Monolithic lithium niobate photonic circuits for Kerr frequency comb generation and modulation.

Microresonator Kerr frequency combs could provide miniaturised solutions for a wide range of applications. Many of these applications however require further manipulation of the generated frequency comb signal using photonic elements with strong second-order nonlinearity (χ⁽²⁾). To date these functionalities have largely been implemented as discrete components due to material limitations, which comes at the expense of extra system complexity and increased optical losses. Here we demonstrate the generation, filtering and electro-optic modulation of a frequency comb on a single monolithic integrated chip, using a nanophotonic lithium-niobate platform that simultaneously possesses large electro-optic (χ⁽²⁾) and Kerr (χ⁽³⁾) nonlinearities, and low optical losses. We generate broadband Kerr frequency combs using a dispersion-engineered high-Q lithium-niobate microresonator, select a single comb line using an electrically programmable add-drop filter, and modulate the intensity of the selected line. Our results pave the way towards monolithic integrated frequency comb solutions for spectroscopy, data communication, ranging and quantum photonics. Kerr microcombs promise the miniaturization of frequency comb sources, but many applications require additional second-order nonlinearities. Here, Wang et al. demonstrate that comb generation and second-order functionalities can be monolithically integrated on a single lithium niobate chip. [ABSTRACT FROM AUTHOR]