by Mat Dirjish

CEA-Leti’s latest research highlights major progress in the integration of quantum cascade lasers (QCLs) with silicon photonic platforms for mid-infrared (MIR) applications. The research compares three complementary hybrid laser architectures that collectively advance the practicality, flexibility, and scalability of MIR photonics.

Mid-infrared light plays a critical role in technologies such as gas sensing, chemical spectroscopy, biomedical diagnostics, and security. Although important, MIR photonic systems remain large, costly, and difficult to manufacture at scale. Integrating MIR light sources directly onto silicon photonic platforms offers a path toward smaller and more manufacturable systems.

The research demonstrates and compares three hybrid III-V/silicon QCL architectures, each addressing a different integration challenge:

1. Hybrid Distributed Feedback QCL on Silicon-on-Nothing-on-Insulator with Adiabatic Coupling. This approach enables single-mode emission around 4.3 µm with optical power transfer from the III-V active region into silicon waveguides. High-index-contrast silicon photonics provide precise feedback and light routing, making this architecture viable for scalable photonic integrated circuits targeting spectroscopy and chemical sensing.
2. Hybrid QCL with an External Silicon Distributed Bragg Reflector Cavity. This configuration, decouples optical gain and optical feedback. The III-V material provides amplification, while wavelength selection and feedback occurs in silicon using distributed Bragg reflector (DBR) cavities. This separation offers greater design flexibility and opens a path toward tunable and multifunctional MIR sources for spectroscopic and sensing systems.
3. Ultra-Compact QCL Micro-Sources Based on Photonic Crystals & Micro-Rings. Miniature light sources in these devices achieve footprints below 100 µm² by leveraging strong optical confinement and resonant effects. The resulting extreme miniaturization enables dense on-chip integration and supports new system architectures where size, power consumption, and integration density are critical.

Summarily, the collective results indicate that silicon photonics can play an active role in mid-infrared laser systems. They show how different architectures trade off stability, flexibility, and footprint, providing designers with a practical toolkit for MIR photonic systems.

Alexis Hobl, lead author of the “Advanced Architectures for Hybrid III-V/Silicon Quantum Cascade Lasers: Toward Integrated Mid-Infrared Photonic Platforms” paper, explains, “By combining quantum cascade lasers with silicon photonics, we are bringing mid-infrared sources closer to the level of integration and scalability that silicon platforms have already achieved in the near-infrared.”

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