  We present quantum cascade laser (QCL) frequency comb devices with engineered
waveguides for managing the dispersion. The QCL waveguide consists of multiple
sections with different waveguide widths. The narrow and wide sections of the
waveguide are designed in a way to compensate the group velocity dispersion
(GVD) of each other and thereby produce a flat and slightly negative GVD for
the QCL. The QCL exhibits continuous comb operation over a large part of the
dynamic range of the laser. Strong and narrow-linewidth intermode beatnotes are
achieved in more than 300 mA wide operation current range. The comb device
features also considerably high output power (>380 mW) and wide optical
bandwidth (>55 cm-1)
