Systematic investigation of millimeter-wave optic modulation performance in thin-film lithium niobate

Millimeter-wave(mmWave)band(30–300 GHz)is an emerging spectrum range for wireless communication,short-range radar,and sensor applications.mmWave-optic modulators that could efficiently convert mmWave signals into the optical domain are crucial components for long-haul transmission of mmWave signals through optical networks.At these ultrahigh frequencies,however,the modulation performances are highly sensitive to the transmission line loss as well as the velocity-and impedance-matching conditions,while precise measurements and modeling of these parameters are often non-trivial.Here we present a systematic investigation of the mmWave-optic modulation performances of thin-film lithium niobate modulators through theoretical modeling,electrical verifications,and electro-optic measurements at frequencies up to 325 GHz.Based on our experimentally verified model,we demonstrate thin-film lithium niobate mmWave-optic modulators with a measured 3-dB electro-optic bandwidth of 170 GHz and a 6-dB bandwidth of 295 GHz.The device also shows a low RF half-wave voltage of 7.3 V measured at an ultrahigh modulation frequency of 250 GHz.This work provides a comprehensive guideline for the design and characterization of mmWave-optic modulators and paves the way toward future integrated mmWave photonic systems for beyond-5G communication and radar applications.