  In this letter we experimentally demonstrate efficient generation of
mid-infrared frequency combs. Our method is based on continuous-wave-seeded
femtosecond optical parametric generation in a nonlinear waveguide. It is
capable of converting near-infrared pump to signal and idler regions with
energy conversion efficiency of 74% and threshold as low as 25 pJ. The idler
comb carrier-envelope offset frequency is precisely stabilized and can be
dynamically controlled. The idler offset frequency adjustments are inherently
independent of the repetition rate making the system highly versatile.
Furthermore, we increased the idler optical bandwidth by driving the process
with broadband pump obtained via supercontinuum generation.
