  Acousto-optic integration offers numerous applications including low-loss
microwave signal processing, nonreciprocal light propagation, frequency comb
generation, and broadband acousto-optic modulation. State-of-the-art
acousto-optic systems are mainly implemented entirely using in-house
fabrication processes, which despite excellent performance typically suffer
from low yield and are not compatible with mass production through foundry
processes. Here, we demonstrate a highly efficient wideband acousto-optic
modulator (AOM) implemented on a silicon photonics foundry process enabling
high-yield low-cost mass production of AOMs with other photonic and electronic
devices on the same substrate. In the reported structure, a 150 ${\mu}$m long
AlScN-based acoustic transducer launches surface acoustic waves (SAW), which
modulate the light passing through a silicon optical waveguide. A modulation
efficiency of -18.3 dB over a bandwidth of 112 MHz is achieved, which to our
knowledge is the highest reported efficiency and bandwidth combination among
silicon based AOMs, resulting in about an order of magnitude
$BW(V_{\pi}L)^{-1}$ figure-of-merit improvement compared to the
state-of-the-art CMOS compatible AOMs. The monolithically integrated
acousto-optic platform developed in this work will pave the way for low-cost,
miniature microwave filters, true time delays, frequency combs, and other
signal processors with the advanced functionality offered by foundry-integrated
photonic circuits.
