Nonlinear generalized source method for modeling second-harmonic generation in diffraction gratings

TL;DR

This paper presents a new numerical method extending the generalized source method to model second-harmonic generation in nonlinear diffraction gratings, demonstrating improved accuracy and efficiency for complex photonic structures.

Contribution

The paper introduces a novel nonlinear extension of the generalized source method with Fourier-factorization, enabling accurate modeling of second-harmonic generation in complex gratings.

Findings

Enhanced accuracy with modified Fourier-factorization

Demonstrated strong second-harmonic enhancement in gratings

Validated against reference methods

Abstract

We introduce a versatile numerical method for modeling light diffraction in periodically patterned photonic structures containing quadratically nonlinear non-centrosymmetric optical materials. Our approach extends the generalized source method to nonlinear optical interactions by incorporating the contribution of nonlinear polarization sources to the diffracted field in the algorithm. We derive the mathematical formalism underlying the numerical method and introduce the Fourier-factorization suitable for nonlinear calculations. The numerical efficiency and runtime characteristics of the method are investigated in a set of benchmark calculations: the results corresponding to the fundamental frequency are compared to those obtained from a reference method and the beneficial effects of the modified Fourier-factorization rule on the accuracy of the nonlinear computations is demonstrated. In order to illustrate the capabilities of our method, we employ it to demonstrate strong enhancement of second-harmonic generated in one- and two-dimensional optical gratings resonantly coupled to a slab waveguide. Our method can be easily extended to other types of nonlinear optical interactions by simply incorporating the corresponding nonlinear polarization sources in the algorithm.