A High-Speed Thin-Film Lithium Niobate Modulator Compatible With Heterogeneous Integration

Thin-film lithium niobate (TFLN) integration platform is a leading candidate for photonics terahertz communication and sensing systems. The heterogeneous integration of indium phosphide (InP)-based active components with TFLN promises the realization of fully integrated terahertz transceivers on a single chip. Silicon-substrate TFLN is particularly attractive for this purpose due to its favorable thermal properties and heterogeneous integration compatibility. However, the development of high-speed modulators on this platform has been fundamentally impeded by the challenges of microwave-optical velocity mismatch and high radio-frequency (RF) loss. In this work, we overcome this limitation through the synergistic use of a slow-wave electrode design and selective silicon substrate etching. This approach collectively ensures low RF loss, excellent velocity matching, and full compatibility with heterogeneous integration processes. The demonstrated modulator achieves a half-wave voltage-length product of 2.2 V·cm and an electro-optic bandwidth exceeding 67 GHz, with an extrapolated 3-dB bandwidth beyond 122 GHz. This work establishes a foundational platform for the future development of heterogeneous integrated photonic terahertz transceiver chips.