Integrated Brillouin photonics in thin-film lithium niobate

Stimulated Brillouin scattering (SBS) is revolutionizing low-noise lasers and microwave photonics. However, a scalable and efficient integrated platform for Brillouin photonics has remained elusive. Here, we leverage the well-established thin-film lithium niobate (TFLN) platform to address these long-standing limitations. We report two distinct SBS processes on this platform, driven by surface acoustic wave (SAW) with 20-megahertz linewidth or bulk acoustic waves with a linewidth 200 times broader. Exploiting the strong SAW SBS gain, we demonstrate a narrowband internal net gain amplifier overcoming propagation losses. In addition, we achieve a stimulated Brillouin laser in TFLN, featuring a tuning range exceeding 20 nanometers and enabling high-purity radio frequency signal generation with an intrinsic linewidth of 9 hertz. Furthermore, we develop a programmable, multifunctional integrated Brillouin microwave photonic processor capable of notch filtering, bandpass filtering, or true time delay. This work bridges SBS with advanced TFLN technologies such as high-speed modulators and wide-band optical frequency combs, unlocking new paradigms for integrated Brillouin photonics.