Dual-band silicon nitride-loaded lithium niobate electro-optic modulator with a record-breaking speed of 600 Gbps

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Electro-optic modulators (EOMs) are pivotal for optical communication systems, converting electrical signals to the optical domain. To further maximize spectral efficiency and boost transmission capacity, endowing EOMs with dual-band operation capability has become imperative. Here, we demonstrate a dual-band silicon nitride-loaded thin-film lithium niobate modulator that supports energy-efficient operation in both the O- and C-band using a unified photonic-electronic architecture. The device integrates dual-band grating couplers and bidirectional dual-band multiplexers with capacitively loaded traveling-wave electrodes engineered for high-speed modulation. By tailoring the waveguide geometry to minimize inter-band group-index disparity, the modulator achieves simultaneous velocity matching across widely separated wavelengths. The proposed EOM achieves PAM-8 transmission at a raw line rate of 600 Gbps before FEC overhead at both 1310 and 1550 nm, with corresponding power consumption of 0.82 and 0.89 fJ/bit, respectively. Our results establish a scalable route toward multi-band thin-film lithium niobate photonic interconnects for future high-capacity optical communication systems.