Surface acoustic wave-photonic devices in silicon nitride integrated circuits

Acoustic waves are introduced to a silicon nitride photonic integrated circuit. The acoustic waves are generated through thermo-elastic actuation in a metallic grating and monitored using photo-elastic modulation in a racetrack resonator readout waveguide. The stimulation of three acoustic modes of the layers structure is observed. The frequencies and group velocities of the three modes agree with calculations. The acoustic frequency reaches 1.3 GHz. The concept introduces high-frequency modulation to the otherwise passive silicon nitride platform. The efficiency of photo-elastic modulation is modest: estimated as 6 × 10⁻⁸ refractive index units for 1 W of optical pump power. With future work, the concept may find applications in microwave photonic signal processing, optical and mechanical sensors, and characterization of materials and layers.