Chi2 and chi3 harmonic generation at a critical power in inhomogeneous doubly resonant cavities

TL;DR

This paper establishes conditions for perfect frequency conversion in doubly resonant nonlinear cavities, demonstrating that 100% efficiency can be achieved at a specific critical power with minimal input power, supported by theoretical and simulation analysis.

Contribution

It generalizes coupled-mode theory to include both chi2 and chi3 nonlinearities in inhomogeneous cavities, providing explicit formulas for designing highly efficient frequency converters.

Findings

Achieves 100% frequency conversion efficiency at a specific critical power.

Predicts milliwatt-level power requirements for high-efficiency conversion.

Validates theoretical predictions with FDTD simulations.

Abstract

We derive general conditions for 100 percent frequency conversion in any doubly resonant nonlinear cavity, for both second- and third-harmonic generation via chi2 and chi3 nonlinearities. We find that conversion efficiency is optimized for a certain critical power depending on the cavity parameters, and assuming reasonable parameters we predict 100 percent conversion using milliwatts of power or less. These results follow from a semi-analytical coupled-mode theory framework which is generalized from previous work to include both chi2 and chi3 media as well as inhomogeneous (fully vectorial) cavities, analyzed in the high-efficiency limit where down-conversion processes lead to a maximum efficiency at the critical power, and which is verified by direct finite-difference time-domain (FDTD) simulations of the nonlinear Maxwell equations. Explicit formulas for the nonlinear coupling coefficients are derived in terms of the linear cavity eigenmodes, which can be used to design and evaluate cavities in arbitrary geometries.