  Electro-optic modulators with low voltage and large bandwidth are crucial for
both analog and digital communications. Recently, thin-film lithium niobate
modulators have enable dramatic performance improvements by reducing the
required modulation voltage while maintaining high bandwidths. However, the
reduced electrode gaps in such modulators leads to significantly higher
microwave losses, which limit electro-optic performance at high frequencies.
Here we overcome this limitation and achieve a record combination of low RF
half-wave voltage of 1.3 V while maintaining electro-optic response with 1.8-dB
roll-off at 50 GHz. This demonstration represents a significant improvement in
voltage-bandwidth limit, one that is comparable to that achieved when switching
from legacy bulk to thin-film lithium niobate modulators. Leveraging the
low-loss electrode geometry, we show that sub-volt modulators with $>$ 100 GHz
bandwidth can be enabled.
