Capacitive-loaded traveling wave electrodes on thin film lithium niobate for sub-terahertz operation

This paper presents the experimental demonstration of a capacitive-loaded traveling wave electrode (CLTWE) on a thin-film lithium niobate electro-optic modulator designed for ultra-wideband operation, up to the sub-terahertz region. The parametric structural analysis of the T-rail in the CLTWE and its periodicity were varied to evaluate its high-frequency loss and phase index behavior. Modulator designs having various T-rail periodicities were fabricated with the S-parameters and the optical response of the TFLN modulators was characterized up to 220 GHz. The measured results reveal that the cutoff frequency of the CLTWE strongly depends on the T-rail periodicity. The 20-mm long Mach-Zehnder Modulator (MZM) with 50 µm T-rail periodicity exhibits a half-wave voltage (V π ) of 1 V with a corresponding 3-dB bandwidth of approximately 125 GHz, and 6-dB bandwidth of 180 GHz.