Single-mode quantum cascade lasers employing asymmetric Mach-Zehnder interferometer type cavities

We employ properly designed asymmetric Mach-Zehnder interferometer structures as effective wavelength filters and monolithically integrate them in conventional Fabry-Perot cavities to facilitate single-mode operation of the lasers. With such asymmetric Mach-Zehnder interferometer type laser cavities, continuously tunable single-mode operation of quantum cascade (QC) lasers is achieved in pulsed mode from 80 K up to room temperature and in continuous-wave mode with side-mode suppression ratio up to ∼35 dB. These devices are fabricated with the same process as simple ridge lasers, therefore providing a promising solution to achieving more cost-effective single-mode QC lasers.