Efficient Second Harmonic Generation from Silicon Slotted Nanocubes with Bound States in the Continuum

TL;DR

This paper demonstrates a novel silicon nanocube array design with air-slots that significantly enhances second harmonic generation by leveraging surface nonlinearity and resonance effects, opening new avenues for nonlinear optical devices.

Contribution

It introduces a slotted nanocube array design that achieves over two orders of magnitude improvement in SHG efficiency from centrosymmetric silicon.

Findings

SHG efficiency of 1.8×10^-4 W^-1 achieved

Over 100-fold enhancement compared to non-slotted arrays

Resonance with bound states in the continuum enhances SHG

Abstract

Optical materials with centrosymmetry, such as silicon and germanium, are unfortunately absent of second-order nonlinear optical responses, hindering their developments in efficient nonlinear optical devices. Here, a design with an array of slotted nanocubes is proposed to realize remarkable second harmonic generation (SHG) from the centrosymmetric silicon, which takes advantage of enlarged surface second-order nonlinearity, strengthened electric field over the surface of the air-slot, as well as the resonance enhancement by the bound states in the continuum. Compared with that from the array of silicon nanocubes without air-slots, SHG from the slotted nanocube array is improved by more than two orders of magnitude. The experimentally measured SHG efficiency of the silicon slotted nanocube array is high as 1.8*10^-4 W^-1, which is expected to be further engineered by modifying the air-slot geometries. Our result could provide a new strategy to expand nonlinear optical effects and devices of centrosymmetric materials.