Hybrid integration of InGaN lasers in a foundry-fabricated visible-light photonics platform

This article presents a novel approach to hybrid integration of InGaN laser diodes (LDs) with foundry-fabricated visible-light silicon photonics platforms, employing passive-alignment flip-chip bonding. The work demonstrates the successful integration of blue (450 nm) LDs with silicon nitride (SiN) waveguides and photonic devices, such as thermo-optic switches and photodetectors. The integration method achieved a maximum on-chip optical power of 60.7 mW and wall-plug efficiency of 7.8%, which is the highest reported for hybrid-integrated visible-spectrum lasers.

Key Points:

1. Integration Methodology: The method uses passive-alignment flip-chip bonding, which is highly scalable and suitable for high-volume manufacturing. The process involves precise in-plane alignment using lithographically defined alignment marks and mechanical stoppers, and sub-micron accuracy is achieved with a semi-automated die bonder equipped with a vision system.

2. Performance of Bonded LDs: The integrated LDs maintain stable operation at temperatures up to 80°C. The on-chip optical power varies across samples, with a maximum of 60.7 mW achieved, and coupling loss is 1.1 dB. The optical spectra show a slight redshift with increasing drive current, consistent with heating effects.

3. Misalignment Tolerances: The coupling efficiency is affected by misalignment, especially at the 450 nm wavelength, due to the small optical mode size. However, the study found minimal rotational misalignment (within 0.12°) after bonding, and efforts to reduce coupling loss through improved alignment precision are discussed.

4. Active Photonic Integrated Circuit (PIC): A proof-of-concept PIC is presented that includes the hybrid-integrated LD, a Si photodetector, and a thermo-optic switch for optical routing and attenuation. This active PIC showcases the potential for complex, functional PICs based on the hybrid integration of visible-light LDs.

5. Challenges and Future Work: While the flip-chip bonding approach is scalable, challenges remain in reducing variability in laser-to-chip alignment. The paper suggests improvements, such as higher-precision die bonding and optimized waveguide coupler designs, to reduce misalignment losses and increase assembly yield.

6. Applications: This integration platform opens up opportunities for applications in augmented reality, quantum information processing, biosensing, and other visible-light applications. The hybrid integration of visible-wavelength LDs with Si photonics also lays the foundation for wavelength-tunable lasers and advanced microdisplays.

In conclusion, this work highlights a scalable and practical approach for integrating visible-light lasers into photonic circuits, pushing forward the potential of visible-spectrum photonics in diverse emerging technologies.