Surface acoustic wave Brillouin photonics on a silicon nitride chip

Seamlessly integrating stimulated Brillouin scattering (SBS) in a low-loss and mature photonic integration platform remains a complicated task. Virtually all current approaches fall short in simultaneously achieving strong SBS, low losses and technological scalability. Here we incorporate strong SBS into a standard silicon nitride platform by the simple deposition of a tellurium oxide layer, a commonly used material in acousto-optic modulators. In these heterogeneously integrated waveguides, we harness SBS interactions actuated by surface acoustic waves leading to more than two-orders-of-magnitude gain enhancement. Three applications of this platform are demonstrated: (1) a silicon-nitride-based Brillouin amplifier with 5-dB net optical gain, (2) a compact intermodal stimulated Brillouin laser capable of high-purity radio-frequency signal generation with a 7-Hz intrinsic linewidth and (3) a widely tunable microwave photonic notch filter with an ultranarrow linewidth of 2.2 MHz enabled by Brillouin-induced opacity. These advancements can unlock an array of new radio-frequency and optical technologies to be directly integrated in silicon nitride.