• DOI:10.1103/PhysRevB.106.125411
• Corpus ID: 249209855

Boosted second-harmonic generation in the LiNbO$\mathrm{_3}$ metasurface governed by high-Q guided resonances and bound states in the continuum

@inproceedings{Zheng2022BoostedSG,
  title={Boosted second-harmonic generation in the LiNbO\$\mathrm\{\_3\}\$ metasurface governed by high-Q guided resonances and bound states in the continuum},
  author={Ze-yuan Zheng and Lei Xu and Lujun Huang and Daria A. Smirnova and Peilong Hong and Cuifeng Ying and Mohsen Rahman},
  year={2022}
}

• Ze-yuan Zheng, Lei Xu, +4 authors Mohsen Rahman
• Published 31 May 2022
• Physics

To date, second-harmonic generation (SHG) at nanoscale has been concentrated on employing high-refractive-index nanostructures, owing to the strong field confinement at deep subwavelength scales based on optically resonant effects. However, low-index nanostructures generally exhibit weaker resonant effects and lower field confinement. To address this issue, by harnessing the large nonlinearity of LiNbO 3 , we propose a novel approach to employ guided resonances and bound states in the continuum (BICs) with a LiNbO 3 metasurface consisting of a LiNbO 3 disk array sitting on a LiNbO 3 thin film. Such a system can transform the guided modes supported by LiNbO 3 thin film into high-quality guided resonances which can be excited directly under plane-wave illumination. Importantly, we further demonstrate strong field confinement inside LiNbO 3 thin film with tailorable Q-factor by realising a Friedrich-Wintgen BIC. Such a unique mode engineering enables a record-high SHG efficiency of 5% under a pump intensity as low as 0.4 MW / cm 2 . Moreover, we reveal the influence of nonlinear resonances and cross-coupling on the SHG by showing the anomalous SHG and efficiency tuning with the rotation of the crystal axis. Our work offers a new route to constructing enhanced SHG based on high-Q guided resonances and BICs, including low-index and high-index nonlinear materials.