  We present a simple method for fully-stabilized mid-infrared optical
frequency comb generation based on single-pass femtosecond optical parametric
generation that is seeded by a continuous-wave laser. We have implemented the
method in a periodically poled lithium niobate crystal that produces a
frequency comb tunable across 3325 - 4000 nm (2380 - 3030 cm-1). The method
generates the mid-infrared (idler) comb with known and stabilized
Carrier-Envelope Offset (CEO) frequency without the need to directly detect it.
The idler CEO is continuously tunable for almost half of the repetition rate
and can be modulated, while maintaining its central frequency. Together with
the high output power (up to 700 mW) and low intensity noise (0.018% integrated
in 10 Hz - 2 MHz bandwidth) this makes the demonstrated mid-infrared frequency
comb promising for many applications such as high-precision molecular
spectroscopy, frequency metrology and high harmonic generation.
