Ultrabroadband integrated modulators involving materials beyond those available in silicon manufacturing increasingly rely on the Pockels effect. Among electro-optic materials, lithium tantalate offers comparable Pockels coefficients to lithium niobate but with significantly improved photostability, lower birefringence, higher optical damage threshold, and enhanced DC bias stability. Here we demonstrate wafer-scale heterogeneous integration of lithium tantalate films on low-loss silicon nitride photonic integrated circuits, achieving low optical losses ( ~ 14.2 dB/m) while combining the mature processing of silicon nitride waveguides with the ultrafast electro-optic response of thin-film lithium tantalate. The resulting devices achieve a 6 V half-wave voltage, and support modulation bandwidths of up to 100 GHz. We use single intensity modulators and in-phase/quadrature (IQ) modulators to transmit PAM4 and 16-QAM signals reaching up to 333 and 581 Gbit/s net data rates, respectively. Our results establish lithium tantalate-on-silicon nitride as a viable platform for RF photonics, interconnects, and analog signal processing.

Research Background

Silicon nitride photonic chips have become an important platform for on-chip nonlinear optics, efficient frequency conversion, traveling-wave optical parametric amplification, and other fields due to their advantages of low optical propagation loss, strong nonlinearity, high power handling capability, and CMOS compatibility. However, limited by its intrinsic material properties, silicon nitride does not exhibit the Pockels electro-optic effect. Existing silicon nitride-based modulators therefore typically rely on the thermo-optic or acousto-optic effects, which easily encounter bottlenecks in terms of bandwidth and modulation efficiency.

To meet the demand for high-efficiency, high-speed, and wide-bandwidth modulation in current applications such as communications and optical computing, researchers often require thin-film ferroelectric materials for constructing corresponding on-chip photonic devices. Currently, mainstream electro-optic platforms include thin-film lithium niobate (TFLN) and thin-film lithium tantalate (TFLT). Thin-film lithium niobate (TFLN) has been the conventional choice, while thin-film lithium tantalate (TFLT) has attracted significant attention in recent years. This is because, while retaining a comparable electro-optic coefficient, thin-film lithium tantalate offers superior performance in terms of stability in high-power devices, birefringence, optical damage threshold, and photorefraction. In addition, the industrial application of thin-film lithium tantalate in 5G/6G radio-frequency filters has led to a more complete supply chain for optical-grade substrates, further enhancing its engineering appeal.

Against the above background, integrating the low-loss advantage of silicon nitride waveguides with the high-speed electro-optic effect of thin-film lithium tantalate, and achieving wafer-level, repeatable, and high-volume fabrication, has become one of the current research hotspots.