Optical Coupling between Resonant Dielectric Nanoparticles and Dielectric Nanowires Probed by Third Harmonic Generation Microscopy

Abstract

Localized electromagnetic modes and negligible Ohmic losses dictate the growing interest to subwavelength all-dielectric nanoparticles. Although an exhaustive volume of literature dealt with interaction of all-dielectric nanostructures with free-space electromagnetic fields, they received little attention as integrated photonic elements. We present an experimental and numerical study of optical coupling between a resonant subwavelength silicon nanodisk and a silicon nanowire, as probed by third harmonic generation microscopy and full-wave simulations. First, by placing the nanodisks at different distances from the nanowire, we observed third harmonic intensity modulation by a factor of up to 4.5. This modulation is assigned to changes in the local field enhancement within the nanodisks caused by their coupling to the nanowires and subsequent shifting and broadening of their magnetic-type resonances. Interestingly, although the nanowire presents an additional loss channel for the nanodisk, we observed an increase in the local field strength within the nanodisk, as verified by rigorous full-wave simulations. Inversely, for the gap sizes that are smaller than ≈200 nm, we observe the influence of the nanoparticles on the propagation properties of the fundamental waveguide modes of the nanowire. The better understanding of the mutual influence of the Mie-resonant nanoparticles and waveguiding structures heralds integration of the former on-photonic chips.