Silicon Optomechanical Membrane Waveguides Based on Subwavelength Engineering of Photons and Phonons

On-chip Brillouin optomechanics has great potential for applications in communications, sensing, and quantum technologies. However, achieving tight confinement of near-infrared photons and gigahertz phonons in integrated waveguides remains a crucial challenge to yield high on-chip Brillouin gain. This challenge is solved in silicon-on-insulator (SOI) waveguides by removing the silica under-cladding. Here we show that subwavelength engineering of the longitudinal and transversal dimensions of Si membranes facilitates independent control of the photonic and phononic modes, allowing for strong Brillouin scattering. Here, we present two strategies to realize suspended silicon waveguides simultaneously confining the optical and mechanical modes in the core, based on subwavelength engineering. These structures provide significant Brillouin gain and allow optomechanical coupling with high-frequency mechanical modes.