One example system comprises a substrate and a waveguide disposed on the substrate to define an optical path on the substrate. The waveguide is configured to guide, inside the waveguide and along the optical path, a light signal toward an edge of the waveguide. The edge defines an optical interface between the waveguide and a fluidic optical medium adjacent to the edge of the waveguide. The system also includes an optical fluid and a fluid actuator configured to adjust a physical state of the optical fluid based on a control signal. The adjustment of the physical state of the optical fluid causes an adjustment of the fluidic optical medium adjacent to the edge.