Defect-induced nonlinearity in 2D nanoparticles.

Jie Xu,Eric Plum

doi:10.1364/oe.443977

Abstract

Optical nonlinearity depends on symmetry and symmetries vanish in the presence of defects. Vacancy defects in centrosymmetric crystals and thin films are a well-known source of even-order optical nonlinearity, e.g. causing second harmonic generation. The emerging ability to manipulate defects in two-dimensional materials and nanoparticles provides an opportunity for engineering of optical nonlinearity. Here, we demonstrate the effect of defects on the nonlinear optical response of two-dimensional dielectric nanoparticles. Using a toy model, where bound optical electrons of linear atoms are coupled by nonlinear Coulomb interactions, we model defect-induced nonlinearity. We find that defects at particle edges contribute strongly to even-order optical nonlinearity and that unique nonlinear signatures of different defect states could provide the smallest conceivable QR-codes and extremely high density optical data storage, in principle approaching 1 bit per atom.

Highlights

Harmonic generation is of key importance for wavelength conversion of optical signals and optical information processing
Defects at corners induce the strongest dipole moment Py,x, while this component does not arise from defects that maintain the horizontal or vertical mirror symmetry of the nanoparticle
We argue that 2D defect patterns could act as the smallest conceivable 2D barcodes, i.e. nano-QR-codes, that could be read based on their nonlinear optical properties

Summary

Introduction

Harmonic generation is of key importance for wavelength conversion of optical signals and optical information processing. We first study a square particle with 25 atoms (D4 symmetry, with square lattice) and introduce one vacancy defect at three different positions. When the defect occurs at a corner (Fig. 2b), x or y-polarized excitation generates dipole moments along both the x and y directions, and we observe Px,x=Py,y and Px,y= Py,x.

Results

Conclusion