Highly efficient second harmonic generation of thin film lithium niobate nanograting near bound states in the continuum

Abstract

Bound states in the continuum (BICs) are ubiquitous physical phenomena where such states occur due to strong coupling between leaky modes in side lossy systems. BICs in meta-optics and nanophotonics enable optical mode confinement to strengthen local field enhancement in nonlinear optics. In this study, we numerically investigate second-harmonic generation (SHG) in the vicinity of BICs with a photonic structure comprising one-dimensional nanogratings and a slab waveguide made of lithium niobate (LiNbO3, LN). By breaking the symmetry of LN nanogratings, BICs transition to quasi-BICs, which enable strong local field confinement inside LN slab waveguide to be supported, thereby resulting in improving SHG conversion with lower pump power of fundamental frequency (FW). With a peak intensity of 1.33 GW cm−2 at the FW, our structure features a second-harmonic conversion efficiency up to 8.13 × 10−5 at quasi-BICs. We believe that our results will facilitate the application of LN in integrated nonlinear nanophotonic.

Second-Harmonic Generation in Resonant Nonlinear Metasurfaces Based on Lithium Niobate

“…First experimental demonstrations showed resonances in nanogratings 53 and SHG from single chemically synthesized LN nanocubes exhibiting Mie-type resonances. 54 Furthermore, enhanced SHG in a one-dimensional LN nanograting 55,56 was demonstrated.…”

Enhanced generation of nondegenerate photon pairs in nonlinear metasurfaces

“…Notably, this can be facilitated by designing Bound State in the Continuum (BIC) resonances, [3][4][5][6][7] which support a high confinement of the optical field within the nonlinear material. [8][9][10] In addition to classical frequency mixing, nonlinear MSs can also, through Spontaneous Parametric Down-Conversion (SPDC), generate entangled photons with a strong degree of spatial coherence. 11 SPDC in carefully engineered MSs has the potential to drive fundamental advances in the field of ultracompact multi-photon sources 12 that operate at room temperature, which are suitable for integration in end-user devices with applications that include quantum imaging 13 and free-space communications.…”

Polarization-controlled dynamically switchable high-harmonic generation from all-dielectric metasurfaces governed by dual bound states in the continuum

“…In particular, a novel design strategy based on the concept of bound states in the continuum (BIC) enables high-Q resonances in all-dielectric metasurfaces, where the tight confinement of light inside the meta-atoms allows for efficient nonlinear frequency conversion [18][19][20] . To date, all-dielectric metasurfaces governed by BIC physics have demonstrated their ability to substantially boost second-harmonic generation (SHG) [21][22][23][24][25][26][27] , and third-harmonic generation (THG) [28][29][30][31][32][33][34] , with efficiency higher and pump intensity lower than previously recorded values. In a most recent report, empowered by the BIC resonance in asymmetric silicon metasurfaces, efficient harmonics up to the 11 th order has been observed 35 .…”