3D integration enables ultralow-noise isolator-free lasers in silicon photonics

Area of Science:

• Photonics
• Materials Science
• Electrical Engineering

Background:

• Photonic integrated circuits (PICs) are vital for telecommunications and data centers.
• Current PICs are limited in high-precision applications like microwave synthesizers and atomic clocks due to laser phase noise and integration challenges.
• Integrating ultralow-noise lasers and optical isolators on-chip is crucial for advancing these applications.

Purpose of the Study:

• To develop ultralow-noise lasers for silicon photonics that operate without optical isolators.
• To demonstrate the feasibility of three-dimensional (3D) integration for advanced PICs.
• To overcome the limitations of semiconductor laser phase noise and on-chip optical isolator integration.

Main Methods:

• Utilized three-dimensional integration techniques combining monolithic and heterogeneous processing.
• Integrated III-V gain media with ultralow-loss silicon nitride waveguides (optical loss ~0.5 dB/m).
• Fabricated PICs with ultrahigh-quality-factor cavities enabling isolator-free operation.

Main Results:

• Demonstrated ultralow-noise lasers and microwave synthesizers on a single silicon photonic chip.
• Achieved isolator-free operation due to the ultrahigh-quality-factor cavity.
• Showcased superior scalability, stability, and reliability for complex functionalities.

Conclusions:

• Three-dimensional integration on ultralow-loss PICs is a critical step towards advanced optical systems on silicon.
• This approach enables compact, robust, and high-performance photonic integrated circuits for demanding applications.
• The developed PICs overcome key barriers in laser noise and optical isolation for future photonic technologies.