  We demonstrate mid-infrared (mid-IR) supercontinuum generation (SCG) with
instantaneous bandwidth from 2.2 to 5 {\mu}m at 40 dB below the peak, covering
the wavelength range desirable for molecular spectroscopy and numerous other
applications. The SCG occurs in a tapered As2S3 fiber prepared by in-situ
tapering and is pumped by femtosecond pulses from the subharmonic of a
mode-locked Er-doped fiber laser. Interference with a narrow linewidth c.w.
laser verifies that the coherence properties of the near-IR frequency comb have
been preserved through these cascaded nonlinear processes. With this approach
stable broad mid-IR frequency combs can be derived from commercially available
near-IR frequency combs without an extra stabilization mechanism.
