Sub-terahertz bandwidth capactively-loaded thin-film lithium niobate electro-optic modulators based on an undercut structure

Abstract

A thin film lithium niobate (TFLN) electro-optic modulator based on a partially removed benzocyclobutene (BCB) bonding layer is proposed for sub-terahertz bandwidth. Low-loss microwave transmission is realized by periodic capacitively loaded travelling-wave electrodes (CL-TWEs) with an undercut structure, and the air-filled region beneath the modulator arms is adjusted to secure impedance and velocity matching. A low half-wave voltage length product of 1.2 V·cm can be achieved with 2-µm-gap loaded electrodes, while the 3-dB electro-optic modulation bandwidth for 10 mm modulation length is estimated beyond 300 GHz, thus allowing sub-terahertz operation.