conversion efficiency; a performance that is superior to previous OPO
demonstrations and other sources in this wavelength range. This work opens a
new avenue toward MIR frequency comb generation with high power and efficiency
and suggests the great potential of soliton generation based on quadratic
nonlinearity in the MIR spectral region.
