Slow-light modulator with shielded traveling wave electrode on a thin-film lithium niobate platform

Thin-film lithium niobate (TFLN) electro-optic modulators have demonstrated high modulation efficiency and ultra-wide bandwidth. To further improve performance and integration, TFLN-based slow-light (SL) modulators have garnered considerable attention. However, the electro-optic velocity mismatch, caused by the significantly faster propagation speed of microwave signals compared to optical waves in SL modulators, limits modulation bandwidth. To overcome this limitation, we propose a novel SL modulator with shielded traveling-wave electrodes on the TFLN platform. The shielded electrodes effectively reduce the microwave signal propagation velocity, enabling velocity matching between electrical and optical waves, thereby increasing bandwidth without sacrificing modulation efficiency. Simulation results show a modulation efficiency of 0.97 V·cm and a 3-dB electro-optic bandwidth of 120 GHz for a 2 mm long modulator with a 30 Ω terminating resistance. This approach not only doubles the modulation efficiency of conventional TFLN modulators but also achieves a higher bandwidth.