On March 12, 2026, a groundbreaking research study, led by Researcher Hu Yaowen and Professor Gong Qihuang from Peking University's School of Physics, in collaboration with Professor Marko Loncar of Harvard University, was published in the esteemed international academic journal Nature Physics. Utilizing a thin-film lithium niobate platform, the team experimentally observed strongly coupled electro-optic frequency combs for the first time, comprehensively elucidated their universal dynamics, and achieved microwave-driven, on-chip programmable control of optical frequency combs. This milestone signifies the evolution of resonant electro-optic frequency combs from 'fixed-function light sources' to a new era of 'fully programmable photonic platforms.'

Frequency combs based on the electro-optic effect are instrumental in precision metrology, spectroscopy, photonic interconnects, and quantum computing. Traditional resonant electro-optic frequency combs establish controllable coupling within optical microcavities through microwave modulation, generating new frequency components with uniform spacing. However, they have long been limited by the 'nearest-neighbor coupling' mode, resulting in comb and pulse shapes that are highly sensitive to the pump wavelength and exhibit suboptimal system stability.

This study marks the first direct experimental observation of strongly coupled electro-optic frequency combs. By fine-tuning the modulation depth and optical detuning, the team unveiled the complete nonlinear state space of resonant electro-optic frequency combs. As modulation transitions into the strong coupling regime, single-tone microwaves establish parallel coupling channels among multiple cavity modes, generating multi-pulse states and transforming the frequency comb envelope from smooth decay to periodic oscillation.

Furthermore, the research showcased the capability to flexibly adjust the repetition rate and significantly enhance comb bandwidth and spectral shape through multi-tone microwave driving. This provides a more robust physical pathway for on-chip programmable pulse sources, with broad application potential in communications, metrology, microwave photonics, and arbitrary waveform generation.