An Integrated Low-Voltage Broadband Lithium Niobate Phase Modulator

Electro-optic phase modulators are critical components in modern communication, microwave photonic, and quantum photonic systems. Important for these applications is to achieve modulators with low half-wave voltage at high frequencies. Here, we demonstrate an integrated phase modulator, based on a thin-film lithium niobite platform, which simultaneously features small on-chip loss (~1 dB) and low half-wave voltage over a large spectral range (3.5-4.5 V at 5-40 GHz). By driving the modulator with a strong 30-GHz microwave signal corresponding to around four half-wave voltages, we generate an optical frequency comb consisting of over 40 sidebands spanning 10 nm in the telecom L-band. The high-electro-optic performance combined with the high-RF power-handling ability (3.1 W) of our integrated phase modulator is crucial for future photonics and microwave systems.