Fourth-harmonic UV light generation in integrated silicon nitride microresonators

TL;DR

This paper demonstrates the first fourth-harmonic generation in integrated silicon nitride microresonators, enabling UV light production on-chip for applications in quantum emitters, spectroscopy, and bio-imaging.

Contribution

It reports the first observation of UV fourth-harmonic generation in integrated Si3N4 resonators, extending nonlinear photonics capabilities into the UV spectrum.

Findings

Achieved fourth-harmonic generation near 400 nm in Si3N4 resonators.

Systematic analysis of power dependence for harmonic generation.

Extended the operational bandwidth of Si3N4 photonics into the UV range.

Abstract

Integrated silicon nitride (Si3N4) resonators have emerged as a leading platform for nonlinear photonics, yet generating light at wavelength in the ultraviolet (UV) has remained elusive in single-resonator systems. Here we report the first observation of fourth-harmonic generation reaching the blue and ultraviolet spectral regions in an integrated Si3N4 microring resonator. We systematically investigate the input-power dependence of the wavelength ranges supporting second-, third-, and fourth-harmonic generation, and study the input-power-dependent variation of the circulating fourth-harmonic signal in the UV. These results extend the operational bandwidth of integrated Si3N4 nonlinear photonic platforms to the lower edge of the material transparency window, enabling on-chip UV frequency conversion. Near-ultraviolet generation around 400 nm will enable on-chip excitation of defect-based quantum emitters in hexagonal boron nitride, enhance Raman spectroscopy through increased scattering cross-sections at shorter wavelengths, and support compact fluorescence-based bio-imaging platforms exploiting intrinsic cellular fluorophores.