GaInAs/AlInAs/InP quantum cascade lasers (QCLs) have established themselves as reliable and versatile semiconductor
laser sources in the mid-infrared wavelength region. Due to the presence of unique molecular absorption lines, in
combination of water-free atmospheric transmission windows, this spectral range is of particular importance for sensing,
medical, material processing and homeland security applications. Being compact electrically pumped and able to operate
at room-temperature, QCLs are ideal choice for wavelengths between 3.5 - 12 microns. However, wavelengths above
and below are more challenging to obtain.
In our work, we use intracavity nonlinear frequency mixing in mid-infrared QCLs to extend the spectral coverage for
GaInAs/AlInAs/InP devices. We demonstrate that passive nonlinear structures, consisting of coupled quantum wells can
be grown on top of the mid-IR QCL active region. Such nonlinear structures can be designed to possess a resonant
nonlinear response for the pump frequency. Such concept, in combination with quasi-phase-matching technique can be
used for efficient short-wavelength lasing by second-harmonic generations. We demonstrated room-temperature lasing
down to 2.6 micrometer. For long-wavelengths, particularly THz frequencies, a novel waveguide concept was
introduced. Here, we used a leaky THz waveguide concept, for a difference-frequency generation device. Phase
matching was achieved by Cherenkov phase-matching scheme. This concept led to ultra-broadband THz emission at
room-temperature (1.2-4.5 THz) with pulsed output powers as high as 14 μW.