Dual-laser self-injection locking to an integrated microresonator

TL;DR

This paper demonstrates dual-laser self-injection locking to an integrated microresonator, achieving simultaneous linewidth narrowing, noise suppression, and phase stabilization of two lasers, with potential applications in advanced photonic systems.

Contribution

It introduces the first experimental demonstration of dual-laser SIL on an integrated microresonator, including a comprehensive theoretical analysis of their nonlinear interactions.

Findings

Simultaneous spectrum collapse of both lasers

Linewidth narrowing and high-frequency noise suppression

Coherent addition of laser outputs

Abstract

Diode laser self-injection locking (SIL) to a whispering gallery mode of a high quality factor resonator is a widely used method for laser linewidth narrowing and high-frequency noise suppression. SIL has already been used for the demonstration of ultra-low-noise photonic microwave oscillators and soliton microcomb generation and has a wide range of possible applications. Up to date, SIL was demonstrated only with a single laser. However, multi-frequency and narrow-linewidth laser sources are in high demand for modern telecommunication systems, quantum technologies, and microwave photonics. Here we experimentally demonstrate the dual-laser SIL of two multifrequency laser diodes to different modes of an integrated Si$_3$N$_4$ microresonator. Simultaneous spectrum collapse of both lasers, as well as linewidth narrowing and high-frequency noise suppression , as well as strong nonlinear interaction of the two fields with each other, are observed. Locking both lasers to the same mode results in a simultaneous frequency and phase stabilization and coherent addition of their outputs. Additionally, we provide a comprehensive dual-SIL theory and investigate the influence of lasers on each other caused by nonlinear effects in the microresonator.