Thermally Tunable Quantum Cascade Laser With an External Germanium-on-SOI Distributed Bragg Reflector

Quantum cascade lasers (QCLs) are essential components for mid-infrared optical spectroscopy. Currently, widely tunable QCLs are using an external diffraction grating to tune the laser wavelength. In this paper we present a compact tunable QCL that is thermally tuned by a distributed Bragg reflector (DBR) implemented on a Germanium-on-SOI (Ge-on-SOI) waveguide circuit. The 5.1x  $\mu \rm m$ wavelength laser, operating in pulsed mode at room temperature, is continuously tuned over 50 nm.