On-chip electro-optically tunable narrow linewidth Brillouin microlasers implemented in thin film lithium niobate

Abstract

On-chip narrow linewidth microlasers with real-time wavelength tunability are highly desirable for various applications including precision metrology, quantum technology, and coherent information processing. Realizing such laser remains a challenge despite significant advances made by various groups in recent years [Nat. Commun. 13, 5344 (2022); Nature 615, 411 (2023); Appl. Phys. Lett. 124, 131101 (2024); Nat. Photonics 13, 60 (2019)]. In this work, we overcome these hurdles and demonstrate on-chip electro-optically tunable Brillouin microlasers in compact lithium niobate on insulator (LNOI) microdisks with diameters of 31.5 um and 117.0 um by using cross-polarized SBS arrangement. A quasi-continuum band of bound shear mechanical modes inside the suspended microdisk are revealed for the first time, allowing feasible phase matching of stimulated Brillouin lasing (SBL). We achieve efficient cross-polarized optomechanical coupling and SBL via the significant photoelastic tensors of lithium niobate (e.g., p41=-1.51). This approach yields a 118 Hz intrinsic linewidth and a comparatively low threshold power of 3.15 mW. A real-time electro-optic tuning of the cross-polarized Brillouin scheme with a tuning efficiency of ~93.1 kHz/V is also achieved, further showcasing potential of LNOI platform for next-generation tunable photonic systems.