Tailorable stimulated Brillouin scattering in nanoscale silicon waveguides

TLDR

Nanoscale modal confinement radically enhances Kerr and Raman nonlinearities in silicon waveguides, yet stimulated Brillouin scattering remains suppressed in conventional nanophotonics, limiting Brillouin‑based silicon technologies. We aim to demonstrate, for the first time, stimulated Brillouin scattering in silicon waveguides using a new class of hybrid photonic–phononic waveguides. The hybrid waveguides combine photonic and phononic confinement to enable forward‑stimulated Brillouin scattering. These waveguides achieve a traveling‑wave forward‑stimulated Brillouin nonlinearity over 1,000 times larger than prior systems, strongly coupling to phonons from 1 to 18 GHz and enabling integration of silicon photonics, MEMS, and CMOS signal‑processing on chip.

Abstract

Abstract Nanoscale modal confinement is known to radically enhance the effect of intrinsic Kerr and Raman nonlinearities within nanophotonic silicon waveguides. By contrast, stimulated Brillouin-scattering nonlinearities, which involve coherent coupling between guided photon and phonon modes, are stifled in conventional nanophotonics, preventing the realization of a host of Brillouin-based signal-processing technologies in silicon. Here we demonstrate stimulated Brillouin scattering in silicon waveguides, for the first time, through a new class of hybrid photonic–phononic waveguides. Tailorable travelling-wave forward-stimulated Brillouin scattering is realized—with over 1,000 times larger nonlinearity than reported in previous systems—yielding strong Brillouin coupling to phonons from 1 to 18 GHz. Experiments show that radiation pressures, produced by subwavelength modal confinement, yield enhancement of Brillouin nonlinearity beyond those of material nonlinearity alone. In addition, such enhanced and wideband coherent phonon emission paves the way towards the hybridization of silicon photonics, microelectromechanical systems and CMOS signal-processing technologies on chip.