Enhanced Second-Harmonic Generation in Thin-Film Lithium Niobate Circular Bragg Nanocavity

TL;DR

This paper demonstrates a significant enhancement in second-harmonic generation in thin-film lithium niobate using circular Bragg nanocavities, achieving record conversion efficiency and polarization independence, advancing nanoscale nonlinear optics.

Contribution

The study introduces nanocavities formed by circular Bragg gratings supporting resonant modes to greatly enhance SHG in thin-film lithium niobate, surpassing previous efficiencies.

Findings

Record-high normalized conversion efficiency of 1.21×10^{-2} cm^2/GW.

SHG enhancement of 42,000 times compared to TFLN.

Achieved polarization-independent SHG in elliptical Bragg nanocavities.

Abstract

Second-order nonlinearity gives rise to many distinctive physical phenomena, e.g., second-harmonic generation, which plays an important role in fundamental science and various applications. Lithium niobate, one of the most widely used nonlinear crystals, exhibits strong second-order nonlinear effects and electro-optic properties. However, its moderate refractive index and etching sidewall angle limit its capability in confining light into nanoscales, restricting its application in nanophotonics. Here, we exploit nanocavities formed by second-order circular Bragg gratings, which support resonant anapole modes to achieve highly enhanced SHG in thin film lithium niobate. The CBG nanocavity exhibits a record-high normalized conversion efficiency of $1.21\times10^{-2}\mathrm{cm^2/GW}$ under the pump intensity of $1.9$ $\mathrm{MW/cm^2}$. An SHG enhancement of $42,000$ is realized compared to TFLN. Besides, we also show s- and p-polarization independent SHG in elliptical Bragg nanocavities. This work could inspire studying nonlinear optics at the nanoscale on TFLN as well as other novel photonic platforms.