Efficient Third Harmonic Generation in Composite Aluminum Nitride / Silicon Nitride Microrings

TL;DR

This paper demonstrates high-efficiency third harmonic generation in a composite aluminum nitride/silicon nitride microring resonator, enabling advanced on-chip frequency conversion and broadband comb applications.

Contribution

It introduces a novel composite microring design that optimizes phase matching and mode overlap for efficient third harmonic generation.

Findings

Achieved a maximum conversion efficiency of 180% W^{-2}.

Optimized microring geometry for high Q factor and mode overlap.

Enabled efficient frequency conversion over a broad wavelength range.

Abstract

Aluminum nitride and silicon nitride have recently emerged as important nonlinear optical materials in integrated photonics respectively for their quadratic and cubic optical nonlinearity. A composite aluminum nitride and silicon nitride waveguide structure, if realized, will simultaneously allow highly efficient second and third harmonic generation on the same chip platform and therefore assists 2f-3f self-referenced frequency combs. On-chip third harmonic generation, being a higher order nonlinear optics effect, is more demanding than second harmonic generation due to the large frequency difference between the fundamental and third harmonic frequencies which implies large change of refractive indices and more strigent requirements on phase matching. In this work we demonstrate high-efficiency third harmonic generation in a high Q composite aluminum nitride / silicon nitide ring cavity. By carefully engineering the microring resonator geometry of the bilayer structure to optimize the quality factor, mode volume and modal overlap of the optical fields, we report a maximum conversion efficiency of $180\%\,\mathrm{W^{-2}}$. This composite photonic chip design provides a solution for efficient frequency conversion over a large wavelength span, broadband comb generation and self-referenced frequency combs.