Quantum cascade lasers optical power enhancement through the optimization of high-reflection coatings

In this work, we optimized high-reflection (HR) coatings to increase the optical power of quantum cascade lasers (QCLs). Using Electron Beam Physical Vapor Deposition, we developed a simple method for creating broadband multilayer HR coatings without additional steps like photolithography. This process involved depositing an insulating layer of yttrium oxide, an adhesion layer of titanium, and a gold thin film for reflectivity. We examined the impact of obtained coatings on the light-voltage-current (LIV) characteristics of QCLs, noting increased optical power and reduced threshold current. Optimized HR structures were applied in different QCLs, including devices emitting radiation with a wavelength of 4 µm, and in QCLs emitting radiation with a wavelength of 13 µm. Eventually, based on the obtained LIV, and obtained wall plug efficiencies, the impact of the obtained HR coatings for QCLs emitting a given wavelength has been discussed.