Intramodal stimulated Brillouin scattering in suspended AlN waveguides

Aluminum nitride (AlN), a wide-bandgap III-V material, offers excellent transparency in the optical communication band and a favorable refractive index for strong optical confinement, making it a promising platform in stimulated Brillouin scattering (SBS). Here, we observe, for the first time, optically excited SBS in suspended AlN-on-silicon waveguides. A Brillouin gain coefficient of 91.8 m^-1 W^-1 is achieved at an acoustic frequency of 2.32 GHz, with a linewidth of 10.1 MHz. The Brillouin nonlinear response can be tailored by varying the waveguide dimensions. Furthermore, the Bragg grating-based Fabry-Pérot (FP) resonator enhances the gain coefficient to 150.37 m^-1 W^-1 and results in a narrowed linewidth of 9.87 MHz. These results not only validate the feasibility of strong intrinsic Brillouin interaction in suspended AlN waveguides but also pave the new way for CMOS-compatible on-chip Brillouin amplifiers, lasers, and isolators.