Chip-scale nonlinear bandwidth enhancement via birefringent mode hybridization

On-chip quantum information network requires qubit transfer between different wavelengths while preserving quantum coherence and entanglement, which requires the availability of broadband upconversion. Herein, we demonstrate a mode-hybridization-based broadband nonlinear frequency conversion on X-cut thin film lithium niobate. With the spontaneous quasi-phase matching and quasi-group-velocity matching being simultaneously satisfied, broadband second-harmonic generation with a 3-dB bandwidth up to 13 nm has been achieved in a micro-racetrack resonator. The same mechanism can work on the frequency conversion of the ultrashort pulse in the bent waveguide structure. This work will be beneficial to on-chip tunable frequency conversion and quantum light source generation on integrated photonic platforms and further enable on-chip large-capacity multiplexing, multichannel optical information processing, and large quantum information networks.