Compact low-voltage lithium niobate racetrack modulator on a silicon nitride platform through micro-transfer printing

Thin-film lithium niobate (TFLN) modulators have been pushing the limits of high-speed modulation to higher bandwidths and lower driving voltages. However, these typically occupy large footprints, limiting their integration density. For many applications, compact low-voltage modulators are desired where the bandwidth is limited by other factors, e.g., lifetimes of atomic transitions. Furthermore, integration on a CMOS-compatible platform is desirable for scaling to larger systems and to leverage existing technologies. In this work, we heterogeneously integrate a compact low-voltage lithium niobate racetrack modulator of 250 μ m × 500 μ m on a silicon nitride (SiN) platform. The device consists of a racetrack-shaped X-cut TFLN slab, which is micro-transfer printed onto a SiN all-pass racetrack resonator. The modulator achieves a tuning efficiency of 1.7 pm V −1 (or 3.5 pm V −1 for double-arm operation) and a Q-factor of 285,000 (with intrinsic Q i = 608,000), ensuring low operating voltages up to a measured 3-dB bandwidth of 1.18 GHz. These results pave the way toward densely integrated compact low-voltage amplitude modulators on a scalable CMOS platform.