High-efficiency and broadband on-chip electro-optic frequency comb generators

Abstract

Developments in integrated photonics have led to stable, compact, and broadband comb generators that support a wide range of applications including communication1, ranging2, spectroscopy3, frequency metrology4, optical computing5,6, and quantum information7,8. Broadband optical frequency combs can be generated in electro-optical cavities, where light passes through a phase modulator multiple times while circulating in an optical resonator9–12. However, broadband electro-optic frequency combs are currently limited by low conversion efficiencies. Here, we demonstrate an integrated electro-optic frequency comb with a conversion efficiency of 30% and an optical span of 132 nm, based on the coupled-resonator platform on thin-film lithium niobate13. We further show that, enabled by the high efficiency, the device acts as an on-chip femtosecond pulse source (336 fs pulse duration), which is important for applications in nonlinear optics, sensing, and computing. As an example, in the ultra-fast and high-power regime, we demonstrate the observation of a combined EO-χ^((3)) frequency comb. Our device paves the way for practical optical frequency comb generators as well as provides a platform to investigate new regimes of optical physics that simultaneously involve multiple nonlinearities.