  The generation of optical frequency combs via direct electrical pumping of
semiconductor lasers is an attractive alternative to the well-established
mode-locked laser sources in terms of compactness, robustness and
integrability. However, the high chromatic dispersion of bulk semiconductor
materials can prevent the generation of frequency combs or lead to undesired
pulse lengthening. In this letter, we present a novel dual waveguide for
intracavity dispersion compensation in semiconductor lasers. We apply the
concept to a short mid-infrared wavelength quantum cascade laser operating in
the first atmospheric window (\lambda $ \approx$ 4.6 \mu m). As a result,
stable comb operation on the full dynamical range is achieved in this device.
Unlike previously proposed schemes, the dual waveguide approach can be applied
to various types of semiconductor lasers and material systems. In particular,
it could enable efficient group velocity dispersion compensation at
near-infrared wavelengths where semiconductor materials exhibit a large value
of that parameter.
