Enhanced stimulated Brillouin scattering in valley Hall photonic-phononic topological waveguides.

Stimulated Brillouin scattering (SBS) provides a robust and versatile foundation for the development of mode-locked lasers, microwave signal generators, and optical gyroscopes across diverse optical platforms. Nonetheless, the relatively low efficacy of Brillouin interactions in traditional silicon photonic waveguides presents a barrier to the advances of silicon-based Brillouin laser technology. The emergence of hybrid photonic-phononic waveguides has brought to light the robust and adaptable nature of Brillouin interactions in silicon, marking a significant advancement. Here we numerically calculated the SBS gain in the valley Hall photonic-phononic topological insulator (VH-PTI), which confines the phonons in the optical waveguide to achieve light transmission under large-angle bending. Our results show that the SBS gain at 9.101 GHz is G/Q = 14.94 W·m, enhanced by 1.4 times compared to the highest reported value so far. In addition, we realized arbitrary location decoupling on the chip, introducing a topological state into SBS devices. This work provides a way to implement VH-PTI into silicon photonic circuits for Brillouin laser applications.