High-Efficiency Thin-Film Lithium Niobate Modulator Enabled by Slow-Wave Electrode

Thin-film lithium niobate (TFLN) modulators have emerged as a critical technology in modern photonic systems due to their exceptional performance metrics, including low driving voltage, ultrahigh bandwidth, and compact footprint. These attributes make them indispensable for applications in high-speed optical communications, coherent transmission systems, and microwave photonics. However, conventional electro-optic modulators are fundamentally constrained by a well-known tradeoff between operational bandwidth and half-wave voltage. To circumvent this limitation, we implemented a novel electrode design incorporating periodically capacitance-loaded travelingwave structures combined with substrate etching for precise velocity matching. In this work, we demonstrate a compact TFLN modulator with a device length of 5.8 mm, achieving a remarkable half-wave voltage length product of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$2.2 \mathrm{V} \cdot \text{cm}$</tex> while maintaining an electro-optic bandwidth of 67 GHz at 2 dB roll-off.