We recently introduced laminate metamaterials composed of a dielectric ABC layer sequence made by atomic-layer deposition. The ABC sequence breaks inversion symmetry, allowing for second-harmonic generation. Here, we discuss 3D polymeric woodpile photonic crystals conformally coated with such ABC laminate metamaterials (unpublished). In our experiments on such meta-crystals with 24 layers and 600 nm rod spacing at around 800-900 nm fundamental wavelength, we find up to 1000-fold enhancement of the second-harmonic conversion efficiency as compared to the same ABC laminate on a planar glass substrate (for 45 degrees angle of incidence with respect to the substrate and p-polarization). To clarify the underlying mechanism, we have performed extensive numerical calculations based on solving the full-wave problem for the fundamental wave, computing the second-harmonic 3D source-term distribution assuming tensor elements for the ABC laminate as found previously, and numerically computing the resulting emitted second-harmonic wave. This analysis indicates that the enhancement is consistent with guided-mode resonant excitations at the fundamental wavelength inside of the 3D meta-crystal slab, leading to a standing-wave behavior providing beneficial local-field enhancements.

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Andreas Wickberg, Aimi Abass, Hui-Hsin Hsiao, Carsten Rockstuhl, and Martin Wegener, "Second-harmonic generation by 3D ABC-laminate meta-crystals (Conference Presentation)," Proc. SPIE 10719, Metamaterials, Metadevices, and Metasystems 2018, 107191K (Presented at SPIE Nanoscience + Engineering: August 22, 2018; Published: 17 September 2018); https://doi.org/10.1117/12.2317934.5836032264001.