Self-Injection locking to silicon-nitride microresonator

In this study, we develop a theoretical model and experimentally demonstrate semiconductor laser diode self-injection locking to a silicon nitride chip-integrated Fabry-Pérot microresonator. Using this approach we demonstrate semiconductor laser with Lorentzian linewidth below 400 Hz in the compact form-factor.

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Picture: Integrated Fabry-Perot Microresonator on Silicon-Nitride Photonic Chip

Many advanced laser applications benefit from low-noise and narrow-linewidth lasers. A highly attractive approach that enables compact and low-noise semiconductor laser diodes (LD) is self-injection-locking (SIL) to an external high-quality integrated microresonator. In this study, we extend the SIL technique to chip-integrated Fabry-Pérot (FP) microresonators. We developed a theoretical model for SIL with side-coupled FP microresonators and experimentally characterised SIL with this geometry. The side coupler enables precise and deterministic control of the injection amplitude crucial for SIL. We demonstrate a low-frequency noise semiconductor laser, limited by only by the fundamental thermo-refractive noise of the FP microresonator. These results complement existing SIL techniques and are directly relevant to compact low-noise laser systems.

Reference:

Alexander E. Ulanov, Thibault Wildi, Utkarsh Bhatnagar, and Tobias Herr, "Laser diode self-injection locking to an integrated high-Q Fabry–Perot microresonator," Opt. Lett. 49, 6261-6264 (2024)

https://opg.optica.org/ol/fulltext.cfm?uri=ol-49-21-6261&id=561971