Brillouin-Active Subwavelength Silicon Membrane Waveguides

On-chip Brillouin scattering plays a key role in numerous applications in the domain of signal processing and microwave photonics due to the coherent bidirectional coupling between near-infrared optical signals and GHz mechanical modes. Here, we propose and demonstrate a novel subwavelength waveguide design to achieve narrow linewidth and strong optomechanical interaction. We experimentally demonstrate optomechanical coupling with 5–8 MHz linewidth and a coupling strength of GB = 1360 W−1m−1. A Stokes gain of 1.5 dB and anti-Stoke attenuation of −2 dB is observed for a 6 mm-long waveguide with 35.5 mW of input power. We show tuning of the mechanical frequency between 5 and 8 GHz by geometrical optimization without loss of the optomechanical coupling strength.