Optical anapole mode in nanostructured lithium niobate for enhancing second harmonic generation

TL;DR

This paper demonstrates enhanced second harmonic generation in lithium niobate nanodisks by exciting anapole modes, using hyperbolic metamaterials to tune the wavelength, achieving higher efficiency for practical nonlinear optical applications.

Contribution

It introduces a novel nanostructure design using hyperbolic metamaterials to excite anapole modes in lithium niobate for improved SHG efficiency and tunability.

Findings

Achieved SHG conversion efficiency of ~0.01% at 282 nm wavelength.

Enhanced SHG across a wide range of pump wavelengths via ENZ hyperbolic metamaterial design.

Suppressed far-field scattering and confined internal fields boost nonlinear conversion.

Abstract

Second harmonic generation (SHG) with a material of large transparency is an attractive way of generating coherent light sources at exotic wavelength range such as VUV, UV and visible light. It is of critical importance to improve nonlinear conversion efficiency in order to find practical applications in quantum light source and high resolution nonlinear microscopy, etc. Here an enhanced SHG with conversion efficiency up to the order of 0.01% at SH wavelength of 282 nm under 11 GW/cm2 pump power via the excitation of anapole in lithium niobite (LiNbO3, or LN) nanodisk through the dominating d33 nonlinear coefficient is investigated. The anapole has advantages of strongly suppressing far-field scattering and well-confined internal field which helps to boost the nonlinear conversion. Anapoles in LN nanodisk is facilitated by high index contrast between LN and substrate with properties of near-zero-index via hyperbolic metamaterial structure design. By tailoring the multi-layers structure of hyperbolic metamaterials, the anapole excitation wavelength can be tuned at different wavelengths. It indicates that an enhanced SHG can be achieved at a wide range of pump light wavelengths via different design of the epsilon-near-zero (ENZ) hyperbolic metamaterials substrates. The proposed nanostructure in this work might hold significances for the enhanced light-matter interactions at the nanoscale such as integrated optics.