Highly-efficient, narrow-linewidth Brillouin microlasers implemented in compact thin-film lithium niobate microresonators

TL;DR

This paper demonstrates a highly efficient, narrow-linewidth Brillouin microlaser in a compact thin-film lithium niobate microresonator, achieving record-high performance in efficiency and low threshold for integrated photonics.

Contribution

It introduces a novel approach combining cross-polarized scattering and mode splitting to optimize resonance conditions in TFLN microresonators for Brillouin lasing.

Findings

Achieved a 2.88 Hz intrinsic linewidth.

Realized 57.92% on-chip conversion efficiency.

Lowered pump threshold to 1.03 mW.

Abstract

Stimulated Brillouin microlasers offer chip-scale light sources with high spectral purity and low phase noise--key attributes for applications spanning precision metrology, quantum technologies, and coherent information processing. However, simultaneously bringing both pump and scattered waves into resonance often compromises photon confinement or modal volume, resulting in limited conversion efficiency and elevated thresholds. In this work, a novel approach is proposed to generate Brillouin microlasers with high efficiency, low threshold, and narrow linewidth, by combining a cross-polarized stimulated Brillouin scattering scheme with intentional Stokes mode splitting to compensate for mode detuning. Triple-resonance and phase-matching conditions are simultaneously achieved in a 114-um-diameter thin-film lithium niobate (TFLN) microresonator, enabling precise alignment with both the ~10-GHz Brillouin shift and the ~100-MHz narrow gain bandwidth. The resulting Brillouin microlaser achieves a narrow intrinsic linewidth of 2.88 Hz, a short-term integral linewidth of 185 Hz, an on-chip conversion efficiency of 57.92%, and a pump threshold as low as 1.03 mW. Both the conversion efficiency and the lasing threshold represent record-high performance for the TFLN platform to date.