Mid-infrared beam shaping concepts are presented, which rely on coherent emission from QCLs. Grating coupled
surface emitting quantum cascade ring lasers allow for far-field tuning, ranging from highly symmetric spot- to ringshaped
beam patterns, depending on the grating period. In single-mode operation, the devices exhibit low beam
divergence, represented by a full width at half maximum of ~3°. Moreover, a tree shaped resonator is investigated, which
enables coherent parallel coupling of six laser elements into a single waveguide by means of several Y-junctions. The
lasers were investigated in terms of optical power, near and far field characterization. Phase-locking was observed and
leads to in-phase emission on both sides of the devices. Both concepts demonstrate the feasibility of high-brightness midinfrared
quantum cascade lasers with prospective applications in spectroscopy and high power laser arrays.
A monolithic coupling scheme in which two active waveguides merge into a single waveguide to form a Y-shaped
resonator is demonstrated for mid-infrared quantum cascade lasers. Lasers with emission wavelengths of 10.5 μm and
4.2 μm were processed from lattice-matched GaAs/AlGaAs and strain-compensated InP/InGaAs/AlAs/AlInAs
structures. Phase-locking is observed in the laser cavities, resulting in coherent interference of the emitted radiation. Far
fields were recorded on both sides of the devices and analyzed in respect to their radiative origin. By matching the
recorded far field intensity profiles to corresponding near field distributions, the lateral mode distribution within the
resonator is derived. Depending on the length of the coupling section, even or odd cavity modes evolve. Moreover, a
comparison between the fabricated devices shows the emission wavelength's impact on the coupling performance of the
Y-junction. The results demonstrate the feasibility of coherent laser resonators with prospective applications in
interferometric sensing and high power laser arrays.
We report second-harmonic and sum-frequency generation in GaAs based quantum cascade lasers. Different waveguide designs and active regions were investigated as well as a doping dependence study of the second-order susceptibility in one of the investigated structures is shown. We present farfield measurements which give information about the modal behavior depending on the waveguide design and dimensions. We also demonstrate that grating-coupled surface emission is a highly efficient way to couple out the second-harmonic radiation.
In this paper we present single mode quantum cascade lasers (QCLs) based on the GaAs and the InP material systems. We show results for first- and second-order distributed feedback (DFB) QC lasers with surface gratings. The InP based lasers are grown by metalorganic vapor phase epitaxy (MOVPE) and show single mode continuous wave emission up to 200 K. In pulsed operation we achieved single mode surface emission peak output powers exceeding 1 Watt at room temperature. The presented GaAs/AlGaAs laser features an air/AlGaAs waveguide, combined with a second-order distributed feedback grating. That laser shows 3 Watts of single mode output power via the surface at 78 K.