Electrically tunable ferroelectric NbOBr2-integrated nonlinear photonics

Niobium oxide dihalides such as NbOCl2, featured by vanishing interlayer electronic coupling, present thickness-scalable strong second-harmonic generation (SHG), which has demonstrated their compelling performance of free-space nonlinear optics (NLO). However, practical on-chip photonic applications demand not only high NLO efficiency but also robust electrical tunability, a critical capability that has remained elusive until now. Our work reports the first realization of an in-situ electrically tunable NLO response within a NbOBr2-photonic integrated circuit (PIC). This material uniquely combines two critical features: exceptional tunability enabled by in-plane ferroelectricity and a strong second-order susceptibility resulting from its intrinsic broken-inversion symmetry. In this on-chip photonic circuitry scenario, NbOBr2 showcases larger SHG efficiency than NbOCl2 because of its low index contrast and completely outperforms NbOCl2 in the modulation capability thanks to much stronger in-plane ferroelectricity of NbOBr2. We achieve dynamic, non-volatile SHG intensity modulation exceeding 53%, with polarization states retained even after removing the external electric field. This work establishes the integration of 2D ferroelectric NbOBr2 into PICs as a transformative approach for developing scalable and reconfigurable ultracompact NLO devices, opening new avenues for versatile applications in tunable light sources, optical information processing, and quantum photonics.