Breaking voltage-bandwidth limits in integrated lithium niobate modulators using micro-structured electrodes

Electro-optic modulators with low voltages and large bandwidths are crucial for both analog and digital communication. Recently, thin-film lithium niobate modulators have emerged as a strong candidate for next generation electro-optic solutions. These modulators offer significantly improved voltage-bandwidth performances over the existing bulk lithium niobate modulators while preserving key material advantages such as linear response, high extinction ratio, high optical power handling ability, and low optical losses. However, reduced electrode gaps in miniaturized thin-film modulators lead to higher microwave losses, which limit electro-optic performances at high frequencies. Here we overcome this limitation to achieve a record combination of low RF half-wave voltage (V-pi) of 1.3 V while maintaining electro-optic response with 1.8 dB roll-off at 50 GHz using micro-structured electrodes. Our demonstration represents a significant improvement in voltage-bandwidth performance, one that is comparable to the performance gain in switching from legacy bulk to thin-film lithium niobate modulators. Such a micro-structured electrode design could enable sub-volt modulators with >100 GHz bandwidth. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement