Dynamic electrical control of on-chip second-harmonic generation with ferroelectric NbOBr₂

Niobium oxide dihalide films show a second-harmonic generation (SHG) efficiency scaling with their thickness, owing to their weak interlayer electronic coupling, but their use in integrated nonlinear photonics has been limited by the lack of robust electrical tuneability. Here we integrate ferroelectric NbOBr₂, of thicknesses ranging from 20 nm to 40 nm, with a silicon nitride microring resonator to realize electrically reconfigurable SHG on a photonic chip. NbOBr₂ combines strong second-order susceptibility from intrinsic inversion-symmetry breaking with electrically switchable in-plane ferroelectric polarisation. By modulating the Schottky barrier at the NbOBr₂-metal interface, ferroelectric switching controls carrier injection, free carrier absorption and dispersion, thereby tuning the cavity-enhanced nonlinear response. The device achieves an SHG conversion efficiency of 158% W^-1 under continuous-wave excitation and a 53% electrical modulation depth. The polarisation states can also be programmed over multiple levels and retained after switching, enabling non-volatile control of the optical response. Using the fundamental and frequency-converted outputs as complementary channels, we further demonstrate dual-channel edge detection.