Suspended thin-film lithium niobate modulator for broadband mid-infrared light modulation and frequency comb generation

The mid-infrared (MIR) spectral region is central to sensing, spectroscopy, and free-space optical communication, yet coherent and broadband electro-optic (EO) control remains limited by material loss, bandwidth constraints, and high switching voltages. Existing approaches based on quantum cascade laser modulation, nonlinear frequency conversion, or bulk EO devices suffer from fundamental trade-offs between efficiency, bandwidth, and scalability. Here we report a suspended thin-film lithium niobate (TFLN) MIR EO platform co-designed with velocity- and impedance-matched traveling-wave microwave electrodes. We achieve record-low half-wave voltages of 2.3–4.3 V across 2.4–3.6 μm and EO bandwidths up to 50 GHz, corresponding to a record voltage-bandwidth figure-of-merit of 17.4 GHz/V. High-frequency operation with 4.5–6.5 V is demonstrated at 25–35 GHz, together with 30-GHz-line-spacing MIR EO frequency comb generation spanning 0.8 THz. We further validate the platform in a free-space communication link, establishing a scalable high-performance MIR optoelectronic platform.