Heterogeneous integration of lithium niobate and silicon nitride waveguides for wafer-scale photonic integrated circuits on silicon

TLDR

Nonlinear photonic integrated circuits require high optical nonlinearities and low loss. The study demonstrates a heterogeneous platform by bonding lithium niobate thin films onto a silicon nitride waveguide layer on silicon. The platform uses bonded LN thin films on Si₃N₄ waveguides with tapers that enable low‑loss mode transitions. It delivers large second‑ and third‑order nonlinear coefficients and low propagation loss, enabling modulators, frequency conversion, and quantum communications.

Abstract

An ideal photonic integrated circuit for nonlinear photonic applications requires high optical nonlinearities and low loss. This work demonstrates a heterogeneous platform by bonding lithium niobate (LN) thin films onto a silicon nitride (Si3N4) waveguide layer on silicon. It not only provides large second- and third-order nonlinear coefficients, but also shows low propagation loss in both the Si3N4 and the LN-Si3N4 waveguides. The tapers enable low-loss-mode transitions between these two waveguides. This platform is essential for various on-chip applications, e.g., modulators, frequency conversions, and quantum communications.