  We present a monolithic solution to extract efficiently light from terahertz
quantum cascade lasers with metal-metal waveguides suitable for broadband
frequency comb applications. The design is optimized for a bandwidth of 500 GHz
around a center frequency of 2.6 THz. A five-fold increase in total output
power is observed compared to standard metal-metal waveguides. The extractor
features a single-lobed far-field pattern and increases the frequency comb
dynamical range to cover more than 50 % of the laser dynamic range. Frequency
comb operation up to a spectral bandwidth of 670 GHz is achieved.
