Non-resonant Bragg scattering four-wave-mixing at near visible wavelengths in low-confinement silicon nitride waveguides

Quantum state coherent frequency conversion processes-such as Bragg scattering four wave mixing (BSFWM)-hold promise as a flexible technique for networking heterogeneous and distant quantum systems. In this letter, we demonstrate BSFWM within an extended (1.2-m) low-confinement silicon nitride waveguide and show that this system has the potential for near unity quantum coherent frequency conversion in visible and near-visible wavelength ranges. Using sensitive heterodyne laser spectroscopy at low optical powers, we characterize the Kerr coefficient (~1.55 W^{-1} m^{-1}) and linear propagation loss (~0.0175 dB/cm) of this non-resonant waveguide system, revealing a record-high nonlinear figure of merit (NFM = gamma/alpha is approximately equal to 3.85 W^{-1}) for BSFWM of near visible light in non-resonant silicon nitride waveguides. We demonstrate how, at high yet achievable on-chip optical powers, this NFM would yield a comparatively large frequency conversion efficiency, opening the door to near-unity flexible frequency conversion without cavity enhancement and resulting bandwidth constraints.