volume | PIER Journals

Abstract

Nonlinear light-matter interactions have greatly benefited from high-Q resonances, which enhance the local field at the pump frequency, strengthening the nonlinear polarization at the harmonic frequency. However, despite the strong harmonic buildup, the collected signal often remains limited by the absence of efficient radiative channels. To address this issue, we propose an all-dielectric nonlocal ternary metagrating that combines a high-Q quasi-guided-mode resonance at the fundamental frequency (ω) with a moderate-Q radiative guided-mode resonance at the third-harmonic frequency (3ω), leading to significantly enhancing the third-harmonic generation (THG) process. By reducing the Brillouin zone to one-third of its original size, the ternary design folds the dispersive guided-mode branches to the Γ-point, enriching the modal landscape. In addition, the ternary geometry reduces coupling into unwanted higher-order diffraction channels near 3ω, thereby favoring the desired harmonic radiative response. Experimentally, the device achieves an estimated collected THG conversion efficiency of approximately 1.86×10^-6, confirming the practical potential of the dual-resonant scheme. These findings establish a practical route toward dual-resonant enhancement that reduces reliance on extremely high-Q or flat-band resonances, offering a more fabrication-friendly, experimentally accessible platform for nonlinear photonic applications such as Raman spectroscopy, nonlinear imaging, and quantum photonics.

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Dr. Esha Maqbool

Dr. Guangdong Wang

Dr. Kaili Sun

Prof. Zhanghua Han