Low-voltage, high-bandwidth electro-optical modulators are crucial for both analog and digital communications. Recently, thin-film lithium niobate modulators have dramatically improved performance by reducing the required modulation voltage while maintaining high bandwidth. However, minimizing electrode gaps in these modulators results in significantly higher microwave losses, limiting electro-optical performance at high frequencies. This paper overcomes this limitation, achieving a record-breaking combination of a low half-wave RF voltage of 1.3 V while maintaining electro-optical response with a roll-off of 1.8 dB at 50 GHz. This demonstration represents a significant improvement in the voltage bandwidth limit, comparable to that achieved by moving from traditional lithium niobate modulators to thin-film modulators. By leveraging low-loss electrode geometry, we demonstrate that sub-voltage modulators with a bandwidth of 100 GHz are achievable.
