High spectral brightness QCLs

Multi-watt continuous wave operation has been demonstrated for broad-area, Fabry-Perot Quantum Cascade Lasers (QCLs). In addition to high optical power, increase in operational range for infrared countermeasures requires low atmospheric propagation losses for emitted radiation. Single-line operation tailored to low atmospheric losses can be achieved for QCLs utilizing the distributed feedback grating etched into the laser waveguide along full cavity length. An alternative solution explored here is to utilize the grating as an outcoupler, so-called distributed Bragg reflector (DBR) configuration. Since output facet reflectivity of only several percent is needed for high-performance QCLs, the DBR section can be made very short, on the order of several hundred microns, leaving the rest of the (optimized) laser waveguide unchanged. Top-metal DBR configuration with grating etched into the top cladding layers of the QCL structure offers the advantage of a low fabrication cost. Therefore, broad-area DBR QCLs with a top-metal grating promise a significant improvement in spectral brightness and at the same time a low fabrication cost. The main design principles for these devices will be discussed in this talk along with preliminary experimental data.