Hybrid Integration of Quantum Cascade Lasers with Germanium-on-Silicon waveguides for Mid-Infrared Sensing Applications

TL;DR

This paper introduces a scalable hybrid integration method combining quantum cascade lasers with germanium-on-silicon waveguides, enabling efficient mid-infrared light coupling for sensing and communication applications.

Contribution

A novel flip-chip bonding technique for quantum cascade lasers onto germanium-on-silicon chips with high coupling efficiency and passive alignment, compatible with CMOS processes.

Findings

Achieved up to 45% end-fire coupling efficiency in pulsed operation.

Coupled optical power of 20-30 mW into waveguides.

Demonstrated a scalable, CMOS-compatible integration approach.

Abstract

We present a novel 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, acheiving end-fire coupling efficiency of up to 45% (3.5 dB loss) in pulsed operation. Optical power estimates indicate 20-30 mW coupled into the waveguides. 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 realisation of novel light sources.