Giant Enhancement and Sign Inversion of Optical Kerr Nonlinearity in Random High Index Nanocomposites near Mie Resonances

Abstract

The optical Kerr effect of nanocomposites consisting of high refractive index (GaP) spheres is studied by means of three-dimensional finite-difference time-domain (FDTD) simulations at the wavelength of 532 nm. The effective nonlinear refractive index of 0.8 µm thick nanocomposites and metasurfaces is evaluated. It is shown that the optical Kerr nonlinearity of the nanocomposites rises by orders in proximity to Mie resonances and may exceed the second-order refractive index of the bulk material. The nonlinearity enhancement is more pronounced for the metasurfaces. Unexpectedly, the sign of the effective optical Kerr coefficient is inverted for some range of the sphere sizes above the Mie resonances.

Optical Kerr Nonlinearity of Disordered All-Dielectric Resonant High Index Metasurfaces with Negative Refraction

“…1) begins from the negative values since the contribution of particles with sizes close to the electric dipole resonance prevails. This contribution is negative owing to the inversion of n 2 eff sign for such particles [5]. For a monodisperse disordered metasurface with 132 particles with r = 101 nm arranged on 4 × 4 µm area (one half of bidispersive metasurface) n 2 eff = −(1.4 ± 0.4) × 10 −15 m 2 /W.…”

“…[5], random monodisperse metasurfaces of gallium phosphide (GaP) spheres near Mie resonances were shown by three-dimensional FDTD modeling to have an optical Kerr effect exceeding by two orders of intensity that of the bulk gallium phosphide. Moreover, being single negative metamaterials, the monodisperse metasurfaces with sphere sizes in the vicinity of the Mie resonances reveal the inversion of the sign of the second-order nonlinear refractive index [5]. The possibility of negative refraction by the disordered metasurface consisting of GaP spheres with two radii close to the first magnetic and electric Mie resonances was demonstrated in Ref.…”

“…The simulation parameters in the present study were same as given in Ref. [5]: the size of the FDTD computational domain was 4 × 4 × 30 µm, the space resolution of the simulations was 5 nm. The examined sample was a disordered monolayer comprising the equal numbers of GaP spheres of two radii surrounded by vacuum.…”

“…It is appropriate at this point to recall that in Ref. [5] the monodisperse monolayers of the spheres exhibit the inversion of effective second-order refractive index near the Mie resonances.…”

“…Fig. 3 illustrates the dependencies of the effective second-order nonlinear refractive index n 2 eff and third-order Kerr optical susceptibility χ value of n 2 eff due to the inversion of optical Kerr coefficient near the electric dipole Mie resonance [5]. For the higher volume fractions of nanoparticles, n 2 eff becomes positive and has a peak when n 0 eff crosses zero.…”