Advanced Electrode Design for Low-Voltage High-Speed Thin-Film Lithium Niobate Modulators

In this paper, we present a novel transmission line architecture in thin-film lithium niobate (TFLN) platforms to improve the velocity match between the microwave and the optical wave. Compared to conventional coplanar waveguide (CPW), the microwave index ($n_m$) of the proposed slotted electrodes can be optimized from 2.1 to 3 while maintaining the high modulation efficiency and 50-$\Omega$ impedance match. Equivalent-circuit model analysis and finite-element simulation are performed. The simulated half-wave voltage (V$_\pi$) of 1.2 V and E-O modulation bandwidth greater than 80 GHz is obtained for a 2-cm-long modulator. By utilizing the slotted slow-wave electrode, TFLN Mach-Zehnder modulators with CMOS-compatible operating voltage and 3-dB modulation bandwidth greater than 100 GHz are potentialized.