Acousto-Optic Modulation on Silicon-Aluminum Nitride Hybrid-Integrated Platform for Cryogenic Applications

Silicon platforms are widely recognized as an industry standard for photonic integrated circuits. However, conventional tuning mechanisms, such as thermo-optic and plasma dispersion effects, impose limitations in advanced applications, such as quantum computing, where low-loss and cryogenic operation are critical. Acousto-optic (AO) modulation offers a promising alternative, broadening the scope of silicon photonics. Here, we investigate an aluminum nitride (AlN)-silicon hybrid platform to enable AO modulation on silicon waveguides. The AO interaction is enhanced through a Fabry-Perot resonant cavity, achieving a π-phase shift voltage (V_π) of 27.8 V and a half-wave voltage-length product (V_πL) of 0.55 V·cm with a modulation length of 200 μm. We also demonstrate AO modulation under cryogenic conditions, where the device performance metrics improve to 16.5 V and 0.33 V·cm, respectively. Fabricated using complementary metal-oxide-semiconductor-compatible processes, this AlN-silicon device offers seamless integration with photonic and electronic components, underscoring its potential for next-generation photonic systems.