Brillouin-based phase shifter in a silicon waveguide

Integrated silicon microwave photonics offers great potential in microwave phase shifter elements, and promises compact and scalable multi-element chips that are free from electromagnetic interference. Stimulated Brillouin scattering, which was recently demonstrated in silicon, is a particularly powerful approach to induce a phase shift due to its inherent flexibility, offering an optically controllable and selective phase shift. However, to date, only moderate amounts of Brillouin gain have been achieved and theoretically this would restrict the phase shift to a few tens of degrees, significantly less than the required 360°. Here, we overcome this limitation with a phase enhancement method using RF interference, showing a 360° broadband phase shifter based on Brillouin scattering in a suspended silicon waveguide. We achieve a full 360° phase shift over a bandwidth of 15 GHz using a phase enhancement factor of 25, thereby enabling a practical broadband Brillouin phase shifter for beam forming and other applications.