Lithium niobate (, LN) has been the dominant material platform for optical modulators widely used in optical fiber communications due to its excellent physical properties, such as its high electro-optic (EO) Pockels coefficient, low optical absorption, high intrinsic modulation bandwidth, and long-term material reliability[1,2]. However, conventional LN modulators based on low-index-contrast optical waveguides show weak EO interactions, limiting further improvement of modulation efficiency and reduction of device size. Recently, thin film LN-on-insulator (LNOI) has emerged as a promising platform for high-performance integrated modulators, as it offers strong optical confinement and thus high integration density. Several studies have demonstrated the integrated Mach–Zehnder modulators (MZMs) with low drive voltage, low optical insertion loss, and high EO bandwidths on both the LNOI platform[3,4] and silicon-based LN hybrid platform[5–7]. The modulation efficiency of integrated LN modulators with dry-etched LN waveguides has increased to [3,8], which is significantly higher than that of conventional modulators with ion-diffused or proton-exchanged waveguides (). Even so, an integrated LN modulator in the traveling-wave Mach–Zehnder configuration still has modulation lengths of 1–2 cm to achieve low-voltage energy-efficient modulation. Such footprint sizes are still too large for future optical interconnect applications.