Low Vπ thin-film lithium niobate modulator fabricated with photolithography

Thin-film lithium niobate (TFLN) modulators are expected to be an ideal solution to achieve a super-wide modulation bandwidth needed by the next-generation optical communication system. To improve the performance, especially to reduce the driving voltage, we have carried out a detailed design of the TFLN push-pull modulator by calculating 2D maps of the optical losses and V-pi for different ridge waveguide depths and electrode gaps. Afterwards the modulator with travelling wave electrodes was fabricated through i-line photolithography and then characterized. The measured V-pi for a modulator with 5-mm modulation arm length is 3.5 V, corresponding to voltage-length product of 1.75 V.cm, which is the lowest among similar modulators as far as we know. And the measured electro-optic response has a 3-dB bandwidth beyond 40 GHz, which is the limitation of our measurement capability. The detailed design, fabrication and measurement results are presented. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement