Heterogeneously-integrated lasers on thin film lithium niobate

We demonstrate a versatile heterogeneous integration platform unifying III-V gain with thin-film lithium niobate (TFLN) photonic circuits to create high-performance lasers with integrated functionality. This breakthrough overcomes the critical barrier to fully integrated photonic systems by combining optical gain, low-loss cavities, and phase control on a single chip. We present two distinct laser architectures: a distributed feedback laser achieving 11.0 kHz intrinsic linewidth and 4.0 mW in-fiber power through self-injection locking to a high-Q TFLN resonator, and a Vernier ring laser exhibiting 44 nm continuous tuning range with $>$ 40 dB side-mode suppression ratio. Crucially, the heterogeneous integration of the gain section with TFLN's components provides a promising path to implementing direct intracavity modulation, which is a functionality that typically requires discrete components. This inherent capability makes our platform a foundational advancement for future compact, robust systems in coherent communications, ultrafast optical metrology, quantum photonic processors, and microwave photonic systems operating at GHz bandwidths, marking a significant advancement toward complete photonic system integration.