Visible second-harmonic generation from a 2D material–silicon hybrid chip

Complementary metal-oxide-semiconductor (CMOS)-compatible photonic integrated circuits (PICs) capable of operating at visible wavelengths are critical for advanced quantum systems, including trapped-ion quantum computers. However, standard silicon (Si) PICs are fundamentally unsuitable for this task due to silicon's strong intrinsic material absorption, which prevents the efficient propagation of visible light in Si waveguides. In this work, we present a hybrid two-dimensional (2D) integrated silicon-on-insulator (SOI) PIC platform that enables out-of-plane visible light emission through second-harmonic generation (SHG). This emission arises from a monolayer tungsten diselenide (WSe₂) with broken inversion symmetry, which is encapsulated within hexagonal boron nitride (hBN) to avoid degradation. Our approach bypasses Si absorption by leveraging the transparency of Si waveguides at the infrared pump wavelength, while nonlinear frequency conversion occurs exclusively in the 2D material at the out-coupling interface to convert the infrared photons into visible light. This work opens a promising pathway toward realizing CMOS-compatible, on-chip visible light sources for quantum technologies.