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

Abstract

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 LiNbO3 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 LiNbO3 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 $MW/c{\mathrm{m}}^2$. 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.

11 pages, 7 figures

References in corpus (5)

• Resonantly enhanced second-harmonic generation using III-V semiconductor all-dielectric metasurfaces
• Electromagnetic multipole theory for optical nanomaterials
• Formation of long-lived, scarlike modes near avoided resonance crossings in optical microcavities
• Continuous wave second harmonic generation enabled by quasi-bound-states in the continuum on gallium phosphide metasurfaces
• Nonlinear imaging with all-dielectric metasurfaces

Cited by in corpus (6)

• High-efficiency optical frequency mixing in an all-dielectric metasurface enabled by multiple bound states in the continuum
• Enhanced sum-frequency generation from etchless lithium niobate empowered by dual quasi-bound states in the continuum
• Directionally Tunable Co- and Counter-Propagating Photon Pairs from a Nonlinear Metasurface
• Doubly resonant photonic crystal cavity using merged bound states in the continuum
• Inverse Design of Nonlinear Metasurfaces for Sum Frequency Generation
• Electro-optically tunable second-harmonic generation in lithium niobate metasurfaces boosted by Brillouin zone folding induced bound states in the continuum