Optimal design of heterogeneously integrated silicon nitride-lithium niobate modulator

Abstract Heterogeneously integrated lithium niobate (LN) electro-optic modulators have great potential for high-speed applications, but challenges remain in optimizing performance, particularly in terms of modulation efficiency, bandwidth, and the trade-offs. This work presents an optimized design for a silicon-nitride (Si 3 N 4 )-loaded modulator on a thin-film lithium niobate (TFLN) platform, consisting of 300 nm-thick LN film and 300 nm-thick Si 3 N 4 optical waveguide. By systematically optimizing the dielectric layer thickness, electrode parameters, and achieving velocity and impedance matching, we demonstrate a modulator with a bandwidth exceeding 200 GHz. Our collaborative optimization scheme highlights the critical role of reducing the silicon oxide box layer thickness for velocity matching. We show that multiple structural configurations can achieve bandwidths greater than 120 GHz with V π · L ＜ 4 V·cm, providing feasibility in low-loss design and fabrication. These findings offer valuable design guidelines for high-performance electro-optic modulators suitable for data communications.