  We report on a heterogeneous active region design for terahertz quantum
cascade laser based frequency combs. Dynamic range, spectral bandwidth as well
as output power have been significantly improved with respect to previous
designs. When operating individually the lasers act as a frequency comb up to a
spectral bandwidth of 1.1 THz, while in a dispersed regime a bandwidth up to
1.94 THz at a center frequency of 3 THz can be reached. A self-detected
dual-comb setup has been used to verify the frequency comb nature of the
lasers.
