Hybrid integration of quantum cascade lasers with germanium-on-silicon waveguides for mid-infrared sensing applications.

We present a scheme for hybrid integration of quantum cascade laser bars with germanium-on-silicon waveguides operating in the mid-infrared. The laser bars are flip-chip bonded onto a germanium-on-silicon target chip without active alignment, achieving end-fire coupling efficiencies of up to 50% (3.03 dB loss) in pulsed operation. Optical power estimates indicate over 50 mW is coupled into the waveguide. The passive alignment approach, combined with a CMOS-compatible photonic integrated circuit fabrication process, offers a scalable pathway to fully integrated mid-infrared photonic systems for sensing, free-space communications, and the realization of novel light sources.